Author Topic: 10 MHz photodiode?  (Read 524 times)

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Offline Dave92F1Topic starter

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10 MHz photodiode?
« on: October 16, 2023, 04:24:39 pm »
I want to make an optical probe for an oscilloscope, to measure flash duration from a stroboscope.

The flashes are on the rough order of 1 uS each, so I'd like about 10 MHz of bandwidth. Noise and gain aren't too critical (I'm mostly interested in timing, not light quantity).

Also, I'm lazy, so it would be great to find an integrated photodiode/amplifier in one part, like the TI OPT-101 (only much faster; the OPT-101 tops out somewhere around 50 kHz depending on the feedback resistor).

Suggestions?
 

Offline TimFox

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Re: 10 MHz photodiode?
« Reply #1 on: October 16, 2023, 04:50:32 pm »
I don't have a suggestion for a pre-made integrated unit.
In general, to get a fast response from a photodiode, you want to apply a reasonable reverse bias to the series combination of the diode and a 50 ohm load (which can be at the 'scope input, but must be DC-coupled to complete the circuit).
The usual figure for the sensitivity of a silicon photodiode is 0.4 A/W:  do you know the light output of your stroboscope and the optical geometry?
 

Online Kleinstein

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Re: 10 MHz photodiode?
« Reply #2 on: October 16, 2023, 04:53:38 pm »
With a flash there is no need for an amplfier. The photodiode could directly work on some 50 or 100 ohm impedance, e.g. from the scope or a termination close to the sope.
For better speed one may want bias the diode in reverse, e.g. from a 9 V battery with a local capacitor (e.g. 100 nF) for the RF return path around the battery and towards the coax cable.
I have seen such setup used for sub µs laser pulses and a GHz BW scope.
 


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