low frequency micropower vco needed

I know it works for ring oscillators used as VCO's, but as soon as you add R/C's I'm not sure if it still works.

(The ring oscillator is really varying gm.)

...Jim Thompson

Post it to...

news:alt.binaries.schematics.electronic

...Jim Thompson

I need a low frequency vco (to operate between 55 and 65 Khz) that draws very little power (microamp supply current if possible). Goggle turns up uhf and microwave vco's that draw 10's of ma. It needs to be a square wave, but can live with a triangle or sine wave output.

A single chip solution would be preferred, but can build it from discrete components if necessary.

I'd like to have it sweep between 55 and 65 Khz with the varying control voltage.

A cmos r/c oscillator might work just fine, but I can't figure out how to vary the frequency with a dc input voltage:>:

Any suggestions?

Thanks,

That works because the 4584 has hysteresis. I think an ordinary inverter will vary only a small amount.

I have made custom chips where the inverters had current mirrors in the rails.

...Jim Thompson

Thanks Jim,

It sounds too good to be true though, is it really that easy?

Again, thanks Jim.

After I read your first message, I googled with different keywords. As a result, I did find a schematic which showed a 4584 cmos gate oscillator with the input (Vcc) varied to control the output frequency. With an R of 2.2 meg and a C of 220 pf, the author claims that 2.5v in produces 1 Khz out and 9v in produces 20.8Khz out.

I'd post it, but I think binary attachments are forbidden here.

Thank you so much for taking to the time to reply, I appreciate it.

Frequency shouldn't change more than a few percent with Vdd over the normal operating range of a CMOS gate.

You could make a VCO with an op-amp and a comparator, but how about the VCO portion of a 4046?

Best regards, Spehro Pefhany

That's a ST hex inverter.

just post a link, like this one:

Best regards, Spehro Pefhany

I looked at the 74HC and 74HCT variants on the Phillips www site. They make some similar chips with slightly varying part numbers, but I checked them all.

These chips are intended to run as high as 19 Mhz, and they all draw way to much quiescent power too. There might be a chance of one working if there was a slower speed part, but I don't see anything like that. I'm not sure why they draw so much current when they aren't switching, but they do.

Thanks,

The On MC74HC4046A has maximum Iq of 4uA -55 to 25°C, 40 uA < 85°C. That's not so bad.

Best regards, Spehro Pefhany

OK, th e file is at:

It appears to met my needs very nicely, although I don't need nearly as much frequency variability as this circuit provides.

If a standard 4000 series gate can provide a 10 percent variance, I could probably use it.

I think the 4584 is easily available and cheap enough, I'll probably use it.

Thanks to all who helped out.

news: snipped-for-privacy@4ax.com

Best regards, Spehro Pefhany

Use a cmos 555 Typically draws 60uA

Peter

I looked at the Phillips parts (previously) and didn't see any thing nearly that low. Your 4 ua sounds more like the current drawn when the chip is not selected or in standby mode.

I checked the ONSemi MC74HC4046A. It states on the first page that the quiescent current consumption is 80 ua, and that is with the vco disabeled.

I did not see any graphs for vco frequency vs supply current, which would be very useful to have.

If you know of a part that uses 4 ua of supply current with the vco active, drop me a line.... I'm getting far different numbers.

Thanks,

That's what Iq means. If you want it actually do something it draws more current.

You might want to read past the executive summary on the first page. That 80uA might be a mistake. The closest figure to that in the actual specs is 160uA max at

Ok.

Best regards, Spehro Pefhany

Hey JT, don't all Schmitt triggers have hysterisis, which is what makes them special???

Yes.

Not in that exact circuit. You put 15V Vdd on a 74HC14 and it *will* fail.

Best regards, Spehro Pefhany