Power-efficient, Precise Discriminator for a High Time Resolution, Low-Noise Charge Detection ROIC

Abstract

Pixel charge detectors are responsible for counting the number of collected electrons and converting it into an electrical signal. The proposed charge detector pixel readout integrated circuit (ROIC), implemented in 40nm TSMC technology, should be able to detect an amount of charge as low as 160aC, with a high time resolution of 2.5ns, using limited power consumption and area occupation. The discriminator, as the ROIC's last block, should distinguish the analog information of the previous block called “signal shaper”, from a certain noise level, and convert it into 1-bit binary code. The mode of operation is named as an event counting.In this thesis, two versions of the discriminator are studied and compared: with an active and passive shaper (filter). The goal is to find the optimal solution with respect to performance and power efficiency. The discriminator with an active filter (which provides an output pulse with an amplitude of 225mV and power consumption of 170μW, achieves an offset of 5mV and a noise voltage of 290μVrms referred to the input, and consumes a power of 36μW. Its speed performance and temperature stability have been experimentally verified. The discriminator with a passive shaper (which consumes no power) can detect an input signal with 10mV amplitude, with 240μV input noise, and a power consumption of 88μW. Its performance is partly tested through the post-layout simulation.The achieved SNR with the active filter is 14.6, and the passive filter is 15.1. Both solutions (discriminator for active and passive filter) demonstrate an acceptable SNR. The solution with a passive filter provides a better overall power efficiency but cannot detect incoming events during the calibration period which lasts 10ns and occurs every 90μs.Electrical Engineerin