SBAS572B May 2013 – March 2019 ADS8864
This section describes an application circuit (as shown in Figure 64) optimized for using the ADS8864 with lowest distortion and noise performance at a throughput of 400 kSPS. The input signal is processed through a high-bandwidth, low-distortion amplifier in an inverting gain configuration and a low-pass RC filter before being fed into the ADC.
As a rule of thumb, the distortion from the input driver must be at least 10 dB less than the ADC distortion. The distortion resulting from variation in the common-mode signal is eliminated by using the amplifier in an inverting gain configuration that establishes a fixed common-mode level for the circuit. This configuration also eliminates the requirement of a rail-to-rail swing at the input of the amplifier. Therefore, the circuit uses the low-power OPA836 as an input driver, which provides exceptional ac performance because of its extremely low-distortion, high-bandwidth specifications.
In addition, the components of the charge-kickback filter are such that the noise from the front-end circuit is kept low without adding distortion to the input signal.