SBAS844 May   2017 ADC32RF42

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Family Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 AC Performance Characteristics
    7. 7.7 Digital Requirements
    8. 7.8 Timing Requirements
    9. 7.9 Typical Characteristics
  8. 8 Parameter Measurement Information
    1. 8.1 Input Clock Diagram
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  Analog Inputs
        1. 9.3.1.1 Input Clamp Circuit
      2. 9.3.2  Clock Input
      3. 9.3.3  SYSREF Input
        1. 9.3.3.1 Using SYSREF
        2. 9.3.3.2 Frequency of the SYSREF Signal
      4. 9.3.4  DDC Block
        1. 9.3.4.1 Operating Mode: Receiver
        2. 9.3.4.2 Operating Mode: Wide-Bandwidth Observation Receiver
        3. 9.3.4.3 Decimation Filters
          1. 9.3.4.3.1 Divide-by-4
          2. 9.3.4.3.2 Divide-by-6
          3. 9.3.4.3.3 Divide-by-8
          4. 9.3.4.3.4 Divide-by-9
          5. 9.3.4.3.5 Divide-by-10
          6. 9.3.4.3.6 Divide-by-12
          7. 9.3.4.3.7 Divide-by-16
        4. 9.3.4.4 Digital Multiplexer (MUX)
        5. 9.3.4.5 Numerically-Controlled Oscillators (NCOs) and Mixers
      5. 9.3.5  NCO Switching
      6. 9.3.6  SerDes Transmitter Interface
      7. 9.3.7  Eye Diagrams
      8. 9.3.8  Alarm Outputs: Power Detectors for AGC Support
        1. 9.3.8.1 Absolute Peak Power Detector
        2. 9.3.8.2 Crossing Detector
        3. 9.3.8.3 RMS Power Detector
        4. 9.3.8.4 GPIO AGC MUX
      9. 9.3.9  Power-Down Mode
      10. 9.3.10 ADC Test Pattern
        1. 9.3.10.1 Digital Block
        2. 9.3.10.2 Transport Layer
        3. 9.3.10.3 Link Layer
    4. 9.4 Device Functional Modes
      1. 9.4.1 Device Configuration
      2. 9.4.2 JESD204B Interface
        1. 9.4.2.1 JESD204B Initial Lane Alignment (ILA)
        2. 9.4.2.2 JESD204B Frame Assembly
        3. 9.4.2.3 JESD204B Frame Assembly in Bypass Mode
        4. 9.4.2.4 JESD204B Frame Assembly with Decimation (Single-Band DDC): Complex Output
        5. 9.4.2.5 JESD204B Frame Assembly with Decimation (Single-Band DDC): Real Output
        6. 9.4.2.6 JESD204B Frame Assembly with Decimation (Single-Band DDC): Real Output
        7. 9.4.2.7 JESD204B Frame Assembly with Decimation (Dual-Band DDC): Complex Output
        8. 9.4.2.8 JESD204B Frame Assembly with Decimation (Dual-Band DDC): Real Output
      3. 9.4.3 Serial Interface
        1. 9.4.3.1 Serial Register Write: Analog Bank
        2. 9.4.3.2 Serial Register Readout: Analog Bank
        3. 9.4.3.3 Serial Register Write: Digital Bank
        4. 9.4.3.4 Serial Register Readout: Digital Bank
        5. 9.4.3.5 Serial Register Write: Decimation Filter and Power Detector Pages
    5. 9.5 Register Maps
      1. 9.5.1  Example Register Writes
      2. 9.5.2  Register Descriptions
        1. 9.5.2.1 General Registers
          1. 9.5.2.1.1 Register 000h (address = 000h), General Registers
          2. 9.5.2.1.2 Register 002h (address = 002h), General Registers
          3. 9.5.2.1.3 Register 003h (address = 003h), General Registers
          4. 9.5.2.1.4 Register 004h (address = 004h), General Registers
          5. 9.5.2.1.5 Register 010h (address = 010h), General Registers
          6. 9.5.2.1.6 Register 011h (address = 011h), General Registers
          7. 9.5.2.1.7 Register 012h (address = 012h), General Registers
      3. 9.5.3  Master Page (M = 0)
        1. 9.5.3.1 Register 020h (address = 020h), Master Page
