[time-nuts] Photodiodes for high frequency OPLL

Attila Kinali attila at kinali.ch
Sat Mar 30 15:03:52 EDT 2013

On Sat, 30 Mar 2013 17:29:45 +0000
lists at lazygranch.com wrote:

> You lose me at damping per decade? Is damping the right word?
> Do you mean high frequency rolloff?

Er.. yes. Frequency rolloff... Sorry, my native language got the better of me.

> Most texts on photodiodes go into bootstrapping them to reduce the
> effect of capacitance. But if you design fully differential amplifier
> circuits, they have the same effect as bootstrapping. Jerald Graeme's
> "Photodiode Amplifiers" goes into this. I'm not a fan of Gain technology
> as a company, but Graeme's book are good texts. 

Thanks! I just ordered this book.
Although i will have to build a discrete amplifier for the first stage
until i can mix the signal down to something that can be handled easier.

> The bootstrapping circuits use simpler buffers to keep the voltage
> potential across the diode low, while the fully differential circuits
> depend on gain bandwidth product to do the same.

Well, as i currently lean torwards using an avalanche photodiode,
which needs an operating voltage in the range of 100V, keeping the
potential accross the diode low is not really an issue :-)

How do the fully differential circuits get to keep the potential low?
As far as i can tell, from the circuits i've seen so far, the differential
circuits just use the single ended signal from the diode take the difference
to a bias voltage.

			Attila Kinali
The people on 4chan are like brilliant psychologists
who also happen to be insane and gross.
		-- unknown

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