315MHz Oscillator

[Wes Stewart]

Best bet might be to use a 105mhz 5th overtone crystal in series resonance
in a 2 transistor butler circuit.
A tuned circuit at 315mhz in the collector of the 2nd transistor will then
give you the high frequency you need,
followed by a further filter and buffer stage.

I started reading this thread late (in the middle) and was going to
comment. Then I figured I better see all of the replies.

Good thing. Colin's idea is about what I was going to say.

 

[Jim Thompson]

Hello Jim,


Nah, I'd use 3904s or cheaper in the first two stages and if I'd feel
really generous maybe a BFS17 in the last.

And all that nuisance bias? If you must, use 3904's as diff pairs.

What's it going to cost?



Usually boutique parts, lots of $$.

Yay! Yay! Let's hear it for boutique chips... keeps Q45's in the
garage ;-)

Seriously... it will be inexpensive.

...Jim Thompson

 

[Joerg]

Hello Jim,

And all that nuisance bias? If you must, use 3904's as diff pairs.

But that would add 1.5 cents to the BOM budget. Per stage :-(

Yay! Yay! Let's hear it for boutique chips... keeps Q45's in the
garage ;-)

Seriously... it will be inexpensive.

That would be nice. I could see some apps in I/Q detection.

 

[[email protected]]

You can't really do 315 MHz directly crystal-controlled.

You can - it is a fairly expensive route, but the products are
available pretty much off the shelf.

Douglas Dwyer has posted here on the subject, but he seems to have
stopped posting on the 18th May 2005.

 

[Chris Jones]

I started reading this thread late (in the middle) and was going to
comment. Then I figured I better see all of the replies.

Good thing. Colin's idea is about what I was going to say.

Something vaguely similar that I have tried was to use a crystal oscillator
module near 100MHz and then triple it by making a square wave and filtering
out everything except the third harmonic. To make the square wave, I
passed the oscillator signal through some CMOS logic inverters (one
inverter as an input stage driving several in parallel for the output
stage). I found that the fastest 3.3V logic variety is quite a bit faster
than old AC series and works much better. Then I filtered the output to get
a fairly clean signal around 300 MHz. You can simulate the LC filter in
SPICE and if you use surface mount inductors and allow for some parasitic
capacitance in the SPICE simulation, then the real circuit actually works
pretty much like the simulation. I think I put a zero at the fundamental
and another one at the second harmonic and another one at the fifth
harmonic. It ended up being very small and cheap, apart from the 100MHz
crystal oscillator module which was not cheap and not particularly small.

Chris

 

[Barry Lennox]

I need to design a 315MHz crystal oscillator with an output power of
0dBm and output impedance of 50ohm. I tried looking at crystal
oscillator designs but nothing I've seen goes up that high. Can anyone
give me ideas regarding this matter?

Dunno if you can still get them, but the Motorola MC13176 is perfect
for this. It has an internal 32x multiplier, so a 9.84375 MHz xtal
will give you 315. The power out is a little higher at about 4 dBm,
but that's easy to attenuate.

Barry Lennox