RG64 — high count rate multichannel ASIC with energy window selection for X-ray imaging applications

We report on the performance of a low noise and high count rate readout ASIC with binary architecture and energy window section for X-ray imaging applications using semiconductor detectors. The ASIC called RG64 is designed in 0.35 μm CMOS process and its total area is 3900×5000 μm². The core of RG64 consists of 64 readout channels. Each channel is built of a charge sensitive amplifier with a second order shaper of peaking time 75 ns, two independent discriminators with an 8-bit offset correction circuit and two independent 20-bit counters with RAM memory buffers. The ENC of the circuit reaches the value of about 126 el. rms with 1 pF input load and 5 mW power consumption per single channel. The mean gain in the multichannel ASIC is about 50 μV/el., with the dispersion from channel to channel of 0.9 %. The deviation of the effective threshold voltage spread for given energy can be set below 7 el. rms (calculated to CSA input). High count rate measurements have been performed up to 2 Mcps of average rate of input pulses, both for AC and DC coupling silicon strip detectors with the X-ray photons of energy 8.04 keV. The RG64 can operate both in the continuous readout mode and in the readout mode separate from exposure.