        2. 9.5.3.2 Register 032h (address = 032h), Master Page
        3. 9.5.3.3 Register 039h (address = 039h), Master Page
        4. 9.5.3.4 Register 03Ch (address = 03Ch), Master Page
        5. 9.5.3.5 Register 05Ah (address = 05Ah), Master Page
        6. 9.5.3.6 Register 03Dh (address = 3Dh), Master Page
        7. 9.5.3.7 Register 057h (address = 057h), Master Page
        8. 9.5.3.8 Register 058h (address = 058h), Master Page
      4. 9.5.4  ADC Page (FFh, M = 0)
        1. 9.5.4.1 Register 03Fh (address = 03Fh), ADC Page
        2. 9.5.4.2 Register 042h (address = 042h), ADC Page
      5. 9.5.5  Offset Corr Page Channel A (610000h, M = 1)
        1. 9.5.5.1 Register 068h (address = 068h), Offset Corr Page Channel A
      6. 9.5.6  Offset Corr Page Channel B (610100h, M = 1)
        1. 9.5.6.1 Register 068h (address = 068h), Offset Corr Page Channel B
      7. 9.5.7  Digital Gain Page (610005h, M = 1 for Channel A and 610105h, M = 1 for Channel B)
        1. 9.5.7.1 Register 0A6h (address = 0A6h), Digital Gain Page
      8. 9.5.8  Main Digital Page Channel A (680000h, M = 1)
        1. 9.5.8.1 Register 000h (address = 000h), Main Digital Page Channel A
        2. 9.5.8.2 Register 0A2h (address = 0A2h), Main Digital Page Channel A
      9. 9.5.9  Main Digital Page Channel B (680100h, M = 1)
        1. 9.5.9.1 Register 0A2h (address = 0A2h), Main Digital Page Channel B
      10. 9.5.10 JESD Digital Page (690000h, M = 1)
        1. 9.5.10.1  Register 001h (address = 001h), JESD Digital Page
        2. 9.5.10.2  Register 002h (address = 002h ), JESD Digital Page
        3. 9.5.10.3  Register 003h (address = 003h), JESD Digital Page
        4. 9.5.10.4  Register 004h (address = 004h), JESD Digital Page
        5. 9.5.10.5  Register 006h (address = 006h), JESD Digital Page
        6. 9.5.10.6  Register 007h (address = 007h), JESD Digital Page
        7. 9.5.10.7  Register 016h (address = 016h), JESD Digital Page
        8. 9.5.10.8  Register 017h (address = 017h), JESD Digital Page
        9. 9.5.10.9  Register 032h-035h (address = 032h-035h), JESD Digital Page
        10. 9.5.10.10 Register 036h (address = 036h), JESD Digital Page
        11. 9.5.10.11 Register 037h (address = 037h), JESD Digital Page
        12. 9.5.10.12 Register 03Ch (address = 03Ch), JESD Digital Page
        13. 9.5.10.13 Register 03Eh (address = 03Eh), JESD Digital Page
      11. 9.5.11 Special Page Channel A
        1. 9.5.11.1 Register 019h (address = 019h), Special Page Channel A
      12. 9.5.12 Special Page Channel B
        1. 9.5.12.1 Register 019h (address = 019h), Special Page Channel B
      13. 9.5.13 Decimation Filter Page
        1. 9.5.13.1  Register 000h (address = 000h), Decimation Filter Page
        2. 9.5.13.2  Register 001h (address = 001h), Decimation Filter Page
        3. 9.5.13.3  Register 002h (address = 2h), Decimation Filter Page
        4. 9.5.13.4  Register 005h (address = 005h), Decimation Filter Page
        5. 9.5.13.5  Register 006h (address = 006h), Decimation Filter Page
        6. 9.5.13.6  Register 007h (address = 007h), Decimation Filter Page
        7. 9.5.13.7  Register 008h (address = 008h), Decimation Filter Page
        8. 9.5.13.8  Register 009h (address = 009h), Decimation Filter Page
        9. 9.5.13.9  Register 00Ah (address = 00Ah), Decimation Filter Page
        10. 9.5.13.10 Register 00Bh (address = 00Bh), Decimation Filter Page
