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

2.6 Single-Ended and Differential Mode

The TLV320ADCX12O/PCMX120-Q1 family supports both single-ended and differential signals. A single-ended signal can be sent through a 2-wire connection (input signal, ground). If this signal has to be transmitted over a noisy environment then a shielded cable can be used. The shield is connected to ground acting like a Faraday cage to the signal wire. Noise picked up along the cable length is conducted by the shield to ground.

A differential signal is a 3-wire connection (positive, negative, and ground). Two equal in amplitude and phase inverted signals are sent over the positive and negative lines. The positive and negative lines need to run very close to each other. A shielded twisted pair is one way to route differential signals.

Noise signals picked up on both positive and negative lines are identical waveforms provided the lines run close to each other. These are termed Common Mode Signals. The TLV320ADCX12O/PCMX120-Q1 family has a common mode rejection of 60 db. The differential input circuit of the ADC only processes the out-of-phase signal on the positive and negative pins. The signal attenuates the common mode noise signals by 60 db providing a great benefit by picking up a valid audio signal in an extremely noisy environment.

Table 2-7 shows the setup of the input as single-ended or differential.

Table 2-7 Input Source Selection for the Record Channel
P0_R60_D[6:5]: CH1_INSRC[1:0]Input Channel 1 Record Source Selection
00 (default)Analog differential input for channel 1 (this setting is valid only when the GPI1 and GPO1 pin functions are disabled)
01Analog single-ended input for channel 1 (this setting is valid only when the GPI1 and GPO1 pin functions are disabled)
10Digital PDM input for channel 1 (configure the GPIx and GPOx pin accordingly for PDMDIN1 and PDMCLK)
11Reserved (do not use this setting)
GUID-20230501-SS0I-9XC0-FQZ4-HX50Z4ZQFVS0-low.svgFigure 2-7 Single-Ended AC Coupled Circuit
GUID-20230501-SS0I-LGXQ-9DW8-RG2B12FRMF7D-low.svgFigure 2-8 Differential AC Coupled Circuit
  • DC Bias on input pins is internally fixed at Vref/2.
  • For the differential mode, Vin and ^Vin are phase inverted signals.

Table 2-8 shows the analog signal levels that correspond to Full Scale Digital Value (0 dBFS).

Table 2-8 Analog Signal Levels
AVDDVREF/2VRMS Single EndedVRMS Differential
3.3 V1.375 V1 VRMS2 VRMS
1.8 V0.6875 V0.5 VRMS1 VRMS