There seems to virtually no information available on the origins, theory and applications of the Baxandall super pair....
A Google search brings up very little other than references to a couple of threads on this very site (which discuss only stability issues) and I can find nothing to attribute the circuit to Peter Baxandall. It's almost as if someone on DIY audio has plucked the circuit out of thin air!?
The idea seems to be shrouded in mystery! Maybe someone on this site can shine a little light on the subject?
A Google search brings up very little other than references to a couple of threads on this very site (which discuss only stability issues) and I can find nothing to attribute the circuit to Peter Baxandall. It's almost as if someone on DIY audio has plucked the circuit out of thin air!?
The idea seems to be shrouded in mystery! Maybe someone on this site can shine a little light on the subject?
Maybe this sheds some light, maybe not...
http://www.diyaudio.com/forums/solid-state/25172-baxandall-super-pair-9.html#post1966136
http://www.diyaudio.com/forums/solid-state/25172-baxandall-super-pair-9.html#post1966136
I had already seen this post but had not followed it to the end. It seemed to be only about stability issues so I lost interest.....
There are some partial answers there anyway. if I can access the referenced articles anyway!
There are some partial answers there anyway. if I can access the referenced articles anyway!
Well it would seem that the references by Walt are, in the main, only accessible to those who are payed up members of the IEEE.....
Oh well.
Oh well.
in "Active Filters for Integrated Circuits" W.E.Heinlein and W. H. Holmes, 1974 the circuit is called a "Super Pair"
since the ref in Heinlein was to Baxandall it seemed obvious to call it Baxandall Super Pair
but Walt's excellent reference list seems to give priority to Larson?
since the ref in Heinlein was to Baxandall it seemed obvious to call it Baxandall Super Pair
but Walt's excellent reference list seems to give priority to Larson?
I don't suppose anyone has a copy of:
Baxandall P.J., and Swallow E.W., ‘Constant current source with unusually high internal resistance and good temperature stability’, Electronic Letters, 1966, Vol. 2 , No 9, pp 351-352.
and would be willing to PM me with it?
Jez.
Baxandall P.J., and Swallow E.W., ‘Constant current source with unusually high internal resistance and good temperature stability’, Electronic Letters, 1966, Vol. 2 , No 9, pp 351-352.
and would be willing to PM me with it?
Jez.
I see fig2 in Pease shows a 22r as base stopper for the second transistor, rather than a high value base stopper for the first transistor.
Hi jez, I have copies of the follow up on this artical , you may want to have a look at, It does look like P J Baxandall was the first user of this transistor combination.
Note that Les Larson filed before the Baxandall-Swallow article appeared, even though the patent issued considerably later. According to a private communication with John Addis I had recently, Larson discovered the topology when he, John, and a number of other luminaries were at Tektronix, and it was known internally as the super-alpha. The Tek people did not communicate much with the outside world in those days as things were so competitive in the 'scope business --- nor has much changed!
Exciting development in the history of Larsen-Baxandall-Swallow
Well, exciting to historians at least! I've been cataloging books in storage during these tough economic times, with an eye to selling some, and inevitably unearthing some that I may have acquired and barely looked at. As I mentioned in the preceding post I have also been corresponding with the great designer John Addis, who worked with Larsen at Tektronix. He vouches for Larsen's independent origination at Tek of what they called the super-alpha circuit.
But on Sunday I ran across an old paperback from Texas Instruments, Volume II of Communications Handbook, from 1965. There, in an article by Webster, Transistors in Wide-band Low-Distortion Amplifiers, in a section Circuit Arrangements for Distortion Reduction, is a simplified super-alpha stage! The reference is to an article in a magazine, Semiconductor Products, an article by F.S. Boxall, Base Current Feedback and Feedback Compound Transistor. The date of publication: September-October 1958!
I had to assure John that I had no doubt that Larsen conceived of the circuit independently (as I had, for that matter, and then had a heck of a time finding information to establish that I was a trifle late in this!). And Boxall, on whom I could find, so far, no other information, apparently presented the circuit as part of the IRE Convention of 1957 --- this based on a cite in a mostly-unclassified document available online, the proceedings of the Third Semi-Annual ANP Radiation Effects Symposium. Those IRE Convention Proceedings I found for sale online and are coming my way as we speak via the US Mail, but those of you with IEEE membership can probably access them without charge.
