Low noise charge sensitive preamplifier dc stabilized without a physical resistor

The invention is a novel charge sensitive preamplifier (SCP) which has no resistor in parallel with the feedback capacitor. No resetting circuit is required to discharge the feedback capacitor. The DC stabilization of the preamplifier is obtained by means of a second feedback loop between the preamplifier output and the common base transistor of the input cascode. The input transistor of the preamplifier is a JFET with the gate-source junction forward biased. The detector leakage current flows into this junction. In particular, this invention, in addition to eliminating the feedback resistor, eliminates the need for external devices between the detector and the preamplifier, and it eliminates the need for external circuitry to sense the output voltage and reset the CSP. Furthermore, the noise level of the novel CSP is very low, comparable with the performance achievable with other more complex solutions.