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Re: gEDA-user: Anticapacitor?
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- Subject: Re: gEDA-user: Anticapacitor?
- From: Bob Paddock <bob.paddock@xxxxxxxxx>
- Date: Thu, 8 Dec 2005 19:41:40 -0500
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On Wednesday 07 December 2005 06:04 am, Karel Kulhavy wrote:
> Is it possible to make a passive network from coils and capacitors that
> would approximate negated reactance of 6pF capacitor in the frequency
> range from 1MHz to 10MHz?
>
> It has to be passive device because I want to use it to compensate out
> capacitance of photodiode in low-noise broadband preamplifier.
You can use a Common-Base transistor to isolate the photodiode capacitance.
National Semi. shows a circuit doing this based on their LMH6642 op-amp.
http://www.national.com/dt/LMH_Qual.pdf see page #22 for the Common-Base isolate,
LMH6642 data sheet shows the circuit as well.
Karel, you might want to had this link to your web site, gives good overview of photodiode
issues:
http://www.national.com/onlineseminar/2004/photodiode/PhotodiodeAmplifers.pdf
http://www.national.com/onlineseminar/2004/photodiode/photodiode_transcript.pdf
The 'Anitcapacitor' reminded me of the 'Nonlinear Capacitor' , THAT Corp. App. Note 103:
http://www.thatcorp.com/datashts/600034-1.pdf
I always thought it was cool solution in search of a problem...