From: Winfield Hill
Subject: Re: Prof Searle's 100MHz 30dB 1968-era 3-trannie amplifier
Date: 19 Jan 2003 14:54:13 -0800
Organization: Rowland Institute
References: <3E2358BE.email@example.com> <3E2A0C89.7FAB@sneakemail.com> <3E2A4E8D.78BE@sneakemail.com> <3E2A868D.1D0E@sneakemail.com> <3E2AE81D.73AC@sneakemail.com>
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Jim Thompson wrote...
> Winfield Hill wrote
>|Jim Thompson wrote...
>|> Pre-Searle: MC1552/53 Video Amplifier (I devised the biasing scheme,
>|> basic feedback-triple design by Solomon; I also was the math grunt,
>|> computing gain, feedback stability and noise, circa 1964... when I
>|> was 24 years old, 39 years ago :-)
>| That was a nice design, Jim, something to be proud of. I remember
>| using it way back when. But it has four transistors in the active
>| signal path, rather than three, and goes to 40 or 50MHz with a gain
>| of 34dB into a 1k load, rather than 100MHz into ? 50 ohms. Hmm, it
>| appears Prof Searle's design was no slouch. :>)
> The fourth transistor is a follower, and the feedback loop from that
> emitter is a *DC* loop. The AC loop is the same as Searle's;
> Searle's DC loop is different... mine sets Vo = Vcc/2.
Then you remember his specific circuit configuration? I take
it that it was different from the shunt-series pair I posted?
> Searle's design uses discrete transistors, one of the hottest devices
> available, fT = 8GHz (were MMBRC941's available in Searle's day? ...I
> think not... there were 914's, but I don't remember 941's), mine uses
> a very early I/C process with 25.4um x 48.1um emitters, fT = 750MHz
Whoa, 8GHz transistors in 1968, that's pretty impressive. My 1983
Motorola databook lists up to 1.6 and 2.0GHz SOT-23 types under VHF
amplifiers, plus 4.0 and 5.5GHz types (MMBR930 at 30mA, 5V) under
RF SOT-23 Transistors, and that's the highest available for 1983.
> Searle's circuit uses 42mA, mine 12.5mA.
That's pretty detailed memory, do you know his circuit?
I'm simply speculating, not having ever seen it.