gEDA-user: Barrie Gilbert

[Harry Eaton]

Dan McMahill wrote:

>
> 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.
>
H. Jones I believe. Bob Widlar didn't design that particular cell 
structure nor specifically generalize the trans-linear principle early 
on, but he was among the first to design circuits that actually used the 
translinear behavior of monolithic transistors.

>
> 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 )
>
> For example, you can build a circuit where I1 * I2 = I3 * I4
>
Of course the Is's need not be identical, just ratiometrically matched 
(I know you know that Dan, but maybe not others here).  Ratios in Is can 
be achieved through scaling emitter areas, or more precise retios 
through paralleling devices. One key point is that this really only 
works well in a monolothic design where tight thermal and doping 
matching can be achieved. For non-constant Is, the equation above is 
just I1/Is1 * I2/Is2 = I3/Is3 * I4/Is4.

Cheers,
harry