光電放大器：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.

光電放大器用于放大由光電導、光電二極管和光電池所得到的光強度信號，如圖14、15、16。這些光電傳感器的輸出電壓與線性度和（響應）速度有關。顯然，如果任由光電導電池的端電壓隨其電導變化而變化，那么其輸出電流與入射光強度之間就不會遵循嚴格的比例關系。此外，光電二極管的漏電流和光電池的內部損耗也是其端電壓的函數(shù)。
電流——電壓轉換電路利用在光電檢測器的輸出端加上一個恒定的電壓來巧妙地解決了整體上的線性度問題。對于光電池來說，這個電壓為0V；對于光電導或光電二極管來說，是一個偏置電壓。

光電檢測器件，在負載為適當?shù)牡妥杩箷r，其信號轉換速度將得到優(yōu)化?，F(xiàn)行的光電檢測器在0負載的情況下，響應速度可以達到毫秒數(shù)量級，半導體光電器件稍慢，但是在低阻抗負載的情況下，其速度也會得到質的提高。反饋電阻R1的取值由電池的靈敏度和要求的最大動態(tài)范圍，或者需要的電流——電壓轉換比例決定。R2分情況選?。涸诠怆姵睾凸怆姸O管時不需要這個電阻，在光電導的時候，電阻的阻值應該能使在工作范圍內，由OP輸入偏置電流所帶來的誤差最小。