# What is a voltage controlled oscillator and what does it look like?

#### unbuildpain

##### Member level 3
What is a voltage controlled oscillator and what does it look like?

On online tutorials, I keep coming across this VCO or voltage controlled oscillator, what is it? What does it look like? Or is it a custom circuit I have to build? Can it be made to oscillate to any frequency or is there a limit?

#### wwfeldman

a voltage controlled oscillator is exactly what is says
it is an oscillator - that is, it produces sin or square waves at some frequency
the frequency is controlled by an input voltage
for example, the control voltage may run from 0 to 10 V and it may produce a frequency from 1kHz to 25 kHz

i was using one about 30 years ago that was a 16 pin DIP - about 0.3 inches wide and about 1.6 inches long, about 1/4 inch high

each VCO has a frequency range over which it can be adjusted, according to its control voltage range

#### KlausST

##### Super Moderator
Staff member
Hi,

Why don't you do a simple internet search on your own?
You will find descriptions, example circuits discrete and integrated and specifications...

In short:
* Oscillator = frequency generator
* voltage controlled = input voltage determines output frequency

Is there a limit?:
* can the input voltage be unlimited high = infinite ( like million volts) ? --> no
* can the output frequency be unlimited high? --> no

Klaus

#### unbuildpain

##### Member level 3
Hi,

Why don't you do a simple internet search on your own?
You will find descriptions, example circuits discrete and integrated and specifications...

In short:
* Oscillator = frequency generator
* voltage controlled = input voltage determines output frequency

Is there a limit?:
* can the input voltage be unlimited high = infinite ( like million volts) ? --> no
* can the output frequency be unlimited high? --> no

Klaus
Before actually asking here, I searched Google and all the images it showed were of schematics of circuits. I got confused if it was a part or circuit.

What is highest voltage and frequency oscillation cheap ones support?

#### d123

Hi,

I had a look recently at standard parts, of the few I looked at the datasheets of some were max. ~10V, some were ~30V. It depends how old the IC design is.

XR2209 is a typical/classic (old, obsolete-ish) VCO. The link is to the datasheet on Farnell, have a read, it's an easy one to start with.

#### unbuildpain

##### Member level 3
Hi,

I had a look recently at standard parts, of the few I looked at the datasheets of some were max. ~10V, some were ~30V. It depends how old the IC design is.

XR2209 is a typical/classic (old, obsolete-ish) VCO. The link is to the datasheet on Farnell, have a read, it's an easy one to start with.
Thanks. Can those be used to create 350MHz to 5GHz?

#### d123

... I'd guess ~1 MHz - maybe - for cheap ones but may be wrong.

I found the problem was not highest voltage or frequency but that they generally need 'too high' a supply voltage and can require 'too much' supply current for low-power, low-voltage circuits.

You can experiment with op amp versions yourself to get a basic idea, most op amp cookbooks have at least a 'lab signal generator' schematic and some are adjustable.

unbuildpain

### unbuildpain

points: 1

#### d123

Thanks. Can those be used to create 350MHz to 5GHz?
Not the ones I saw, they were old and 'slow'.

Do a parametric product search of VCOs on suppliers' and manufacturers' websites to see if anything matches your needs.

#### unbuildpain

##### Member level 3
Nah, to low, It goes above 3.2 THz
Why do you think it goes over 3.2THz? Are you trolling?

#### BigBoss

If you need a VCO that will work between 350 MHz-5GHz, it's not possible to design and build up such VCO with this huge wide-band.
VCOs have generally max. 2 octaves bandwidth or less.If you intend to use that frequency band, you have to use a VCO which works at highest frequency then you should divide this frequency by aid of divider but finding a discrete divider for that band is so difficult.
Best option is to use PLL+VCO ICs of Analog Devices ( or similar circuits of any other manufacturer ).
Or using multiple VCOs together with switching circuit to achieve desired frequency and signal.
There are many cost effective ready-to-use PLL+VCO circuits in the market.

#### wwfeldman

google is not really the best place to search for available components
try a distributor like DigiKey, Mouser, Newark (or Farnell in UK), Jameco ; there are other distributors
they have search engines - i like DigiKey's search process