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

4.9 Measure a High Voltage Waveform (+-50 V)

Use the below arrangement in Figure 4-16. Vin is a +-50 V waveform. This arrangement uses mic bias to create the 1.375 V which determines the common mode at the input of the ADC.

GUID-20230501-SS0I-Q8RF-WJWW-BVQDTHHWFHV7-low.svgFigure 4-16 Circuit to Digitize 100 V PP Signal
GUID-20230501-SS0I-HXTN-GBBS-XRMSBHVLXBB0-low.svgFigure 4-17 Input Pin Waveforms at INxP and INxM

Operate the OP AMP with a +- 3.3V dual supply.

Op amp A3 creates -1.375 V at the output and at INxP, creating a current of 1.375/20 kΩ into the input pin of A3. This creates a DC Level of 1.375 V on the output of A3. The output of A2 is also biased at 1.375 V.

A 50-V positive signal brings the INxP point from 1.375 V to 0 V. As shown in the equations below a R of 720 KΩ is used with a +-50 V input signal.

Equation 53. VinR=In Inverting pin of A3 is at virtual gnd.
Equation 54. In×20 kΩ=1.375 V. This brings output of A3 from 1.375 V to zero.   
Equation 55. Vin×20 kΩR=1.375 V  
Equation 56.  R=Vin×20 kΩ/1.375 V