315MHz Oscillator

[[email protected]]

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?

 

[colin]

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 =^.^=

 

[Joerg]

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?

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.

 

[Tim Wescott]

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.

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

 

[Luhan]

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?

Buy one...

http://www.laipac.com/easy_868_eng.htm

Luhan

 

[[email protected]]

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?

You can get elelctrochemically thinned crystals which are intended to
stabilise oscillators running at up to about 800MHz,

Vectron sell such oscillators.

http://www.vectron.com/products/xo/xo_standard_index.htm

I think that there are other manufacturers who sell similar parts.

 

[Kevin White]

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?

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

 

[Mike Monett]

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?

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:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm

 

[[email protected]]

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?

Melexis TH72002.26 ASK transmitter IC. I have a few dozen spare if you
are interested.

 

[[email protected]]

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?

something like this?
http://atmel.com/dyn/resources/prod_documents/doc4510.pdf

-Lasse

 

[[email protected]]

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?

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

 

[Joerg]

Hello Tim,

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.

I have the German "UHF Unterlage". It's about the size of a Webster's
dictionary.

Isn't this that common cell phone frequency? Can't you just buy one off
the shelf?

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.

 

[Joerg]

Hello Kevin,

If you are using this for remote control you are limited by FCC part 15
to a very low radiated power.

And watch them harmonics ;-)

FCC and others usually want to see a nice class-B behavior up there.

 

[[email protected]]

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...

 

[Joerg]

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.

 

[John Woodgate]

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?

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.

 

[Rene Tschaggelar]

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?

The NBC12430 might come close.

Rene

 

[Jim Thompson]

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.

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

 

[Joerg]

Hello John,

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.

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.

 

[Joerg]

Hello Jim,

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.

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.

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 ?

What's it going to cost?

BTW, there are "mesa" crystals that will do at least 180MHz.

Usually boutique parts, lots of $$.