crystal oscillator question...thx

[Sommes]

How to adjust the oscillation frequency from the output frequency of 1MHz
crystal oscillator?
Thanks

 

[colin]

"Sommes" <j@jl.com> wrote in message
news:cllevg$t29$1@news-02.connect.com.au...

How to adjust the oscillation frequency from the output frequency of 1MHz
crystal oscillator?
Thanks

A variable capacitor, or varicap diode in series with one of the capacitors
wil give you upto a few 100ppm adjustment depending on crystal.

a PLL will alow u to adjust it in discrete jumps, or u can just divide it by
any binary number with a pre setable counter
or multiply witha mixer/multiplier to get twice the frequency, or filter out
the 3,5 harmonics etc.

Colin =^.^=

 

[Sommes]

I am doing a analog project.
The topic: High stability variable oscillator
Select and test an appropriate digital oscillator circuit for producing an
accurate variable oscillation from 1kHz to 1MHz

What I think is I have to use crystal oscillator to make stable oscillation.
I will chose 1MHz crystal oscillation...after I may need to adjust 1MHz to
1KHz range.

Please let me know the right track...Thanks...

 

[Tim Wescott]

Sommes wrote:

I am doing a analog project.
The topic: High stability variable oscillator
Select and test an appropriate digital oscillator circuit for producing an
accurate variable oscillation from 1kHz to 1MHz

What I think is I have to use crystal oscillator to make stable oscillation.
I will chose 1MHz crystal oscillation...after I may need to adjust 1MHz to
1KHz range.

Please let me know the right track...Thanks...


Crystal oscillators are quite stable, but you pay for that with a very

narrow frequency range. Pulling a crystal oscillator by +/- 1000ppm is
a lot; pulling it by 3 orders of magnitude is simply out of the question.

It sounds like you're doing a school project.

I suggest you get a copy of the ARRL handbook. What with oscillators
being of core importance to radio design it has a lot of practical
cookbook kind of information on this topic. Wes Hayward's "Introduction
to Radio Frequency Design" wouldn't be out of place if you decided on an
LC oscillator.

Here's some suggestions for how you can pull this off:

1. Find out what "High stability" means in the context of your project
definition. One man's "High stability" is the next one's "jittery piece
of crap"; the threshold value for this has a huge impact on how long
you're going to spend.

2. Ask what is meant by "digital oscillator"? I assume that means
digital output, what else does it mean?

3. Ask what is meant by "variable" - continuously variable? Variable
in discrete steps? How big can the steps be?

4. Find out if you have any other constraints -- output level, spectral
purity, etc.

5. Finally, there are a number of oscillator topologies that you may
want to look into. Depending on the answers to the questions above you
will want to look at:

* RC oscillators (linear or multivibrator),
* LC oscillators (i.e. Colpitts, Hartley, etc.),
* NCOs (numerically controlled oscillator) or
* phase-locked loops (with RC or LC oscillator core).

You can find information on any of these on the Web. Any of these can
have the range extended by building an oscillator that goes from 500kHz
to 1MHz and doing a series of divide-by-two operations to get down to
1kHz.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Paul Burridge]

On Tue, 26 Oct 2004 13:36:54 GMT, "colin"
<no.spam.for.me@ntlworld.com> wrote:

"Sommes" <j@jl.com> wrote in message
news:cllevg$t29$1@news-02.connect.com.au...
How to adjust the oscillation frequency from the output frequency of 1MHz
crystal oscillator?
Thanks



A variable capacitor, or varicap diode in series with one of the capacitors
wil give you upto a few 100ppm adjustment depending on crystal.

a PLL will alow u to adjust it in discrete jumps, or u can just divide it by
any binary number with a pre setable counter
or multiply witha mixer/multiplier to get twice the frequency, or filter out
the 3,5 harmonics etc.

Well if you mix it and filter, you could get *any* other frequency,
not just a multiple or a discrete step!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Tam/WB2TT]

"Sommes" <j@jl.com> wrote in message
news:cllo8s$c8m$1@news-02.connect.com.au...