        11. 9.5.13.11 Register 00Ch (address = 00Ch), Decimation Filter Page
        12. 9.5.13.12 Register 00Dh (address = 00Dh), Decimation Filter Page
        13. 9.5.13.13 Register 00Eh (address = 00Eh), Decimation Filter Page
        14. 9.5.13.14 Register 00Fh (address = 00Fh), Decimation Filter Page
        15. 9.5.13.15 Register 010h (address = 010h), Decimation Filter Page
        16. 9.5.13.16 Register 011h (address = 011h), Decimation Filter Page
        17. 9.5.13.17 Register 014h (address = 014h), Decimation Filter Page
        18. 9.5.13.18 Register 016h (address = 016h), Decimation Filter Page
        19. 9.5.13.19 Register 01Eh (address = 01Eh), Decimation Filter Page
        20. 9.5.13.20 Register 01Fh (address = 01Fh), Decimation Filter Page
        21. 9.5.13.21 Register 020h (address = 020h), Decimation Filter Page
        22. 9.5.13.22 Register 033h-036h (address = 033h-036h), Decimation Filter Page
        23. 9.5.13.23 Register 037h (address = 037h), Decimation Filter Page
        24. 9.5.13.24 Register 038h (address = 038h), Decimation Filter Page
        25. 9.5.13.25 Register 039h (address = 039h), Decimation Filter Page
        26. 9.5.13.26 Register 03Ah (address = 03Ah), Decimation Filter Page
      14. 9.5.14 Power Detector Page
        1. 9.5.14.1  Register 000h (address = 000h), Power Detector Page
        2. 9.5.14.2  Register 001h-002h (address = 001h-002h), Power Detector Page
        3. 9.5.14.3  Register 003h (address = 003h), Power Detector Page
        4. 9.5.14.4  Register 007h-00Ah (address = 007h-00Ah), Power Detector Page
        5. 9.5.14.5  Register 00Bh-00Ch (address = 00Bh-00Ch), Power Detector Page
        6. 9.5.14.6  Register 00Dh (address = 00Dh), Power Detector Page
        7. 9.5.14.7  Register 00Eh (address = 00Eh), Power Detector Page
        8. 9.5.14.8  Register 00Fh, 010h-012h, and 016h-019h (address = 00Fh, 010h-012h, and 016h-019h), Power Detector Page
        9. 9.5.14.9  Register 013h-01Ah (address = 013h-01Ah), Power Detector Page
        10. 9.5.14.10 Register 01Dh-01Eh (address = 01Dh-01Eh), Power Detector Page
        11. 9.5.14.11 Register 020h (address = 020h), Power Detector Page
        12. 9.5.14.12 Register 021h (address = 021h), Power Detector Page
        13. 9.5.14.13 Register 022h-025h (address = 022h-025h), Power Detector Page
        14. 9.5.14.14 Register 027h (address = 027h), Power Detector Page
        15. 9.5.14.15 Register 02Bh (address = 02Bh), Power Detector Page
        16. 9.5.14.16 Register 037h (address = 037h), Power Detector Page
        17. 9.5.14.17 Register 038h (address = 038h), Power Detector Page
        18. 9.5.14.18 Power Detector Page (Direct Addressing, 16-Bit Address, 5400h)
          1. 9.5.14.18.1 Register 032h-035h (address = 032h-035h), Power Detector Page
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Start-Up Sequence
      2. 10.1.2 Hardware Reset
      3. 10.1.3 SNR and Clock Jitter
        1. 10.1.3.1 External Clock Phase Noise Consideration
      4. 10.1.4 Power Consumption in Different Modes
      5. 10.1.5 Using DC Coupling in the ADC32RF42
        1. 10.1.5.1 Bypassing the Offset Corrector Block
          1. 10.1.5.1.1 Effect of Temperature
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
        1. 10.2.1.1 Transformer-Coupled Circuits
      2. 10.2.2 Detailed Design Procedure
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Community Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

