24Hz to 60Hz PLL?

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=A0 =A0 =A0 ...Jim Thompson

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If you are going for low noise, you really want the added stage of logic clean up that you get by doing the converting to analog outside the chip.

It really isn't infinite. On the 74HC74 it is less than infinite because the set up time to cause the output to toggle is longer than the setup to cause it to be the same. I don't recall how big the effect is but it is a small nonzero value. Perhaps with a different flip-flop it is greater than infinity and so it averages out.

Also a simple tri-state gate that you only enable while the carry out of the counter chain is true works as a nice sort of phase detector. It is a little like a no dead band version of the 2 flip-flop on in that for most of the cycle, the filter capacitor has no current.

The bang-bang loops that I've done were EclipsLite ECL. The EL51 flop seems to have a little setup/hold hysteresis, roughly 1 picosecond, but that doesn't bother a relatively narrowbend loop, like locking a VCXO to some external reference. It's hard to beat a differential-input flipflop bang-bang detector when you want to hold a couple of picoseconds absolute timing longterm.

Any jitter in the reference or the VCO smears out the transfer function of the bangbang pd, making it effectively finite gain. I do the loop math based on some assumption of some jitter.

John

It has been done already many years ago

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=A0 =A0 =A0 ...Jim Thompson

ranges.

Yes, you have to do that partly because doing math with infinite values is a lot harder.

In all digital stuff, I have used the change in state of the flip-flop to provide the real part to make the loop stable. Basically what I did was:

INC/DEC ! ----------------! ----- ! ! ----- !AND>----Gain one Signal-----!D Q!----+--+----!D Q! --! --!> ! --!> ! ! ! ----- ! ! Q/!-- ! ! NCO/M-- Clock

The Number Controlled Oscillator is just a divide by N counter where the few bottom bits of N are controlled by the upper bits of another counter that is hooked to the INC/DEC control. The "Gain One" signal causes the NCO to increment by 2 on the next clock cycle. This some of the phase lag making the system stable. Without it the output wobbles either side of the correct value. instead of quickly and randomly jittering. The wobble makes a lot of low frequency noise in the output.

Of course "It has been done already many years ago". I invented dirt. Also much of modern PLL technology. ...Jim Thompson

Come on, Jim. We all know that the dirt was just a byproduct of you doing your designs with chisels, on stone tablets. ;-)

By 1967-68, when I was doing PLL, we already had quadrille pads. However we didn't yet have calculators... except for giant Philco on-desk machines bigger than today's towers ;-) ...Jim Thompson

Wouldn't the purchasing office spring for something like a Friden EC-130? Delay line memory, a sexy CRT display, and only $2200 in 1964 dollars...

I went to a mall in Dothan, Alabama in 1972 or 73 while I was stationed at Ft. Rucker. The mall had two levels. The one at ground level was full, but the underground level only had one store, and all it sold was calculators. I wondered for years how long it lasted. :)

I'm surprised they didn't have "The Scotch Tape Store" or "Spatula City". ;-)

The boards for those were made (and installed) by Philco-Ford, Santa Clara. When I did my short stint at P-F in 1968 (I left Motorola with John Welty), I convinced them to dump it... they were, in essence, shipping $1K with each unit :-(

In August 1968 the politicians who didn't like Welty decided to close that division. The asked me how I'd like to go to Blue Bell. I replied, "How'd you like to kiss my ass?" Really. So I called Walt Seelbach (Mr. MECL) at Motorola and went straight back, to ultimately work on PLL's.

The one and only time I left Arizona :-( ...Jim Thompson

No, just $400 to $600 calculators and over 50 storefronts that were still vacant.

AVR? Is that one of the Z80 compatible chips the Chinese use to run MP/3 players, cameras etc? I'd like to see 8 bit CP/M running on one and starting with an MP/3 player with flash memory, USB and an LCD for cheap would make it more interesting.

See the CP/M usenet group.

On a sunny day (Sat, 6 Mar 2010 02:14:21 -0800 (PST)) it happened Greegor wrote in :

You could then run my CP/M clone on it too, if it supports Z80 instructions:

But I do not think AVR knows about LDIR? LD (IX-12), value? hehe

ld

Yes, they are made by Norwegian Chinese and headquartered in San Jose Chinatown. Chinese is a genetic term for hard working technical people.

Good enough to control and power the ASICs.

Can CP/M runs in 4 to 8K RAM? Oh, wait. AVR can't run from RAM.

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My parts came today. I tried my design, and it locks solid on the right frequency finally. The new loop filter is awesome. Kudos to Helmut for his damped loop filter. Also, my NE555 debounce circuit fixed the frequency error problem. Yaaaah!

@Jan I will be trying your design next and see how it compares to mine in lock time.

Thanks All Chris Maness