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,

A

On Mon, 02 May 2005 10:48:57 -0400, Albre wrote:

I need a low frequency vco
[snip]

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::


Vary VDD

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Thanks Jim,

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

A

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::


Vary VDD

Albre wrote in message ...
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,

A



Use a cmos 555
Typically draws 60uA


Peter

On Mon, 02 May 2005 11:53:54 -0400, Albre wrote:

Thanks Jim,

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

A

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::


Vary VDD



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 Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

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.

A


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

A

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::


Vary VDD



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

On Mon, 02 May 2005 10:18:00 -0700, the renowned Jim Thompson
wrote:

On Mon, 02 May 2005 11:53:54 -0400, Albre wrote:

Thanks Jim,

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

A

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::


Vary VDD



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.

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"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

On Mon, 02 May 2005 13:39:42 -0400, Albre wrote:

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.

A

[snip]

Post it to...

news:alt.binaries.schematics.electronic

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

On Mon, 02 May 2005 13:50:08 -0400, Spehro Pefhany
wrote:

On Mon, 02 May 2005 13:39:42 -0400, the renowned Albre wrote:

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.

That's a ST hex inverter.

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

just post a link, like this one:

http://www.discovercircuits.com/PDF-FILES/4584vco.pdf


Best regards,
Spehro Pefhany

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 Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

On Mon, 02 May 2005 13:39:42 -0400, the renowned Albre wrote:

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.

That's a ST hex inverter.

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

just post a link, like this one:

http://www.discovercircuits.com/PDF-FILES/4584vco.pdf


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
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.

Thanks,

A


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

On Mon, 02 May 2005 13:50:15 -0400, the renowned Albre wrote:


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,

A

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"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

OK, th e file is at:

http://www.discovercircuits.com/PDF-FILES/4584vco.pdf

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.

A

"Spehro Pefhany" wrote in message
...
On Mon, 02 May 2005 13:50:15 -0400, the renowned Albre wrote:


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,

A

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
--

Barry hat on.

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............

Oh Perlease!, I'm gagging for it

BNA

On Mon, 02 May 2005 18:44:33 GMT, the renowned "Genome"
wrote:


Barry hat on.

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.

Perhaps, but his "microamp level" statement is sufficiently hazy that
10uA or 50uA might also be okay... he mentions 10mA as being
unsuitable.

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.

Well, 1) except for all the differences, but hey, you've convinced me.

Would you care to respond and give me an opportunity to............

Oh Perlease!, I'm gagging for it

BNA

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"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

On Mon, 02 May 2005 13:40:54 -0400, Spehro Pefhany
wrote:

On Mon, 02 May 2005 10:18:00 -0700, the renowned Jim Thompson
wrote:

On Mon, 02 May 2005 11:53:54 -0400, Albre wrote:

Thanks Jim,

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

A

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::


Vary VDD



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.

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

---


--
John Fields
Professional Circuit Designer

"Spehro Pefhany" wrote in message
...
On Mon, 02 May 2005 18:44:33 GMT, the renowned "Genome"
wrote:

[Derf Transform Applied]



Barry hat on.

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.

Perhaps, but his "microamp level" statement is sufficiently hazy that
10uA or 50uA might also be okay... he mentions 10mA as being
unsuitable.

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.

Well, 1) except for all the differences, but hey, you've convinced me.

Would you care to respond and give me an opportunity to............

Oh Perlease!, I'm gagging for it

BNA



Okay, go for it.

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.

1uA (maximum? typical?)

I see that you understand. Perhaps we should wait for the OP to respond so
we can further discern his actual requirements.

at 70kHz operating current

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.

VCO, with realistic parasitic capacitances.

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.


Best regards,
Spehro Pefhany

Welcome

BNA

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.

Thanks again to all who had suggestions.

A



Barry hat on.

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.
k

On Mon, 02 May 2005 14:36:49 -0500, the renowned John Fields
wrote:

On Mon, 02 May 2005 13:40:54 -0400, Spehro Pefhany
wrote:

On Mon, 02 May 2005 10:18:00 -0700, the renowned Jim Thompson
wrote:

On Mon, 02 May 2005 11:53:54 -0400, Albre wrote:

Thanks Jim,

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

A

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::


Vary VDD



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.

