JAJSS86 November 2023 OPA891
PRODMIX
This section demonstrates multiplexing several analog input signals to a high-performance driver amplifier which subsequently drives a single high-resolution, high-speed SAR analog-to-digital converter (ADC). This example uses the ADS8411 and the TS5A3159 or TS5A3359 as the ADC and the multiplexer, respectively. This application uses the OPAx891 as the operational amplifier.
As detailed in Figure 7-4, the example system consists of an ADC (ADS8411), a driving operational amplifier (OPA891), a multiplexer (TS5A3159), an AC source, a DC source, and two driving operational amplifiers.
The driving amplifiers OPA1 and OPA2 are shown as two OPA891 amplifiers. Alternatively, use a single OPA2891 to save on cost and board space. The purpose of these op-amps is to make the input sources present a low impedance to rest of the circuit. Additionally, to maintain signal fidelity, these operational amplifiers must have low noise and distortion. The third OPA891, labeled OPA3 in Figure 7-4, is used to maintain switching speed and drive the ADC. The passive band-pass filter before the ADC reduces unwanted noise.