Sinusoidal VCO

[Pooya Monajemi]

Hi...
I need a sinusoidal VCO in the megahertz range... like 1-2 MHz. Can't find
any. Everything I find is square wave output, and it's not easy to filter
that square to get a sinusoid.


Thanks.

 

[John Larkin]

On Sun, 9 May 2004 11:16:22 -0700, "Pooya Monajemi" <pmonajem@uci.edu>
wrote:

Hi...
I need a sinusoidal VCO in the megahertz range... like 1-2 MHz. Can't find
any. Everything I find is square wave output, and it's not easy to filter
that square to get a sinusoid.


Thanks.

Consider an Analog Devices DDS chip.

John

 

[Michael Black]

"Pooya Monajemi" (pmonajem@uci.edu) writes:

Hi...
I need a sinusoidal VCO in the megahertz range... like 1-2 MHz. Can't find
any. Everything I find is square wave output, and it's not easy to filter
that square to get a sinusoid.


Thanks.


Because you're looking from the wrong viewpoint.

If you were coming form an RF viewpoint, you'd take any LC oscillator
and add a varactor for voltage control of the frequency. In other
words, you start with an oscillator that works well at RF, and happens
to put out a sinewave, and then you merely change the variable capacitor
to one that can be controlled via voltage.

Of course, you will not see the range that one expects from an RC
based oscillator.

Michael

 

[Bob]

Try the MAX038 ic from Maxim:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1257

Bob



"Pooya Monajemi" <pmonajem@uci.edu> wrote in message
news:c7lsh90p9j@enews3.newsguy.com...

Hi...
I need a sinusoidal VCO in the megahertz range... like 1-2 MHz. Can't
find
any. Everything I find is square wave output, and it's not easy to filter
that square to get a sinusoid.


Thanks.

 

[Rich Grise]

"Michael Black" <et472@FreeNet.Carleton.CA> wrote in message
news:c7mf66$o9u$1@freenet9.carleton.ca...

"Pooya Monajemi" (pmonajem@uci.edu) writes:
Hi...
I need a sinusoidal VCO in the megahertz range... like 1-2 MHz. Can't
find
any. Everything I find is square wave output, and it's not easy to
filter
that square to get a sinusoid.


Thanks.


Because you're looking from the wrong viewpoint.

If you were coming form an RF viewpoint, you'd take any LC oscillator
and add a varactor for voltage control of the frequency. In other
words, you start with an oscillator that works well at RF, and happens
to put out a sinewave, and then you merely change the variable capacitor
to one that can be controlled via voltage.

Of course, you will not see the range that one expects from an RC
based oscillator.

I don't know why not - if you've got a VCO from 10-11MHz, and an ordinary

osc. at, say, 12 MHz, then their beat freq. would be 1-2 MHz. And fairly
easy to filter.

Cheers!
Rich

 

[Michael Black]

"Rich Grise" (null@example.net) writes:

"Michael Black" <et472@FreeNet.Carleton.CA> wrote in message
news:c7mf66$o9u$1@freenet9.carleton.ca...
"Pooya Monajemi" (pmonajem@uci.edu) writes:
Hi...
I need a sinusoidal VCO in the megahertz range... like 1-2 MHz. Can't
find
any. Everything I find is square wave output, and it's not easy to
filter
that square to get a sinusoid.


Thanks.


Because you're looking from the wrong viewpoint.

If you were coming form an RF viewpoint, you'd take any LC oscillator
and add a varactor for voltage control of the frequency. In other
words, you start with an oscillator that works well at RF, and happens
to put out a sinewave, and then you merely change the variable capacitor
to one that can be controlled via voltage.

Of course, you will not see the range that one expects from an RC
based oscillator.

I don't know why not - if you've got a VCO from 10-11MHz, and an ordinary
osc. at, say, 12 MHz, then their beat freq. would be 1-2 MHz. And fairly
easy to filter.

Cheers!
Rich


But that's adding to the circuitry. It is an obvious solution to

the issue of not being able to cover a wider range.

Considering he posted to basics, and didn't actually specify exactly
what he needed, I did not go into that.

I was really trying to address the issue of someone coming from the
audio world, where wide range RC VCOs are pretty easy and common. They
get to RF, and are puzzled over how to get a sinewave, or why the waveform
is not particularly good. The answer is simple, they are using a circuit
that is fine for audio, but is being stretched at RF. There was a time
when RC VCOs were a new thing, and they were the novelty, but now they've
become the common vantage point. I don't see the limited range of a varactor
tuned LC oscillator as a disadvantage compared to a wide range RC VCO, merely
the result of different design schemes. Any disadvantage of a too narrow
tuning range LC VCO is because you need a wider range.

Michael