Cool, thanks! Frank --- In [email protected], James Wagner <[EMAIL PROTECTED]> wrote: > > When you use only a 3-transistor cell, you basically have only a > two-quadrant multiplier. Or, more correctly, the Gilbert cell is > multiplying a current of the form A+BSin(W*t) (where A>B). So, there is > no condition for the signal applied to the lower current source that > results in zero output. > > Jim, KA7EHK > New forum member > > --- Frank <[EMAIL PROTECTED]> wrote: > > > Ray, > > Thanks for the link. In the problem statement I put forward, I was > > imagining extra transistors that implement a constant current source > > under the three for the Gilbert cell. That of course is wrong and > > does > > not work. The way you explained, the bottom transistor of the three > > is > > the variable current source, makes total sense to me. > > > > Frank > > > > --- In [email protected], "Ray Anderson" <ray.anderson@> > > wrote: > > > > > > Frank- > > > > > > > > > > > > A real quick intuitive hand-waving explanation is: > > > > > > > > > > > > The bottom transistor isn't functioning as a constant current > > source, > > > but is functioning as a controlled current source (controlled by > > the > > > transistors base voltage). This controlled current is fed to the > > upper > > > two transistors that function as a simple differential amplifier. > > By > > > varying the emitter current on this differential pair the gain of > > the > > > differential pair varies. > > > > > > > > > > > > See the following web page for a more detailed tutorial on the > > > functioning of the Gilbert cell: > > > http://members.tripod.com/michaelgellis/gilbert.html > > > > > > > > > > > > -Ray WB6TPU > > > > > > > > > > > > > > > > > > ________________________________ > > > > > > From: [email protected] > > [mailto:[EMAIL PROTECTED] On > > > Behalf Of Frank > > > Sent: Wednesday, February 27, 2008 4:15 PM > > > To: [email protected] > > > Subject: [soft_radio] Re: The MC1496 Is Now Quadrature- QUESTION: > > > unbalanced bottom of Gilbert cell > > > > > > > > > > > > Hello, > > > I always had a bit of trouble understanding how a Gilbert cell that > > > > > is made up of only three mixing transistors work. A constant > > current > > > source below the bottom transistor is supposed to keep the current > > > steady, so I do not see how it is possible for a voltage variation > > > on the base of the bottom transistor can change the current at the > > > collector. I tend to see the bottom transistor as a common base > > > current buffer. > > > > > > For the 6 transistor Gilbert cell, I could see the constant current > > > > > source being diverted alternately to the two pairs of transistors > > at > > > the top by the bottom pair. > > > > > > Could somebody explain to me in an intuitive fashion how a 3- > > > transistor Gilbert cell works???? Could somebody point me to a chip > > > > > or a design with a 3-transistor Gilbert cell. > > > Thanks, > > > > > > Frank > > > > > > > > > > > > > ____________________________________________________________________________________ > Looking for last minute shopping deals? > Find them fast with Yahoo! Search. http://tools.search.yahoo.com/newsearch/category.php?category=shopping >
