A pixel readout chip designed in 90nm CMOS process for high count rate imaging systems

We report on the design of a prototype IC called PX90 dedicated for readout of hybrid pixels detectors in X-ray imaging applications. The PX90 has dimensions 4×4 mm
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and was designed in CMOS 90 nm technology with 9 metals layers. The core of the IC is a matrix of 40×32 pixels with the size of 100×100 ¿m
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. A 60×60 ¿m
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square passivation opening in each pixel allows to connect PX90 to a pixel detector using stud bump bonding techniques. Each pixel contains two charge sensitive amplifiers with Krummenacher feedback scheme, two second stage amplifiers, two discriminators and two 16-bit ripple counters. The stages are DC-coupled and the front-end electronics uses fully differential readout scheme. To minimize the effective threshold spread at the discriminators inputs two 8bit and 7-bit trim DACs are used. The data are read out from a single LVDS output with clock frequency of 200 MHz. The effective pulse shaping is 27 ns and it's determined mainly by the time constants in CSA. The measurements show an ENC of 204 el. rms without detector and 240 - 249 el. rms with stud bump bonded detector. The average gain is 28 ¿V/el. and the effective threshold variation (using trim DAC) is 1.8 mV at the discriminator input. Each pixel contains about 1800 transistors and has a static power consumption of 47 ¿W for nominal bias condition.