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

2.2 Input Pin Waveforms with AC Coupling

When a 1-V RMS signal is passed through a coupling capacitor as shown in Figure 2-2, the signal rides over VREF/2.

GUID-20230501-SS0I-XC9G-MBXN-VLD6BXPT4XD6-low.svgFigure 2-2 Circuit for Input Pin With AC Coupling
GUID-20230501-SS0I-6S7D-FKG8-RJWVKKFLZZP5-low.svgFigure 2-3 Input Pin Waveform With AVDD of 3.3 V

For a 3.3-V supply, a VREF/2 is 1.375 V. The highest point of a 1-VRMS signal on the pin is 2.8 V which is lower then AVDD of 3.3 V. A signal larger then AVDD can not be given to ADC input as that can damage the input pins.

GUID-20230501-SS0I-LGL8-KTHB-CFCQ0X73J6ZC-low.svgFigure 2-4 Input Pin Waveform With AVDD of 1.8 V

For a 1.8-V supply, a VREF/2 is 0.6875 V. The highest point of a 0.5-VRMS signal on the pin is 1.4 V which is lower then AVDD of 1.8 V.