The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
Date: Thu, 28 Nov 2002 17:45:43 -0500
From: Raymond Rogers
User-Agent: Mozilla/5.0 (X11; U; Linux i586; en-US; rv:1.0.1) Gecko/20020823 Netscape/7.0
X-Accept-Language: en-us, en
Subject: Re: photodetector circuit, high speed with good ambient light rejection
X-Comments: This message was posted through Newsfeeds.com
X-Comments2: IMPORTANT: Newsfeeds.com does not condone, nor support, spam or any illegal or copyrighted postings.
X-Comments3: IMPORTANT: Under NO circumstances will postings containing illegal or copyrighted material through this service be tolerated!!
X-Report: Please report illegal or inappropriate use to
X-Abuse-Info: Please be sure to forward a copy of ALL headers, INCLUDING the body (DO NOT SEND ATTACHMENTS)
Organization: Newsfeeds.com http://www.newsfeeds.com 80,000+ UNCENSORED Newsgroups.
Dr C.I. Swift wrote:
> Need to make such a circuit good for up to 90MHz. will have a considerable
> DC light component so want too reject this.
> Is it possible to reverse bias the photodiode, running it to ground via an
> inductor in series with the resistor? The idea being the ac component will
> seee a higher impedence and therefore produce a higher voltage.
> Or should I stick to the transimpedence amplifier with a feedback resistor
> small enough so that the system does not saturate and then just ac couple
> the signal to further amplification stages.
> Any help or suggestions would be greatfully recieved
> Many thanks
You have had several suggestions here. They must have had much better
luck than I had. I have always had to use a common base configuration.
The emmitter reverse biases the diode to a fixed low level. The
voltage is set by the base; which is adequatly bypassed. The current
through the diode is read off of the collector. It's called cascode.
You might look at:
This paper seems to cover most bases.
The cascode circuit is on page 3.
Of course I come from a time when Op-amps were not as good; but it never
hurts to reduce the source impedance seen by the diode, since that is a
limiting factor on bandwidth.
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 80,000 Newsgroups - 16 Different Servers! =-----
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup