光电放大器：Photocell Amplifiers

光电放大器：Photocell Amplifiers

Amplifiers for photoconductive, photodiode and photovoltaic cells are shown in Figures 14, 15, 16 respectively. All photogenerators display some voltage dependence of both speed and linearity. It is obvious that the current through a photoconductive cell will not display strict proportionality to incident light if the cell terminal voltage is allowed to vary with cell conductance. Somewhat less obvious is the fact that photodiode leakage and photovoltaic cell internal losses are also functions of terminal voltage.
The current-to-voltage converter neatly sidesteps gross linearity problems by fixing a constant terminal voltage, zero in the case of photovoltaic cells and a fixed bias voltage in the case of photoconductors or photodiodes.
Photodetector speed is optimized by operating into a fixed low load impedance. Currently available photovoltaic detectors show response times in the microsecond range at zero load impedance and photoconductors, even though slow, are materially faster at low load resistances. The feedback resistance, R1, is dependent on cell sensitivity and should be chosen for either maximum dynamic range or for a desired scale factor. R2 is elective: in the case of photovoltaic cells or of photodiodes, it is not required in the case of photoconductive cells, it should be chosen to minimize bias current error over the operating range.

光电放大器用于放大由光电导、光电二极管和光电池所得到的光强度信号，如图14、15、16。这些光电传感器的输出电压与线性度和（响应）速度有关。显然，如果任由光电导电池的端电压随其电导变化而变化，那么其输出电流与入射光强度之间就不会遵循严格的比例关系。此外，光电二极管的漏电流和光电池的内部损耗也是其端电压的函数。
电流——电压转换电路利用在光电检测器的输出端加上一个恒定的电压来巧妙地解决了整体上的线性度问题。对于光电池来说，这个电压为0V；对于光电导或光电二极管来说，是一个偏置电压。

光电检测器件，在负载为适当的低阻抗时，其信号转换速度将得到优化。现行的光电检测器在0负载的情况下，响应速度可以达到毫秒数量级，半导体光电器件稍慢，但是在低阻抗负载的情况下，其速度也会得到质的提高。反馈电阻R1的取值由电池的灵敏度和要求的最大动态范围，或者需要的电流——电压转换比例决定。R2分情况选取：在光电池和光电二极管时不需要这个电阻，在光电导的时候，电阻的阻值应该能使在工作范围内，由OP输入偏置电流所带来的误差最小。