Mentioned in the Webster article in addition: a similar circuit by Aldridge described as a "cascade', in the IRE Transactions on Circuit Theory, June 1962. It will be interesting to see if this resembles what's come to be called the Hawksford cascode.
Brad
Well, exciting to historians at least! I've been cataloging books in storage during these tough economic times, with an eye to selling some, and inevitably unearthing some that I may have acquired and barely looked at. As I mentioned in the preceding post I have also been corresponding with the great designer John Addis, who worked with Larsen at Tektronix. He vouches for Larsen's independent origination at Tek of what they called the super-alpha circuit.
But on Sunday I ran across an old paperback from Texas Instruments, Volume II of Communications Handbook, from 1965. There, in an article by Webster, Transistors in Wide-band Low-Distortion Amplifiers, in a section Circuit Arrangements for Distortion Reduction, is a simplified super-alpha stage! The reference is to an article in a magazine, Semiconductor Products, an article by F.S. Boxall, Base Current Feedback and Feedback Compound Transistor. The date of publication: September-October 1958!
I had to assure John that I had no doubt that Larsen conceived of the circuit independently (as I had, for that matter, and then had a heck of a time finding information to establish that I was a trifle late in this!). And Boxall, on whom I could find, so far, no other information, apparently presented the circuit as part of the IRE Convention of 1957 --- this based on a cite in a mostly-unclassified document available online, the proceedings of the Third Semi-Annual ANP Radiation Effects Symposium. Those IRE Convention Proceedings I found for sale online and are coming my way as we speak via the US Mail, but those of you with IEEE membership can probably access them without charge.
Mentioned in the Webster article in addition: a similar circuit by Aldridge described as a "cascade', in the IRE Transactions on Circuit Theory, June 1962. It will be interesting to see if this resembles what's come to be called the Hawksford cascode.
Brad
Aldridge has landed
Yes, as conjectured, Aldridge has shown the cascode with base current feedback in his 1962 IRE note. He's quite chary with his favors, as all we get are dotted lines between the upper cascode transistor and either common or the input device emitter, but it's clear what is going on.
So I suggest we call the same-polarity driven or bootstrapped cascade or cascode the Aldridge cascade/cascode, and the two-complementary-transistor topology the Boxall pair. I hope Aldridge and Boxall are still with us in body and mind, and can tolerate this notoriety 😀 And Baxandall and Hawksford are hardly diminished by turning out being scooped on these, and Larsen, although unjustifably neglected by history, has had the bad fortune of most of his contributions remaining proprietary. If Les is still with us as well, he should know that John Addis retains a high regard for his skills as a circuit designer 😎
Brad Wood
Yes, as conjectured, Aldridge has shown the cascode with base current feedback in his 1962 IRE note. He's quite chary with his favors, as all we get are dotted lines between the upper cascode transistor and either common or the input device emitter, but it's clear what is going on.
So I suggest we call the same-polarity driven or bootstrapped cascade or cascode the Aldridge cascade/cascode, and the two-complementary-transistor topology the Boxall pair. I hope Aldridge and Boxall are still with us in body and mind, and can tolerate this notoriety 😀 And Baxandall and Hawksford are hardly diminished by turning out being scooped on these, and Larsen, although unjustifably neglected by history, has had the bad fortune of most of his contributions remaining proprietary. If Les is still with us as well, he should know that John Addis retains a high regard for his skills as a circuit designer 😎
Brad Wood
Slightly different question, but is there such an article or patent for different-polarity driven or bootstrapped cascodes?
