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Old 18th September 2005, 10:10 AM   #1
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Default cross-quad and cascomp circuits

I've read several threads about Professor Hawksford, and I know that he has the cross-quad and cascomp circuits for input stages in a couple of his papers.

Could someone tell me exactly what the advantages are of these circuits (that is, why someone would want to use them)?

Thank you!
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Old 18th September 2005, 09:09 PM   #2
jcx is offline jcx  United States
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http://db.audioasylum.com/cgi/m.mpl?...rophead&n=3169


http://www.analog.com/UploadedFiles/...917MAT04_d.pdf

(fig 6)


Hawksford also explored some related diff pair input linearization techniques

J4 DISTORTION CORRECTION CIRCUITS FOR AUDIO AMPLIFIERS, M.O.J. Hawksford, JAES, vol.29, no.7, 8, July/August 1981

At http://www.essex.ac.uk/ese/research/...lications.html

Somewhere you might also find Gilbert’s “multi-tanh” proposal

Its not clear that these techniques are necessary in audio amplifier design - high loop gain, emitter degen and bootstrapped cascode appear to be enough for super low distortion in audio amp inputs
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Old 18th September 2005, 10:39 PM   #3
Steven is offline Steven  Netherlands
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Quote:
Originally posted by jcx

Somewhere you might also find Gilbert’s “multi-tanh” proposal

http://iroi.seu.edu.cn/jssc9899/33ss...01-gilbert.pdf

Steven
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Old 18th September 2005, 11:54 PM   #4
dimitri is offline dimitri  United States
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Quote:
Quinn's US pat 4897611
it is either 4,146,844 or 4,692,712

4897611 is very high gain positive fb cmos amp
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Old 19th September 2005, 03:34 PM   #5
jcx is offline jcx  United States
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thanx dimitri

4146844 fig 4 looks like what I was thinking of, don't know were my ref came from

I believe the cascomp was actually used in tektronix front end amplifiers - unusual for a patented circuit


The main utility of these enhancements would be in situations where you cannot have high global loop gain

in audio amplifiers it is quite possible to keep the differential input V << 1mV with high loop gain - then the ordinary diff pair is linear enough to not be the limmiting factor
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Old 21st September 2005, 01:29 PM   #6
dimitri is offline dimitri  United States
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Default Gilbert curcuit

I1/2=I2=I3=1ma, I4=20mA
Quinn added series cascode after this
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Old 21st September 2005, 01:34 PM   #7
dimitri is offline dimitri  United States
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transfer characteristic and differential gain, it is interesting that the diff stage (Q2, Q3) and current amp (Q4-Q7) nonlinearities are compensated
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Old 21st September 2005, 01:41 PM   #8
dimitri is offline dimitri  United States
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see also: B.Gilbert, A new wide band amplifier technique, IEEE J. SSC, 1998, pp.353-365
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Old 22nd September 2005, 01:22 AM   #9
mikeks is offline mikeks  United Kingdom
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Default Re: cross-quad and cascomp circuits

Quote:
Originally posted by rtarbell
...Could someone tell me exactly what the advantages (of cross-quad and cascomp circuits for input stages)....

Virtually no value to the designer of discrete amps...
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Old 22nd September 2005, 07:40 PM   #10
Tom2 is offline Tom2  United States
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Dimitri, 1968 instead of 1998.

Quote:
see also: B.Gilbert, A new wide band amplifier technique, IEEE J. SSC, 1998, pp.353-365
IEEE J. SSC, 1968, pp.353-365

rtarbell,
Also the book "Analog Circuit Design", edited by Jim Williams and published by EDN, has two chapters by John Addis and Barrie Gilbert that might help answer your question.

Tom
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