10 Application and Implementation

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.

10.1 Application Information

10.1.1 Start-Up Sequence

The steps in Table 116 are recommended as the power-up sequence when the ADC32RF42 is in bypass mode with a 12-bit output (LMFS = 42810).

Table 116. Initialization Sequence

STEP DESCRIPTION PAGE, REGISTER ADDRESS AND DATA COMMENT
1 Supply all supply voltages. There is no required power-supply sequence for the 1.15 V, 1.2 V, and 1.9 V supplies, and can be supplied in any order. — —
2 Provide the SYSREF signal. — —
3 Pulse a hardware reset (low-to-high-to-low) on pin 48. — —
4 Write the register addresses described in the PowerUpConfig file. See the files located in SBAA226 The Power-up config file contains analog trim registers that are required for best performance of the ADC. Write these registers every time after power up.
5 Write the register addresses mentioned in the ILConfigNyqX_ChA file, where x is the Nyquist zone. See the files located in SBAA226 Based on the signal band of interest, provide the Nyquist zone information to the device.
6 Write the register addresses mentioned in the ILConfigNyqX_ChB file, where x is the Nyquist zone. See the files located in SBAA226 This step optimizes device’ performance by reducing interleaving mismatch errors.
6.1 Wait for 50 ms for the device to estimate the interleaving errors. — —
7 Depending upon the Nyquist band of operation, choose and write the registers from the appropriate file, NLConfigNyqX_ChA, where x is the Nyquist zone. See the files located in SBAA226 Third-order nonlinearity of the device is optimized by this step for channel A.
7.1 Depending upon the Nyquist band of operation, choose and write the registers from the appropriate file, NLConfigNyqX_ChB, where x is the Nyquist zone. See the files located in SBAA226 Third-order nonlinearity of the device is optimized by this step for channel B.
8 Configure the JESD interface and DDC block by writing the registers mentioned in the DDC Config file. See the files located in SBAA226 Determine the DDC and JESD interface LMFS options. Program these options in this step.

10.1.2 Hardware Reset

Figure 199 and Table 117 show timing information for the hardware reset.

ADC32RF42 hardware_reset_sbas747.gif Figure 199. Hardware Reset Timing Diagram

Table 117. Hardware Reset Timing Information

MIN TYP MAX UNIT
t1 Power-on delay from power-up to active high RESET pulse 1 ms
t2 Reset pulse duration: active high RESET pulse duration 1 µs
t3 Register write delay from RESET disable to SEN active 100 ns

10.1.3 SNR and Clock Jitter

The signal-to-noise ratio (SNR) of the ADC is limited by three different factors, as shown in Equation 5: quantization noise, thermal noise, and jitter. The quantization noise is typically not noticeable in pipeline converters and is 84 dB for a 14-bit ADC. The thermal noise limits the SNR at low input frequencies and the clock jitter sets the SNR for higher input frequencies.

Equation 5. ADC32RF42 snr_adc_eq_sbas747.gif

Equation 6 calculates the SNR limitation resulting from sample clock jitte:

Equation 6. ADC32RF42 snr_jitter_eq_sbas747.gif

The total clock jitter (TJitter) has two components: the internal aperture jitter (90 fS) is set by the noise of the clock input buffer and the external clock jitter. Use Equation 7 to calculate TJitter:

Equation 7. ADC32RF42 total_clck_jitter_sbas747.gif

External clock jitter can be minimized by using high-quality clock sources and jitter cleaners as well as band-pass filters at the clock input. A faster clock slew rate also improves the ADC aperture jitter.

The ADC32RF42 has a thermal noise of approximately 63 dBFS and an internal aperture jitter of 90 fS. Figure 200 shows an SNR plot with various amounts of external jitter for different input frequencies.

ADC32RF42 D048_ADC32RF45.gif Figure 200. ADC SNR vs Input Frequency and External Clock Jitter

10.1.3.1 External Clock Phase Noise Consideration

Figure 201 shows how external clock jitter can be calculated by integrating the phase noise of the clock source out to approximately two times of the ADC sampling rate (2 × fS). In order to maximize the ADC SNR, an external band-pass filter is recommended to be used on the clock input. This filter reduces the jitter contribution from the broadband clock phase noise floor by effectively reducing the integration bandwidth to the pass band of the band-pass filter. This method is suitable when estimating the overall ADC SNR resulting from clock jitter at a certain input frequency.

ADC32RF42 adc_snr_sbas747.gif Figure 201. Integration Bandwidth for Extracting Jitter from Clock Phase Noise

However, as shown in Figure 202, when estimating the affect of a nearby blocker (such as a strong in-band interferer to the sensitivity), the phase noise information can be used directly to estimate the noise budget contribution at a certain offset frequency.

