SBAA551 June   2022 ADS8661 , ADS8665 , ADS8671 , ADS8675 , ADS8681 , ADS8685 , ADS8689 , ADS8691 , ADS8695 , ADS8699 , INA823 , INA826 , LM317L , LM337L , MUX509 , TPS2661 , TPS560430

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Circuit Description
    1. 2.1 Input Stage
    2. 2.2 Multiplexer Stage
    3. 2.3 Instrumentation Amplifier
    4. 2.4 Analog-to-Digital Converter
    5. 2.5 Power Supply
  5. 3Results
    1. 3.1 Accuracy and Noise Performance
    2. 3.2 Common-Mode Rejection of Input Signal
    3. 3.3 Input Impedance
    4. 3.4 Settling Time
    5. 3.5 Input Protection
  6. 4Summary
  7. 5References

3.2 Common-Mode Rejection of Input Signal

The common-mode rejection ratio (CMRR) is the ability to suppress unwanted common-mode signals superimposed to the differential signal. A CMRR test is performed by comparing the output codes for a 1-V differential voltage with and without a VCM signal applied. The following table shows that with no VCM signal, the system had an output code deviation of –1 code. Comparatively, the design showed a deviation of –4 to +3 codes with –11.5-V and +11.5-V VCM, resulting in a measured VCM rejection of > 81 dB.

Table 3-2 Common-Mode Rejection Performance
VCM Input VRANGE Measured Expected Δcode
–11.5 V 1 V ±2.56 V 45563 45568 –5
0 V 1 V ±2.56 V 45567 45568 –1
+11.5 V 1 V ±2.56 V 45570 45568 +2