The ADS412x and ADS414x devices are lower-sampling speed variants in the ADS41xx family of analog-to-digital converters (ADCs). These devices use innovative design techniques to achieve high dynamic performance, while consuming extremely low power at 1.8-V supply. The devices are well-suited for multi-carrier, wide bandwidth communications applications.
The ADS412x and ADS414x devices have fine gain options that can be used to improve SFDR performance at lower full-scale input ranges, especially at high input frequencies. They include a dc offset correction loop that can be used to cancel the ADC offset. At lower sampling rates, the ADC automatically operates at scaled down power with no loss in performance.
The ADS412x and ADS414x devices are available in a compact VQFN-48 package and are specified over the industrial temperature range (–40°C to +85°C).
PART NUMBER | PACKAGE | BODY SIZE (NOM) |
---|---|---|
ADS4122 | VQFN (48) | 7.00 mm × 7.00 mm |
ADS4125 | ||
ADS4142 | ||
ADS4145 |
Changes from B Revision (January 2016) to C Revision
Changes from A Revision (March 2011) to B Revision
NOINDENT:
The thermal pad is connected to DRGND.PIN | I/O | DESCRIPTION | ||
---|---|---|---|---|
NAME | ADS412x | ADS414x | ||
AGND | 9, 12, 14, 17, 19, 25 | 9, 12, 14, 17, 19, 25 | I | Analog ground |
AVDD | 8, 18, 20, 22, 24, 26 | 8, 18, 20, 22, 24, 26 | I | 1.8-V analog power supply |
CLKM | 11 | 11 | I | Differential clock input, complement |
CLKP | 10 | 10 | I | Differential clock input, true |
CLKOUTM | 4 | 4 | O | Differential output clock, complement |
CLKOUTP | 5 | 5 | O | Differential output clock, true |
D0_D1_M | 37 | 33 | O | Differential output data D0 and D1 multiplexed, complement |
D0_D1_P | 38 | 34 | O | Differential output data D0 and D1 multiplexed, true |
D2_D3_M | 39 | 37 | O | Differential output data D2 and D3 multiplexed, complement |
D2_D3_P | 40 | 38 | O | Differential output data D2 and D3 multiplexed, true |
D4_D5_M | 41 | 39 | O | Differential output data D4 and D5 multiplexed, complement |
D4_D5_P | 42 | 40 | O | Differential output data D4 and D5 multiplexed, true |
D6_D7_M | 43 | 41 | O | Differential output data D6 and D7 multiplexed, complement |
D6_D7_P | 44 | 42 | O | Differential output data D6 and D7 multiplexed, true |
D8_D9_M | 45 | 43 | O | Differential output data D8 and D9 multiplexed, complement |
D8_D9_P | 46 | 44 | O | Differential output data D8 and D9 multiplexed, true |
D10_D11_M | 47 | 45 | O | Differential output data D10 and D11 multiplexed, complement |
D10_D11_P | 48 | 46 | O | Differential output data D10 and D11 multiplexed, true |
D12_D13_M | — | 47 | O | Differential output data D12 and D13 multiplexed, complement |
D12_D13_P | — | 48 | O | Differential output data D12 and D13 multiplexed, true |
DFS | 6 | 6 | I | Data format select input. This pin sets the DATA FORMAT (twos complement or offset binary) and the LVDS, CMOS output interface type. See Table 5 for detailed information. |
DRGND | 1, 36, PAD | 1, 36, PAD | I | Digital and output buffer ground |
DRVDD | 2, 35 | 2, 35 | I | 1.8-V digital and output buffer supply |
INM | 16 | 16 | I | Differential analog input, negative |
INP | 15 | 15 | I | Differential analog input, positive |
NC | 21, 31, 32, 33, 34 | 21, 31, 32 | – | Do not connect |
OE | 7 | 7 | I | Output buffer enable input, active high; this pin has an internal 180-kΩ pullup resistor to DRVDD. |
OVR_SDOUT | 3 | 3 | O | This pin functions as an out-of-range indicator after reset, when register bit READOUT = 0, and functions as a serial register readout pin when READOUT = 1. |
RESERVED | 23 | 23 | I | Digital control pin, reserved for future use |
RESET | 30 | 30 | I | Serial interface RESET input. When using the serial interface mode, the internal registers must initialize through hardware RESET by applying a high pulse on this pin or by using the software reset option; see the Serial Interface section. When RESET is tied high, the internal registers are reset to the default values. In this condition, SEN can be used as an analog control pin. RESET has an internal 180-kΩ pulldown resistor. |
SCLK | 29 | 29 | I | This pin functions as a serial interface clock input when RESET is low. When RESET is high, SCLK has no function and should be tied to ground. This pin has an internal 180-kΩ pulldown resistor. |
SDATA | 28 | 28 | I | This pin functions as a serial interface data input when RESET is low. When RESET is high, SDATA functions as a STANDBY control pin (see Table 7). This pin has an internal 180-kΩ pulldown resistor. |
SEN | 27 | 27 | I | This pin functions as a serial interface enable input when RESET is low. When RESET is high, SEN has no function and must be tied to AVDD. This pin has an internal 180-kΩ pullup resistor to AVDD. |
VCM | 13 | 13 | O | Outputs the common-mode voltage (0.95 V) that can be used externally to bias the analog input pins. |
PIN | I/O | DESCRIPTION | ||
---|---|---|---|---|
NAME | ADS412x | ADS414x | ||
AVDD | 8, 18, 20, 22, 24, 26 | 8, 18, 20, 22, 24, 26 | I | 1.8-V analog power supply |
AGND | 9, 12, 14, 17, 19, 25 | 9, 12, 14, 17, 19, 25 | I | Analog ground |
CLKM | 11 | 11 | I | Differential clock input, complement |
CLKP | 10 | 10 | I | Differential clock input, true |
CLKOUT | 5 | 5 | O | CMOS output clock |
D0 | 37 | 33 | O | 12-bit, 14-bit CMOS output data |
D1 | 38 | 34 | O | 12-bit, 14-bit CMOS output data |
D2 | 39 | 37 | O | 12-bit, 14-bit CMOS output data |
D3 | 40 | 38 | O | 12-bit, 14-bit CMOS output data |
D4 | 41 | 39 | O | 12-bit, 14-bit CMOS output data |
D5 | 42 | 40 | O | 12-bit, 14-bit CMOS output data |
D6 | 43 | 41 | O | 12-bit, 14-bit CMOS output data |
D7 | 44 | 42 | O | 12-bit, 14-bit CMOS output data |
D8 | 45 | 43 | O | 12-bit, 14-bit CMOS output data |
D9 | 46 | 44 | O | 12-bit, 14-bit CMOS output data |
D10 | 47 | 45 | O | 12-bit, 14-bit CMOS output data |
D11 | 48 | 46 | O | 12-bit, 14-bit CMOS output data |
D12 | — | 47 | O | 12-bit, 14-bit CMOS output data |
D13 | — | 48 | O | 12-bit, 14-bit CMOS output data |
DFS | 6 | 6 | I | Data format select input. This pin sets the DATA FORMAT (twos complement or offset binary) and the LVDS, CMOS output interface type. See Table 5 for detailed information. |
DRGND | 1, 36, PAD | 1, 36, PAD | I | Digital and output buffer ground |
DRVDD | 2, 35 | 2, 35 | I | 1.8-V digital and output buffer supply |
INM | 16 | 16 | I | Differential analog input, negative |
INP | 15 | 15 | I | Differential analog input, positive |
NC | 21, 31, 32, 33, 34 | 21, 31, 32 | – | Do not connect |
OE | 7 | 7 | I | Output buffer enable input, active high; this pin has an internal 180-kΩ pullup resistor to DRVDD. |
OVR_SDOUT | 3 | 3 | O | This pin functions as an out-of-range indicator after reset, when register bit READOUT = 0, and functions as a serial register readout pin when READOUT = 1. |
RESERVED | 23 | 23 | I | Digital control pin, reserved for future use |
