We present the development of a charged particle pixel array imager operating in single hit detection mode. This
challenging imaging device called GigaTracker (GTK) developed for the CERN NA62 experiment is intended to
measure the position and arrival time of a pion/kaon beam with an intensity of 108*cm-2*s-1. Each particle hit is detected
in position with a precision of ~100 &mgr;m and in time with a precision of 100 ps (rmsc). The readout pixel ASIC circuit in
130 nm CMOS technology comprise an array of 1800 pixels of 300 x 300 &mgr;m2. It is connected via bump bonding to an
ultra fast solid state pixel sensor array matching the same pixel pattern. The performance of high rate and high timing
precision together with an extreme sensitivity of the pixel channel discriminating input signals with a charge as low as 1
fC (6000 electrons) are very demanding; two imaging readout architectures are presented, one with on pixel analogue
based time-to-digital-converter (TDC), the other one with digital based TDC placed at the end of each column. The
design of two pixel discriminators, a constant fraction discriminator and a time-over-threshold discriminator with time
walk correction technique will be discussed. The design challenges of two architectures will be also discussed.
Due to the high particle intensity, a huge data flow has to be handled. Hereby only data of pixels, which actually have
been hit are buffered on chip and automatically transferred off the chip. The data rate per chip is 4 Gbit/s. We present
circuit design challenges and SPICE simulations of both approaches.