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

---





Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

On Mon, 02 May 2005 19:53:34 GMT, the renowned "Genome"
wrote:


"Spehro Pefhany" wrote in message
.. .

Okay, go for it.

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.

Ah, okay, perhaps I misunderstooood what you meant when you said you
were "gagging for it". Perhaps that's just as well.

1uA (maximum? typical?)

I see that you understand. Perhaps we should wait for the OP to respond so
we can further discern his actual requirements.

at 70kHz operating current

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.

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.

VCO, with realistic parasitic capacitances.

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.

Yes.


Best regards,
Spehro Pefhany

Welcome

BNA



Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

I read in sci.electronics.design that Genome
wrote (in ) about 'low frequency
micropower vco needed', on Mon, 2 May 2005:

BNA

Have you undergone a major mutation?
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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,

A


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

On Mon, 02 May 2005 16:24:04 -0400, the renowned Albre wrote:

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.

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

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.

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 125C. It's very temperature dependent, of
course.

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

It will be very much dependent on the RC values- the resistors set
currents in current mirrors.

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,

Ok.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

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 125C. It's very temperature dependent, of
course.


OK, I'll go back and look att he Phillips parts again and compare.

I find that the 4584 is not as available as the 74HC14. Both are
schmitt trigger inverters. If I base my vco on the 74HC14, will it
still allow me to change the frequency of the oscillator by changing
the Vcc?

The schematic that looks most promissing is at:

http://www.discovercircuits.com/PDF-FILES/4584vco.pdf

I hope to substitute the 74hc14 in place of the 4584.

OK, yes or no?

Thanks all.

A

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


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

A

On Mon, 02 May 2005 17:13:56 -0400, the renowned Albre wrote:



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 125C. It's very temperature dependent, of
course.


OK, I'll go back and look att he Phillips parts again and compare.

I find that the 4584 is not as available as the 74HC14. Both are
schmitt trigger inverters. If I base my vco on the 74HC14, will it
still allow me to change the frequency of the oscillator by changing
the Vcc?

Yes.

The schematic that looks most promissing is at:

http://www.discovercircuits.com/PDF-FILES/4584vco.pdf

I hope to substitute the 74hc14 in place of the 4584.

OK, yes or no?

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


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

In article , Albre wrote:
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::

How about using a CD4053 as the inverters in a CMOS oscillator.


X1
+5V---O
--------
GND--O !
Y1 .X0 !
GND----O . !
----/\/\--------+---!!----+
VC------O !
.Y0 !
.---------------------------


Something like this is what I have in mind. The CD4053 has some problems
when you use it in an oscillator. The output tends to have a glitch in it
as it switches. You may have to put an extra cap to ground at the control
input of the X1 section.

The range of VC is fairly restricted because it must be above about 1/2Vcc
to get any oscillation at all.


--
--
forging knowledge

I don't understand the circuit. Can you give a www url or other link
to a more detailed circuit.

Or, post a gif or pdf in abse please.

I do not need a wide frequency shift, so the 1/2 of Vcc limit might be
ok.

Thanks,

A



How about using a CD4053 as the inverters in a CMOS oscillator.


X1
+5V---O
--------
GND--O !
Y1 .X0 !
GND----O . !
----/\/\--------+---!!----+
VC------O !
.Y0 !
.---------------------------


Something like this is what I have in mind. The CD4053 has some problems
when you use it in an oscillator. The output tends to have a glitch in it
as it switches. You may have to put an extra cap to ground at the control
input of the X1 section.

The range of VC is fairly restricted because it must be above about 1/2Vcc
to get any oscillation at all.


--

In article , Albre wrote:
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?

The oscillator section of the CD4046, 74HC4046 PLL.

Mark Zenier Washington State resident

Albre wrote:

I find that the 4584 is not as available as the 74HC14. Both are
schmitt trigger inverters. If I base my vco on the 74HC14, will it
still allow me to change the frequency of the oscillator by changing
the Vcc?

I'd think a schmitt trigger oscillator would be quite insensitive to
channges in Vcc, as long as the hysteresis is a constant fraction of the
supply voltage. That leaves out any effect of series resistance in teh
output stage.

