TIDUF13 November 2022 ADS117L11 , ADS127L11
According to the target specifications, the input signal can be as high as 23 V. With AC coupling, the maximum signal level is ±10 V, to enable a 5-V signal chain, a resistive divider follows the coupling capacitor, with a scaling factor of 10:1. This brings down the signal to ±1.0 V. The resistive divider is referred to the mid-supply of 2.5 V generated by the ADC to perform level shifting, the output signal becomes 2.5 V ±1.0 V after the shifting. The non-inverting buffer stage has a gain of 2, so the output of the buffer is ±2.0 V. The buffer inverting pin is also referred to the mid-supply of 2.5 V, so the output of the buffer is 2.5 V ±2.0 V.
The fully-differential amplifier converts the single-ended signal into a differential signal and adds a gain of 2. The output common-mode of the differential amplifier is also set to 2.5 V. The maximum differential output of the amplifier is therefore ±4.0 V, while the single-ended outputs are 2.5 V ±2.0 V.
A reference voltage of 4.096 V is used to maximize the DR. With the previously-given signal levels, the proper amplifier devices can be selected that have the required input and output range, and have the least noise contribution.