256-channel differential to single ended antialiasing filter for pulse shape analysis in nuclear physics experiments

In view of the first application in the framework of the FARCOS project, we designed a compact 6U board that provides in a single module 256 channels featuring: i) differential to single-ended low-noise conversion with $100 \Omega $ input impedance, ii) a second order or a fourth order anti-aliasing filter, iii) a selectable output offset voltage. The first stage is responsible of the conversion from the differential mode to single-ended and features an additional input for offset regulation. The second stage is the filtering stage, designed as a Sallen-Key cell with cutoff frequency of 40 MHz. The design relies on very small case dual operational amplifiers and clusters 4 channels in a common design sharing the offset regulation section. The 4-channel cluster occupies an area of 3.5 mm $\times 110$ mm. The paper illustrates the designed module topology and the results of the characterization of a 4-channel cluster.