Current Mirror Discussion - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th November 2008, 10:45 PM   #11
GK is offline GK  Australia
Account disabled at member's request
 
Join Date: Jan 2006
Quote:
Originally posted by AKSA
Kleinschmidt,

I expected your usual whining comment. You have PSpiced it, not built it, never heard it..... get on with it man, do the work, and learn to trust your ears.

This gem is found in a 1999 Halcro US patent, so I would suggest you refer your august arguments with Bruce Candy. After all, his amps are reputedly amongst the best in the world, and they boast extremely low distortion, which would be mandatory for you. Good enough for him and the world, it seems. Where do you stand? Where is your commercial amplifier? How many patents in this area do you hold?

One can only speculate on the state of mind of someone who appears to know it all, and is so certain of everything he does and says. Upbringing, genetics, who knows. The contempt you radiate is self-damaging, and a complete waste of energy, particularly for one who in his own mind at least, is very clever. Time you behaved with a dignity befitting your intellect......

Thanks for the predictable diatribe.
You diode idea for improving the current mirror linearity is nonsense. I explained why and provided a workable alternative.

Deal with it
  Reply With Quote
Old 10th November 2008, 11:09 PM   #12
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
Hey, Glen,

It's not my idea!! It's a Halcro concept! Deal with it!
__________________
Aspen Amplifiers P/L (Australia)
www.aksaonline.com
  Reply With Quote
Old 10th November 2008, 11:24 PM   #13
diyAudio Member
 
Terry Demol's Avatar
 
Join Date: Apr 2002
Location: *
Quote:
Originally posted by G.Kleinschmidt



Hardly.

That diode only has potential to make the current mirror linearity worse � in fact I just proved my hunch in LTspice � at 20kHz the LTP non-linearity of a �Blameless� increased significantly (~50%).

It is sub optimal to add a diode in the signal path of a linear circuit like this such that it is forward biased with a current as low as the base currents of the current-mirror transistors.

If you want to better the current mirror by any significant amount then your options are the 4 transistor Widlar or the 3-transistor version attached below. Note the 470-ohm resistor? This ensures high frequency linearity by developing an adequate quiescent emitter current for Q16.

And no, this 470-ohm resistor is not a potential fix for the diode fudge.

Cheers,
Glen
WRT addition of diode, at this point I disagree Glen.

I spiced up a quick circuit and did fft on OP current linearity.

The LTP needs to be run at decent degeneration and at very
low AC current swing to clearly show the mirrors effect.

However, once the surrounding circuitry is linearised sufficiently
so it 'disappears' from the results, the diode can half the distortion
depending on operating points.

The 3 transistor version mentioned is the obvious next step to
isolate mirrors base currents and add some further improvements.
  Reply With Quote
Old 10th November 2008, 11:39 PM   #14
Variac is offline Variac  United States
diyAudio Editor
 
Variac's Avatar
 
Join Date: Dec 2001
Location: San Francisco, USA
Stay calm guys! Both of you can be a lot more pleasant.

By the way , the work "nonsense" is very close to insulting enought fora trip to the bin. You know that Glenn.

  Reply With Quote
Old 10th November 2008, 11:55 PM   #15
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
I tend to agree with Glen on this, because the 'mirror' transistor is supposed to be a diode. However, IF there is an advantage of adding an extra diode, then a transistor follower should even be better, as it creates the same conditions for the 'mirror' transistor, but would be more linear.
  Reply With Quote
Old 11th November 2008, 12:58 AM   #16
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Smoky Mountains , Tennessee
After reading about it..

http://www.odyseus.nildram.co.uk/RFI...ent_Mirror.pdf

I guess I'll try the diode ,buffered widlar (Glen's), and finally,
as a reference ,a standard mirror.

Halcro...WOW , 20-50K$ amps , he sues any who violate his
IP , still I found some schematics (and the diode) in an amp
that was really drooled over in the 90's.

PS .. best to make a pluggable SMT "daughtercard" for input
section , play around with cheap $.01-10c devices..

