CD4060 Xtl Osc. Circuit
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From: Jim Thompson on 14 Mar 2010 16:31 On Sun, 14 Mar 2010 13:25:18 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> On Sun, 14 Mar 2010 09:51:52 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> Jim Thompson wrote: >>>> On Sun, 14 Mar 2010 09:05:27 -0700, Joerg <invalid(a)invalid.invalid> >>>> wrote: >>>> >>>>> Jim Thompson wrote: >>> [...] >>> >>>>>> My rule of thumb, which seems to work with every inverter-style >>>>>> crystal oscillator I've ever tried: Use capacitors as recommended by >>>>>> the crystal specification... if it says 15pF, that means 30pF on EACH >>>>>> end to ground. Then choose the resistor based on 45� phase shift with >>>>>> the first capacitor (at the crystal frequency). >>>>>> >>>>> 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. >>>> >>> Ok, different thing. Mostly you can get away without although that's not >>> always the nice way of doing things. >>> >>> >>>> Which brings to mind... does the CD4060 have the DC loop resistor >>>> built-in? It would appear not. >>>> >>> AFAIR not. >>> >>> >>>> And I should pay closer attention to details :-( The OP has 100K >>>> there... needs to be 10-20Meg. >>>> >>> I usually go for 1M. >> >> CD series stuff doesn't have a lot of gm. But 1Meg is good for >> something like 74HCU04. >> > >For the CD4060 they recommend even higher values, page 3: > >http://www.fairchildsemi.com/ds/CD%2FCD4060BC.pdf Didn't I say 10-20Meg ?:-) > > >> DO NOT USE buffered inverters for crystal oscillators! >> > >Depends on the frequency but generally yes, don't use those if you can >avoid it. Makes for lousy stability and possible non-starts. > > >>> 10M may not work outdoors when humidity is high and >>> some condensation occurs. >> >> Mine are usually on-chip :-) >> > >Yup, a poly resistor is nice. But you can't put crystals on the chip :-) Wanna bet ?:-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Joerg on 14 Mar 2010 16:34 Jim Thompson wrote: > On Sun, 14 Mar 2010 13:25:18 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Sun, 14 Mar 2010 09:51:52 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> Jim Thompson wrote: >>>>> On Sun, 14 Mar 2010 09:05:27 -0700, Joerg <invalid(a)invalid.invalid> >>>>> wrote: >>>>> >>>>>> Jim Thompson wrote: >>>> [...] >>>> >>>>>>> My rule of thumb, which seems to work with every inverter-style >>>>>>> crystal oscillator I've ever tried: Use capacitors as recommended by >>>>>>> the crystal specification... if it says 15pF, that means 30pF on EACH >>>>>>> end to ground. Then choose the resistor based on 45� phase shift with >>>>>>> the first capacitor (at the crystal frequency). >>>>>>> >>>>>> 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. >>>>> >>>> Ok, different thing. Mostly you can get away without although that's not >>>> always the nice way of doing things. >>>> >>>> >>>>> Which brings to mind... does the CD4060 have the DC loop resistor >>>>> built-in? It would appear not. >>>>> >>>> AFAIR not. >>>> >>>> >>>>> And I should pay closer attention to details :-( The OP has 100K >>>>> there... needs to be 10-20Meg. >>>>> >>>> I usually go for 1M. >>> CD series stuff doesn't have a lot of gm. But 1Meg is good for >>> something like 74HCU04. >>> >> For the CD4060 they recommend even higher values, page 3: >> >> http://www.fairchildsemi.com/ds/CD%2FCD4060BC.pdf > > Didn't I say 10-20Meg ?:-) >> >>> DO NOT USE buffered inverters for crystal oscillators! >>> >> Depends on the frequency but generally yes, don't use those if you can >> avoid it. > > Makes for lousy stability and possible non-starts. > I never had those problems. But I also prefer non-buffered inverters for that. >> >>>> 10M may not work outdoors when humidity is high and >>>> some condensation occurs. >>> Mine are usually on-chip :-) >>> >> Yup, a poly resistor is nice. But you can't put crystals on the chip :-) > > Wanna bet ?:-) > With MEMS you could, lots of things are possible. But unlikely as good as a real crystal. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Vladimir Vassilevsky on 14 Mar 2010 16:36 Joerg wrote: > Yup, a poly resistor is nice. But you can't put crystals on the chip :-) Isn't it what Maxim does in their clock ICs ? VLV
From: Joerg on 14 Mar 2010 16:43 Vladimir Vassilevsky wrote: > > > Joerg wrote: > >> Yup, a poly resistor is nice. But you can't put crystals on the chip :-) > > Isn't it what Maxim does in their clock ICs ? > 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 :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Vladimir Vassilevsky on 14 Mar 2010 17:10
Joerg wrote: > Vladimir Vassilevsky wrote: > >> >> >> Joerg wrote: >> >>> Yup, a poly resistor is nice. But you can't put crystals on the chip :-) >> >> >> Isn't it what Maxim does in their clock ICs ? >> > > 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 |