On Wed, Sep 06, 2006 at 06:55:35AM -0400, Dan McMahill wrote: > Bob Paddock wrote: > >On Wednesday 06 September 2006 03:36, Karel Kulhavy wrote: > > > >>Anyone knows what exactly is called Gilbert cell? > > > > > >The Gilbert Cell is named after Barrie Gilbert of Analog Devices, > >invented in 1968. > > > >http://www.ieee.org/organizations/pubs/newsletters/sscs/jan03/jssc_classic.html > > > >The Gilbert Cell has become common in RF designs, used as a double balanced > >mixer. It is a four quadrant multiplier. Somewhere in my files I have a > >paper > >by Gilbert where he states that he never really meant it to be used the > >way, > >that has been the most common usage. He recommended an obscure > >division technique instead. I'll dig the paper up this evening. > > Bonus points to anyone who can name the real inventor of the mixer in > question here. Hint: It wasn't Gilbert even though it's called a > Gilbert cell. > > >>How many transistors does it actually have? > > > > > >http://rfdesign.com/mag/503rfdf1.pdf > > > > > >>Is it possible to make a well working Gilbert cell with ordinary > >>non-matched > >>transistors? > >>And btw do you know what translinear mean? > > > > > >One set of frequencies is translated linearly to an other set of > >frequencies. > >Using non-matched transistors will not be linear, resulting in spurious > >outputs. > > no. That is not what translinear means. Translinear circuits in this > context refers to the class of circuits where you find a loop consisting > just of bipolar junctions and have an equal number in each direction. > The idea is that Ic = Is * exp(Vbe/Vt) where Is depends on the device, > Vt is the thermal voltage (kT/q), Ic is collector current, and Vbe is > the base-emitter voltage. If you write out KVL around this loop of > base-emitter junctions you get: > > sum( Vbe_cw ) = sum( Vbe_ccw) > > where Vbe_cw = junctions where the voltage is positive in the clockwise > direction and Vbe_ccw = junctions where the voltage is positive in the > counter clockwise direction. > > Now assume all the Is are the same and some simple math shows that > > product( Ic_cw ) = product( Ic_ccw )
Exactly, like MOSFET is a silicon analogue of electron tube, BJT is a silicon analogue of slide ruler. > > For example, you can build a circuit where I1 * I2 = I3 * I4 > > and you can build a squaring circuit or a square root circuit. > > These circuits work on large signals. What if spurious resistances kick in? Or the signal gets so large that one transistor heats up? Doesn't it crook then? CL< > > I'll try to find a reference to post tonight and I'll sketch out a more > concrete example. > > -Dan > > > > _______________________________________________ > geda-user mailing list > geda-user@moria.seul.org > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user