RESET | 30 | 30 | I | Serial interface RESET input. When using the serial interface mode, the internal registers must initialize through hardware RESET by applying a high pulse on this pin or by using the software reset option; see the Serial Interface section. When RESET is tied high, the internal registers are reset to the default values. In this condition, SEN can be used as an analog control pin. RESET has an internal 180-kΩ pulldown resistor. |
SCLK | 29 | 29 | I | This pin functions as a serial interface clock input when RESET is low. When RESET is high, SCLK has no function and must be tied to ground. This pin has an internal 180-kΩ pulldown resistor. |
SDATA | 28 | 28 | I | This pin functions as a serial interface data input when RESET is low. When RESET is high, SDATA functions as a STANDBY control pin (see Table 7). This pin has an internal 180-kΩ pulldown resistor. |
SEN | 27 | 27 | I | This pin functions as a serial interface enable input when RESET is low. When RESET is high, SEN has no function and must be tied to AVDD. This pin has an internal 180-kΩ pullup resistor to AVDD. |
UNUSED | 4 | 4 | – | Unused pin in CMOS mode |
VCM | 13 | 13 | O | Outputs the common-mode voltage (0.95 V) that can be used externally to bias the analog input pins. |
MIN | MAX | UNIT | ||
---|---|---|---|---|
Supply voltage, AVDD | –0.3 | 2.1 | V | |
Supply voltage, DRVDD | –0.3 | 2.1 | V | |
Voltage between AGND and DRGND | –0.3 | 0.3 | V | |
Voltage between AVDD to DRVDD (when AVDD leads DRVDD) | 0 | 2.1 | V | |
Voltage between DRVDD to AVDD (when DRVDD leads AVDD) | 0 | 2.1 | V | |
Voltage applied to input pins | INP, INM | –0.3 | minimum (1.9, AVDD + 0.3) | V |
CLKP, CLKM(2), DFS, OE | –0.3 | AVDD + 0.3 | ||
RESET, SCLK, SDATA, SEN | –0.3 | 3.9 | ||
Operating free-air temperature, TA | –40 | 85 | °C | |
Operating junction temperature, TJ | 125 | °C | ||
Storage temperature, Tstg | –65 | 150 | °C |
VALUE | UNIT | |||
---|---|---|---|---|
V(ESD) | Electrostatic discharge | Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) | ±2000 | V |
Charged-device model (CDM), per JEDEC specification JESD22-C101(2) | ±500 |
MIN | NOM | MAX | UNIT | |||
---|---|---|---|---|---|---|
SUPPLIES | ||||||
AVDD | Analog supply voltage | 1.7 | 1.8 | 1.9 | V | |
DRVDD | Digital supply voltage | 1.7 | 1.8 | 1.9 | V | |
ANALOG INPUTS | ||||||
Differential input voltage(1) | 2 | VPP | ||||
Input common-mode voltage | VCM ± 0.05 | V | ||||
Maximum analog input frequency with 2-VPP input amplitude(2) | 400 | MHz | ||||
Maximum analog input frequency with 1-VPP input amplitude(2) | 800 | MHz | ||||
CLOCK INPUT | ||||||
Input clock sample rate | ADS4122, ADS4142, low-speed mode enabled by default | 3 | 65 | MSPS | ||
ADS4125, ADS4145, low-speed mode enabled | 3 | 80 | ||||
ADS4125, ADS4145, low-speed mode disabled | > 80 | 125 | ||||
Input clock amplitude differential (VCLKP – VCLKM) |
Sine wave, ac-coupled | 0.2 | 1.5 | VPP | ||
LVPECL, ac-coupled | 1.6 | |||||
LVDS, ac-coupled | 0.7 | |||||
LVCMOS, single-ended, ac-coupled | 1.8 | V | ||||
Input clock duty cycle | Low-speed enabled | 40% | 50% | 60% | ||
Low-speed disabled | 35% | 50% | 65% | |||
DIGITAL OUTPUTS | ||||||
CLOAD | Maximum external load capacitance from each output pin to DRGND | 5 | pF | |||
RLOAD | Differential load resistance between the LVDS output pairs (LVDS mode) | 100 | Ω | |||
TA | Operating free-air temperature | –40 | 85 | °C |
THERMAL METRIC(1) | ADS412x, ADS414x |
UNIT | |
---|---|---|---|
RGZ (VQFN) | |||
48 PIN | |||
RθJA | Junction-to-ambient thermal resistance | 29 | °C/W |
RθJCtop | Junction-to-case (top) thermal resistance | N/A | °C/W |
RθJB | Junction-to-board thermal resistance | 10 | °C/W |
ψJT | Junction-to-top characterization parameter | 0.3 | °C/W |
ψJB | Junction-to-board characterization parameter | 9 | °C/W |
RθJCbot | Junction-to-case (bottom) thermal resistance | 1.1 | °C/W |
PARAMETER | TEST CONDITIONS | MIN | TYP | MAX | UNIT | ||
---|---|---|---|---|---|---|---|
Resolution | 14 | Bits | |||||
SNR | Signal-to-noise ratio, LVDS | fIN = 10 MHz | ADS4142 (65 MSPS) | 73.9 | dBFS | ||
ADS4145 (125 MSPS) | 73.7 | ||||||
fIN = 70 MHz | ADS4142 (65 MSPS) | 73.5 | |||||
ADS4145 (125 MSPS) | 73.4 | ||||||
fIN = 100 MHz | ADS4142 (65 MSPS) | 73.2 | |||||
ADS4145 (125 MSPS) | 73.1 | ||||||
fIN = 170 MHz | ADS4142 (65 MSPS) | 69 | 72.4 | ||||
ADS4145 (125 MSPS) | 70 | 72.2 | |||||
fIN = 300 MHz | ADS4142 (65 MSPS) | 70.5 | |||||
ADS4145 (125 MSPS) | 71.3 | ||||||
SINAD | Signal-to-noise and distortion ratio, LVDS | fIN = 10 MHz | ADS4142 (65 MSPS) | 73.5 | dBFS | ||
ADS4145 (125 MSPS) | 73.2 | ||||||
fIN = 70 MHz | ADS4142 (65 MSPS) | 73.3 | |||||
ADS4145 (125 MSPS) | 73 | ||||||
fIN = 100 MHz | ADS4142 (65 MSPS) | 73 | |||||
ADS4145 (125 MSPS) | 72.6 | ||||||
fIN = 170 MHz | ADS4142 (65 MSPS) | 68 | 72.3 | ||||
ADS4145 (125 MSPS) | 69 | 71.8 | |||||
fIN = 300 MHz | ADS4142 (65 MSPS) | 69.2 | |||||
ADS4145 (125 MSPS) | 70.6 | ||||||
SFDR | Spurious-free dynamic range | fIN = 10 MHz | ADS4142 (65 MSPS) | 87 | dBc | ||
ADS4145 (125 MSPS) | 86 | ||||||
fIN = 70 MHz | ADS4142 (65 MSPS) | 86.5 | |||||
ADS4145 (125 MSPS) | 85.5 | ||||||
fIN = 100 MHz | ADS4142 (65 MSPS) | 87 | |||||
ADS4145 (125 MSPS) | 82 | ||||||
fIN = 170 MHz | ADS4142 (65 MSPS) | 71 | 85 | ||||
ADS4145 (125 MSPS) | 72.5 | 81.5 | |||||
fIN = 300 MHz | ADS4142 (65 MSPS) | 72.5 | |||||
ADS4145 (125 MSPS) | 77 | ||||||
THD | Total harmonic distortion | fIN = 10 MHz | ADS4142 (65 MSPS) | 84 | dBc | ||
ADS4145 (125 MSPS) | 83 | ||||||
fIN = 70 MHz | ADS4142 (65 MSPS) | 84 | |||||
ADS4145 (125 MSPS) | 83.5 | ||||||
fIN = 100 MHz | ADS4142 (65 MSPS) | 84 | |||||
ADS4145 (125 MSPS) | 81 | ||||||
fIN = 170 MHz | ADS4142 (65 MSPS) | 69.5 | 82.5 | ||||
ADS4145 (125 MSPS) | 70.5 | 80 | |||||
fIN = 300 MHz | ADS4142 (65 MSPS) | 72.5 | |||||
ADS4145 (125 MSPS) | 75.5 | ||||||
HD2 | Second-order harmonic distortion | fIN = 10 MHz | ADS4142 (65 MSPS) | 88 | dBc | ||
ADS4145 (125 MSPS) | 87 | ||||||
fIN = 70 MHz | ADS4142 (65 MSPS) | 87 | |||||
ADS4145 (125 MSPS) | 85.5 | ||||||
fIN = 100 MHz | ADS4142 (65 MSPS) | 88 | |||||
ADS4145 (125 MSPS) | 82 | ||||||
fIN = 170 MHz | ADS4142 (65 MSPS) | 71 | 87 | ||||
ADS4145 (125 MSPS) | 72.5 | 84 | |||||
fIN = 300 MHz | ADS4142 (65 MSPS) | 72.5 | |||||
ADS4145 (125 MSPS) | 77 | ||||||
HD3 | Third-order harmonic distortion | fIN = 10 MHz | ADS4142 (65 MSPS) | 87 | dBc | ||
ADS4145 (125 MSPS) | 86 | ||||||
fIN = 70 MHz | ADS4142 (65 MSPS) | 86.5 | |||||
ADS4145 (125 MSPS) | 87 | ||||||
fIN = 100 MHz | ADS4142 (65 MSPS) | 87 | |||||
ADS4145 (125 MSPS) | 85 | ||||||
fIN = 170 MHz | ADS4142 (65 MSPS) | 71 | 85 | ||||
ADS4145 (125 MSPS) | 72.5 | 81.5 | |||||
fIN = 300 MHz | ADS4142 (65 MSPS) | 85 | |||||
ADS4145 (125 MSPS) | 84 | ||||||
Worst spur (other than second and third harmonics) |
fIN = 10 MHz | ADS4142 (65 MSPS) | 96 | dBc | |||
ADS4145 (125 MSPS) | 95 | ||||||
fIN = 70 MHz | 95 | ||||||
fIN = 100 MHz | ADS4142 (65 MSPS) | 94 | |||||
ADS4145 (125 MSPS) | 95 | ||||||
fIN = 170 MHz | ADS4142 (65 MSPS) | 77.5 | 92 | ||||