It seems to be more difficult to get different-polarity driven or bootstrapped cascodes working properly than same-polarity driven or bootstrapped cascodes, therefore I would be most interested in studying such an article or patent, should it exist.
jonathan carr
It seems to be more difficult to get different-polarity driven or bootstrapped cascodes working properly than same-polarity driven or bootstrapped cascodes, therefore I would be most interested in studying such an article or patent, should it exist.
jonathan carr
Jonathan, I am supposing that you are talking about a "folded-cascode" version of the Aldridge cascade? I haven't seen such in the form of an article or patent, which of course vide the above history, is no guarantee that such does not exist. Have you investigated these in sim or breadboard, and when you say "working properly", was it a problem with instability?
When I get his permission I have some case history information from John Addis to share about stabilization of a version of Boxall that he did for Preamble Instruments (acquired by iirc LeCroy). As another thread in here reports on a lot of difficulties stabilizing "Baxandall super pairs", although John's story concerns some parts with f sub t's to 5 GHz, it's likely that with the typical relaxed layouts favored by experimenters in this forum, his conclusions are probably applicable to lower-bandwidth parts with more in the way of parasitics.
Brad
PS: as the Fair Use doctrine shouldn't get its panties in too much of a bunch, I scanned the two pages of the Webster article in the long out-of-print TI book, and will be happy to send to anyone who PMs me with his or her email. No obligations, no salesmen will call 🙂
Brad: Yes, I am referring to a folded cascode in which the cascode component is signal-driven. Post 1 of the following thread shows an example.
http://www.diyaudio.com/forums/analogue-source/200447-folded-cascode-hijinks-pn4391.html
Rather than encountering oscillation problems, what I have tended to see is a worsening of distortion compared to when the bases of the folded-cascode are held constant.
Not nearly as motivating as the Boxall pair (nearly wrote Baxandall!), which is usually a bear to debug, but can bring a significant performance improvement.
BTW, I very much appreciate your historical insights. FWIW, the patent on the driven same-polarity cascode was filed in 1964 by Roy M. Hayes of Tektronix, and it was granted in 1969. The US patent number is 3423685, and the patent calls the circuit "bootstrapped cascode differential amplifier".
cheers, jonathan
http://www.diyaudio.com/forums/analogue-source/200447-folded-cascode-hijinks-pn4391.html
Rather than encountering oscillation problems, what I have tended to see is a worsening of distortion compared to when the bases of the folded-cascode are held constant.
Not nearly as motivating as the Boxall pair (nearly wrote Baxandall!), which is usually a bear to debug, but can bring a significant performance improvement.
BTW, I very much appreciate your historical insights. FWIW, the patent on the driven same-polarity cascode was filed in 1964 by Roy M. Hayes of Tektronix, and it was granted in 1969. The US patent number is 3423685, and the patent calls the circuit "bootstrapped cascode differential amplifier".
cheers, jonathan
Fascinating! So Aldridge (1962) apparently trumps Hayes, but didn't bother to pursue a patent. I will say that having seen the very sketchy indication in his IRE note of the feedback path for the bootstrapped cascode (or as Aldridge refers to it, the cascade --- understandable as cathodes are conspicuous by their absence, although amusingly Aldridge shows a tube symbol to illustrate his transistor model), I can see where the document wouldn't just jump out at the patent examiner. Probably his employer was nervous enough about what was being disclosed to begin with.
Once again I must reiterate that I'm not accusing anyone of any theft here, just noting the priority of when people get ideas.
I'll check those other threads out. A quick attempt at some sims with garden-variety parts (2SC1815, 2SA1015) seems to indicate a little more compensation required of the folded cascode, and at that I'm cheating a bit with "perfect" current generators for biasing. Thanks for those references, and for using Boxall, from whom afaik I receive no promotional considerations 🙂
Brad
Once again I must reiterate that I'm not accusing anyone of any theft here, just noting the priority of when people get ideas.
I'll check those other threads out. A quick attempt at some sims with garden-variety parts (2SC1815, 2SA1015) seems to indicate a little more compensation required of the folded cascode, and at that I'm cheating a bit with "perfect" current generators for biasing. Thanks for those references, and for using Boxall, from whom afaik I receive no promotional considerations 🙂
Brad
So I looked at the thread with the 4391 and bipolar, including the followup with the more conventional CB stage which the author reports having lower distortion. My conjecture: the CB stage has some complementary even-order to compensate for the JFET and LED bias overall transconductance variations-with-signal.