ADC32RF42 phase_noise_info_sbas747.gif Figure 202. Small Wanted Signal in Presence of Interferer

At the sampling instant, the phase noise profile of the clock source convolves with the input signal (for example, the small wanted signal and the strong interferer merge together). If the power of the clock phase noise in the signal band of interest is too large, the wanted signal cannot not be recovered.

The resulting equivalent phase noise at the ADC input is also dependent on the sampling rate of the ADC and frequency of the input signal. Equation 8 describes how the ADC sampling rate scales the clock phase noise.

Equation 8. ADC32RF42 adc_nsd_eq_sbas747.gif

Using this information, the noise contribution resulting from the phase noise profile of the ADC sampling clock can be calculated.

10.1.4 Power Consumption in Different Modes

The ADC32RF42 consumes approximately 4.01 W of power when both channels are active with a 12-bit,
1.5-GSPS output and a DDC option is not used (bypass mode). When different DDC options are used, the power consumption on the DVDD supply changes by a small amount but remains unaffected on other supplies. In the applications requiring just one channel to be active, channel A must be chosen as the active channel and channel B can be powered down. Power consumption reduces to approximately 2.66 W in single-channel operation with a 12-bit, 1.5-GSPS output (bypass mode).

Table 118 shows power consumption in different DDC modes for dual-channel and single-channel operation.

Table 118. Power Consumption in Different DDC Modes

DECIMATION OPTION ACTIVE
CHANNEL		 ACTIVE DDC AVDD1P9 (mA) AVDD1P2 (mA) DVDD1P2 (mA) TOTAL POWER (mW)
Bypass mode Channel A, B NA 1150 604 1000 4029.6
Divide-by-4 Channel A, B Single 1150 604 1148 4199.8
Divide-by-8 Channel A, B Dual 1142 602 1236 4283.5
Divide-by-8 Channel A, B Single 1142 601 1025 4039.7
Divide-by-16 Channel A, B Dual 1142 601 1000 4010.95
Divide-by-16 Channel A, B Single 1142 599 984 3990.25
Bypass mode Channel A NA 631 588 680 2657.1
Divide-by-4 Channel A Single 630 570 738 2701.2
Divide-by-8 Channel A Dual 627 568 806 2771.4
Divide-by-8 Channel A Single 627 561 690 2629.95
Divide-by-16 Channel A Dual 627 568 770 2730
Divide-by-16 Channel A Single 627 561 669 2605.8

10.1.5 Using DC Coupling in the ADC32RF42

The ADC32RF42 can be used in dc-coupling applications. However, the following points must be considered when designing the system:

  1. Ensure that the correct common-mode voltage is used at the ADC analog inputs.

    2. The analog inputs are internally self-biased to VCM through approximately a 33-Ω resistor. The internal biasing resistors also function as a termination resistor. However, if a different termination is required as shown in Figure 203, the external resistor RTERM can be differentially placed between the analog inputs. The amplifier VOCM pin is recommended to be driven from the CM pin of the ADC to help the amplifier output common-mode voltage track the required common-mode voltage of the ADC.

    ADC32RF42 dc_coupling_app_sbas747.gif
    Set the INCR CM IMPEDANCE bit to increase the RCM from 0 Ω to > 5000 Ω.
    RDC is approximately 65 Ω.
    Figure 203. The ADC32RF42 in a DC-Coupling Application
  2. Ensure that the correct SPI settings are written to the ADC.

    3. As shown in Figure 204, the ADC32RF42 has a digital block that estimates and corrects the offset mismatch among four interleaving ADC cores for a given channel.

    ADC32RF42 offset_corr_lck_sbas747.gif Figure 204. Offset Corrector in the ADC32RF42

    The offset corrector block nullifies dc, fS / 8, fS / 4, 3 fS / 8, and fS / 2. The resulting spectrum becomes free from static spurs at these frequencies. The corrector continuously processes the data coming from the interleaving ADC cores and cannot distinguish if the tone at these frequencies is part of signal or if the tone originated from a mismatch among the interleaving ADC cores. Thus, in applications where the signal is present at these frequencies, the offset corrector block can be bypassed.

