Dual-Slope Converter Re-invented

It's a little suspicious that he uses such antique parts, too--c'mon, a CA3140? Really? Ten points for the person who finds the original publication of that circuit.

Cheers

Phil Hobbs

These magazines get really hard up for unique design ideas >:-] ...Jim Thompson

Not that it's a bad idea to use a dual-slope if you're hard up for a good cheap ADC, and can accept slow.

Of course it's not a bad idea... just not novel. And not even a comment that it's a twist on an old classic method.

Worse, the author probably doesn't even know :-( ...Jim Thompson

I doubt they care, they just need stuff to fill the space between adds

but maybe someone will learn something

-Lasse

And even worse, the editor probably doesn't know. Art

The editors don't care. As Lasse pointed out, it filled the space, so the editors are happy. ...Jim Thompson

I was tempted to sign in and point out that it's a dual-slope ADC, but I figured you should get first crack at it.

Go ahead, be my guest. Nobody listens to me. ...Jim Thompson

Linearity is a problem in dual-slope, from capacitor DI.

The EDN circuit looks flakey to me; it has a hangup state. I suspect it's not very temperature stable either.

Am 03.09.2013 19:39, schrieb Phil Hobbs:

I still have the 1974 RCA IC data book somewhere in the shelf. It's probably contained.

cheers, Gerhard

and I don't know how it is in other places but I believe that here magazines, papers and such are exempt from VAT if they have at least

-Lasse

Postal rates are the big thing, here.

Not sure it's a reinvention of a dual slope converter, but someone needs to tell Dmitryov [sp?] that measuring his pulse with 0.02% accuracy does not mean he has measured the analog voltage with the same accuracy.

So what's a good low DI cap? New ceramics are low loss. (never looked at step response.)

Yeah it would have been nice if it talked about circuit pitfalls. I did this switched current oscillator, there was always some charge inject ion from the switch... (I also screwed up the voltage reference.)

I read this edn thing today (doing a summing amp with both +/- inputs) that referenced a '76(?) Analog dialogue by D. Sheingold. There was a pdf on A D website, but hardly readable...Of course these days it seems silly not to just add a few more opamps. (or a uC if that's your bent.)

George H.

I feel like washing my hands after handling the schematic.

Best regards, Spehro Pefhany

This arrangement I posted before is immune to capacitor DI:

It is basically a sawtooth oscillator made from a schmitt driving an integrator. But last time I played with it I was getting down to 4ppm linearity.

(typo; opamp is MAX4238).

I thought it looked like a delta-sigma, but only because it's serial and I'm missing something deeper about the resemblance.

Hi John, I think I saw that posted before. How does it cure the capacitor DI? (And what's DI? When I first read JL's post I read it as DA...dielectric absorption... now I'm doubly confused.) Is it important that you use two different 'flavors' of schmitt trigger? Could you use one schmitt and then just an inverter with minimal hysteresis?

Thanks, George H.