A discriminator and shaper circuit realized in CMOS technology for BABAR

An analog chip is designed to receive from a PM, trough a 50 Ω coaxial cable signals rising in 3 ns, falling in 8 ns, and to provide: (i) digital signals for timing purposes, (ii) multiplexed analog output, proportional to the input, for spectral measurements. There are 8 channels per chip with a common gain adjustment for the preamplifier, and individual control for the offset and threshold setting. The discriminator sensitivity is 2 mV. The dynamic range is from 2 mV to 100 mV. The noise equivalent at the input is ≅100 μV. The RMS time dispersion is less than 500 ps for 3 mV threshold. The shaping amplifier is of bipolar shape with 80 ns peaking time and 2.5 V mean output voltage. The crosstalk between channels is less than 2%