Half-Volt Power Supply Charge-Sensitive Amplifier - Discriminator Chain for Binary Readout in Small-Footprint Pixel Detectors

A signal processing chain, comprising of a chargesensitive amplifier, discriminator and interface to the event-driven readout network tailored for small footprint O(20 micrometer pitch) pixel detectors with binary readout is presented. The circuit operates with only 0.5 V power supply, delivering high sensitivity of 1 mV/electron and ENC below 10 electrons. The design is based on the self-cascoded field effect transistor topology in the CSA’s first stage for efficient charge multiplication, using translinear pole-zero cancellation effect. The second stage is an integrator, realizing charge to voltage conversion with a currentchoked source follower that enables resetting. The final stage is a discriminator in the form of a simple Schmitt gate with an unconventional threshold setting given by the power supply of the Schmitt gate. The design was carried out to consume about 75 nW of power, but providing response with TimeWalk not exceeding a couple of hundreds nanoseconds. The design was realized in a 65 nm process suitable for Monolithic Active Pixel Sensors on the increased resistivity substrate and uses highly minimized number of bias lines to increase immunity to mismatches.