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?
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.
Colin =^.^=
There are two popular methods:
a. PLL: A free running varicap oscillator is locked to a lower frequency crystal of your choice.
b. Multiplier stages: You build an oscillator at, for example, 11.67MHz, run it hard into a limiting stage that makes its signal highly non-linear, then run it through several multiplier stages where their output tank circuits are tuned to a harmonic. As an example, the first stage would resonate at 35MHz, the 2nd at 105MHz and the last at 315MHz. All those stages must be operated in a non-linear mode. In RF engineer speak that is called class C.
If you are very unfamiliar with this matter I suggest to study ham radio literature from organizations such as the ARRL.
-- Regards, Joerg http://www.analogconsultants.com
Specifically the UHF Experimenter's Handbook (May be "VHF/UHF"). They have a recommended multiplier circuit, as well as some projects with other multiplier strips. It'll be bigger than many au courant circuits, but it'll have significantly lower noise -- it's designed for CW or SSB reception in the microwaves, so it has to be good.
Isn't this that common cell phone frequency? Can't you just buy one off the shelf?
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
Buy one...
Luhan
You can get elelctrochemically thinned crystals which are intended to stabilise oscillators running at up to about 800MHz,
Vectron sell such oscillators.
I think that there are other manufacturers who sell similar parts.
-- Bill Sloman, Nijmegen
This is a common frequency for short range remote control. Purchase a ready built unit from one of the many vendors or if you must build your own use either an LC oscillator or for more stabilty a SAW filter designed for this application.
LC oscillators don't have very good stability but are a good match for super-regenerative receivers that are commonly used in these applications.
Fundamental mode crystals don't go this high and are usually limited to
20MHz with some vendors going higher. Even overtone oscillators won't directly go this high and so will need to be followed with a multiplier as described by other responses.If you are using this for remote control you are limited by FCC part 15 to a very low radiated power.
kevin
Yes. Saronix, Pletronics and other manufacturers supply Mesa high frequency crystals. Also check SAW for higher frequencies.
When you start designing your oscillator, be careful about crystal dissipation. Many crystals can be damaged by running at too high power.
The best method of determining the power dissipation is now in SPICE. See my article below for information on how to do this. Regards,
Mike Monett
Antiviral, Antibacterial Silver Solution:
Melexis TH72002.26 ASK transmitter IC. I have a few dozen spare if you are interested.
something like this?
-Lasse
There are specialty fundamental crystals that go this high (very expensive, last time I checked) , or you could design an overtone crystal oscillator (not trivial), but, if you're designing for an unlicensed transmitter application, most inexpensive units use printed-L, lumped-C tank circuits and the old one-transistor whachamacallit tapped-C oscillator common in old UHF tuner local oscillators.
Surface-acoustic wave (SAW) devices provide much better stability at modest additional cost.
If you really need crystal stability, see Joerg's comments on multipliers and PLLs.
James Arthur
Hello Tim,
I have the German "UHF Unterlage". It's about the size of a Webster's dictionary.
No, AFAIK it's one of those ISM-style bands for keyless entry and gizmos like that.
There is a third method but that one is not for the faint of heart and that's why I did not recommend it: Run a 315MHz LC oscillator and "mode lock" it to a square wave of a fraction of that frequency.
-- Regards, Joerg http://www.analogconsultants.com
Hello Kevin,
And watch them harmonics ;-)
FCC and others usually want to see a nice class-B behavior up there.
-- Regards, Joerg http://www.analogconsultants.com
The thing is that I'm not going to use it for a remote control, I need it as a sinusoidal input to the next circuit inside a device....I'll check out the things you mentioned but I don't think any of the IC solutions will help me out....Besides, I sort of have to design it using a crystal oscillator if it's possible...
If it doesn't have to be dirt cheap and you need frequency agility consider a DDS chip. Analog Devices, for example.
-- Regards, Joerg http://www.analogconsultants.com
In message , dated Tue, 15 Aug 2006, snipped-for-privacy@gmail.com writes
You can't really do 315 MHz directly crystal-controlled. You need to use a multiplier. Start with a 17.5 MHz crystal and multiply by 3, then 3 again, then 2.
You will need some amplification between multipliers. There are other ways (an infinite number) but that will work.
-- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk 2006 is YMMVI- Your mileage may vary immensely. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
The NBC12430 might come close.
Rene
-- Ing.Buero R.Tschaggelar - http://www.ibrtses.com & commercial newsgroups - http://www.talkto.net
All odd multiplications are better. Do X3, X3, X3 from an 11.6666MHz crystal.
Use diff pairs to get good squaring, load each stage with appropriate frequency tank.
There will soon be a 2X/4X chip available from AZMicrotek that won't require tanks... good up to ~620MHz output... designed by... guess who ?:-)
BTW, there are "mesa" crystals that will do at least 180MHz.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Hello John,
I don't know which country the OP lives in but often you can buy cheap overtone crystals for 45MHz. Remote controlled toy cars, microphones, garage door openers etc. Now if you are really brazen you could pick the seventh and go straight to 315MHz from there. But one should be prepared for flying eggs and tomatoes in the design review.
-- Regards, Joerg http://www.analogconsultants.com
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.
What's it going to cost?
Usually boutique parts, lots of $$.
-- Regards, Joerg http://www.analogconsultants.com
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