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:>:
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |
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| 1962 | I love to cook with wine. Sometimes I even put it in the food.
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
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
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
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
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
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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.
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
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
If you cared to take some time and consider the data provided by the OP then I am sure you will notice that he requested that the supply current was in the order of a microamp. Obviously your solution is unsuitable by a factor of four and, perhaps, an order of magnitude.
Pick one of the following
1) I have personally designed such circuits which worked perfectly.
2) I have personally been involved with people who design such circuits and had many interesting discussions in order to steer them in the right direction.
3) I have personally been involved with people who design such circuits and had many interesting discussions with them so I know what I'm on about.
4) I was personally involved in a project where such a circuit was designed. No-one took my advice and it didn't work.
5) I was personally involved in a project where such a circuit was designed. My advice was taken, it didn't work and they were subsequently proved to be wrong. If they would have taken my advice properly then it would have worked.
Now, I think I have asserted my credentials and thus proved that you are wrong and I am right.
Would you care to respond and give me an opportunity to............
Perhaps, but his "microamp level" statement is sufficiently hazy that
10uA or 50uA might also be okay... he mentions 10mA as being unsuitable.
Well, 1) except for all the differences, but hey, you've convinced me.
Okay, go for it. 1uA (maximum? typical?) at 70kHz operating current VCO, with realistic parasitic capacitances.
Best regards, Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
I see no reason to *go for it*. If you know the answer then I look forward to your explanation. I will not waste my time with needless arguments.
I see that you understand. Perhaps we should wait for the OP to respond so we can further discern his actual requirements.
Yes, but if you read OPs question again you will see he was asking for
65kHz-70kHz operation. This is a very narrow range to achieve given your original solution of a 74HC4046 which operates to 19MHz.
You are quite right. I should have posted to ask the OP to further define his actual requirements. This is probably a battery application and we should be more concerned about the gradual draw down due to internal impedances.
If it was possible to do it with picoamps, I'd say go for it! It's not likely to happen for awhile though.
I said 'microamps'. The statement was meant to discourage those replies from people that had milliamp solutions-after all, some people consider milliamps to be low power.
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Ah, okay, perhaps I misunderstooood what you meant when you said you were "gagging for it". Perhaps that's just as well.
3.0/11 MHz min at 3/4.5V Vdd for the one I mentioned, but that's more like 19MHz when you convert to GBP. Anyway you don't want CMOS sitting inbetween the rails too much of the total period or it will blow away the uA limit. Or get rid of the CMOS bit. IIRC there were some really low power oscillators that put high-value resistors in the drains of the MOSFETs in a 4007.
Yes.
Best regards, Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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