焦平面输入电路研究

Input circuit of focal plane arrays

在混合式焦平面阵列中,探测器和读出电路的耦合通过输入级电路实现。为分析输入电路对探测器-放大器系统性能的影响,用分立元件设计制作了一个三级的前置放大器并进行了模拟实验,实验表明放大器输入级噪声是造成探测器信噪比下降的主要因素,应用中应该选用具有特定噪声性能的放大器与探测器匹配。研究了焦平面中常用的直接注入(DI)和电容反馈放大电路(CTIA)与探测器耦合时在噪声、输入阻抗、工作点匹配等方面应具备的条件。提出了临界输入阻抗的概念,实验表明,当电路的输入阻抗低于此临界值时(对于GaN p!i!n光伏探测器来说约为106Ω),焦平面才能获得较高的注入效率。

In hybrid focal plane arrays, the coupling between detector and readout circuit is realized by input circuit. In this paper, in order to study the influence of the preamplifier on detector and amplifier system, the simulation experiments had been done with a preamplifier which made by separate transistors. Experiment indicates that the noise of input stage is main factor which leads to the decrease of the SNR of the detector, so appropriate amplifier which has certain noise performance should be selected to match the detector. And then, the conditions of the coupling in FPA between the detector with the direct injection （DI） circuit and capacitive transimpedance amplifier （CTIA） have been studied.The concept of the critical input resistance was put forward in this paper. Experiment indicates that theFPA will gain high injection efficiency only when the input resistance is lower than the critical value（10^6 Ω for GaN p-i-n detector）.