cross-quad and cascomp circuits

[rtarbell]

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!

[jcx]

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

[Steven]

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

[dimitri]

Quinn's US pat 4897611

it is either 4,146,844 or 4,692,712

4897611 is very high gain positive fb cmos amp

[jcx]

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

[dimitri]

I1/2=I2=I3=1ma, I4=20mA
Quinn added series cascode after this

[dimitri]

transfer characteristic and differential gain, it is interesting that the diff stage (Q2, Q3) and current amp (Q4-Q7) nonlinearities are compensated

[dimitri]

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

[mikeks]

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...

[Tom2]

Dimitri, 1968 instead of 1998.

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