A 12-Channel CMOS Preamplifier-Shaper-Discriminator ASIC for APD and Gas Counters

A 12-Channel (Ch) CMOS Preamplifier-Shaper-Discriminator ASIC designed for avalanche photodiode (APD) and gas counter readout has been fabricated on a 2.4 mmtimes2.4 mm die area using ROHM 0.35-muCMOS technology. This mixed signal ASIC consists of both analog and digital components and a window type discriminator is easily implemented through the use of a digital encoder to encode outputs from two comparators. The charge sensitive preamplifier is based on gain-boosted (regulated) cascode topology. The gain (voltage output to charge input) is 0.9 mV/fC and has been tested to have a low optimum Equivalent Noise Charge (ENC) of about 370 e
^-
+30 e
^-
/pF rms at a shaping time of 0.5 mus. The gain of the shaper is about 2.5 mV/fC and its peaking time can be varied from about 0.3 mus to 0.8 mus via an external pin. This chip is capable of sensing bipolar signals and is linear at least up to 320 fC for negative charge and 150 fC for positive charge. The average ENC of each channel has been calculated to be about 640 e
^-
+30 e
^-
/pF. The power consumption of the chip is approximately 0.13 W