I am doing a analog project.
The topic: High stability variable oscillator
Select and test an appropriate digital oscillator circuit for producing an
accurate variable oscillation from 1kHz to 1MHz

What I think is I have to use crystal oscillator to make stable
oscillation.
I will chose 1MHz crystal oscillation...after I may need to adjust 1MHz to
1KHz range.

Please let me know the right track...Thanks...


You are going to divide the 1 MHz by 1000 to get 1 KHz, right?

Tam

 

[Gareth]

Paul Burridge wrote:

On Tue, 26 Oct 2004 13:36:54 GMT, "colin"
no.spam.for.me@ntlworld.com> wrote:


"Sommes" <j@jl.com> wrote in message
news:cllevg$t29$1@news-02.connect.com.au...

How to adjust the oscillation frequency from the output frequency of 1MHz
crystal oscillator?
Thanks



A variable capacitor, or varicap diode in series with one of the capacitors
wil give you upto a few 100ppm adjustment depending on crystal.

a PLL will alow u to adjust it in discrete jumps, or u can just divide it by
any binary number with a pre setable counter
or multiply witha mixer/multiplier to get twice the frequency, or filter out
the 3,5 harmonics etc.


Well if you mix it and filter, you could get *any* other frequency,
not just a multiple or a discrete step!

How can you do that (unless you have another variable oscillator to mix
it with, which seems a bit pointless)?

Gareth.

--
-----------------------------------------------------------------------
To reply to me directly:

Replace privacy.net with: totalise DOT co DOT uk and replace me with
gareth.harris

 

[Paul Burridge]

On Tue, 26 Oct 2004 19:51:25 +0100, Gareth <me@privacy.net> wrote:

How can you do that (unless you have another variable oscillator to mix
it with, which seems a bit pointless)?

Exactly, but there are times when it's necessary to do this and it is
in fact pretty much 'de rigeur' in most radio circuitry.
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[colin]

"Norm Dresner" <ndrez@att.net> wrote in message
news:gbBfd.776771$Gx4.734674@bgtnsc04-news.ops.worldnet.att.net...

See comments in-line

"Gareth" <me@privacy.net> wrote in message
news:2u7lrkF27cldoU1@uni-berlin.de...
Sommes wrote:
I am doing a analog project.
The topic: High stability variable oscillator
Select and test an appropriate digital oscillator circuit for
producing
an
accurate variable oscillation from 1kHz to 1MHz

What I think is I have to use crystal oscillator to make stable
oscillation.
I will chose 1MHz crystal oscillation...after I may need to adjust
1MHz
to
1KHz range.

Please let me know the right track...Thanks...

You say it is an analog project? I think that would rule out things
like Phase Locked Loops (PLLs) and synthesizers.


Not really. Starting with a square wave it's moderately easy to
create
a triangle and not all that hard to approximate a sine wave either.
There's
really nothing much like a PLL to get accuracy (but not necessarily
short-term precision). Or Direct Digital Synthesis. DDS is expensive but
it'll put out very nice sine waves of rather controllable frequencies.

One easy way to get a frequency which is variable from 1KHz to 1MHz
would be to use a 555 timer. This will be nowhere near as accurate as a
crystal but it may be accurate enough for your project. I don't know,
but have a look at:


For accuracy, nothing beats a crystal -- unless it's a better crystal or
an
atomic clock which, I'm pretty sure is out of the OP's budget. But the
question of accuracy may be a red herring. It might be sufficient to have
a
555 with a digital frequency readout and a 10-turn pot for time setting.
Of
course, that doesn't produce very good stability. And if it's an analog
output that the OP really wants directly from the oscillator then the
555's
binary output isn't what would get him a good grade.

http://www.doctronics.co.uk/555.htm

Another option would be to use an oscillator IC, e.g LTC6900, which can
be adjusted from 1 KHz to 20 MHz. See:


What about the venerable "Intersil" 8038 (or whoever makes it these
days) or one of the Exar things like the (IIRC) 2240 which has it's own
binary divider.

http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1010,C1096,P2186

Again this is nowhere near as accurate as a crystal, but may do what you
want.


Norm

if you can say what sort of acuracy you need and what is used to set the
frequency (ie a voltage or binary number etc) we might be more able to help.

Colin =^.^=