Need VCO for 14 MHz PLL

Hello John,

If you could run the logic just on the +6V side maybe HC would work.

Regards, Joerg

Hello Jim,

Yes, I have read that somewhere. Some Asian mfgs have also allowed operation down to 1.5V. But I work mostly in med and there everything has to be cast in stone. IOW if it ain't in the data sheet you can't do it.

Did you get the kitchen drawers done?

Regards, Joerg

wired

'Q'

Yes, indeed.

Hello Jim,

Same with the CD series. It is technically ok down to 3V but there it's like molasses at 110F.

The only chip where I did the architecture and some of the analog parts had 45V and 5V. It was one of the automotive processes. Our budget allowed exactly one shot and lo and behold it worked. Whew...

It also had to be much smaller than possible so we had to throw "ballast". It was the electromigration versus lifetime thing. The chip engineer wasn't too enthused because that isn't the way they usually work. But in our case it was for a disposable device.

Your chips are probably also required to run well into the picosecond range. Ours didn't have to, nothing was above 40MHz. So we could go easy on the routing.

Regards, Joerg

Hi Winfield,

Year ago I used to do that with flyback or other transformer-based switchers and multiple taps. But when voltages go down to 1.8V and the tolerances are tight that becomes impractical because you can't regulate individually. Unless there are LDO regulators in tow but these have their own stability issues.

Regards, Joerg

Hello Jim,

Mine right now is a puny 400kHz :-(

Regards, Joerg

Hello Jim,

Similar to an on-chip pressure sensor? If yes and it isn't confidential, what is your favorite fab to do that with?

Regards, Joerg

If you have to operate at the corners of temp/Vcc then they may be ruled out.

A much more stable VCO oscillator is an LC oscillator with a varactor.

Tim.

Win wrotes:

Reminds me of mixing PMOS with NMOS with TTL in the 70's. Remember how EPROM's and DRAM's and dynamic shift registers used to need all sorts of funny voltages like -22.5, -18, -12, +7, etc? Don't forget those WOM chips needing 6.3VAC either :-)

Joerg replies:

I like the latest generation LDO's for my one-off-will-never-be-used-off-my-bench gadgets. If a chip needs 1.8V, then a 1.8V LDO goes on the board.

I occasionally get out my precision voltmeters and many of the low-noise LDO's have remarkably good outputs. Always way better than the specs for DC tolerance and always within the published noise specs.

Never had a problem following the spec-sheet charts. I contrast this with my usage of 3-terminal 780x style regulators, where occasional batches seemed to always oscillate, resulting in us banning that brand. You're in trouble when you've banned all the brands!

But for someone looking to put a bunch of mixed-voltage chips on the same board and mass produce it, I certainly do appreciate that it's a pain.

Tim.

Sad to say, laser vendor specs their detector output as being stable to ~ 0.1 ppm, but, with a frequency accuracy of +/- 10%. Not even sure how this odd combination of specs is arrived at by design, but, it's what I'm working with. Means that VCXO is ruled out.....

W Letendre

The VCTXO's are remarkably good AND available off-the-shelf for many frequencies.

This guy (who does have the requisite measurement equipment!) shows how many of them are good to the part per billion in stability if treated nicely:

But when the original poster mentioned 555's and 4046's, maybe we've hit the overkill stage :-).

Tim.

Yes, have a look at the Linear Technology Oscillators 69xx Series. There a linear voltage can be used.

Rene

Hello Jim,

Cool. So you might visit Erfurt some day where they do their MEMS stuff. Nice historic town.

Regards, Joerg

Hello Tim,

We once got a bloody nose because one of the LDOs (early 90's) had a habit that wasn't on the data sheet. It became unstable when the source impedance exceeded a certain value. Not good.

I never use 78xx but stay with Old Faithful, the LM317 series. Keeps the inventory levels down because there is only one adjustable type. But most of the time I design in switchers.

Regards, Joerg

Hello Tim,

That also makes sure you don't need to worry about de-icing them in winter ;-)

That is probably also the lowest cost method in this case.

Regards, Joerg