dual gate mosfet oscillator

John Larkin Wrote in message:

NXP seems to make several with a 6 v drain to source breakdown (BF1210?) that look like they could work.

What part did you have in mind? 3 volts sounds low for a dual-gate.

Wow, that's a strange part. They don't say what's inside.

BF1210 comes up as "discontinued". ...Jim Thompson

Past the last-buy date on that one. "No replacement." I wonder whether they'd been asked to produce this sort of specialized device for a particular customer's special application, tried to commercialize it, and found that there wasn't sufficient demand to make it worth keeping the part active?

The BF1105R is still made (Mouser and Future have them in stock).

At $0.39 each (Mouser onesies price) it seems like an experiment would be practical :-)

Maybe use a Schottky diode output level detector to feed back to the upper gate bias?

Do you mean an oscillator that works with a 200 - 500 MHz crystal? Are there such crystals?

Some circuits in that range use a VCO operating at a high frequency, phase-locked to a lower frequency crystal oscillator.

Fred

I know that there are "mesa-etched" crystals above 100MHz, but I haven't seen one as high as 500MHz. ...Jim Thompson

Probably noisy. Plus their f_max is usually around 700 MHz, so they don't have a lot of gain up there, which is a problem with high overtone crystals. (Or are you using one of the fancy-schmance high fundamental ones?)

Cheers

Phil Hobbs

Looks like a long tail pair with the G2s connected together. You normally bypass those to ground anyway, so it might work pretty well for some things.

Cheers

Phil Hobbs

It's pretty much not worth building your own XOs these days. Packaged oscillators are so good and cheap.

Some of the synthetic oscillators, like the Fox Xpresso and the Silabs parts, go to really high frequencies and are cheaper than you can buy the parts to make an oscillator.

It's asymmetric, and G2 draws current. Good thing it's obsolete.

Two decades ago, the highest frequency I had seen was a 116 MHz 5th overtone crystal, but as far as I understand a lot higher frequencies are currently available.

With overtone crystals, you need a tank (LC) circuit at the required frequency, otherwise the crystal might oscillate at the fundamental frequency :-).

On a sunny day (Thu, 27 Mar 2014 09:13:24 +0200) it happened snipped-for-privacy@downunder.com wrote in :

I bought a bunch of 100 MHz oscillator modules from ebay... ebay item 261003544995

And sure enough: ebay 261319059458

And that was a 5 second search.

Don't those oscillator modules usually require a supply voltage of 3.3 to 5 volts to work, though?

I looked at Mouser for the silabs parts...for a 500 MHz module they wanted 40 bucks, and it needed 3.3 volts...and it was non stock. :(

Oscillator modules, of course, come in lots of varieties; some are PLL and locked to a quartz crystal well below the output frequency; it isn't just small-integer-multiple 'overtone' tricks that are in these modules! See

On a sunny day (Fri, 28 Mar 2014 03:28:29 -0700 (PDT)) it happened whit3rd wrote in :

Right and who cares what is in it as long as it meets specs.

The phase noise of some of those synthesized modules has to be seen to be believed.

Cheers

Phil Hobbs

On a sunny day (Fri, 28 Mar 2014 08:38:58 -0400) it happened Phil Hobbs wrote in :

That pdf says:

Parameter Symbol Test Condition Min Typ Max Unit Phase Jitter (RMS)1 J 12 kHz to 20 MHz (OC-48) -- 0.25 0.40 ps for FOUT > 500 MHz 50 kHz to 80 MHz (OC-192) -- 0.26 0.37 ps Phase Jitter (RMS)1 J 12 kHz to 20 MHz (OC-48) -- 0.36 0.50 ps for FOUT of 125 to 500 MHz 50 kHz to 80 MHz (OC-192)2 -- 0.34 0.42 ps Phase Jitter (RMS) J 12 kHz to 20 MHz (OC-48)2 -- 0.62 -- ps for FOUT of 10 to 160 MHz CMOS Output Only 50 kHz to 20 MHz2 -- 0.61 -- ps Notes: 1. Refer to AN256 for further information.

BTW the 100 MHz from ebay is direct I think, I use it the DVB-S modulator, and the constellation is very stable, mm and a free running VCO on top of that to mix it up. But I do not have the nice equipment to check it with that you have, only this:

Sure, synthesized, I dunnit with FPGA as I posted here for GPS generation... bit of low-pass to drive the VCO, no problem.