Cute amplifier - bootstrapped

unless you use a series input resistor for voltage to current conversion.

That's stupid.

You're being Larkinesque evasive (and obfuscative... have you been taking lessons ?:-)

Write the equations. Already!

Tick-tock.

You're going down. It always happens to sycophants, you take the fall, Larkin walks away >:-} ...Jim Thompson

snipped-for-privacy@gmail.com

unless you use a series input resistor for voltage to current conversion.

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understand

and

James'

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Thompson is sure one bad engineer.

Okay, we're done.

Tick-tock! I knew you'd never deliver... you're not capable. Tick-tock! ...Jim Thompson

Yes, your PNP "current source" is the same as Tim's "shunt current source." It was featured as design idea in one of the rags some years back--Electronic Design perhaps?

It's pretty cute too, the principal drawback being that the output can't swing as low.

e:

You can make a comparator for submillivolt signal levels but you're going t o have to do some serious bandlimiting and low noise design, and you'll als o be in the realm of thermal emf, air current, and component placement shie lding.

you use a series input resistor for voltage to current conversion.

to

Naturally.

That's a mixed metaphor but with the circuit in question, in fact, yes you can and I explained how below.

And I explained it was the 'boostrap' you found 'cute'. So far I don't know what you're trying to 'argue' about.

Of course it does. If one wants an audio amp it stinks but if one wants to amplify 40 kHz then not so much.

Feedback doesn't 'come and go' simply because of your 'intent', feedback is feedback, and, while you might argue it's 'small', unless the source impedance is 0 (good luck on that) then there's feedback.

The raw circuit didn't give an 'application' and, without that, the source impedance is unknown and, so, the amount of negative feedback is unknown.

Potentially one, but who's counting?

You have no idea how 'little [the] loss of gain' is because the premise states "with undefined source impedances."

What test frequency at what source impedance?

understand

and

I think they, quite naturally, look at 'the whole ball of wax'.

Yes, a CCS is the 'modern' common approach since transistors, especially on die, are virtually 'free' but they weren't free 'back in the good ole days' so a cap bootstrap was less expensive.

Clearly not 'irrelevant'.

You don't think people ever look at a design to see if maybe they might want to use it, or parts of it?

you use a series input resistor for voltage to current conversion.

That's what it was 'put there for' but your 'intent' doesn't erase the feedback.

Maybe, maybe not (more on that below) but the world consists of more than 40 kHz.

Now see what that caps impedance is at 20 Hz. See? The application 'matters'.

The original drawing shows what looks like an INPUT going a blocking cap, not a 'capacitive transducer', and with no definition of what that source impedance is you can't calculate gain.

Don't be silly. Adding a defined feedback ratio doesn't "kill all the gain."

Nonsense.

No one claimed it was a 'general purpose' anything and one glance at the values should have told you it wasn't for 'audio', at least of the 'human' kind. You seemed to have finally arrived at that realization but are now backsliding.

It's simply a bootstrap intended to increase the effective impedance of the collector load and used to be more common back when active devices were expensive, especially the vacuum tube era.

you use a series input resistor for voltage to current conversion.

to

An amp does not have to have 'infinite' impedance to avoid being 'at the mercy of'.

Well, there ya got me. With everyone jabbering 'audio' all over the place I made the mistake of thinking we were talking about audio.

I know it does because I used one like it for a microphone preamp.

I wasn't talking about the emitter input impedance. I was talking about the feedback ratio of the 220k and ??, since the input impedance is undefined.

Part of the problem is, as drawn, it implies an undefined 'input' through a blocking cap... and that is problematic.

You've been making noble sounds about 'improving' things and I'm just pointing out that the larger the DC feedback resistor is the less stable the bias is.

understand

and

Per your assumptions below, yes.

I'm just clarifying where there seems to have been uncertainty. There's nothing to argue about AFAICT.

The application doesn't matter for the intended subject, which was showing that you can bootstrap a collector load resistor.

Granted. I mentioned it in passing around post 25 or so, but only in passing since it simply wasn't germane to the thing being demonstrated: bootstrapping a collector load. I try to strip extraneous detail out of descriptions, don't you?

I missed that qualifier. Yes, with that assumption, you're correct. That wasn't my assumption; I assumed a capacitive, low-impedance source.

f as spec'd in the drawings and all the results--40KHz. Source impedance WAG'd @ 10nF, e.s.r. unknown (believed < 100r).

YES, the BOOTSTRAP!!!! Increases gain and swing, hence the post. The rest of it is bog-standard practice. (Apparently the bootstrap is standard too, I just hadn't seen it.)

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to have to do some serious bandlimiting and low noise design, and you'll a lso be in the realm of thermal emf, air current, and component placement sh ielding.

I've never done that--the feedback from the output switching is such a nuisance (the dang things want to oscillate), it's easier to preamplify a little.

I discovered the oscillations in detail in the comparator of my first homemade dual-slope a/d (and that wasn't even anything hot, just an LM311). 16 bits in an industry when/where 12 bits reigned. (I thought it'd be hard, but it wasn't.) Linear Tech had app notes saying you should include a few mV of hysteresis to avoid that...

Still seems like good practice, when practical.

I don't think I was the one who introduced the word "audio".

I just tried to introduce some engineering into the discussion, but failed... seems this is a "faith" group rather than engineering.

How do you explain the following simulations...

I did properly guess that the input device was actually a capacitive transducer (C2, when I saw the 40KHz peak), and James acknowledged that.

The "bootstrap" doesn't buy any net "gain", but it does buy some bandwidth.

The "discussion" does buy the entry of every punk in the world who can't even do Ohm's Law, but needs to hear his head roar ;-) ...Jim Thompson

That 500 KV output; is that peak or RMS?

Obviously means V/V

Larkin is just trying to pick a fight... ignore him... he's clueless.

The point is that the "bootstrap" did NOT buy more gain, it did buy some additional bandwidth.

Just the bootstrap piece, if we look "north" just into _it_, looks like a resonant circuit. That still puzzles me. ...Jim Thompson

Oh, the gain is 500,000.

With James' values, the bootstrap increases the voltage gain by over

Incidentally, 31 dB is a gain of just about 40, which one can WAG from guessing the DC bias situation.

Obviously.

Jim Thompson a écrit :

Huh??? The bootstrap buys gain where it bootstraps. (read the bootstrap low corner frequency is way too high for you to see it effective at low frequency) Just boost the bootstrap value to 100u or 1000u and see the difference.