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Old 22nd March 2012, 12:42 PM   #3911
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by Wavebourn View Post
Freedom from dictature of marketing departments, what to measure, and how to judge.
Me too, freedom from any dictatorships, be they of the Marketing Department, the Proletariat or the IMF...

Ciao T
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Old 22nd March 2012, 01:14 PM   #3912
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by godfrey View Post
I quite like the idea of simply adding a 3 Ohm power resistor in series with the output, since it also provides very effective protection for the output devices.
I was more thinking of adding 0.22R in the ground lead and using some clever feedback circuit to make it appear to be 3 Ohm...

Quote:
Originally Posted by godfrey View Post
The circuit looks like it will have very high output impedance, but lousy PSRR as shown, since any ripple current through R2 is fed straight through to the output. One could always add some filtering or regulation for R2's voltage though.
Given that our VAS has a cascode as well, we can make both cascodes identical and use a 2-terminal CRD (current regulator diode) plus a suitable resistor to take up excess dissipation and massively increase the PSRR of the Cascode.

For the ring of 2 base voltage, same principle and as we have to bias some diode strings to provide clamping and limiting for best overload recovery we can use this "waste" current to bias the diode strings.

Then again, if we cascode the Load CCS, why not replace the resistor in the original CCS with a J-Fet CCS and use the original CCS Transistor as cascode? A BF862 should able to work OK at such low voltages...

Ciao T
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Old 22nd March 2012, 01:58 PM   #3913
dvv is offline dvv  Serbia
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Quote:
Originally Posted by tvrgeek View Post
Much to take in here. In the last few days, I have learned as much about the sim as the circuit. I am both impressed, and disappointed.
Just like a marriage, right?
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Old 22nd March 2012, 02:01 PM   #3914
dvv is offline dvv  Serbia
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I lost track of who was it that did the testing of those CCS versions. Whoever it was, please test these two as well, the same way the others were tested.

One is a classic resistor-zener in parallel with capacitor-resistor; quite a few of those are still floating around.

The other is more interesting, and I for one am hoping it will return solid results.

Thank you in advance.
Attached Files
File Type: pdf 2 CCS.pdf (23.4 KB, 28 views)
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Old 22nd March 2012, 04:02 PM   #3915
bcarso is offline bcarso  United States
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Quote:
Originally Posted by janneman View Post
Brad, doesn't this ring of two have poor neg supply PSRR?

jan
Glad you asked Actually, the ring of two is not very good for PSRR, true; but the Aldridge-cascoded version allows the tuning of the LED's (or other diodes') bias R and the "error amp" bias R to provide excellent PSRR. With high-beta ~2SC1815 parts for the example I gave, and with tvr's 210 ohms in the emitter, using 9.53k for the error amp and 210k for the LED is about optimal --- the residue is nearly pure 2nd harmonic of the rail signal at midband frequencies. I'll publish the examples and performance results in a bit. BTW, I've not used the ring-of-two that often, and tvr's developing design was the impetus for considering the Aldridge cascode version and a very pleasant surprise.

Of course we still are focusing on high impedance, not on stability, which has the Vbe temperature coefficient of ~ -2mV/degree K, hence about -0.33%/degree K for a 600mV Vbe. And noise is not outstanding, since the "reference voltage" is Vbe and thus the emitter resistor is fairly small. However, at this point in the circuit it should hardly dominate.


Brad
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Old 22nd March 2012, 04:45 PM   #3916
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by dvv View Post
I lost track of who was it that did the testing of those CCS versions. Whoever it was, please test these two as well, the same way the others were tested.
I would like to throw in a monkey wrench from the leftfield.

Why not keep a simple, straightforward ring of 2 CCS, but bootstrap it instead to output?

I can think of several options that could accomplish that, but why not a DC shifted PNP emitter follower and taking the current for the error amp transistor from the output?

I think the PSRR as well as effective impedance should be quite horrorshow*.

Ciao T

* Horrorshow - nadsat slang for "good" from "A Clockwork orange" - derived the cockney way from the russian хорошо (kha-ra-SHO)
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Old 22nd March 2012, 05:02 PM   #3917
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Horrowshow is better transcription for хорошо than kha-ra-SHO, actually. However, oh is pronounced lke ah, it is right.
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Old 22nd March 2012, 05:06 PM   #3918
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by Wavebourn View Post
Horrowshow is better transcription for хорошо than kha-ra-SHO, actually. However, oh is pronounced lke ah, it is right.
Yes, remembering what little russian remains (I learned it in school and spend halve a year in Moskow in '87) I'm rather fond of using it.

Ciao T
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Old 22nd March 2012, 05:13 PM   #3919
dvv is offline dvv  Serbia
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Quote:
Originally Posted by ThorstenL View Post
Hi,

I would like to throw in a monkey wrench from the leftfield.

Why not keep a simple, straightforward ring of 2 CCS, but bootstrap it instead to output?

I can think of several options that could accomplish that, but why not a DC shifted PNP emitter follower and taking the current for the error amp transistor from the output?

I think the PSRR as well as effective impedance should be quite horrorshow*.

Ciao T

* Horrorshow - nadsat slang for "good" from "A Clockwork orange" - derived the cockney way from the russian хорошо (kha-ra-SHO)
Eh? Come again?

T., I think a small diagram would make things comprehensible again.
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Old 22nd March 2012, 05:41 PM   #3920
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Quote:
Originally Posted by ThorstenL View Post
Hi,



Yes, remembering what little russian remains (I learned it in school and spend halve a year in Moskow in '87) I'm rather fond of using it.
My daughter speaks German pretty well, she learns it in school. Tomorrow we are meeting an exchange student from Germany. 2 years after will be her turn to go to Germany...
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