# VCo with disable function

1. ## VCO with disable function

I found the op-amp based VCO circuit in link https://www.multisim.com/content/uYo...ed-oscillator/

I want to turn of the VCO when the inputs is around +/-5mV dc. Can it be possible

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2. ## Re: VCo with disable function

Sure. But how you'd do it, will depend on details of
what you want from this.

You could cut power (a load switch IC or two) and
this would save a fair bit of current from the quiet
VCO supply. But there are issues with the turnon
and turnoff behaviors, are there chirps and pops on
audio or radio (whatever the application might be)?
How long does the VCO take from power-on to
stable and right? Maybe you want to isolate the
VCO's output and ground the downstream amplifier
input before cutting PA power, but keep the VCO
alive and on an even keel if it's a critical frequency
reference (op amp VCO, I kinda doubt; just illustrating
a general point).

Whatever you want to do can probably be done.
There's power management and signal switching
chip solutions galore and the problem is choosing.

Like they say in the movies, "happiness consists
of wanting the right things".

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3. ## Re: VCo with disable function

I meant "Turn off" being able to see no pulses when input is +5mV or less. For inputs greater than this value, pulses should be present.

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4. ## Re: VCo with disable function

I understand your latest post so that you don't worry about the possible problems addressed by dick_freebird. E.g. startup behavior doesn't matter.

Notice that the VCO stops operation with the integrator in saturation for Vin < 0. If you don't rely on Vin proportional output frequency, you could apply -5 mV input offset. Output state in stop state can be either high or low, however.

Otherwise use a comparator to stop the oscillator.

5. ## Re: VCo with disable function

Hi,

I meant "Turn off" being able to see no pulses when input is +5mV or less.
Could you please be more exact.
do you mean:
* HIGH
* LOW
* high impedance
* donīt care
* anything else?

This all has to be implemented differently...

Klaus

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6. ## Re: VCo with disable function

"Turn off" is to see logic low and I was able to implement this function. I need some help regarding the choice of op amp and the switching device (ref #1). My requirement is DC-1MHz VCO for 0-10V DC.

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