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I've come across an interesting transimpedance amplifier toplogy, that reportedly reduces voltage and current noise and compensates for large photodiode capacitance. However, as I'm working with an avalanche photdiode, and I need to bias it with at least 65V - how exactly would I be able to adapt the circuit for such high voltages?

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  • \$\begingroup\$ It looks to me that this biases the photodiode at about -9 volts - maybe lowering the -15 volt rail will get more reverse bias? \$\endgroup\$
    – Andy aka
    May 22, 2014 at 10:52

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Your source, of course, is http://www.electrooptical.net/www/frontends/frontends.pdf.

A direct adaptation is fairly simple. Rbias should be connected to -15, as shown, but the 20K resistor must be tied to a separate bias voltage, Vb. For a given diode bias voltage Vd, Vb = 1.67 Vd. In your case, this would call for a Vb of about -100 volts.

All of this supposes that you need the performance. Do you? What photodiode current level are you expecting? What is the photodiode capacitance when biased? How much bandwidth do you need? What SNR do you need? Go back to the article. Start with your expected current level and desired output voltage. This determines the value of the transimpedance amplifier resistance. Now use this, along with the diode capacitance and the input capacitance of your op amp, to model a simple TIA with a small feedback amplifier. Calculate the bandwidth. Is this adequate? If so, go no farther. There is an old saying: those who ask for more bandwidth than they need get what they deserve.

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  • \$\begingroup\$ +1, for citing the source and, even more, for the saying about bandwith. I should put a poster with this slogan above my 50 MHz vintage scope (556) that works as good as new for most things even today... \$\endgroup\$
    – zebonaut
    May 23, 2014 at 8:20
  • \$\begingroup\$ My issue currently is not so much with the bandwidth, but the noise magnitude. My application would require a few dozen kHz, despite the APD responding in the ps range. The fact that the APD has a huge capacitance (320 pF) and a verly low dark current (~0.15 uA, looking to measure changes around 0.8 uA) made me afraid of noise isses. I've come across this design because I was looking for a low noise transimpedance solution, and it did seem a rather effective one. Right now however I suspect I would be able to achieve that with a simple TIA as long as I carefully choose a low noise op-amp. \$\endgroup\$
    – joaocandre
    May 26, 2014 at 14:47

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