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

4.5 Condenser Microphone: Differential AC-Coupled Input

Features: High SNR for far field voice recording

Select the POM-2730L-HD-R microphone with TLV320ADC6120 ADC.

POM-2730L-HD-R Specifications:

Sensitivity -30 db, 0 db = 1 V/Pascal with optimum load resistor. Output Impedance 2.2k, SNR 74 db SPL of 94 db or 1 Pascal.

TLV320ADCX120 Settings:

  • Vref = 2.75 V
  • Zin = 2.5 kΩ
  • AC Coupled
  • Analog differential input. P0 R58 (7:6) = mode 0
  • DRE ON

The microphone can be modeled as a current source where the output current is proportional to the incoming sound pressure. The voltage of this source is IxR and the output impedance is R. I is output current and R is the biasing resistance of the mic circuit.

GUID-20230501-SS0I-15SD-L1PM-KNTCWCVQRHMV-low.svg Figure 4-11 AC Coupled Differential Microphone Circuit
Equation 37. C > 1 2 × 3.14 × F m i n × ( Z i n + R )
Equation 38. C > 1 2 × 3.14 × 20 × ( 2.5 K + 1.1 K )                     F o r   F m i n = 20   a n d   Z i n = 2.5 k
Equation 39. C > 2.2 u f