PLL tricks

[Bill Sloman]

On 30/09/2014 12:37 PM, dagmargoodboat@yahoo.com wrote:

On Monday, September 29, 2014 11:29:41 AM UTC-4, Bill Sloman wrote:
On 29/09/2014 11:38 PM, dagmargoo...@yahoo.com wrote:
On Sunday, September 28, 2014 10:21:28 PM UTC-4, Bill Sloman wrote:
On Monday, 29 September 2014 10:57:24 UTC+10, dagmarg...@yahoo.com wrote:
Kevin wrote:
dagmargoo...@yahoo.com wrote:
Kevin wrote:

snip

The (38.88 x 4) is just one oscillator. It has to be better
than an LC oscillator at 150MHz locked on to its input of 10 MHz.
Any LC variation give direct frequency modulation, which is way,
way worse than a tank drifting a bit. The output frequency of a
tank must still be exactly equal to its input for a fixed change
in component values. A tank oscillator will have a fixed steady
state shift.

Right. I'm not suggesting a 155.52 MHz L-C oscillator! I mean a
155.52 MHz 5th-overtone quartz crystal oscillator, Q>=70k.

You bang the tank and it rings--so far so good. But if the tank isn't
*perfectly* tuned, it rings off frequency, and the 'ring' cycles wander
off phase, right?

Wrong. It isn't the tank that generates the harmonics, but the non-linear response of the multiplying diode.

a. Who said anything about a multiplying diode?

All frequency multipliers depend on a non-linear element - pretty much
always a diode through it may be burined in a transistor of some sort

b. If you're using an SRD, there's a nearly infinite comb of frequencies in
the output.

But confined to the harmonics of the frequency being used to drive the
multiplier. The Fourier transform of a "Dirac Spike" which has area, but
no width, is all the harmonics up to infinity. Real spikes out
step-recovery diodes do have a finite width which does limit the maximum
frequency.

The tank can only respond to the frequencies present in the output of the
multiplier. It's essentially a linear part, so can't do any kind of
frequency multiplication or inter-modulation on its own.

The tank is typically driven with a rectangular wave or a pulse.
If you ping a tank, it rings at its natural frequency. Period. (So to speak.)

An L-C tank doesn't know or care when the next pulse is coming; you're
implicitly arguing that it does.

Sadly for your reputation, real multipliers are pinged repeatedly at a
constant frequency. What the tank circuit does is to sum a lot of pings
over a period determined by it's Q (which is a lot longer than the width
of the spike or the interval between spikes if the tank circuit is going
to serve any useful purpose).

My reputation's not in danger. Your understanding of real multipliers is
in great danger of being improved, however.

Not by you - on the evidence available so far.

What you see coming out is another periodic waveform

You do know that tank multiplied oscillators are industry used standard
methods in achieving low phase noise in preference to PLLs?

That's not his crucial element of ignorance - or rather of knowing
something that ain't quite so.

There's a subtlety I'm not familiar with, apparently, that's why I asked,
but I'm very well acquainted with ordinary r.f. frequency multipliers,
since I studied them and invented a new one. We made millions of them.

No, I didn't, though I believe you.

You'd need a varactor, phase-detector, and a feedback loop to keep the
tank tuned perfectly true, AFAICT, introducing additional problems on
several fronts.

The tank does not have to be perfectly tuned. The tuning doesn't effect the
phase noise. It effects the sub harmonics. For example, tuning at 25 deg C,
then moving to -40 deg, might lose you about 6db from a -50dbc close in
subharmonic.

I'm looking at it in the time domain, and can only imagine you must be
thinking of a different topology than I am.

No, you are not looking at it in the time domain, but rather thinking about
it - rather inaccurately - from a time domain perspective.

Actually I *am* thinking about it from a time domain perspective, not to
mention lots of real-life on-the-bench actual experience. You know, with
notes and everything.

Run some simulations and see what happens.

Yes, you ought to.

Version 4
SHEET 1 880 680
WIRE 16 128 -64 128
WIRE 128 128 16 128
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WIRE -64 160 -64 128
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FLAG -64 272 0
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SYMBOL voltage -64 144 R0
WINDOW 123 0 0 Left 2
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SYMATTR InstName V1
SYMATTR Value PULSE(0 1 0 20n 20n 500n 2.5u)
SYMBOL diode 128 112 M90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName D1
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SYMATTR InstName L1
SYMATTR Value 20�H
SYMATTR SpiceLine Rser=.1
SYMBOL cap 240 160 R0
SYMATTR InstName C1
SYMATTR Value 1nF
TEXT -98 296 Left 2 !.tran 20u

Try simulating an actual tank circuit, rather than a circuit in which
the LC tank is clamped by the source while the diode is conducting - 20%
of the time in your fatuous example.

