Study of the effects of parasitic capacitance on large integrated feedback resistors for charge-sensitive preamplifiers

Abstract

A study of the impedance and noise of an integrated poly-silicon resistor with distributed capacitive coupling to bulk is presented. The system is analyzed by using a closed-form calculus which produces non approximated results. In particular, deviations from ideal conditions are shown when that kind of resistor is used as a continuous-discharge feedback device for charge-sensitive preamplifiers. The effect of using a feedback resistor with capacitive coupling to bulk is an evident deformation of the shape of the signals. An innovative technique is presented, which allows overcoming the problem of the distortions in the CSP output signals. Several n-wells are placed under the resistor and driven with an auxiliary low-impedance divider which minimizes the voltage variations on the plates of the parasitic capacitors. In this way the pulses provided by the charge-sensitive preamplifiers show again a clean R-C exponential-decay shape and are so optimized for signal shaping and adequate for high-resolution spectroscopy.

Impedance and Noise Closed-Form Model of Large-Area Integrated Resistors With High Stray Capacitance to be Used as Feedback Discharge Devices in Charge-Sensitive Preamplifiers for Nuclear Spectroscopy

“…On the other hand it is common to realize integrated polysilicon resistors with a n-well acting as a guard. As was previously pointed out in [8] and later in [9], despite the nonidealities described in the previous section, it is possible to obtain an approximated ideal-resistor behaviour from a chain of RWDCs. The core of this idea is to separate the RWDC in various segments, each one with its own underlying n-well driven with appropriate voltages so as to cancel out, in firstorder approximation, the capacitive effects.…”

Evaluation of the spectroscopic performance of the integrated multi-channel charge-sensitive preamplifier of TRACE with a silicon detector prototype

“…Future studies will address the issue of the external 1 GΩ resistor. Integrated solutions based on polysilicon resistors are being investigated [14], [15].…”

An Innovative Analog Circuit to Retrieve Energy Information From Signals of Deeply Saturated Preamplifiers Connected to Semiconductor Detectors

“…Except for the feedback resistance, which effect is negligible, the input node is isolated, because it is only connected to capacitive elements tied to ground. When the pre-amplifier is operating in a conventional mode, the charge released by the detector in the short term is collected by the feedback capacitor and in the long term is removed from it by the feedback resistor, being it discrete [13], [14], integrated [15], [16] or made by an active trans-conductor [17]. The amplitude of the output signal is proportional to the amount of charge collected: for this reason the information about the radiation energy is retrieved performing amplitude spectroscopy on the output signals.…”