"Gary Peek" <mylastname@mycompanyname.com> wrote in message news:9mvfj.2433$jJ5.703@newssvr11.news.prodigy.net...> It includes "AN-88, CMOS Linear Applications". Search for it, > I found a Fairchild equivalent on their web site.I like the note on the first page, "Application note, July 1973, revised April 2003." Whaddaya think they changed? I suspect that's just when they turned it into a PDF file.
Using CMOS logic for amplifying small signals
Started by ●January 4, 2008
Reply by ●January 4, 20082008-01-04
Reply by ●January 4, 20082008-01-04
Spehro Pefhany wrote:> On Fri, 04 Jan 2008 10:35:48 -0800, Joerg > <notthisjoergsch@removethispacbell.net> wrote: > >> Spehro Pefhany wrote: >>> On Fri, 04 Jan 2008 11:48:46 -0500, "Mr. B" <un@dis.closed> wrote: >>> >>>> Something has occurred to me, and I was wondering if anyone knew more about >>>> this. Could a CMOS logic inverter, like a 4049, be used as a very high >>>> gain amplifier if it were properly biased? I figured that the DC offset >>>> should be set at just about half the supply voltage, so that the gate was >>>> always between a '1' and a '0'. >>>> >>>> I am not sure if the gate would behave linearly in that region, or if >>>> thermal noise might cause it to reach a valid logic state and not amplify >>>> the signal, but if it would work, it might be a cheap way to make an >>>> amplifier for long wave or AM radio. >>>> >>>> -- B >>> >>> Yes, with UB gate, you just need a relatively high value resistor from >>> input to output, and capacitively couple to the input, but I would >>> suggest not using a buffer like the 4049UB since the quiescent current >>> will be higher than it needs to be. Something like a 4069UB >>> (unbuffered) gate operated at a few volts... in fact that kind of >>> application is pretty much why the UB gates are still around. You can >>> put a bunch in series and get more amplification, but of course you >>> have to capacitively couple the input of each stage from the previous >>> stage. With a buffered gate you will probably make a high frequency >>> oscillator if you try to bias it with a resistor. >>> >> I've used the buffered ones as amps. But one must follow RF guidelines, >> this ain't your old audio amp no more even if used as such. Also, >> sometimes unorthodox supply tricks need to be used, for example current >> limiting the supply so you can set a desired quiescent current >> regardless of process tolerances. Those can be quite high and aren't >> always fully spec'd. > > Of course if you limit the supply current then you get an unknown > limit to output voltage swing... nothing comes for free.. >Well, sure, they aren't meant to drive the speakers during a Stones concert :-) -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●January 4, 20082008-01-04
Gary Peek wrote:> Mr. B wrote: >> Something has occurred to me, and I was wondering if anyone knew more >> about >> this. Could a CMOS logic inverter, like a 4049, be used as a very high >> gain amplifier if it were properly biased? > > It certainly could. I'm looking at a National Semiconductor > databook called CMOS Integrated Circuits, March 1975. > > It includes "AN-88, CMOS Linear Applications". Search for it, > I found a Fairchild equivalent on their web site.But resist the temptation to use the 74C series devices in there. Those seem to be on the way to lalaland. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●January 4, 20082008-01-04
Joel Koltner wrote:> "Gary Peek" <mylastname@mycompanyname.com> wrote in message > news:9mvfj.2433$jJ5.703@newssvr11.news.prodigy.net... >> It includes "AN-88, CMOS Linear Applications". Search for it, >> I found a Fairchild equivalent on their web site. > > I like the note on the first page, "Application note, July 1973, revised April > 2003." Whaddaya think they changed? I suspect that's just when they turned > it into a PDF file. >Maybe they changed the resolution settings for the PDF scanner in 2003 :-) Looks pretty much like National AN-88. The one in my book says July 1973, revised June 1986. Whatever they might have revised back then. I could go look in the real old App Databook. I keep them all, for good reason. While you can still get stuff for the Plymouth Fury some semi mfgs have a habit of dropping docs off the web server the millisecond something goes obsolete. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●January 4, 20082008-01-04
On Fri, 04 Jan 2008 11:48:46 -0500, "Mr. B" <un@dis.closed> wrote:>Something has occurred to me, and I was wondering if anyone knew more about >this. Could a CMOS logic inverter, like a 4049, be used as a very high >gain amplifier if it were properly biased? I figured that the DC offset >should be set at just about half the supply voltage, so that the gate was >always between a '1' and a '0'. > >I am not sure if the gate would behave linearly in that region, or if >thermal noise might cause it to reach a valid logic state and not amplify >the signal, but if it would work, it might be a cheap way to make an >amplifier for long wave or AM radio. > >-- Bhttp://ww1.microchip.com/downloads/en/AppNotes/00236a.pdf Is a microchip application note on using their line of pic products for encoding and decoding X10 home automation signals. On page 5 of the schematics they show a 4069 used as a single channel AM receiver. Two inverters are used as tuned RF amps, two others used as untuned RF amps, and 1 for a detector stage. A little tweaking of values and you'd have your broadcast band radio. Since you can also parallel inverters on the same chip for greater current drive, maybe another chip could be used for the speaker driver? Wireless power transmitter operating at 13 mhz, Cmos inverter operates the oscillator buffer and driver for a pair of mosfets on the PA stage. http://www.edn.com/article/CA6501085...dustryid=44217 whole article (~65kb) Schematics: http://www.edn.com/contents/images/6501085f1.pdf transmitter circuit (45kb) http://www.edn.com/contents/images/6501085f2.pdf receiver circuit (35kb) --
Reply by ●January 4, 20082008-01-04
On Fri, 04 Jan 2008 11:48:46 -0500, Mr. B wrote:> Something has occurred to me, and I was wondering if anyone knew more > about this. Could a CMOS logic inverter, like a 4049, be used as a very > high gain amplifier if it were properly biased? I figured that the DC > offset should be set at just about half the supply voltage, so that the > gate was always between a '1' and a '0'. > > I am not sure if the gate would behave linearly in that region, or if > thermal noise might cause it to reach a valid logic state and not > amplify the signal, but if it would work, it might be a cheap way to > make an amplifier for long wave or AM radio. >If I were doing it, I'd look at the unbuffered version, like 74HCU04, which is essentially 6 MOSFET inverting amplifiers. Good Luck! Rich
Reply by ●January 4, 20082008-01-04
On Jan 4, 8:48=A0am, "Mr. B" <u...@dis.closed> wrote:> ...Could a CMOS logic inverter, like a 4049, be used as a very high > gain amplifier if it were properly biased?Yes, it's possible. CD4007UB is intended to be used that way (and has some extra connection points that you won't find in an inverter).