I chose that example deliberately, to illustrate quite clearly that the
next excitation pulse does not perfectly coincide with the tank waveform
if the tank is off-tune.

It's also not far off *actual* multiplier circuits driven from a
transistor collector. The Efratom rubidium standard John posted uses
a similar scheme.

Last, a switched current source has the same problem, just harder to
spot by inspection.

IOW it's not the slightest bit fatuous. You're way out of bounds.

Dream on.

Version 4
SHEET 1 880 680
WIRE -240 -128 -320 -128
WIRE 256 -128 -240 -128
WIRE 256 -96 256 -128
WIRE 256 32 256 -16
WIRE 192 80 80 80
WIRE 80 128 80 80
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FLAG -320 272 0
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FLAG 256 128 f_out
FLAG -240 -128 input
SYMBOL voltage -320 144 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 2 0 20n 20n 500n 2.5u)
SYMBOL ind 320 144 R0
SYMATTR InstName L1
SYMATTR Value 20�H
SYMATTR SpiceLine Rser=.1
SYMBOL cap 240 160 R0
SYMATTR InstName C1
SYMATTR Value 1nF
SYMBOL pnp 192 128 M180
SYMATTR InstName Q1
SYMATTR Value 2N3906
SYMBOL voltage 80 112 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 1
SYMBOL res 240 -112 R0
SYMATTR InstName R1
SYMATTR Value 200
TEXT -352 296 Left 2 !.tran 2000u

A collector doesn't bugger up the tank circuit when it is conducting.
The Q of the circuit is unnaturally high - 0.1R in a 20uH inductor is
about 1500, which isn't easy to get in real life. You've got to simulate
it for a long time - more than 1500 cycles - before you get a stable output.

I'd say you'd just produced another of your straw men ...

Did you bother looking at the irregular spacing of your circuit's output
peaks? 810nS, 910nS, 810nS.

The subharmonic content does that. The 3F component isn't much bigger
than the 2F and 4F components and they add and subtract differently on
successive cycles. It's what the tank circuit does with the current it
has been given, not something it creates for itself.

> That's 100nS jitter. Q.E.D.

But you haven't understood where it's coming from.

But thanks for the posturing (and the insults). What amazes me, if I might
digress, is how you're so confident.

I wouldn't be - if I were arguing with somebody who knew what they were
talking about. As usual you are adjusting your arguments as you go to
make yourself look better - and I'm pointing out where you've moved the
goal-posts - and how you still contrive to look like a twit.

Wenzel's topology changes things, since it makes 2f very accurately from a
sine wave, not relying on a tuned tank. Ditto 3f, I *think*.
(Wenzel's odd-multiplier might be an excellent low-noise way to square-up
the 10MHz reference.)

I think this is the crucial difference to typical f_multipliers:
Wenzel's topology makes a clean, essentially perfect squarewave directly
from a pure sine input, rather than ringing a tank to produce / select a
desired harmonic, and there aren't any off-time infinite-spectrum impulses
to excite it.

That's different, and it's pretty cool.

Producing a square wave creates all the odd harmonics.

Yes.

"Ringing the tank" doesn't produce anything that wasn't in the
drive waveform.

Absolutely FALSE.

So prove it. My simulation of my collector-driven version of your
1.1254MHz tank circuit does have a noise bump 1.1254MHz, but at -86dB
down it is clearly coming from the numerical noise in the simulation.

The driven signal at 1.2MHz is at -14dB. 72dB difference isn't infinite,
but in the context it ought to be pretty convincing.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On 30/09/2014 1:48 PM, dagmargoodboat@yahoo.com wrote:

On Monday, September 29, 2014 10:48:38 PM UTC-4, Bill Sloman wrote:
On 30/09/2014 11:51 AM, dagmargoo...@yahoo.com wrote:
On Monday, September 29, 2014 11:54:17 AM UTC-4, John Larkin wrote:
On Mon, 29 Sep 2014 06:38:52 -0700 (PDT), dagmargoo...@yahoo.com
wrote:
On Sunday, September 28, 2014 10:21:28 PM UTC-4, Bill Sloman wrote:

The tank can only respond to the frequencies present in the output of the multiplier. It's essentially a linear
part, so can't do any kind of frequency multiplication or inter-modulation on its own.

