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

4.1 Electret Condenser Microphone: Single Ended DC- Coupled Input

Features: Low component count

This application uses POM-2730L-HD-R microphone with TLV320ADC6120 ADC.

POM-2730L-HD-R specifications: RO = 2200 Ω.

TLV320ADCX120 Settings:

  • VREF = 2.75 V
  • ZIN = 10 kΩ to maintain the input impedance does not load the bias circuit
  • Analog single-ended
  • DC coupled
  • P0_R58 (7:6) is set at Mode 1
  • DRE Disabled
GUID-20230501-SS0I-RVJ9-C0QZ-HGHWKLQMTNM1-low.svgFigure 4-1 Single-Ended DC Coupled Condenser Microphone Circuit
GUID-20230501-SS0I-9G9V-C0QJ-H5SKDLNJQM3B-low.svgFigure 4-2 DC Bias Circuit for Microphone

Figure 4-2 shows that RO (output impedance of mic) forms a voltage divider with the bias resistor. Bias microphone output pin to 1.375 VDC to bring ADC input to the optimum level.

Equation 11. ADC input=3.3×ROR+RO =1.375V
Equation 12. R = 3 kΩ
  • A signal of 1 VRMS from the microphone can be handled without clipping at the input pin.
  • The ADC output has a DC offset corresponding to 1.375 V. This offset has to be removed by the internal high pass filter.