SBAS949A February 2020 – February 2021 ADS131M06
Each channel of the ADS131M06 features an integrated programmable gain amplifier (PGA) that provides gains of 1, 2, 4, 8, 16, 32, 64, and 128. The gains for all channels are individually controlled by the PGAGAINn bits for each channel in the GAIN1 register.
Varying the PGA gain scales the differential full-scale input voltage range (FSR) of the ADC. Equation 3 describes the relationship between FSR and gain. Equation 3 uses the internal reference voltage, 1.2 V, as the scaling factor without accounting for gain error caused by tolerance in the reference voltage.
Table 8-1 shows the corresponding full-scale ranges for each gain setting, assuming the internal reference is used.
The input impedance of the PGA dominates the input impedance characteristics of the ADS131M06. The PGA input impedance for gain settings up to 4 behaves according to Equation 4 without accounting for device tolerance and change over temperature. Minimize the output impedance of the circuit that drives the ADS131M06 inputs to obtain the best possible gain error, INL, and distortion performance.
The device uses an input precharge buffer for PGA gain settings of 8 and higher. The input impedance at these gain settings is very high. Specifying the input bias current for these gain settings is therefore more useful. A plot of input bias current for the high gain settings is provided in Figure 6-5.