"Robert Scott" schrieb im Newsbeitrag news: snipped-for-privacy@news.provide.net...
I have been doing some experimenting with a transimpedance amp (LF353) and
>a PIN
> photodiode. So far I have been using only a simple 1M feedback resistor
> with
> zero bias on the diode. Then I noticed in the datasheet for the PIN
> photodiode
> (NEC PH302) it shows a graph of photodiode current as a function of
> reverse
> bias. According to that graph, the photodiode current should be about
> double
> with 2 volts of reverse bias on the diode as compared with zero bias.
> When I
> tried it, the gain of the system remained the same (I have a squarewave
> light
> signal generated by a LED). It did improve the transient response quite a
> bit,
> especially when I rasied the bias to 7 volts (due to the reduced diode
> capacitance, I guess) but I saw no evidence of increased photodiode
> current. Is
> this bogus? I have not seen this stated anywhere else besides the NEC
> PH302
> datasheet, but Graeme in his classic book on Photodiode Amplifiers does
> say that
> PIN diodes are usually used with bias. Why is that? Why PINs and not all
> photodiodes?
>
>
> Robert Scott
> Ypsilanti, Michigan
Hello Robert,
The photo current is independent of the reverse voltage at such low currents. I guess they measured the photo current with an ampere-meter with 100kOhm input resistance.
See figure 3.3 of this application-note.
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Best regards, Helmut