ADS4145 (125 MSPS) | 78.5 | 91 | |||||
fIN = 300 MHz | ADS4142 (65 MSPS) | 87 | |||||
ADS4145 (125 MSPS) | 88 | ||||||
IMD | Two-tone intermodulation distortion | f1 = 100 MHz, f2 = 105 MHz, each tone at –7 dBFS |
ADS4142 (65 MSPS) | 88.5 | dBFS | ||
ADS4145 (125 MSPS) | 87.5 | ||||||
Input overload recovery | Recovery to within 1% (of final value) for 6-dB overload with sine-wave input | 1 | Clock cycles | ||||
PSRR | AC power-supply rejection ratio | For 100-mVPP signal on AVDD supply, up to 10 MHz | > 30 | dB | |||
ENOB | Effective number of bits | fIN = 170 MHz | ADS4142 (65 MSPS) | 11.5 | LSBs | ||
ADS4145 (125 MSPS) | 11.3 | ||||||
DNL | Differential nonlinearity | fIN = 170 MHz | –0.95 | ±0.5 | 1.7 | LSBs | |
INL | Integrated nonlinearity | fIN = 170 MHz | ±1.5 | ±4.5 | LSBs |
PARAMETER | TEST CONDITIONS | MIN | TYP | MAX | UNIT | |
---|---|---|---|---|---|---|
ANALOG INPUTS | ||||||
Differential input voltage | 2 | VPP | ||||
Differential input resistance | At dc, see Figure 106 | > 1 | MΩ | |||
Differential input capacitance | See Figure 107 | 4 | pF | |||
Analog input bandwidth | 550 | MHz | ||||
Analog input common-mode current (per input pin) | 0.6 | µA/MSPS | ||||
VCM | Common-mode output voltage | 0.95 | V | |||
VCM output current capability | 4 | mA | ||||
DC ACCURACY | ||||||
Offset error | –15 | 2.5 | 15 | mV | ||
Temperature coefficient of offset error | 0.003 | mV/°C | ||||
EGREF | Gain error as a result of internal reference inaccuracy alone | –2 | 2 | %FS | ||
EGCHAN | Gain error of channel alone | –0.2 | %FS | |||
Temperature coefficient of EGCHAN | 0.001 | Δ%/°C | ||||
POWER SUPPLY | ||||||
IAVDD | Analog supply current | ADS4122, ADS4142 (65 MSPS) | 42 | 55 | mA | |
ADS4125, ADS4145 (125 MSPS) | 62 | 75 | ||||
IDRVDD(2) | Output buffer supply current, LVDS interface with 100-Ω external termination, low LVDS swing (200 mV) | ADS4122, ADS4142 (65 MSPS) | 28.5 | mA | ||
ADS4125, ADS4145 (125 MSPS) | 35.5 | |||||
Output buffer supply current, LVDS interface with 100-Ω external termination, standard LVDS swing (350 mV) | ADS4122, ADS4142 (65 MSPS) | 40 | 53 | |||
ADS4125, ADS4145 (125 MSPS) | 48 | 57 | ||||
Output buffer supply current(2)(1), CMOS interface(1), 8-pF external load capacitance, fIN = 2.5 MHz |
ADS4122, ADS4142 (65 MSPS) | 15 | ||||
ADS4125, ADS4145 (125 MSPS) | 23 | |||||
Analog power | ADS4122, ADS4142 (65 MSPS) | 76 | mW | |||
ADS4122, ADS4142 (125 MSPS) | 112 | |||||
Digital power, LVDS interface, low LVDS swing | ADS4122, ADS4142 (65 MSPS) | 52 | mW | |||
ADS4122, ADS4142 (125 MSPS) | 66.5 | |||||
Digital power, CMOS interface(1), 8-pF external load capacitance, fIN = 2.5 MHz | ADS4122, ADS4142 (65 MSPS) | 27 | mW | |||
ADS4122, ADS4142 (125 MSPS) | 41.5 | |||||
Global power-down | 10 | 15 | mW | |||
Standby | ADS4122, ADS4142 (65 MSPS) | 105 | mW | |||
ADS4122, ADS4142 (125 MSPS) | 130 |
PARAMETER | TEST CONDITIONS | MIN | TYP | MAX | UNIT | |
---|---|---|---|---|---|---|
DIGITAL INPUTS (RESET, SCLK, SDATA, SEN, OE) | ||||||
High-level input voltage | RESET, SCLK, SDATA, and SEN support 1.8-V and 3.3-V CMOS logic levels | 1.3 | V | |||
Low-level input voltage | 0.4 | V | ||||
High-level input voltage | OE only supports 1.8-V CMOS logic levels | 1.3 | V | |||
Low-level input voltage | 0.4 | V | ||||
High-level input current: SDATA, SCLK(1) | VHIGH = 1.8 V | 10 | µA | |||
High-level input current: SEN | VHIGH = 1.8 V | 0 | µA | |||
Low-level input current: SDATA, SCLK | VLOW = 0 V | 0 | µA | |||
Low-level input current: SEN | VLOW = 0 V | –10 | µA | |||
DIGITAL OUTPUTS (CMOS INTERFACE: D0 TO D13, OVR_SDOUT) | ||||||
High-level output voltage | DRVDD – 0.1 | DRVDD | V | |||
Low-level output voltage | 0 | 0.1 | V | |||
DIGITAL OUTPUTS (LVDS INTERFACE: DA0P/M TO DA13P/M, DB0P/M TO DB13P/M, CLKOUTP/M) | ||||||
High-level output voltage(2) | VODH | Standard swing LVDS | 270 | 350 | 430 | mV |
Low-level output voltage(2) | VODL | Standard swing LVDS | –430 | –350 | –270 | mV |
High-level output voltage(2) | VODH | Low swing LVDS | 200 | mV | ||
Low-level output voltage(2) | VODL | Low swing LVDS | –200 | mV | ||
Output common-mode voltage | VOCM | 0.85 | 1.05 | 1.25 | V |
MIN | TYP | MAX | UNIT | |||
---|---|---|---|---|---|---|
GENERAL | ||||||
tA | Aperture delay | 0.6 | 0.8 | 1.2 | ns | |
Variation of aperture delay between two devices at the same temperature and DRVDD supply | ±100 | ps | ||||
tJ | Aperture jitter | 100 | fS rms | |||
Wakeup time: | Time to valid data after coming out of STANDBY mode | 5 | 25 | µs | ||
Time to valid data after coming out of PDN GLOBAL mode | 100 | 500 | µs | |||
ADC latency(4): | Low-latency mode (default after reset) | 10 | Clock cycles | |||
Low-latency mode disabled (gain enabled, offset correction disabled) | 16 | Clock cycles | ||||
Low-latency mode disabled (gain and offset correction enabled) | 17 | Clock cycles | ||||
DDR LVDS MODE(5)(6) | ||||||
tSU | Data setup time(3): data valid(7) to zero-crossing of CLKOUTP | 2.3 | 3 | ns | ||
tH | Data hold time(3): zero-crossing of CLKOUTP to data becoming invalid(7) | 0.35 | 0.6 | ns | ||
tPDI | Clock propagation delay: input clock rising edge cross-over to output clock rising edge cross-over, sampling frequency ≤ 125 MSPS | 3 | 4.2 | 5.4 | ns | |
Variation of tPDI between two devices at the same temperature and DRVDD supply | ±0.6 | ns | ||||
LVDS bit clock duty cycle of differential clock, (CLKOUTP – CLKOUTM), sampling frequency ≤ 125 MSPS | 48% | |||||
tRISE, tFALL | Data rise time, data fall time: rise time measured from –100 mV to 100 mV, fall time measured from 100 mV to –100 mV, sampling frequency ≤ 125 MSPS | 0.14 | ns | |||
tCLKRISE, tCLKFALL | Output clock rise time, output clock fall time rise time measured from –100 mV to 100 mV, fall time measured from 100 mV to –100 mV, sampling frequency ≤ 125 MSPS | 0.14 | ns | |||
tOE | Output enable (OE) to data delay: time to valid data after OE becomes active | 50 | 100 | ns | ||
PARALLEL CMOS MODE(8) | ||||||
tSETUP | Data setup time: data valid(9) to 50% of CLKOUT rising edge | 3.1 | 3.7 | ns | ||
tHOLD | Data hold time: 50% of of CLKOUT rising edge to data becoming invalid(9) | 3.2 | 4 | ns | ||
tPDI | Clock propagation delay: input clock rising edge cross-over to 50% of output clock rising edge, sampling frequency ≤ 125 MSPS | 4 | 5.5 | 7 | ns | |
Output clock duty cycle of output clock, CLKOUT, sampling frequency ≤ 125 MSPS | 47% | |||||
tRISE, tFALL | Data rise time, data fall time: rise time measured from 20% to 80% of DRVDD, fall time measured from 80% to 20% of DRVDD, sampling frequency ≤ 125 MSPS | 0.35 | ns | |||
tCLKRISE, tCLKFALL | Output clock rise time, output clock fall time: rise time measured from 20% to 80% of DRVDD, fall time measured from 80% to 20% of DRVDD, sampling frequency ≤ 125 MSPS | 0.35 | ns | |||
tOE | Output enable (OE) to data delay: time to valid data after OE becomes active | 20 | 40 | ns |
PARAMETER | MIN | TYP | MAX | UNIT | |
---|---|---|---|---|---|
fSCLK | SCLK frequency (equal to 1/tSCLK) | > dc | 20 | MHz | |
