  A new application-specific integrated circuit (ASIC), the high-speed
charge-to-time converter (QTC) IWATSU CLC101, provides three channels, each
consisting of preamplifier, discriminator, low-pass filter, and charge
integration circuitry, optimized for the waveform of a photomultiplier tube
(PMT). This ASIC detects PMT signals using individual built-in discriminators
and drives output timing signals whose width represents the integrated charge
of the PMT signal. Combined with external input circuits composed of passive
elements, the QTC provides full analog signal processing for the detector's
PMTs, ready for further processing by time-to-digital converters (TDCs).
High-rate (>1MHz) signal processing is achieved by short-charge-conversion-time
and baseline-restoration circuits. Wide-range charge measurements are enabled
by offering three gain ranges while maintaining a short cycle time. QTC chip
test results show good analog performance, with efficient detection for a
single photoelectron signal, four orders of magnitude dynamic range (0:3mV ~
3V; 0:2 ~ 2500 pC), 1% charge linearity, 0.2 pC charge resolution, and 0.1 ns
timing resolution. Test results on ambient temperature dependence, channel
isolation, and rate dependence also meet specifications.
