If you have used a Tektronix plug-in style Oscilloscope, 74XX series,
you have seen some of Barrie's early design work. He designed the
stroke generator that creates the data characters on the screen, e.g.,
the volts and time scales. It's not a raster scan that forms the
characters but the CRT beam is actually deflected in the pattern needed
to create the symbol. He worked for Tek at the time, before his
employment at Analog Devices.
John Dozsa
Karel Kulhavy wrote:
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.
I like how in one article Barrie Gilbert says how modern design is plagued
with DSPs and digital thinking instead of people trying to figure what
wonders are lying in the analogue domain. He seems to be the guy who uses
elegance as the design rule of thumb. Do you know about more people like
him?
CL<
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 )
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.
I'll try to find a reference to post tonight and I'll sketch out a more
concrete example.
-Dan
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