tSLOADS | SEN to SCLK setup time | 25 | ns | ||
tSLOADH | SCLK to SEN hold time | 25 | ns | ||
tDSU | SDATA setup time | 25 | ns | ||
tDH | SDATA hold time | 25 | ns |
MIN | TYP | MAX | UNIT | |||
---|---|---|---|---|---|---|
t1 | Power-on delay from power-up of AVDD and DRVDD to RESET pulse active | 1 | ms | |||
t2 | Reset pulse duration of active RESET signal that resets the serial registers | 10 | ns | |||
1(1) | µs | |||||
t3 | Delay from RESET disable to SEN active | 100 | ns |
SAMPLING FREQUENCY (MSPS) | tsu, SETUP TIME | th, HOLD TIME | tPDI, CLOCK PROPAGATION DELAY | UNIT | ||||||
---|---|---|---|---|---|---|---|---|---|---|
MIN | TYP | MAX | MIN | TYP | MAX | MIN | TYP | MAX | ||
DDR LVDS | ns | |||||||||
65 | 5.5 | 6.5 | 0.35 | 0.6 | ns | |||||
80 | 4.5 | 5.2 | 0.35 | 0.6 | ns | |||||
CMOS (LOW LATENCY ENABLED)(1) | ns | |||||||||
65 | 6.5 | 7.5 | 6.5 | 7.5 | 4 | 5.5 | 7 | ns | ||
80 | 5.4 | 6 | 5.4 | 6 | 4 | 5.5 | 7 | ns | ||
CMOS (LOW LATENCY DISABLED)(1) | ns | |||||||||
65 | 6 | 7 | 7 | 8 | 4 | 5.5 | 7 | ns | ||
80 | 4.8 | 5.5 | 5.7 | 6.5 | 4 | 5.5 | 7 | ns | ||
125 | 2.5 | 3.2 | 3.5 | 4.3 | 4 | 5.5 | 7 | ns |
NOINDENT:
With external 100-Ω termination.NOINDENT:
ADC latency in low-latency mode. At higher sampling frequencies, tDPI is greater than one clock cycle which then makes the overall latency = ADC latency + 1.NOINDENT:
E = Even bits (D0, D2, D4, and so forth). O = Odd bits (D1, D3, D5, and so forth).NOINDENT:
Dn = bits D0, D2, D4, and so forth. Dn + 1 = Bits D1, D3, D5, and so forth.NOINDENT:
Dn = bits D0, D1, D2, and so forth.NOINDENT:
A high pulse on the RESET pin is required in the serial interface mode in case of initialization through hardware reset. For parallel interface operation, RESET must be permanently tied high.The ADS412x and ADS414x devices are high-performance, low-power, 12-bit and 14-bit analog-to-digital converters (ADCs) with maximum sampling rates up to 65 MSPS and 125 MSPS. The conversion process is initiated by a rising edge of the external input clock when the analog input signal is sampled. The sampled signal is sequentially converted by a series of small resolution stages, with the outputs combined in a digital correction logic block. At every clock edge, the sample propagates through the pipeline, resulting in a data latency of 10 clock cycles. The output is available as 12-bit and 14-bit data, in DDR LVDS mode or CMOS mode, and coded in either straight offset binary or binary twos complement format.
The ADS412x and ADS414x family is pin-compatible to the previous generation ADS6149 family; this architecture enables easy migration. However, there are some important differences between the generations, summarized in Table 1.
ADS6149 FAMILY | ADS4145 FAMILY |
---|---|
PINS | |
Pin 21 is NC (not connected) | Pin 21 is NC (not connected) |
Pin 23 is MODE | Pin 23 is RESERVED in the ADS4145 family. It is reserved as a digital control pin for an (as yet) undefined function in the next-generation ADC series. |
SUPPLY | |
AVDD is 3.3 V | AVDD is 1.8 V |
DRVDD is 1.8 V | No change |
INPUT COMMON-MODE VOLTAGE | |
VCM is 1.5 V | VCM is 0.95 V |
SERIAL INTERFACE | |
Protocol: 8-bit register address and 8-bit register data | No change in protocol |
New serial register map | |
EXTERNAL REFERENCE MODE | |
Supported | Not supported |
ADS61B49 FAMILY | ADS41B29, ADS41B49, ADS58B18 FAMILY |
PINS | |
Pin 21 is NC (not connected) | Pin 21 is 3.3 V AVDD_BUF (supply for the analog input buffers) |
Pin 23 is MODE | Pin 23 is a digital control pin for the RESERVED function. Pin 23 functions as SNR Boost enable (B18 only). |
SUPPLY | |
AVDD is 3.3 V | AVDD is 1.8 V, AVDD_BUF is 3.3 V |
DRVDD is 1.8 V | No change |
INPUT COMMON-MODE VOLTAGE | |
VCM is 1.5 V | VCM is 1.7 V |
SERIAL INTERFACE | |
Protocol: 8-bit register address and 8-bit register data | No change in protocol New serial register map |
EXTERNAL REFERENCE MODE | |
Supported | Not supported |
The device has several useful digital functions such as test patterns, gain, and offset correction. All of these functions require extra clock cycles for operation and increase the overall latency and power of the device. Alternately, the device has a low-latency mode in which the raw ADC output is routed to the output data pins with a latency of 10 clock cycles. In this mode, the digital functions are bypassed. Figure 95 shows more details of the processing after the ADC.
The device is in low-latency mode after reset. In order to use any of the digital functions, the low-latency mode must first be disabled by setting the DIS LOW LATENCY register bit to 1. After this process, the respective register bits must be programmed as described in the following sections and in the Serial Register Map section.
The ADS412x and ADS414x include gain settings that can be used to improve SFDR performance. The gain is programmable from 0 dB to 6 dB (in 0.5-dB steps) using the GAIN register bits. For each gain setting, the analog input full-scale range scales proportionally, as shown in Table 2.
The SFDR improvement is achieved at the expense of SNR; for each gain setting, the SNR degrades approximately between 0.5 dB and 1 dB. The SNR degradation is reduced at high input frequencies. As a result, the gain is very useful at high input frequencies because the SFDR improvement is significant with marginal degradation in SNR. Therefore, the gain can be used to trade-off between SFDR and SNR.
After a reset, the device is in low-latency mode and gain function is disabled. To use gain:
GAIN (dB) | TYPE | FULL-SCALE (VPP) |
---|---|---|
0 | Default after reset | 2 |
1 | Programmable | 1.78 |
2 | Programmable | 1.59 |
3 | Programmable | 1.42 |
4 | Programmable | 1.26 |
5 | Programmable | 1.12 |
6 | Programmable | 1 |
The ADS412x and ADS414x have an internal offset correction algorithm that estimates and corrects dc offset up to ±10 mV. The correction can be enabled using the EN OFFSET CORR serial register bit. When enabled, the algorithm estimates the channel offset and applies the correction every clock cycle. The time constant of the correction loop is a function of the sampling clock frequency. The time constant can be controlled using the OFFSET CORR TIME CONSTANT register bits, as described in Table 3.
OFFSET CORR TIME CONSTANT | TIME CONSTANT, TCCLK
(Number of Clock Cycles) |
TIME CONSTANT, TCCLK × 1/fS (sec)(1) |
---|---|---|
0000 | 1M | 8 ms |
0001 | 2M | 16 ms |
0010 | 4M | 33.4 ms |
0011 | 8M | 67 ms |
0100 | 16M | 134 ms |
0101 | 32M | 268 ms |
0110 | 64M | 537 ms |
0111 | 128M | 1.08 s |
1000 | 256M | 2.15 s |
1001 | 512M | 4.3 s |
1010 | 1G | 8.6 s |
1011 | 2G | 17.2 s |
1100 | Reserved | — |
1101 | Reserved | — |
1110 | Reserved | — |
1111 | Reserved | — |
After the offset is estimated, the correction can be frozen by setting FREEZE OFFSET CORR = 1. When frozen, the last estimated value is used for the offset correction of every clock cycle. Note that offset correction is disabled by a default after reset.
