Switchable inverting/non-inverting opamp circuit?

ftp://jjlarkin.lmi.net/Gain_PM1.JPG

or

ftp://jjlarkin.lmi.net/Gain_PM1_b.JPG

But the circuit you suggest, the inverter and the downstream mux, are about equivalent. This does have a lower output impedance in both states.

John

Yup, that was the one I meant -- so simple it's almost alarming that I couldn't remember. I must be getting old :-/ I can replace the switch with a small-signal MOSFET, and have the exact desired solution -- a few thents of an ohm Rdson are no problem with R=10K.

Indeed it does -- but I think I'll just go with the first solution.

Anyway, thanks so much, now I can get on with the really tricky bits :-)

Richard Rasker

use

Sounds like you're talking about the circuit on PDF file page 13 , Voltage Controlled Oscillator Circuit, at

Aren't we all?

That circuit makes a nice synchronous detector.

Anything fun?

John

It sure does.

...

It's a triangle wave sweep generator, with the lowest and highest voltage levels presettable by means of (multiturn) potmeters, and a reasonably fixed frequency of 1 Hz. IOW: it doesn't speed up or down with a smaller respectively wider sweep range, which is essential for reasons that I'm not allowed to discuss. Here's the schematic of most of it:

I think this'll work (several parts are already built in a breadboard setup and tested), although I still have to double-check the polarity of the window detector / flip flop part at the center, controlling the MOSFET in your [non-]inverter.

Richard Rasker

And right after posting this, I spotted a dumb error: in 'Set' mode, the MOSFET should be permanently switched on. Ah well, it's getting late -- I'll fix that tomorrow ...

Richard Rasker

I put it in a hybrid for Hughes (Tucson) in 1971.

There's also a more accurate way. I'd post it but Larkin would claim it as his own ;-) Interested parties inquire privately. ...Jim Thompson

I put it into the Boresight Alignment Kit for the C5A around 1968 or so.

Hell, he never posts circuits any more; he just brags about past glories. He's using me as an excuse for not having ideas. Senile old fool.

What's a more accurate way to flip a DC voltage than using an opamp and two equal-value resistors?

John

FFS Jim why do you bother posting here anymore?

Switched capacitor? See e.g. fig 20 in

Pretty cool.

I presume your E-mail address is accurate? I'll send you a schematic. If you were paying attention, I do respond to _real_ requests for information. But there's VERY few such requests anymore.

Larkin can't stop "cluck clucking", so I can't help but slam the little SOB. When he shuts up, so will I.

What have YOU designed lately? That worked as requested ?:-) I've designed nearly a whole SOC in the past two weeks. ...Jim Thompson

Yes

When he shuts up? As far as I can see he gave the OP exactly what he was after (the simple optional inverter circuit). Which is more than you did.

I don't doubt there are other solutions, I posted one myself that was "more accurate" at DC (depending on assumptions). But the OP was asking for a specific circuit configuration he couldn't remember, it's the one that everyone learns and JL at least took the trouble to sketch it and post it.

Nothing very exciting I'm afraid. I think the last actual analog electronics included the 4-20mA driver circuit that I asked for ideas about a while ago, here.

I do have to do a lot of other stuff, programming, PCB layout, admin...

Flying-capacitor circuits are cool. There are a couple of gotchas, mostly related to charge injection and dielectric absorption. But no resistor ratios to worry about.

John

Be careful not to offend The (self proclaimed) Master Designer. He'll killfile you, and then what would you do?

John

Not in this circuit though I think.

That's the key, 1ppm resistors are kind of pricy :)

Well, you might consider a flying capacitor to be better in not requiring m= atched components. The switches get you into feedthrough of digital signa= ls, though. It can also suffice sometimes to divide by two, then use the = divide point as your GND reference.

t as

Why are you worried about Larkin--if you post it here we'll ALL steal it. That's the idea, isn't it?

Here's part of the low-voltage lock-out of my switch: an ancient Schmitt-trigger.

He won't post anything any more. Because...

2) He has no ideas?

John

ot

up

You would be better off using a fixed amplitude and frequency triangle waveform generator followed by an adjustable gain amplifier/buffer to set the output amplitude, instead of running those adjustable inputs all over the place...