A NOVEL CHARGE SENSITIVE PREAMPLIFIER WITHOUT THE FEEDBACK RESISTOR

A novel charge sensitive preamplifier#1 which has no resistor in parallel with the feedback capacitor is presented. No external device or circuit is required to discharge the feedback capacitor. The detector leakage and signal current flows away through the gate of the input JFET which works with its gate to source junction slightly forward biased. The DC stabilization of the preamplifier is accomplished by an additional feedback loop, which permits to equalize the current flowing through the forward biased gate to source junction and the current coming from the detector. An equivalent noise charge of less than 20 electrons rms has been measured at room temperature by using an input JFET with a transconductance to gate capacitance ratio of 4 mS/5.4 pF.