After a reset, the device is in low-latency mode and offset correction is disabled. To use offset correction:
Figure 96 shows the time response of the offset correction algorithm after being enabled.
The ADS412x and ADS414x have three power-down modes: power-down global, standby, and output buffer disable.
In this mode, the entire device (including the ADC, internal reference, and the output buffers) is powered down, resulting in reduced total power dissipation of approximately 10 mW. The output buffers are in a high-impedance state. The wake-up time from the global power-down to data becoming valid in normal mode is typically 100 µs. To enter the global power-down mode, set the PDN GLOBAL register bit.
In this mode, only the ADC is powered down and the internal references are active, resulting in a fast wake-up time of 5 µs. The total power dissipation in standby mode is approximately 130 mW at 125 MSPS. To enter the standby mode, set the STBY register bit.
The output buffers can be disabled and put in a high-impedance state; wake-up time from this mode is fast, approximately 100 ns. Disabling the output buffers can be controlled using the PDN OBUF register bit or using the OE pin.
In addition, the converter enters a low-power mode when the input clock frequency falls below 1 MSPS. The power dissipation is approximately 80 mW.
Two output data formats are supported: twos complement and offset binary. Each mode can be selected using the DATA FORMAT serial interface register bit or controlling the DFS pin in parallel configuration mode. In the event of an input voltage overdrive, the digital outputs go to the appropriate full-scale level.
The ADS412x and ADS414x provide either 14-bit data or 12-bit data, respectively, and an output clock synchronized with the data.
Two output interface options are available: double data rate (DDR) LVDS and parallel CMOS. These options can be selected using the LVDS CMOS serial interface register bit or using the DFS pin.
In this mode, the data bits and clock are output using low voltage differential signal (LVDS) levels. Two data bits are multiplexed and output on each LVDS differential pair, as shown in Figure 97 and Figure 98.
Even data bits (D0, D2, D4, and so forth) are output at the falling edge of CLKOUTP and the odd data bits (D1, D3, D5, and so forth) are output at the rising edge of CLKOUTP. Both the rising and falling edges of CLKOUTP must be used to capture all 14 data bits, as shown in Figure 99.
The equivalent circuit of each LVDS output buffer is shown in Figure 100. After reset, the buffer presents an output impedance of 100 Ω to match with the external 100-Ω termination.
The VDIFF voltage is nominally 350 mV, resulting in an output swing of ±350 mV with 100-Ω external termination. The VDIFF voltage is programmable using the LVDS SWING register bits from ±125 mV to ±570 mV.
Additionally, a mode exists to double the strength of the LVDS buffer to support 50-Ω differential termination. This mode can be used when the output LVDS signal is routed to two separate receiver chips, each using a 100-Ω termination. The mode can be enabled using the LVDS DATA STRENGTH and LVDS CLKOUT STRENGTH register bits for data and output clock buffers, respectively.
The buffer output impedance behaves in the same way as a source-side series termination. By absorbing reflections from the receiver end, the output impedance of buffer helps improve signal integrity.
In CMOS mode, each data bit is output on a separate pin as the CMOS voltage level, for every clock cycle. The rising edge of the output clock CLKOUT can be used to latch data in the receiver. Figure 101 depicts the CMOS output interface.
Switching noise (caused by CMOS output data transitions) can couple into the analog inputs and degrade SNR. The coupling and SNR degradation increases as the output buffer drive is made stronger. To minimize this degradation, the CMOS output buffers are designed with controlled drive strength. The default drive strength ensures a wide data stable window. TI recommends using short traces (one to two inches or 2.54 cm to 5.08 cm) terminated with less than 5-pF load capacitance, as shown in Figure 102.
With CMOS outputs, the DRVDD current scales with the sampling frequency and the load capacitance on every output pin. The maximum DRVDD current occurs when each output bit toggles between 0 and 1 every clock cycle. In actual applications, this condition is unlikely to occur. The actual DRVDD current is determined by the average number of output bits switching, which is a function of the sampling frequency and the nature of the analog input signal.
where
Figure 86 details the current across sampling frequencies at 2-MHz analog input frequency.
The performance of the ADS41xx can be enhanced by writing certain SPI registers bits with minimal impact (less than 10 mW) on power consumption. Table 4 lists the device high-performance modes.
PARAMETER | DESCRIPTION |
---|---|
Mode 1 | Set the MODE 1 register bits to get best performance across sample clock and input signal frequencies. Register address = 03h, register data = 03h |
Mode 2 | Set the MODE 2 register bit to get best performance at high input signal frequencies greater than 230 MHz. Register address = 4Ah, register data = 01h |
The ADS412x and ADS414x have several modes that can be configured using a serial programming interface, as described in Table 5, Table 6, and Table 7. In addition, the devices have two dedicated parallel pins for quickly configuring commonly used functions. The parallel pins are DFS (analog 4-level control pin) and OE (digital control pin). The analog control pins can be easily configured using a simple resistor divider (with 10% tolerance resistors).
VOLTAGE APPLIED ON DFS | DESCRIPTION (Data Format, Output Interface) |
---|---|
0, 100 mV, –0 mV | Twos complement, DDR LVDS |
(3/8) AVDD ± 100 mV | Twos complement, parallel CMOS |
(5/8) AVDD ± 100 mV | Offset binary, parallel CMOS |
AVDD, 0 mV, –100 mV | Offset binary, DDR LVDS |
VOLTAGE APPLIED ON OE | DESCRIPTION |
---|---|
0 | Output data buffers disabled |
AVDD | Output data buffers enabled |
When the serial interface is not used, the SDATA pin can also be used as a digital control pin to place the device in standby mode. To enable this functionality, the RESET pin must be tied high. In this mode, SEN and SCLK do not have any alternative functions. Keep SEN tied high and SCLK tied low on the board.
VOLTAGE APPLIED ON SDATA | DESCRIPTION |
---|---|
0 | Normal operation |
Logic high | Device enters standby |
The analog-to-digital converter (ADC) has a set of internal registers that can be accessed by the serial interface formed by the SEN (serial interface enable), SCLK (serial interface clock), and SDATA (serial interface data) pins. Serially shifting bits into the device is enabled when SEN is low. Serial data SDATA are latched at every falling edge of SCLK when SEN is active (low). The serial data are loaded into the register at every 16th SCLK falling edge when SEN is low. If the word length exceeds a multiple of 16 bits, the excess bits are ignored. Data can be loaded in multiples of 16-bit words within a single active SEN pulse. The first eight bits form the register address and the remaining eight bits are the register data. The interface can work with SCLK frequency from 20 MHz down to very low speeds (a few hertz) and also with a non-50% SCLK duty cycle.
After power-up, the internal registers must be initialized to the default values. This initialization can be accomplished in one of two ways:
The serial register readout function allows the contents of the internal registers to be read back on the OVR_SDOUT pin. This readback may be useful as a diagnostic check to verify the serial interface communication between the external controller and the ADC.
After power-up and device reset, the OVR_SDOUT pin functions as an over-range indicator pin by default. When the readout mode is enabled, OVR_SDOUT outputs the contents of the selected register serially:
Table 8 summarizes the functions supported by the serial interface.
REGISTER ADDRESS | DEFAULT VALUE AFTER RESET | REGISTER DATA | |||||||
---|---|---|---|---|---|---|---|---|---|
A[7:0] (Hex) | D[7:0] (Hex) | D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
00 | 00 | 0 | 0 | 0 | 0 | 0 | 0 | RESET | READOUT |
01 | 00 | LVDS SWING | 0 | 0 | |||||
03 | 00 | 0 | 0 | 0 | 0 | 0 | 0 | HIGH PERF MODE 1 | |
25 | 00 | GAIN | DISABLE GAIN | TEST PATTERNS | |||||
26 | 00 | 0 | 0 | 0 | 0 | 0 | 0 | LVDS CLKOUT STRENGTH | LVDS DATA STRENGTH |
3D | 00 | DATA FORMAT | EN OFFSET CORR | 0 | 0 | 0 | 0 | 0 | |
3F | 00 | CUSTOM PATTERN HIGH D[13:6] | |||||||
40 | 00 | CUSTOM PATTERN D[5:0] | 0 | 0 | |||||
41 | 00 | LVDS CMOS | CMOS CLKOUT STRENGTH | EN CLKOUT RISE | CLKOUT RISE POSN | EN CLKOUT FALL | |||
42 | 00 | CLKOUT FALL POSN | 0 | 0 | DIS LOW LATENCY | STBY | 0 | 0 | |
43 | 00 | 0 | PDN GLOBAL | 0 | PDN OBUF | 0 | 0 | EN LVDS SWING | |
4A | 00 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | HIGH PERF MODE 2 |
BF | 00 | OFFSET PEDESTAL | 0 | 0 | |||||
CF | 00 | FREEZE OFFSET CORR | 0 | OFFSET CORR TIME CONSTANT | 0 | 0 | |||
DF | 00 | 0 | 0 | LOW SPEED | 0 | 0 | 0 | 0 |
For best performance, two special mode register bits must be enabled: HI PERF MODE 1 and HI PERF MODE 2.