OS
  Reply With Quote
Old 11th November 2008, 02:06 AM   #17
andy_c is offline andy_c  United States
Banned
 
Join Date: Apr 2003
Quote:
Originally posted by AKSA
This gem is found in a 1999 Halcro US patent(...)
This trick seems to be specific to his particular design though. The CE transistor of his VAS has a diode in series with its base. So the idea was apparently to match the Vcb of the two transistors in the mirror, given that odd VAS configuration (VAS diode seeing base current of VAS CE stage, mirror diode seeing base current of mirror stage).

Quote:
Originally posted by AKSA
Where is your commercial amplifier?
Well, Candy ripped off the design of the FET error correction circuitry (including its compensation technique) from Bob Cordell, who has no commercial amplifier AFAIK. And Bob got the original concept from Hawksford, who has no commercial amplifier either. There's plenty of hacks who have commercial audio products, so that doesn't mean anything. Just look at Audio Circle for examples.
  Reply With Quote
Old 11th November 2008, 03:04 AM   #18
GK is offline GK  Australia
Account disabled at member's request
 
Join Date: Jan 2006
Quote:
Originally posted by Terry Demol


WRT addition of diode, at this point I disagree Glen.

I spiced up a quick circuit and did fft on OP current linearity.

The LTP needs to be run at decent degeneration and at very
low AC current swing to clearly show the mirrors effect.

However, once the surrounding circuitry is linearised sufficiently
so it 'disappears' from the results, the diode can half the distortion
depending on operating points.

The 3 transistor version mentioned is the obvious next step to
isolate mirrors base currents and add some further improvements.




I suggest your method of simulation is suspect. This issue is with the linearity of the circuit at high frequency when the LTP is NOT operating at a "low AC current swing".
You simply cannot expect a high degree of HF linearity (working against the BJT junction capacitances) from a diode forward biased with a few tens of uA.
As for this allegedly being a Halcro concept; If true then all I will say is that Bruce Candy is not unknown for passing the occasional furphy in his patent applications.
And anyway the current mirror circuit which typically uses a diode in this configuration to raise the collector voltage of the diode BJT does so in conjunction with another diode to act as an anti-saturation clamp (see the Stocichino (spelling?) fast amp. However this is a different kettle of fish.

Cheers,
Glen
  Reply With Quote
Old 11th November 2008, 03:19 AM   #19
andy_c is offline andy_c  United States
Banned
 
Join Date: Apr 2003
Quote:
Originally posted by G.Kleinschmidt
As for this allegedly being a Halcro concept; If true then all I will say is that Bruce Candy is not unknown for passing the occasional furphy in his patent applications.
Yeah, that was my impression also. What's with that diode in series with the base of the VAS CE amp anyway? One could see why he'd put one in the emitter, to make sure the mirror has enough Vcb under high-current conditions. But the base? Just makes the behavior more dependent on the BJT beta than it should be.
  Reply With Quote
Old 11th November 2008, 04:04 AM   #20
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
I have not seen any diode into base of any vas transistor of aksa
not in those schematic versions shown for free
but maybe it is in some original schematic, those we get if we order the kit

The only diode I can see used is one extra rectiifier for VAS/Input supply rail.
I can not think hugh would put such a diode.
No such thing in this conceptual attachment of hugh:
http://www.diyaudio.com/forums/showt...12#post1652112
Quote:
I've attached a conceptual schematic of the AKSA. Some details are missing, of course, ......
__________________
lineup
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Current mirror for the aleph? 3nity Pass Labs 11 8th August 2013 08:23 AM
High current mirror ? forr Solid State 23 25th June 2009 09:31 AM
Current Mirror: The V-mirror rtarbell Solid State 1 19th November 2008 03:27 PM
no current mirror, current mirror, cascoded current mirror, bjt or jfet VAS? maxpou Solid State 31 17th June 2008 05:31 PM
Current mirror abzug Solid State 7 1st January 2008 08:03 PM


New To Site? Need Help?

All times are GMT. The time now is 07:36 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2