In the highly sensitive detection field, charge-sensitive amplifier is widely used in the preamplifier of detectors, however, the high voltage applied to these detectors (such as CZT nuclear detector) often make serious noise, which may influence the sensitivity of the detector. Despite the traditional passive filter circuit to eliminate the noise of the power, but if the power supply accuracy isn’t high enough and the passive circuit eliminate the power supply noise is incomplete. The noise still may affect the performance of the final system. According to the need of nuclear detection and photoelectric detection, a kind of differential JFET charge-sensitive preamplifier is proposed in this paper, which eliminates the power-supply noise and Johnson noise of bias resistance. First, theoretical analysis of the traditional JFET circuit is proved and simulation of the JFET circuit is performed with ORCAD software, which prove that power-supply noise effect the preamplifier. Next, simulation of the innovative circuit is performed with ORCAD software. Finally, the fabricated circuit board is tested with avalanche photo diode (APD). It is shown that the charge-sensitive preamplifier with differential JFET input can significantly eliminate the power-supply noise and Johnson noise of resistance (both low frequency and high frequency) and realize a high sensitivity.
Low-light-level image intensifier images weak optical signal through electron multiplication process in
Low-light-level night vision device, the key technology of intensifier is electron multiplier, the thesis put forward three
kinds of electron multiplication methods. One is that the electron multiplier device is the avalanche transistor made use
of the semiconductor material, the thesis analyses the photoelectric conversion theory and rapid multiplication avalanche
breakdown conditions with PN junction of the avalanche diode under reverse bias by light excitation; the second
approach is to use gas discharge theory to explains the electron multiplication process in the low-pressure gas and
high-pressure gas discharging breakdown by photon excitation; the third method is photoelectron multiplication gain
theory,in the microchannel plate (MCP) as the second generation image intensifier in vacuum condition and the applied
voltage. The thesis analyses that the electronic gain efficiency is better than the other two methods ,and proposes the
avalanche transistor can be key device of image intensifier.