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | 0 | 0 | 0 | 0 | 0 | RESET | READOUT |
Bits[7:2] | Always write 0 |
Bit 1 | RESET: Software reset applied |
This bit resets all internal registers to the default values and self-clears to 0 (default = 1). | |
Bit 0 | READOUT: Serial readout |
This bit sets the serial readout of the registers. 0 = Serial readout of registers disabled; the OVR_SDOUT pin functions as an overvoltage indicator. 1 = Serial readout enabled; the OVR_SDOUT pin functions as a serial data readout. |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
LVDS SWING | 0 | 0 |
Bits[7:2] | LVDS SWING: LVDS swing programmability(1) |
000000 = Default LVDS swing; ±350 mV with external 100-Ω termination 011011 = LVDS swing increases to ±410 mV 110010 = LVDS swing increases to ±465 mV 010100 = LVDS swing increases to ±570 mV 111110 = LVDS swing decreases to ±200 mV 001111 = LVDS swing decreases to ±125 mV |
|
Bits[1:0] | Always write 0 |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | 0 | 0 | 0 | 0 | 0 | HI PERF MODE 1 |
Bits[7:2] | Always write 0 |
Bits[1:0] | HI PERF MODE 1: High performance mode 1 |
00 = Default performance after reset 01 = Do not use 10 = Do not use 11 = For best performance across sampling clock and input signal frequencies, set the HIGH PERF MODE 1 bits |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
GAIN | DISABLE GAIN | TEST PATTERNS |
Bits[7:4] | GAIN: Gain programmability | ||
These bits set the gain programmability in 0.5-dB steps. | |||
0000 = 0-dB gain (default after reset) 0001 = 0.5-dB gain 0010 = 1.0-dB gain 0011 = 1.5-dB gain 0100 = 2.0-dB gain 0101 = 2.5-dB gain 0110 = 3.0-dB gain |
0111 = 3.5-dB gain 1000 = 4.0-dB gain 1001 = 4.5-dB gain 1010 = 5.0-dB gain 1011 = 5.5-dB gain 1100 = 6-dB gain |
||
Bit 3 | DISABLE GAIN: Gain setting | ||
This bit sets the gain. 0 = Gain enabled; gain is set by the GAIN bits only if low-latency mode is disabled 1 = Gain disabled |
|||
Bits[2:0] | TEST PATTERNS: Data capture | ||
These bits verify data capture. 000 = Normal operation 001 = Outputs all 0s 010 = Outputs all 1s 011 = Outputs toggle pattern |
|||
In the ADS4122/25, output data D[11:0] is an alternating sequence of 010101010101 and 101010101010. In the ADS4142/45, output data D[13:0] is an alternating sequence of 01010101010101 and 10101010101010. |
|||
100 = Outputs digital ramp | |||
In ADS4122/25, output data increments by one LSB (12-bit) every fourth clock cycle from code 0 to code 4095 In ADS4142/45, output data increments by one LSB (14-bit) every clock cycle from code 0 to code 16383 |
|||
101 = Output custom pattern (use registers 3Fh and 40h for setting the custom pattern) 110 = Unused 111 = Unused |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | 0 | 0 | 0 | 0 | 0 | LVDS CLKOUT STRENGTH | LVDS DATA STRENGTH |
Bits[7:2] | Always write 0 |
Bit 1 | LVDS CLKOUT STRENGTH: LVDS output clock buffer strength |
This bit determines the external termination to be used with the LVDS output clock buffer. 0 = 100-Ω external termination (default strength) 1 = 50-Ω external termination (2x strength) |
|
Bit 0 | LVDS DATA STRENGTH: LVDS data buffer strength |
This bit determines the external termination to be used with all of the LVDS data buffers. 0 = 100-Ω external termination (default strength) 1 = 50-Ω external termination (2x strength) |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
DATA FORMAT | EN OFFSET CORR | 0 | 0 | 0 | 0 | 0 |
Bits[7:6] | DATA FORMAT: Data format selection |
These bits selects the data format. 00 = The DFS pin controls data format selection 10 = Twos complement 11 = Offset binary |
|
Bit 5 | ENABLE OFFSET CORR: Offset correction setting |
This bit sets the offset correction. 0 = Offset correction disabled 1 = Offset correction enabled |
|
Bits[4:0] | Always write 0 |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
CUSTOM PATTERN D13 | CUSTOM PATTERN D12 | CUSTOM PATTERN D11 | CUSTOM PATTERN D10 | CUSTOM PATTERN D9 | CUSTOM PATTERN D8 | CUSTOM PATTERN D7 | CUSTOM PATTERN D6 |
Bits[7:0] | CUSTOM PATTERN(1) |
These bits set the custom pattern. |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
CUSTOM PATTERN D5 | CUSTOM PATTERN D4 | CUSTOM PATTERN D3 | CUSTOM PATTERN D2 | CUSTOM PATTERN D1 | CUSTOM PATTERN D0 | 0 | 0 |
Bits[7:2] | CUSTOM PATTERN(1) |
These bits set the custom pattern. | |
Bits[1:0] | Always write 0 |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
LVDS CMOS | CMOS CLKOUT STRENGTH | EN CLKOUT RISE | CLKOUT RISE POSN | EN CLKOUT FALL |
Bits[7:6] | LVDS CMOS: Interface selection |
These bits select the interface. 00 = The DFS pin controls the selection of either LVDS or CMOS interface 10 = The DFS pin controls the selection of either LVDS or CMOS interface 01 = DDR LVDS interface 11 = Parallel CMOS interface |
|
Bits[5:4] | CMOS CLKOUT STRENGTH |
Controls strength of CMOS output clock only. 00 = Maximum strength (recommended and used for specified timings) 01 = Medium strength 10 = Low strength 11 = Very low strength |
|
Bit 3 | ENABLE CLKOUT RISE |
0 = Disables control of output clock rising edge 1 = Enables control of output clock rising edge |
|
Bits[2:1] | CLKOUT RISE POSN: CLKOUT rise control |
Controls position of output clock rising edge | |
LVDS interface: 00 = Default position (timings are specified in this condition) 01 = Setup reduces by 500 ps, hold increases by 500 ps 10 = Data transition is aligned with rising edge 11 = Setup reduces by 200 ps, hold increases by 200 ps |
|
CMOS interface: 00 = Default position (timings are specified in this condition) 01 = Setup reduces by 100 ps, hold increases by 100 ps 10 = Setup reduces by 200 ps, hold increases by 200 ps 11 = Setup reduces by 1.5 ns, hold increases by 1.5 ns |
|
Bit 0 | ENABLE CLKOUT FALL |
0 = Disables control of output clock fall edge 1 = Enables control of output clock fall edge |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
CLKOUT FALL CTRL | 0 | 0 | DIS LOW LATENCY | STBY | 0 | 0 |
Bits[7:6] | CLKOUT FALL CTRL |
Controls position of output clock falling edge | |
LVDS interface: 00 = Default position (timings are specified in this condition) 01 = Setup reduces by 400 ps, hold increases by 400 ps 10 = Data transition is aligned with rising edge 11 = Setup reduces by 200 ps, hold increases by 200 ps |
|
CMOS interface: 00 = Default position (timings are specified in this condition) 01 = Falling edge is advanced by 100 ps 10 = Falling edge is advanced by 200 ps 11 = Falling edge is advanced by 1.5 ns |
|
Bits[5:4] | Always write 0 |
Bit 3 | DIS LOW LATENCY: Disable low latency |
This bit disables low-latency mode, 0 = Low-latency mode is enabled. Digital functions such as gain, test patterns and offset correction are disabled 1 = Low-latency mode is disabled. This setting enables the digital functions. See the Digital Functions and Low Latency Mode section. |
|
Bit 2 | STBY: Standby mode |
This bit sets the standby mode. 0 = Normal operation 1 = Only the ADC and output buffers are powered down; internal reference is active; wake-up time from standby is fast |
|
Bits[1:0] | Always write 0 |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | PDN GLOBAL | 0 | PDN OBUF | 0 | 0 | EN LVDS SWING |
Bit 0 | Always write 0 |
Bit 6 | PDN GLOBAL: Power-down |
This bit sets the state of operation. 0 = Normal operation 1 = Total power down; the ADC, internal references, and output buffers are powered down; slow wake-up time. |
|
Bit 5 | Always write 0 |
Bit 4 | PDN OBUF: Power-down output buffer |
This bit set the output data and clock pins. 0 = Output data and clock pins enabled 1 = Output data and clock pins powered down and put in high- impedance state |
|
Bits[3:2] | Always write 0 |
Bits[1:0] | EN LVDS SWING: LVDS swing control |
00 = LVDS swing control using LVDS SWING register bits is disabled 01 = Do not use 10 = Do not use 11 = LVDS swing control using LVDS SWING register bits is enabled |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | 0 | 0 | 0 | 0 | 0 | 0 | HI PERF MODE 2 |
Bits[7:1] | Always write 0 |
Bit[0] | HI PERF MODE 2: High performance mode 2 |
This bit is recommended for high input signal frequencies greater than 230 MHz. 0 = Default performance after reset 1 = For best performance with high-frequency input signals, set the HIGH PERF MODE 2 bit |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
OFFSET PEDESTAL | 0 | 0 |
Bits[7:2] | OFFSET PEDESTAL | |
These bits set the offset pedestal. When the offset correction is enabled, the final converged value after the offset is corrected is the ADC mid-code value. A pedestal can be added to the final converged value by programming these bits. |
||
