15 Dec
2011
15 Dec
'11
11:37 p.m.
Tony writes:
> On 12/14/2011 08:14 PM, Mouse wrote:
> > On the other, I'm considering an AGC circuit that doesn't use a bulb,
> > but instead uses a FET as a variable resistor, and trying to figure out
> > where it's got anything nonlinear in it (assuming the amplifier is
> > running class A).
>
> Jim Williams (RIP) did a LOT of research on this. The bulb
> outperformed the FET by a gigantic margin. (just sayin'..)
I thoguht in the end he amanged ot get the FET cirucit
to be better than
the light bulb, but it took a lot of work (and probably wasn't worth it).
Good reference: AN-43: http://cds.linear.com/docs/Application%20Note/an43f.pdf
I'm sure Jim Williams thought it was worth it and I really enjoyed reading about it so
it was worth it to me for sure :-)
A highlight was Note 5: "What else should be expected when trying to replace a single
light bulb with a bunch of electronic components? I can hear Figure 39?s #327 lamp
laughing."
I had previously met Sir Denys Wilkinson and he had mentioned something to me about his
pioneering days in nuclear instrumentation (including pinball machine multichannel
analyzers). When he had told me that he had invented the D/A converter I didn't really
believe him but kinda nodded along. Then I read it in Jim Williams' application note -
with an actual reference - I felt a little sheepish in retrospect!
Tim.