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

3.1 Accuracy and Noise Performance

The following table shows accuracy and noise results of the hardware at 25°C. A differential DC voltage is applied to a random input. The result is compared against the expected value. The effective number of bits (NEFF) and the noise-free bits (NNFREE) are calculated by a histogram with 65535 samples at a sampling speed of 20 kSPS. The measured value is the mean of the histogram.

Table 3-1 Accuracy and Noise Performance
Input VREF Measured Expected |Δcode| Sigma NEFF NNFREE
0 V ±12.288 V 32767 32768 1 0.56 16.8 bit 14.1 bit
0 V ±2.56 V 32765 32768 3 0.75 16.4 bit 13.7 bit
5.0 V ±6.144 V 59444 59434 10 0.74 16.4 bit 13.7 bit
10 V ±12.288 V 59442 59434 8 0.61 16.7 bit 14.0 bit
–10 V ±12.288 V 6092 6101 9 0.62 16.6 bit 13.9 bit
10.5 mA 5.12 V 16124 16128 4 0.73 16.4 bit 13.7 bit

As an example, the following histogram shows the 0-V differential input with ±12.288-V voltage input range using TI's ADS8681EVM-PDK ecosystem software.

GUID-20220610-SS0I-XGCB-W6BW-L0BMMSDZB6DQ-low.pngFigure 3-1 Histogram Screen Shot