8-channel CMOS preamplifier and shaper with adjustable peaking time and automatic pole-zero cancellation

An 8-channel preamplifier-shaper circuit for use with detectors having a capacitance in the range 20–50 pF has been designed in 1.2 μ CMOS AMS technology. The shaper is designed so that the peaking time can be adjusted, by steps, in the range 200 ns–2 μs by simple digital control. The pole-zero cancellation circuit uses an original method of sensing the preamplifier feedback capacitor discharging current and producing an identical current to discharge the capacitance of the pole-zero cancellation circuit. The series noise resistance rs = 415 Ω has been measured (270 Ω of which is the protection resistor). The input capacitance of the preamplifier is 10 pF + the strays of the test box 10 pF for a total of 20 pF. The input PMOS transistor has a gm of 5 mA/V (from simulation) at 210 μA drain current. The cross-talk between channels is less than 1%.