The tank is typically driven with a rectangular wave or a pulse.
If you ping a tank, it rings at its natural frequency. Period. (So to speak.)

An L-C tank doesn't know or care when the next pulse is coming; you're
implicitly arguing that it does.

Imagine pinging an LC at, say, F, with its resonant frequency close
to, say 5F. In the time domain, after each ping it rings at its LC
resonant frequency, which is not precisely 5F. And it loses amplitude
between pings. Both make the ringing wobble and add jitter.

Yes, you've repeated my argument.

Bill doesn't get it. So I supplied a sim file, and he still doesn't get it.

The sim file simulates a a high-Q tank circuit whose natural resonance
is heavily damped by the forward impedance of the diode and the voltage
source for 20% of the time - the 0.5usec that the drive current is on in
the 2.5usec period.

It's not simulating anything useful.

Useful? For Pete's sake, it's pretty close to what people do in real life
multipliers.

Really? Post an example of a real-life circuit.

Instead he posts a modified sim with horrible sidebands and phase noise,
as proof it doesn't happen.

Did you run an DFT on the stable output after it had settled down? I
didn't - it was after midnight and I wanted to go to bed.

I've now done it - a DFT on the stretch from 2msec to 10msec, with a
Blackman-Harris window.

The strongest line was at 1.2MHz (the third harmonic of the forcing
current) at -14dB, with 800kHz second at -22dB, 400kHz third at -32dB
and 1.6MHz fourth at -35dB.

There is a peak in the noise floor at 1.125MHz - the resonant frequency
of the tank circuit, but it's at -87dB - and it reflects the noise
injected by the rounding error in the numerical modelling. Real-life
noise levels would be rather lower.

You need to scrape the egg of your face and start thinking, rather than
banging kerosene cans against your chest.

Communicating with the written word is remarkably difficult. I don't think it
would be this hard in person.

Probably not. The phrase "let's see what it really looks like" does
avoid a lot of foolish posturing.

You're lecturing someone who has actually done this, and you don't know
what you're about.

In the frequency domain, the LC lets some other harmonics leak through
(3F, 7F, maybe 4F and 6F if present) so the output is spectrally
dirty, ditto phase noise.

Run the simulation for yourself and do the DFT. 3F is dominant - as I've
mentioned, followed by 2F, F and 4F. 6F and 7F are the next lowest peaks.

Of course I ran the FFT, and I looked at the sidebands. You're blithely
assuming everyone else is dumber than you.

Is that why your simulation ran for 20usec and mine ran for 2msec? When
I wanted an FFT I ran it for 10msec, and rejected the first 2msec.

Your tank circuit would have a Q of 1500 if it ran in isolation. What
does your running the simulation for just 20usec tell us about it's
effective Q?

That you can look at the spectrum and not see the problem is why I posted
an example (and description) in the time domain--to make it plain to every
'scope driver on the planet--but which so far only John has understood.

Your comments about the dominant frequencies in the output don't match
mine, probably because your circuit is an exhibition of incompetence.

> Just look at YOUR OWN CIRCUIT's zero-crossing spacings. They're AWFUL.

Of course they are. Even running with a 2.67usec periodic forcing
function, the second and fourth harmonics are only 20dB down. This shows
up as an amplitude fluctuation from +/-660 to +/-690mV which is easy to
see. The same adding and subtraction process is going to affect the
zero-crossings in the same sort of way.

Kevin Alyward - who really does know about this stuff - talked about
double-tuned tank circuits, and Wenzel's gear fudges the multiplication
process to get reasonably pure harmonics. The crude example would be
exploiting the trignometric identity

cosx^2=cos2x/2-1

as a frequency doubler which you can realise with an AD834 multiplier.
More complicated schemes are possible.

This may strike you as "spectrally dirty" and the zero crossings will
presumably be all over the shop, but an intelligent designer would have
tuned his tank circuit rather closer to a specific harmonic than you have.

Well that's been my whole bleeping point. The thing you said didn't
matter--tank-tuning--does matter, doesn't it?