As many probably know, the advantages to the Aldridge-Hayes, and other versions of base current feedback schemes, tend to concentrate on resolving/reducing issues with signal-voltage-dependent capacitance at the circuit output node, as well as other mechanisms for control electrode losses, and are less noticeable with lower output load resistances at audio frequencies. A nice feature as well is that signal-induced self-heating of the "upper" or "main" transistor, which for bipolars produces changes in current gain, are mostly removed by the ancillary part.
As many probably know, the advantages to the Aldridge-Hayes, and other versions of base current feedback schemes, tend to concentrate on resolving/reducing issues with signal-voltage-dependent capacitance at the circuit output node, as well as other mechanisms for control electrode losses, and are less noticeable with lower output load resistances at audio frequencies. A nice feature as well is that signal-induced self-heating of the "upper" or "main" transistor, which for bipolars produces changes in current gain, are mostly removed by the ancillary part.
Latest on the documentation front for Boxall
So having waited many days for a package sent "Standard Mail" from a bookseller all of ~15 miles away to arrive*, the 1957 IRE National Convention Record Part 2, cited by Hawkins and Happ in "Radiation Stabilization of Transistor Circuits by Active Feedback" (which is available free online as part of the proceedings of the Third Semi-Annual ANP Radiation Effects Symposium, Atlanta, Georgia, 28-30 October 1958) as containing what is apprently the first disclosure by Boxall of his base current feedback scheme, yesterday the package finally arrived. The book was as described by the seller --- but --- does NOT have the Boxall article!! So evidently Hawkins and Happ's cite is incorrect. Perhaps they got the date wrong. The Boxall reference in the TI book is from a old magazine article (Semiconductor Products) and (if correct) dates from 1958.
Now we know what is said more or less anyway, thanks to the Webster article in the TI book, but I had to laugh (despite being out 25 bucks plus shipping) when I realized the IRE Record didn't have the Boxall.
I may try a scattershot approach to the IRE reference, maybe attempting to obtain the 1958 Convention Record, or actually make it to a good-sized university library. It's even possible that somewhere there are bound volumes of the magazine, but these are prime candidates for discards.
Brad
*Wonder why people aren't enthusiastic about the post office? Of course the shipper may have fibbed when they said it had shipped, with no easy way to determine the date on the package, and only my order date on the packing slip --- I contacted them a few days ago to verify, and they haven't bothered with the courtesy of a reply. I pointed out to them that I could have comfortably walked to their location and back in far less time than the package had taken by then.
So having waited many days for a package sent "Standard Mail" from a bookseller all of ~15 miles away to arrive*, the 1957 IRE National Convention Record Part 2, cited by Hawkins and Happ in "Radiation Stabilization of Transistor Circuits by Active Feedback" (which is available free online as part of the proceedings of the Third Semi-Annual ANP Radiation Effects Symposium, Atlanta, Georgia, 28-30 October 1958) as containing what is apprently the first disclosure by Boxall of his base current feedback scheme, yesterday the package finally arrived. The book was as described by the seller --- but --- does NOT have the Boxall article!! So evidently Hawkins and Happ's cite is incorrect. Perhaps they got the date wrong. The Boxall reference in the TI book is from a old magazine article (Semiconductor Products) and (if correct) dates from 1958.
Now we know what is said more or less anyway, thanks to the Webster article in the TI book, but I had to laugh (despite being out 25 bucks plus shipping) when I realized the IRE Record didn't have the Boxall.
I may try a scattershot approach to the IRE reference, maybe attempting to obtain the 1958 Convention Record, or actually make it to a good-sized university library. It's even possible that somewhere there are bound volumes of the magazine, but these are prime candidates for discards.
Brad
*Wonder why people aren't enthusiastic about the post office? Of course the shipper may have fibbed when they said it had shipped, with no easy way to determine the date on the package, and only my order date on the packing slip --- I contacted them a few days ago to verify, and they haven't bothered with the courtesy of a reply. I pointed out to them that I could have comfortably walked to their location and back in far less time than the package had taken by then.
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