How to filter out common-mode interference in concentrator sampling?

Common-mode interference in the concentrator sampling circuit originates from power grid-to-ground potential fluctuations and spatial coupling, manifesting as common-mode voltage fluctuations of the sampled signal to ground. The core of filtering common-mode interference is using a differential amplifier with a high common-mode rejection ratio (CMRR) and providing a low-impedance return path for common-mode noise. The sampled signal first enters the differential amplifier (e.g., INA188, CMRR>120dB). A matching small capacitor (e.g., 10pF) is connected to ground at both the non-inverting and inverting inputs of the amplifier, forming a low-pass filter with the line impedance. Simultaneously, a clean analog ground is provided for the amplifier and connected to the chassis ground via a Y capacitor (2.2nF/Y1) or a common-mode inductor CMZ2012A-900T, providing a discharge path for common-mode noise. If the interference is severe, an isolation amplifier can be used. During PCB routing, differential pairs must be strictly of equal length, equidistant, and routed close to each other. These measures can improve the common-mode interference rejection ratio by more than 60dB.