Re: Basic advance question - design of photodiode amplifiers
- From: John Devereux <john@xxxxxxxxxxxxxx>
- Date: Fri, 24 Apr 2009 08:39:37 +0100
Ecnerwal <LawrenceSMITH@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> writes:
In article <87mya7xkdy.fsf@xxxxxxxxxxxxxxxxxxxxxxx>,
John Devereux <john@xxxxxxxxxxxxxx> wrote:
The negative bias is to reduce the capacitance of the photodiode. You
only need it if you are trying for a high speed circuit. You may well be
able to use a single supply configuration. It depends on the photodiode
and the speed required.
...and most photodiode circuits tend to be in the "high speed" category.
Otherwise a phototransistor is often a better choice - except where a
very non-rohs compliant CdS resistive sensor is better...photodiodes are
usually only chosen when speed is of the essence (in my limited
experience - we used them for looking at laser pulse risetimes...)
I disagree here, there are plenty of slower applications where you need
photodiodes rather than phototransistors. In fact I don't think I've
ever used a phototransistor in a real design, do people still use them?
:) Last one I had was ~30 years ago as a kid.
Photodiodes can give you large active areas when needed and are
extremely linear. They can still be pretty fast - even unbiased - if run
into e.g. an inverting opamp circuit to cancel the capacitance.
--
John Devereux
.
- References:
- Basic advance question - design of photodiode amplifiers
- From: Charlie E .
- Re: Basic advance question - design of photodiode amplifiers
- From: John Devereux
- Re: Basic advance question - design of photodiode amplifiers
- From: Ecnerwal
- Basic advance question - design of photodiode amplifiers
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