A Cryogenic CMOS Preamplifier with Very Large Dynamic Range for HPGe Detectors

A cryogenic CMOS preamplifier fabricated in 180 nm CMOS process has been developed for HPGe detectors with very large dynamic range covering from ~10 eV (dark matter) to 10 MeV (neutrino-less double beta decay). It consists of two-stage amplifiers. The first stage is a normal charge sensitive preamplifier and the second stage has dual gain channels to achieve large dynamic range. In order to achieve low noise, the input transistor of the preamplifier was optimized for 2 pF detector capacitance and the pulse reset was adopted without using a feedback resistor. The ENC was simulated to be 4.63 electrons with 0.1 pA leakage current in 77 K. A “pre-reset’ method was introduced to reduce the dead time for large signals caused by conventional pulse reset, during which the charge of the large signal will not be completely collected. A pre-reset will be triggered when the preamplifier output enters into the incomplete-charge-collection region if no signal presents. Hence the dead time will be significantly reduced to the reset time. The function of pre-reset scheme was verified by transient waveform simulation and experiment results. The output waveforms have also been recorded when the CMOS preamplifier worded at liquid nitrogen temperature.