SBAA583 july   2023 PCM1820 , PCM1820-Q1 , PCM1821 , PCM1821-Q1 , PCM1822 , PCM1822-Q1 , PCM3120-Q1 , PCM5120-Q1 , PCM6120-Q1 , TLV320ADC3120 , TLV320ADC5120 , TLV320ADC6120

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 AC Coupled Systems
    2. 1.2 DC Coupled System
  5. 2AC Coupling Schemes
    1. 2.1 Equivalent Circuit
    2. 2.2 Input Pin Waveforms with AC Coupling
    3. 2.3 Selection of Coupling Capacitor
    4. 2.4 Quick Charge Circuit
    5. 2.5 Selection of Capacitor Type
    6. 2.6 Single-Ended and Differential Mode
    7. 2.7 S.N.R in AC Coupled Circuits
  6. 3DC Coupled Scheme
    1. 3.1 Biasing the Pins
    2. 3.2 Electrical Characteristics
    3. 3.3 Application Circuits
      1. 3.3.1 S.N.R in DC Coupled Circuits
  7. 4Application Examples
    1. 4.1  Electret Condenser Microphone: Single Ended DC- Coupled Input
    2. 4.2  Electret Condenser Microphone: Single Ended AC Coupled Input
    3. 4.3  Selection of a Microphone
    4. 4.4  Condenser Microphone: Differential DC-Coupled Input
    5. 4.5  Condenser Microphone: Differential AC-Coupled Input
    6. 4.6  MEMS Microphone: Differential AC Coupled Input
    7. 4.7  Circuit With No Offset and Response Down to DC
    8. 4.8  Improving SNR by Summing the Output of 2 ADC Channels
    9. 4.9  Measure a High Voltage Waveform (+-50 V)
    10. 4.10 I2C Listing
  8. 5Summary
  9. 6References

2.1 Equivalent Circuit

Figure 2-1 describes the equivalent circuit for the input pin. In a capacitive coupled system, the biasing of the pin is done internally by the voltage as shown in Equation 1, where k is approximately 0.5.

Equation 1. VINxP=k×VREF 
GUID-20230516-SS0I-GXD9-CDG2-PBRZPRXC7C1D-low.svgFigure 2-1 Equivalent Circuit for Input Pin for AC Coupled System

Register settings for the input pin:

  • CH1_CFG0 register (address = 0x3C) Bit 4, CH1_DC=0 selects AC Coupling for channel 1. The setting also selects single-ended or differential mode.
  • The DC voltage on the pin is VREF/2. The value of this reference voltage can be configured using the P0_R59_D[1:0] register bits as shown in Table 2-1.
  • PO_R_60_D{3:2} are used to select the input impedance.
Table 2-1 CH1_CFG0 Register Field Descriptions
BitFieldTypeResetDescription
7CH1_INTYPR/W0hChannel 1 input type
0d = Microphone input
1d = Line input
6-5CH1_INSRC[1:0]R/W0hChannel 1 input configuration
0d = Analog differential input (the GPI1 and GPO1 pin functions must be disabled)
1d = Analog single-ended input (the GPI1 and GPO1 pin functions must be disabled)
2d = Digital microphone PDM input (configure the GPO and GPI pins accordingly for PDMDIN1 and PDMCLK)
3d = Reserved
4CH1_DCR/W0hChannel 1 input coupling (applicable for the analog input)
0d = AC-coupled input
1d = DC-coupled input
3-2CH1_IMP[1:0]R/W0hChannel 1 input impedance (applicable for the analog input)
0d = Typical 2.5-kΩ input impedance
1d = Typical 10-kΩ input impedance
2d = Typical 20-kΩ input impedance
3d = Reserved
1ReservedR0hReserved
0CH1_DREENR/W0hChannel 1 dynamic range enhancer (DRE) and automatic gain controller (AGC) setting
0d = DRE and AGC disabled
1d = DRE or AGC enabled based on the configuration of bit 3 in register 108 (P0_R108)
Table 2-2 VREF Programmable Settings
P0_R59_D[1:0] : ADC_FSCALE[1:0]VREF Output Voltage (Same as Internal ADC VREF)Differential Full-Scale Input SupportedSingle-Ended Full-Scale Input SupportedAVDD Range Requirement
00 (default)2.75 V2 VRMS1 VRMS3 V to 3.6 V
012.5 V1.818 VRMS0.909 VRMS2.8 V to 3.6 V
101.375 V1 VRMS0.5 VRMS1.7 V to 1.9 V
11ReservedReservedReservedReserved
Table 2-3 Input Impedance Selection for the Record Channel
P0_R60_D[3:2] : CH1_IMP[1:0]Channel 1 Input Impedance Selection
00 (default)Channel 1 input impedance typical value is 2.5 kΩ on INxP or INxM
01Channel 1 input impedance typical value is 10 kΩ on INxP or INxM
10Channel 1 input impedance typical value is 20 kΩ on INxP or INxM
11Reserved (do not use this setting)