Thus I would suppose it largely depends on the chip used.

That said, what would it be like to build an oscilaltor and put a FET in
the feedbackm, as a kind of 'variable resistor'? At least that gives you
a defined direction of sensitivity.


Thomas

Hi Ken,

Saw your post in abse, thanks for the info.

I'm not sure whether I'll use the shmitt trigger based solution, or
the ring oscillator you posted. Since I need a relatively small
frequency variation, I'll probably go with the one that gives the
smaller frequency excursion.

Thanks to all who participated in the discussion, I learned alot and
appreciated all the suggestions!

Regards,

A




X1
+5V---O
--------
GND--O !
Y1 .X0 !
GND----O . !
----/\/\--------+---!!----+
VC------O !
.Y0 !
.---------------------------


Something like this is what I have in mind. The CD4053 has some problems

On Tue, 03 May 2005 08:13:01 +0200, Zak wrote:

Albre wrote:

I find that the 4584 is not as available as the 74HC14. Both are
schmitt trigger inverters. If I base my vco on the 74HC14, will it
still allow me to change the frequency of the oscillator by changing
the Vcc?

I'd think a schmitt trigger oscillator would be quite insensitive to
changes in Vcc, as long as the hysteresis is a constant fraction of the
supply voltage.

If that were true. However, the hysteresis is determined by the
_strengths_ of MOS devices, so the hysteresis doesn't track Vcc very
well.

That leaves out any effect of series resistance in teh
output stage.

Thus I would suppose it largely depends on the chip used.

That said, what would it be like to build an oscilaltor and put a FET in
the feedbackm, as a kind of 'variable resistor'? At least that gives you
a defined direction of sensitivity.


Thomas


...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

In article , Albre wrote:
I don't understand the circuit. Can you give a www url or other link
to a more detailed circuit.

There is no more detailed circuit.

Or, post a gif or pdf in abse please.

My provider doesn't carry that group.

I do not need a wide frequency shift, so the 1/2 of Vcc limit might be
ok.

My circuit gives a very wide frequency shift so I think you are better off
with other circuits.



X1
+5V---O
--------
GND--O !
Y1 .X0 !
GND----O . !
----/\/\--------+---!!----+
VC------O !
.Y0 !
.---------------------------


--
--
forging knowledge

Albre wrote:
I need a low frequency vco (to operate between 55 and 65 Khz) that
draws very little power (microamp supply current if possible). Goggle
...
Any suggestions?

What's the lowest supply current op-amp quad (or??) that will operate
nicely at your frequency? (I'm not up to date on micropower OAs.) If a
suitable one exists, here's a possible.

There's a very simple circuit (one OA + 4 resistors) for an amplifier
whose gain can be switched from +1 to -1. You would apply your control
voltage to its input. A fet could be used for the switch.

A second OA would be used as a simple R-C integrator with the output of
the previous applied to its input.

A two-level detector would be used to detect when the integrator output
reached V1 and V2 and its output used to drive the switch.

The slope of the integrator output is directly proportional to the input
- more voltage, steeper slope, less time to get from V1 to V2, higher
frequency.

Ted

On Tue, 03 May 2005 19:28:58 GMT, Ted Edwards
wrote:

Albre wrote:
I need a low frequency vco (to operate between 55 and 65 Khz) that
draws very little power (microamp supply current if possible). Goggle
...
Any suggestions?

What's the lowest supply current op-amp quad (or??) that will operate
nicely at your frequency? (I'm not up to date on micropower OAs.) If a
suitable one exists, here's a possible.

There's a very simple circuit (one OA + 4 resistors) for an amplifier
whose gain can be switched from +1 to -1. You would apply your control
voltage to its input. A fet could be used for the switch.

A second OA would be used as a simple R-C integrator with the output of
the previous applied to its input.

A two-level detector would be used to detect when the integrator output
reached V1 and V2 and its output used to drive the switch.

The slope of the integrator output is directly proportional to the input
- more voltage, steeper slope, less time to get from V1 to V2, higher
frequency.

Ted

I think the '4046 that someone suggested will be the lowest power, and
certainly simplest to set up.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.