CHARGE PREAMPLIFIER

摘要

1468716 Amplifiers; pulse circuits COMMISSARIAT A L'ENERGIE ATOMIQUE 22 Nov 1974 [27 Nov 1973] 50631/74 Heading H3T A charge preamplifier for low noise use, e.g. with a lithium-drifted silicon X-ray detector 6, comprises an input stage connected to an amplification stage connected to an output stage 14, and an optoelectronic negative feedback circuit, the input stage comprising a cooled first FET T 1 1 illumination of which closes the feedback circuit, the load of T 1 1 being provided by a second FET T 2 1 connected in series with a coil L 1 . To reduce noise current fluctuations the impedance of L 1 should be large compared with the reciprocal of the slope of T 2 1. The amplification stage is constituted by differential circuit T 3 1, T 1 feeding into T 2 , the load for which is T 3 . Bias voltages for the output transistors T 4 , T 5 are determined by diodes D 1 , D 2 , D 3 . A low pass filter R 8-10 , C 6 corrects the frequency response of the amplifier. The analogue output at S passes via T 6 to a hysteresis comparator M 1 ; when the output voltage exceeds a threshold set by P 2 and P 3 , M 1 delivers a logical "0" signal to a NOR gate M 2 the other input of which receives the signal integrated by circuit 16. After a delay due to 16, M 2 delivers a logical "1" to bi-state circuit 20 which turns on T 9 , which supplies electroluminescent diode D 4 . The radiation emitted by D 4 falls on the gate junction of T 1 1 and increases its reverse current causing a feedback capacitor C 8 to discharge until the output voltage of the preamplifier falls to the lower threshold of M 1 . The temperature of T 1 1 in cryostat 7 is determined by the current through a Zener diode Z 1 , R 28 being chosen so that the noise voltage at S is minimized. As an alternative to pulsed operation the preamplifier may be operated with the circuit 20 as a class A differential stage, with the base of T 7 directly connected to S, and T 1 1 continuously illuminated by D4.