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Old 12th June 2014, 08:22 AM   #1
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Default All NMOS output amp

Hey. I've got so many NMOS laying around and this idea for using them has been spinning in my head for so long but my usual lazyness keeps me in the 'armchair designer' mode. I hope starting this thread might get my butt in gear and finally build one.
Nothing speacial, just another way of driving an NMOS-only output stage. They simulate quite well, (ok I know the high bias currrent will make anything measure well), but even without NFB it looks promising. (Of course for no loop NFB the local degeneration must be increased). Pretty wide bandwidth as well.
Anyways, what you think?
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Old 12th June 2014, 04:59 PM   #2
jcx is offline jcx  United States
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looks like a waste of a diff pair - 1/2 the current terminate in very low Z - so very little "differential" action going on

here's a 70's circuit:

Click the image to open in full size.

Anyone tried anything like this ?

(the thread's opening post very much like your idea)
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Old 12th June 2014, 10:51 PM   #3
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There is no 'waste' of diff action, the point of the LTPs is to drive the MOSFETs. The loadresistors may be increased in value if that gives comfort, but here my object was to make a wide bandwidth amp. I've sim'ed all kinds of values, and the higher ones do not make it any better, just lowers the upper frequency range. Why an amp that goes to 1MHz? I dunno...why not? Makes it more fun.
I prefer the currentmirror version and intend to build that one first.
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Old 12th June 2014, 11:00 PM   #4
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the '70s circuit' looks interesting, something right up my alley with the mirrors and cascodes and such. Unfortunately the MOSFETs are driven by a high impedance. But of course it can also be modded if one wanted to.
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Old 13th June 2014, 12:27 AM   #5
The Dastardly Dad of Three
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Quote:
Originally Posted by SemperFi View Post
Hey. I've got so many NMOS laying around and this idea for using them has been spinning in my head for so long but my usual lazyness keeps me in the 'armchair designer' mode. I hope starting this thread might get my butt in gear and finally build one.
Nothing speacial, just another way of driving an NMOS-only output stage. They simulate quite well, (ok I know the high bias currrent will make anything measure well), but even without NFB it looks promising. (Of course for no loop NFB the local degeneration must be increased). Pretty wide bandwidth as well.
Anyways, what you think?
Looks pretty semperfi... Is it symmetrical ? As in do the sims show any h2 ? Maybe post the asc and folks can play with it. Kuroda had similar and they were well regarded in told - I think I have the scans someplace in case you want them.
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Old 13th June 2014, 01:56 AM   #6
The Dastardly Dad of Three
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Quote:
Originally Posted by kasey197 View Post
Looks pretty semperfi... Is it symmetrical ? As in do the sims show any h2 ? Maybe post the asc and folks can play with it. Kuroda had similar and they were well regarded in told - I think I have the scans someplace in case you want them.
Edit: Kaneda io Kuroda
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