I need to control an oscillator so that I can generate a frequency in
the range of 4-14MHz with a PIC. I'd really like to chop that range
into 256 or 65536 different freqs that can be controlled by shifting a
word into a shift register.
I hear some people shouting "A/D and VCO!", however, I need this guy
to be ROCK SOLID. As in no temperature drift (or very little). I'm
afraid that a VCO might not give me the stability... or will it? I've
rarely ventured out into the world of analog electronics.
Is there an off the shelf solution? I'd like 1 chip that I could hang
a crystal on and give it a digital number and have it output the
desired frquency. A simple divider won't work since I need the range
to be split up in even increments.
Tim Hoffman writes:
>
> OK, here's a good one:
>
> I need to control an oscillator so that I can generate a frequency in
> the range of 4-14MHz with a PIC. I'd really like to chop that range
> into 256 or 65536 different freqs that can be controlled by shifting a
> word into a shift register.
>
Take a look at the Fox F6053A it's a programmable ttl oscillator.
It can be programmed to work from 360khz to 120 Mhz. It's not cheap at
about $18-$20.
--
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* Rick Sherman * Virtual Computer Corporation
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> I need to control an oscillator so that I can generate a frequency in
> the range of 4-14MHz with a PIC. I'd really like to chop that range
> into 256 or 65536 different freqs that can be controlled by shifting a
> word into a shift register.
>
> I hear some people shouting "A/D and VCO!", however, I need this guy
> to be ROCK SOLID. As in no temperature drift (or very little). I'm
> afraid that a VCO might not give me the stability... or will it? I've
> rarely ventured out into the world of analog electronics.
Iwould expect it to be problematical to get a VCO with a wide range and
really good stability. My first thought would be to use a VCO controlled
by a crystal-refenced PLL: you put the programmable divider between the
VCO output and the PLL input and you get an output frequency of n * Fref.
> Is there an off the shelf solution? I'd like 1 chip that I could hang
> a crystal on and give it a digital number and have it output the
> desired frquency. A simple divider won't work since I need the range
> to be split up in even increments.
I'm not familiar with what's available in this range these days. Last
time I saw something like this it was about a half-dozen TTL chips plus a
handful of discrete parts, but that was a good many years ago.
> I need to control an oscillator so that I can generate a frequency in
> the range of 4-14MHz with a PIC. I'd really like to chop that range
> into 256 or 65536 different freqs that can be controlled by shifting a
> word into a shift register.
>
> I hear some people shouting "A/D and VCO!", however, I need this guy
> to be ROCK SOLID. As in no temperature drift (or very little). I'm
> afraid that a VCO might not give me the stability... or will it? I've
> rarely ventured out into the world of analog electronics.
I think you need a PLL for solid stability. Motorola has a vast
selection of serial/parallel PLL synthesizer ICs in thier
communications data book for very reasonable prices.
Motorola's app. note ANE416 describing a radio synthesizer using the
MC68HC05B4 controller will give you a good idea of how to use these
chips. My article in the 20-Nov-95 issue of Electronic Design has
a very simple V-F converter which could perhaps be adapted to your
application with the appropriate selection of parts.
Tim Hoffman wrote:
>
> OK, here's a good one:
>
> I need to control an oscillator so that I can generate a frequency in
> the range of 4-14MHz with a PIC. ..........
>
> Is there an off the shelf solution? I'd like 1 chip that I could hang
> a crystal on and give it a digital number and have it output the
> desired frquency......
Tim:
You might want to look into the Harris 45102 Numercially Controled Oscillator.
This NCO has 32 bits of frequency control but you could tie the unused ones to
ground if you only want 16 bits of control. The input frequency can be up to
33 MHz on the low cost part and the output frequency varies as (input
word)/2^32.
See the January 1995 issue of electronics now for more info.
vcc.com * The Reconfigurable Computer Company.
