From: Jim Thompson
Subject: Re: Prof Searle's 100MHz 30dB 1968-era 3-trannie amplifier
References: <3E2358BE.firstname.lastname@example.org> <3E2A0C89.7FAB@sneakemail.com> <3E2A4E8D.78BE@sneakemail.com> <3E2A868D.1D0E@sneakemail.com> <3E2AE81D.73AC@sneakemail.com>
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Date: Sun, 19 Jan 2003 20:23:35 GMT
NNTP-Posting-Date: Sun, 19 Jan 2003 15:23:35 EST
Organization: Cox Communications
On 19 Jan 2003 11:27:43 -0800,
Winfield Hill ,
In Newsgroup: sci.electronics.design,
Entitled: "Re: Prof Searle's 100MHz 30dB 1968-era 3-trannie
Wrote the following:
|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. :>)
| - Win
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.
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
Searle's circuit uses 42mA, mine 12.5mA.
I haven't followed this thread until Mike's post... how does Searle's
circuit drive 50 ohms?
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
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