10.1.5.1 Bypassing the Offset Corrector Block

When the offset corrector is bypassed, offset mismatch among interleaving ADC cores appears in the ADC output spectrum. To correct the effects of mismatch, place the ADC in an idle channel state (no signal at the ADC inputs) and the corrector must be allowed to run for some time to estimate the mismatch, then the corrector is frozen so that the last estimated value is held. Table 119 provides the required register writes.

Table 119. Freezing and Bypassing the Offset Corrector Block

STEP REGISTER WRITE COMMENT
STEPS FOR FREEZING THE CORRECTOR BLOCK
1 — Signal source is turned off. The device detects an idle channel at its input.
2 — Wait for at least 0.4 ms for the corrector to estimate the internal offset
3 Address 4001h, value 00h Select Offset Corr Page Channel A
Address 4002h, value 00h
Address 4003h, value 00h
Address 4004h, value 61h
Address 6068h, value C2h Freeze the corrector for channel A
Address 4003h, value 01h Select Offset Corr Page Channel B
Address 6068h, value C2h Freeze the corrector for channel B
4 — Signal source can now be turned on
STEPS FOR BYPASSING THE CORRECTOR BLOCK
1 Address 4001h, value 00h —
Address 4002h, value 00h
Address 4003h, value 00h
Address 4004h, value 61h Select Offset Corr Page Channel A
Address 6068h, value 46h Disable the corrector for channel A
Address 4003h, value 01h Select Offset Corr Page Channel B
Address 6068h, value 46h Disable the corrector for channel B

10.1.5.1.1 Effect of Temperature

Figure 205 and Figure 206 show the behavior of nfS / 8 tones with respect to temperature when the offset corrector block is frozen or disabled.

ADC32RF42 D058_SBAS747.gif Figure 205. Offset Corrector Block Frozen at Room Temperature
ADC32RF42 D060_SBAS747.gif Figure 206. Offset Corrector Block Disabled

10.2 Typical Application

The ADC32RF42 is designed for wideband receiver applications demanding high dynamic range over a large input frequency range. Figure 207 shows a typical schematic for an ac-coupled receiver.

Decoupling capacitors with low ESL are recommended to be placed as close as possible at the pins indicated in Figure 207. Additional capacitors can be placed on the remaining power pins.

ADC32RF42 ac_cpld_rcvr_sbas844.gif Figure 207. Typical Application Implementation Diagram

10.2.1 Design Requirements

10.2.1.1 Transformer-Coupled Circuits

Typical applications involving transformer-coupled circuits are discussed in this section. To ensure good amplitude and phase balance at the analog inputs, transformers (such as TC1-1-13 and TC1-1-43) can be used from the dc to 1000-MHz range and from the 1000-MHz to 4-GHz range of input frequencies, respectively. When designing the driving circuits, the ADC input impedance (or SDD11) must be considered.

By using the simple drive circuit of Figure 208, uniform performance can be obtained over a wide frequency range. The buffers present at the analog inputs of the device help isolate the external drive source from the switching currents of the sampling circuit.

ADC32RF42 ai_input_drive_cir_sbas747.gif Figure 208. Input Drive Circuit

10.2.2 Detailed Design Procedure

For optimum performance, the analog inputs must be driven differentially. This architecture improves common-mode noise immunity and even-order harmonic rejection. As shown in Figure 208, a small resistor (5 Ω to 10 Ω) in series with each input pin is recommended to damp out ringing caused by package parasitics.

10.2.3 Application Curves

Figure 209 and Figure 210 show the typical performance at 100 MHz and 1850 MHz, respectively.

ADC32RF42 D001_SBAS844.gif
SFDR = 73 dBc, SNR = 62.4 dBFS,
SINAD = 62 dBFS, THD = 71 dBc,
HD2 = –75 dBFS, HD3 = –78 dBFS,
SFDR (non HD2, HD3) = 85 dBc, IL spur = 81 dBFS
Figure 209. FFT for 100-MHz Input Frequency
ADC32RF42 D004_SBAS844.gif
SFDR = 70 dBc, SNR = 60.8 dBFS,
SINAD = 60 dBFS, THD = 69 dBc,
HD2 = –72 dBFS, HD3 = –78 dBFS,
SFDR (non HD2, HD3) = 81 dBc, IL spur = 82 dBFS
Figure 210. FFT for 950-MHz Input Frequency