ADS414x VALUE | PEDESTAL | |
011111 011110 011101 — 000000 — 111111 111110 — 100000 |
31 LSB 30 LSB 29 LSB — 0 LSB — –1 LSB –2 LSB — –32 LSB |
|
Bits[1:0] | Always write 0 |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
FREEZE OFFSET CORR | 0 | OFFSET CORR TIME CONSTANT | 0 | 0 |
Bit 7 | FREEZE OFFSET CORR | |
This bit sets the freeze offset correction. 0 = Estimation of offset correction is not frozen (bit EN OFFSET CORR must be set) 1 = Estimation of offset correction is frozen (bit EN OFFSET CORR must be set). When frozen, the last estimated value is used for offset correction every clock cycle. See the Offset Correction section. |
||
Bit 6 | Always write 0 | |
Bits[5:2] | OFFSET CORR TIME CONSTANT | |
These bits set the offset correction time constant for the correction loop time constant in number of clock cycles. | ||
VALUE | TIME CONSTANT (Number of Clock Cycles) | |
0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 |
1M 2M 4M 8M 16M 32M 64M 128M 256M 512M 1G 2G |
|
Bits[1:0] | Always write 0 |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | 0 | LOW SPEED | 0 | 0 | 0 | 0 |
Bits[7:6] | Always write 0 | |
Bits[5:4] | LOW SPEED: Low-speed mode | |
For the ADS4122/42, the low-speed mode is enabled by default after reset. 00, 01, 10, 11 = Do not use |
||
For the ADS4125/55 only: 00, 01, 10 = Low-speed mode disabled (default state after reset); this setting is recommended for sampling rates greater than 80 MSPS. 11 = Low-speed mode enabled; this setting is recommended for sampling rates less than or equal to 80 MSPS. |
||
Bits[3:0] | Always write 0 |
NOTE
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The ADS412x and ADS414x are lower sampling speed members of the ADS41xx family of ultra-low-power analog-to-digital converters (ADCs). The conversion process is initiated by a rising edge of the external input clock and the analog input signal is sampled. The sampled signal is sequentially converted by a series of small resolution stages, with the outputs combined in a digital correction logic block. At every clock edge the sample propagates through the pipeline, resulting in a data latency of 10 clock cycles. The output is available as 14-bit data or 12-bit data, in DDR LVDS mode or CMOS mode, and coded in either straight offset binary or binary twos complement format.
The analog input consists of a switched-capacitor-based, differential, sample-and-hold architecture. This differential topology results in very good ac performance even for high input frequencies at high sampling rates. The INP and INM pins must be externally biased around a common-mode voltage of 0.95 V, available on the VCM pin. For a full-scale differential input, each input INP and INM pin must swing symmetrically between (VCM + 0.5 V) and (VCM – 0.5 V), resulting in a 2-VPP differential input swing. The input sampling circuit has a high
3-dB bandwidth that extends up to 550 MHz (measured from the input pins to the sampled voltage). Figure 105 shows an equivalent circuit for the analog input.
For optimum performance, the analog inputs must be driven differentially. This technique improves the common-mode noise immunity and even-order harmonic rejection. A 5-Ω to 15-Ω resistor in series with each input pin is recommended to damp out ringing caused by package parasitics. Low impedance (less than 50 Ω) must be present for the common-mode switching currents. This impedance can be achieved by using two resistors from each input terminated to the common-mode voltage (VCM).
Note that the device includes an internal R-C filter from each input to ground. The purpose of this filter is to absorb the glitches caused by the opening and closing of the sampling capacitors. The cutoff frequency of the R-C filter involves a trade-off. A lower cutoff frequency (larger C) absorbs glitches better, but also reduces the input bandwidth and the maximum input frequency that can be supported. On the other hand, with no internal R-C filter, high input frequency can be supported but now the sampling glitches must be supplied by the external driving circuit. The inductance of the package bond wires limits the ability of the external driving circuit to support the sampling glitches.
In the ADS412x and ADS414x, the R-C component values are optimized when supporting high input bandwidth (550 MHz). However, in applications where very high input frequency support is not required, filtering of the glitches can be improved further with an external R-C-R filter; see Figure 108 and Figure 109).
In addition, the drive circuit may have to be designed to provide a low insertion loss over the desired frequency range and matched impedance to the source. When designing the drive circuit, the ADC impedance must be considered. Figure 106 and Figure 107 show the impedance (ZIN = RIN || CIN) looking into the ADC input pins.
Two example driving circuit configurations are shown in Figure 108 and Figure 109—one optimized for low bandwidth (low input frequencies) and the other one for high bandwidth to support higher input frequencies. In Figure 108, an external R-C-R filter with 3.3 pF is used to help absorb sampling glitches. The R-C-R filter limits the bandwidth of the drive circuit, making the drive circuit suitable for low input frequencies (up to 250 MHz). Transformers such as ADT1-1WT or WBC1-1 can be used up to 250 MHz.
For higher input frequencies, the R-C-R filter can be dropped. Together with the lower series resistors (5 Ω to 10 Ω), this drive circuit provides higher bandwidth to support frequencies up to 500 MHz (as shown in Figure 109). A transmission line transformer such as ADTL2-18 can be used.
Note that both the drive circuits have been terminated by 50 Ω near the ADC side. The termination is accomplished by a 25-Ω resistor from each input to the 0.95-V common-mode (VCM) from the device. This termination allows the analog inputs to be biased around the required common-mode voltage.
The mismatch in the transformer parasitic capacitance (between the windings) results in degraded even-order harmonic performance. Connecting two identical RF transformers back-to-back helps minimize this mismatch and good performance is obtained for high-frequency input signals. An additional termination resistor pair may be required between the two transformers, as shown in Figure 108 and Figure 109. The center point of this termination is connected to ground to improve the balance between the P (positive) and M (negative) sides. The values of the terminations between the transformers and on the secondary side must be chosen to obtain an effective 50 Ω (for a 50-Ω source impedance).
Figure 108 and Figure 109 use 1:1 transformers with a 50-Ω source. As explained in the Drive Circuit Requirements section, this architecture helps to present a low source impedance to absorb sampling glitches. With a 1:4 transformer, the source impedance is 200 Ω. The higher source impedance is unable to absorb the sampling glitches effectively and can lead to degradation in performance (compared to using 1:1 transformers).
In almost all cases, either a band-pass or low-pass filter is needed to obtain the desired dynamic performance, as shown in Figure 110. Such a filter presents low source impedance at the high frequencies corresponding to the sampling glitch and helps avoid the performance loss with the high source impedance.
To ensure a low-noise, common-mode reference, the VCM pin is filtered with a 0.1-µF low-inductance capacitor connected to ground. The VCM pin is designed to directly drive the ADC inputs. Each ADC input pin sinks a common-mode current of approximately 0.6 µA per MSPS of clock frequency.
The ADS412x and ADS414x clock inputs can be driven differentially (sine, LVPECL, or LVDS) or single-ended (LVCMOS), with little or no difference in performance between them. The common-mode voltage of the clock inputs is set to VCM using internal 5-kΩ resistors. This setting allows the use of transformer-coupled drive circuits for sine-wave clock or ac-coupling for LVPECL and LVDS clock sources. Figure 111 shows an equivalent circuit for the input clock.
A single-ended CMOS clock can be ac-coupled to the CLKP input, with CLKM connected to ground with a 0.1-μF capacitor, as shown in Figure 112. For best performance, the clock inputs must be driven differentially, reducing susceptibility to common-mode noise. For high input frequency sampling, TI recommends using a clock source with very low jitter. Band-pass filtering of the clock source can help reduce the effects of jitter. There is no change in performance with a non-50% duty cycle clock input. Figure 113 shows a differential circuit.
