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From: firstname.lastname@example.org (Thorsten Brandt)
Subject: Re: Variable Gain Amplifier
Date: 19 Oct 2002 10:19:21 -0700
References: <email@example.com> <3DB09C15.firstname.lastname@example.org>
NNTP-Posting-Date: 19 Oct 2002 17:19:21 GMT
Robert Baer wrote in message news:<3DB09C15.email@example.com>...
> Thorsten Brandt wrote:
> > Hi,
> > i'm looking for help and information in order to design a variable
> > gain amplifier with the following spec :
> > bandwidth : 1 Ghz
> > continously variable gain from 1 to 50
> > input imedance : 10kohm/2pf
> > output resistance : 50-100 ohm
> > noise density : < 5nV/Sqrt(Hz)
> > furtheron is a high flatness in the frequency range from DC to 500 MHz
> > very important ! linearity is also important - but this is left open
> > for discussion ... (in a first approach i would say HD2 and HD3 should
> > be lower -50 to -60db for a 200mVpp signal)
> > a fully differential design would be in this context very useful for
> > my application - but it's not a must ...
> > the control of the gain can be done by voltage or by current. the
> > function how the gain depends upon this voltage is not so important
> > (linear or linear-in-db or whatever ...)
> > any help is appreciated : that means discrete design ideas like in the
> > good old days of analog tektronix scopes equally to approaches with
> > more integrated circuits (if available - i haven't found yet any good
> > ones - the best one i found is the AD8367)
> > links to papers, websites and good books would be also very
> > interesting ...
> > best regards
> > Thorsten Brandt
> Firstly, you do not say the frequency range (DC-1GHz or 1-2GHZ or ??),
> but that does not matter.
> What you fail to specify is the input impedance as a function of
> It will not be possible to retain a constant input impedance over
> frequency, and your spec of Z and noise is not exactly conducive to a
> practical design; a 50 ohm or 75 ohm input impedance would be more
but anyway - if you prefer an input resistance of 50-200 ohm - go ahead ...
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