On the performance and limitations of a dual threshold discriminator pixel readout circuit for LHC

The analog front-end of pixel readout electronics with dual threshold discriminator scheme has been measured extensively to determine the optimum performance and performance limitations of the circuit. The preamplifier shows a peaking time of 20 ns without capacitive load, which degrades to only 30 ns with a load of 350 fF. The LEVEL-discriminator has an adjustable threshold in the range of 2000 to 6000e^- with a variable separation to the TIME-discriminator threshold of 800 to 1600e^-. The circuit allows the full suppression of out-of-time signals under the conditions of 350 fF capacitive load and a total power consumption of 40 μW per cell. The untuned threshold dispersion is measured to be 320e^- r.m.s., which reduces to 70e^- r.m.s. after threshold adjust. The overall noise of the circuit reaches a value of about 200e^- r.m.s. with 350 fF capacitive load and 20 nA of parallel current at the preamplifier input. Further measurements characterize the time-over-threshold (TOT) behaviour and the double-pulse resolution of the circuit