A new biasing method for CMOS preamplifier-shapers

We present in this paper a new circuit technique for biasing a CMOS preamplifier-shaper that uses a MOSFET transistor as a feedback resistor for use with radiation detectors. The new method uses circuit mirroring and current feedback to achieve a continuous adaptive biasing of the MOS transistor to stabilize its drain-source resistor. The method was applied to preamplifier-shaper with a charge sensitive preamplifier (CSA) using a PMOS transistor as a resistor feedback. The PMOS transistor is operated in the triode region to achieve a resistor value in the megaohm range. Simulated results showed stability of the feedback resistor over a 180 mv threshold variation of the MOS transistor. Moreover, the technique results in a precise pole-zero cancellation in the shaper