CD4060 Xtl Osc. Circuit

I don't see any local decoupling caps.

-- Boris

Now, now, guys, keep it civilized here, will ya :-)

I am usually happy with around 1M. All it needs to do is to crank it over. Kaaaa-chum-pah ... POOF ... vrooooom. Unless I must start it really fast for some reason but that can require special kicker circuitry.

Huh? You and I are talking two different resistors. I'm talking the series drive resistor; you're talking the DC loop resistor.

Which brings to mind... does the CD4060 have the DC loop resistor built-in? It would appear not.

And I should pay closer attention to details :-( The OP has 100K there... needs to be 10-20Meg. ...Jim Thompson

Ok, different thing. Mostly you can get away without although that's not always the nice way of doing things.

AFAIR not.

I usually go for 1M. 10M may not work outdoors when humidity is high and some condensation occurs.

CD series stuff doesn't have a lot of gm. But 1Meg is good for something like 74HCU04.

DO NOT USE buffered inverters for crystal oscillators!

Mine are usually on-chip :-) ...Jim Thompson

My resistors are always on-chip :-) ...Jim Thompson

Jim Thompson a écrit :

Really that small?

Been some years since I commentd on crystal problems, the ancient UK phone line make it difficult and people seem to be getting more unplesant. To work out the suitability and margin for oscillation I recommend plotting the negative resistance of the circuit versus frequency. That is the negative resistace that appears across the crystal. At the oscillation frequency the negative resistance should exceed the crystal resistance by at least a factor of 2.

The PI network oscillator can be shown to go from positive resistance up to a peak and then reduce over about 2 octaves. It is possible to select an overtone by careful selection of values.My recent discovery is that Switcher CAD can be induced to plot the aboce curves! Note that his is not exclusive to PI networks and I have a broadband DC coupled circuit that works from 1M to hundreds of megs without tuning and selects the overtone purely by resistance , not reliabley though as manufacturers of crystals are getting worse at making cheap consistent product. Currently Im rejecting 10% of bought in pagers as the crystal stops after a few months. This is due to the above and that crystals increase their "start up" resistance with time if not properly manufactured. Note crystal drive level is not the same as circuit activity and optimum activity can be inconsistent with adequate negative resistance. Nice to be back Doug Dwyer

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For the CD4060 they recommend even higher values, page 3:

Depends on the frequency but generally yes, don't use those if you can avoid it.

Yup, a poly resistor is nice. But you can't put crystals on the chip :-)

Didn't I say 10-20Meg ?:-)

Makes for lousy stability and possible non-starts.

Wanna bet ?:-) ...Jim Thompson

I never had those problems. But I also prefer non-buffered inverters for that.

With MEMS you could, lots of things are possible. But unlikely as good as a real crystal.

Isn't it what Maxim does in their clock ICs ?

VLV

I never use Maxim parts. If you mean the former Dallas series 32kHz things those are modules that contain a tuning fork crystal. They may look like a chip but in reality it's modules. And my clients would probably have my head examined if I placed a timing clock oscillator that costs several Dollars :-)

There are not too many choices when you need an RTC. Besides, some Dallas/Maxim parts offer the ability to adjust the clock frequency digitally, so you can phase lock it to external signal. That's not too bad for few dollars.

VLV

If you can get any, that is. Key "Maxim" into the Digikey serch engine, then click on oscillators. All but two are zero stock. Now why does that not surprise me?

If I needed a fancy RTC with phase-locking or other nifty add-ons I'd grab a uC. Much cheaper, and available. MSP430 comes to mind.

circuitry.

You _can_ mount a membrane type crystal onto a chip, though, right now, we're mounting the crystal separately... hybrid board style. ...Jim Thompson

I find it so incongruous... Joerg is designing medical electronics with _cheap_ components :-( ...Jim Thompson

I am not great fan of Maxim as I had burned with them before like everybody else. However you must be fair to them:

"Items in stock: Yes" "You have selected 60 items, spanning 3 pages"

My customers will eat me alive if I design in yet another programmable device. Especially as a DAC, a temperature sensor and some sort of clock adjustment circuitry will be required as well. MCU will drain somewhat x10 standby battery power compared to what is required for a pure RTC.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant