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Dennis Feucht

Case Study: Medical Laser System; Part 2: Photodiode Amplifier

Dennis Feucht
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D Feucht
D Feucht
11/27/2017 3:42:35 PM
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Re: photodiode operation
Thanks for your comment on photodiode modes. Indeed, in zero-volts mode, there should be no effect from the PD capacitance, though it will need to be compensated in the feedback loop. I call the reverse-biased mode the "voltage mode" because there is a voltage across the diode. In the "current mode", with no voltage across the PD, it doesn't seem like much of a "voltage" mode. But these are just labels.

For the laser application, the revised (current?) mode worked better.

11/15/2017 11:53:34 AM
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photodiode operation
"uses the photodiode in the fast but noisy voltage mode." It's my experience that current-mode is the fastest operation.  With no voltage variation there's no loading by the diode's or circuit capacitance.  Gives better linearity also.

Seems like the first paragraph under "Mode" is describing current mode.  And, yes, this gives more dark current if the diode is reverse-biased.

In current mode bootstrapping can virtually eliminate the effects of diode capacitance.

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