The device has an OVR pin that provides information about analog input overload. At any clock cycle, if the sampled input voltage exceeds the positive or negative full-scale range, the OVR pin goes high. The OVR remains high as long as the overload condition persists. The OVR pin is a CMOS output buffer (running off DRVDD supply), independent of the type of output data interface (DDR, LVDS, or CMOS).
For a positive overload, the D[13:0] output data bits are 3FFFh in offset binary output format and 1FFFh in twos complement output format. For a negative input overload, the output code is 0000h in offset binary output format and 2000h in twos complement output format.
When ADS41xx is used at lower sampling rates (< 20 MSPS), set the LOW SPEED register bit (address DFh, bit[5:4]). At low sampling rates, use the device in CMOS interface mode which saves power and results in better setup and hold time compared to LVDS interface mode.
fS = 10 MSPS, fIN = 12 MHz, SNR = 70.9 dBFS, SFDR = 88 dBc, SINAD = 70.8 dBFS, THD = 86 dBc |
fS = 3 MSPS, fIN = 4 MHz |
fS = 5 MSPS, fIN = 3 MHz |
fS = 10 MSPS, fIN = 3 MHz |
fS = 20 MSPS, fIN = 3 MHz |
fS = 50 MSPS, fIN = 3 MHz |
fIN = 3 MHz |
fS = 3 MSPS, fIN = 4 MHz |
fS = 10 MSPS, fIN = 3 MHz |
fIN = 12 MHz |
fS = 10 MSPS, fIN = 12 MHz, SNR = 73.6 dBFS, SFDR = 88 dBc, SINAD = 73.4 dBFS, THD = 86 dBc |
fS = 20 MSPS, fIN = 12 MHz, SNR = 73.9 dBFS, SFDR = 89 dBc, SINAD = 73.7 dBFS, THD = 87 dBc |
fS = 50 MSPS, fIN = 12 MHz, SNR = 73.8 dBFS, SFDR = 88 dBc, SINAD = 73.6 dBFS, THD = 86 dBc |
fS = 3 MSPS, fIN = 4 MHz |
fS = 5 MSPS, fIN = 3 MHz |
fS = 10 MSPS, fIN = 3 MHz |
fS = 20 MSPS, fIN = 3 MHz |
fS = 50 MSPS, fIN = 3 MHz |
RMS = 1.1523 LSB |
RMS = 1.104 LSB |
fIN = 3 MHz |
fS = 10 MSPS, fIN = 3 MHz, SNR = 73.9 dBFS, SFDR = 88 dBc, SINAD = 73.7 dBFS, THD = 86 dBc |
fS = 50 MSPS, fIN = 3 MHz, SNR = 73.8 dBFS, SFDR = 89 dBc, SINAD = 73.6 dBFS, THD = 86 dBc |
fS = 3 MSPS, fIN = 4 MHz |
fS = 10 MSPS, fIN = 3 MHz |
RMS = 1.080 LSB |
RMS = 1.072 LSB |
fIN = 12 MHz |
Figure 162 shows typical power consumption at lower sampling rates on each supply.
Table 9 describes the set-up and hold times for the digital outputs of the ADS41xx with respect to the output clock at low sampling rates.
SAMPLING FREQUENCY (MSPS) | SETUP TIME, tSU | HOLD TIME, tHO | UNIT | ||||
---|---|---|---|---|---|---|---|
MIN | TYP | MAX | MIN | TYP | MAX | ||
CMOS (Low Latency Enabled) | |||||||
5 | 99.4 | 100.4 | 97.9 | 98.7 | ns | ||
10 | 49.0 | 49.7 | 48.5 | 49.3 | ns | ||
20 | 23.3 | 24.2 | 23.9 | 24.8 | ns | ||
30 | 15.0 | 15.8 | 15.7 | 16.6 | ns | ||
40 | 10.7 | 11.4 | 11.5 | 12.5 | ns | ||
50 | 8.2 | 9.0 | 9.1 | 10.0 | ns | ||
CMOS (Low Latency Disabled) | |||||||
5 | 99.6 | 100.3 | 97.8 | 98.5 | ns | ||
10 | 49.1 | 49.7 | 48.2 | 49.1 | ns | ||
20 | 23.6 | 24.2 | 23.6 | 24.6 | ns | ||
30 | 15.2 | 15.7 | 15.3 | 16.4 | ns | ||
40 | 10.9 | 11.4 | 11.2 | 12.3 | ns | ||
50 | 8.4 | 8.9 | 8.6 | 9.8 | ns |
An example schematic for a typical application of the ADS414x is shown in Figure 163.
Example design requirements are listed in Table 10 for the ADC portion of the signal chain. These requirements do not necessary reflect the requirements of an actual system, but rather demonstrate why the ADS412x and ADS414x can be chosen for a system based on a set of requirements.
The analog input of the ADS412x and ADS414x is typically driven by a fully differential amplifier. The amplifier must have sufficient bandwidth for the frequencies of interest. The noise and distortion performance of the amplifier affect the combined performance of the ADC and amplifier. The amplifier is often ac-coupled to the ADC to allow both the amplifier and ADC to operate at the optimal common-mode voltages. The amplifier can be dc-coupled to the ADC if required. An alternate approach is to drive the ADC using transformers. DC coupling cannot be used with the transformer approach.
The ADS412x and ADS414x must be driven by a high-performance clock driver such as a clock jitter cleaner. The clock must have low noise to maintain optimal performance. LVPECL is the most common clocking interface, but LVDS and LVCMOS can be used as well. TI does not advise driving the clock input from an FPGA unless the noise degradation can be tolerated, such as for input signals near dc where the clock noise impact is minimal.
The ADS412x and ADS414x supports both LVDS and CMOS interfaces. The LVDS interface must be used for best performance when operating at maximum sampling rate. The LVDS outputs can be connected directly to the FPGA without any additional components. When using CMOS outputs resistors must be placed in series with the outputs to reduce the output current spikes to limit the performance degradation. The resistors must be large enough to limit current spikes but not so large as to significantly distort the digital output waveform. An external CMOS buffer must be used when driving distances greater than a few inches to reduce ground bounce within the ADC.
Figure 164 shows the results of a 100-MHz signal sampled at 65 MHz captured by the ADS4122.
SNR = 70.11 dBFS, SFDR = 87.74 dBFS, THD = 84.33 dB, SINAD = 70.03 dBFS |
The ADS412x and ADS414x have two power supplies, one analog (AVDD) and one digital (DRVDD) supply. Both supplies have a nominal voltage of 1.8 V. The AVDD supply is noise sensitive and the digital supply is not.
For best performance, the AVDD supply must be driven by a low noise linear regulator and separated from the DRVDD supply. AVDD and DRVDD can share a single supply but must be isolated by a ferrite bead and bypass capacitors, in a PI-filter configuration, at a minimum. The digital noise is concentrated at the sampling frequency and harmonics of the sampling frequency and could contain noise related to the sampled signal. When developing schematics, leave extra placeholders for additional supply filtering.
DC-DC switching power supplies can be used to power DRVDD without issue. AVDD can be powered from a switching regulator. Noise and spurs on the AVDD power supply affect the SNR and SFDR of the ADC and show up near dc and as a modulated component around the input frequency. If a switching regulator is used, then the regulator must be designed to have minimal voltage ripple. Supply filtering must be used to limit the amount of spurious noise at the AVDD supply pins. Extra placeholders must be placed on the schematic for additional filtering. Optimization of filtering in the final system is likely needed to achieve the desired performance. The choice of power supply ultimately depends on the system requirements. For instance, if very low phase noise is required then use of a switching regulator is not recommended.
Because the ADS412x and ADS414x already includes internal decoupling, minimal external decoupling can be used without loss in performance. Note that decoupling capacitors can help filter external power-supply noise; thus, the optimum number of capacitors depends on the actual application. A 0.1-µF capacitor is recommended near each supply pin. The decoupling capacitors must be placed very close to the converter supply pins.
A single ground plane is sufficient to give good performance, provided the analog, digital, and clock sections of the board are cleanly partitioned. See the ADS414x, ADS412x EVM User Guide for details on layout and grounding.
Because the ADS412x and ADS414x already include internal decoupling, minimal external decoupling can be used without loss in performance. Note that decoupling capacitors can help filter external power-supply noise, so the optimum number of capacitors depends on the actual application. The decoupling capacitors must be placed very close to the converter supply pins.
In addition to providing a path for heat dissipation, the thermal pad is also electrically internally connected to the digital ground. Therefore, solder the exposed pad to the ground plane for best thermal and electrical performance. For detailed information, see application notes, QFN Layout Guidelines (SLOA122) and QFN/SON PCB Attachment (SLUA271) that are both available for download at www.ti.com.