No. That's not what I said. What I said was the tank circuit reacted to
the signal fed into it from the multiplier and didn't create any
frequency content of it's own, a point which is sustained by the FFT of
the collector-fed version of your tank circuit.

Which now you admit, but suggest it's my fault for not tuning the tank
better? THAT WAS THE POINT. IF THE TANK IS OFF-TUNE, THE ZERO CROSSINGS
AREN'T *EXACTLY* WHERE YOU WANT THEM.

They aren't exactly where you want them to be when the tank is on tune -
shift the period of your exciting function to 2.67usec and see for
yourself.

My point was that you have to look at what the tank circuit does with
the input that it's given and not waste time imagining that it will
create extra frequency content. In fact the hysterisis in real ferrites
does do a bit of that, but not usually at a level where it matters, and
always at harmonics of the current in the winding driving the ferrite.

Then you try to suggest it's okay. Tell that to John's customers when
they try firing their lasers off those zero-crossings!

If he's buying a packaged 155.52MHz source, the manufacturers of the
source will have worried about that. He shouldn't have to.

I chose an exaggerated example, you quibbled about extraneous stuff, ran
your own sim, and still argue.

Your example happened to be defective, which you still haven't taken on
board, despite the fact that you ran your sim for 20usec and I had to
run mine for 2msec to illustrate what was going on. Think about that.

> And presume to lecture. Simply amazing.

The amazement is all mine - the presumption all yours.

--
Bill Sloman, Sydney

 

[rickman]

On 9/29/2014 11:48 PM, dagmargoodboat@yahoo.com wrote:

On Monday, September 29, 2014 10:48:38 PM UTC-4, Bill Sloman wrote:
On 30/09/2014 11:51 AM, dagmargoo...@yahoo.com wrote:
On Monday, September 29, 2014 11:54:17 AM UTC-4, John Larkin wrote:
On Mon, 29 Sep 2014 06:38:52 -0700 (PDT), dagmargoo...@yahoo.com
wrote:
On Sunday, September 28, 2014 10:21:28 PM UTC-4, Bill Sloman wrote:

The tank can only respond to the frequencies present in the output of the multiplier. It's essentially a linear
part, so can't do any kind of frequency multiplication or inter-modulation on its own.

The tank is typically driven with a rectangular wave or a pulse.
If you ping a tank, it rings at its natural frequency. Period. (So to speak.)

An L-C tank doesn't know or care when the next pulse is coming; you're
implicitly arguing that it does.

Imagine pinging an LC at, say, F, with its resonant frequency close
to, say 5F. In the time domain, after each ping it rings at its LC
resonant frequency, which is not precisely 5F. And it loses amplitude
between pings. Both make the ringing wobble and add jitter.

Yes, you've repeated my argument.

Bill doesn't get it. So I supplied a sim file, and he still doesn't get it.

The sim file simulates a a high-Q tank circuit whose natural resonance
is heavily damped by the forward impedance of the diode and the voltage
source for 20% of the time - the 0.5usec that the drive current is on in
the 2.5usec period.

It's not simulating anything useful.

Useful? For Pete's sake, it's pretty close to what people do in real life
multipliers.

Instead he posts a modified sim with horrible sidebands and phase noise,
as proof it doesn't happen.

Did you run an DFT on the stable output after it had settled down? I
didn't - it was after midnight and I wanted to go to bed.

I've now done it - a DFT on the stretch from 2msec to 10msec, with a
Blackman-Harris window.

The strongest line was at 1.2MHz (the third harmonic of the forcing
current) at -14dB, with 800kHz second at -22dB, 400kHz third at -32dB
and 1.6MHz fourth at -35dB.

There is a peak in the noise floor at 1.125MHz - the resonant frequency
of the tank circuit, but it's at -87dB - and it reflects the noise
injected by the rounding error in the numerical modelling. Real-life
noise levels would be rather lower.

You need to scrape the egg of your face and start thinking, rather than
banging kerosene cans against your chest.

Communicating with the written word is remarkably difficult. I don't think it
would be this hard in person.

Probably not. The phrase "let's see what it really looks like" does
avoid a lot of foolish posturing.

You're lecturing someone who has actually done this, and you don't know
what you're about.

In the frequency domain, the LC lets some other harmonics leak through
(3F, 7F, maybe 4F and 6F if present) so the output is spectrally
dirty, ditto phase noise.

Run the simulation for yourself and do the DFT. 3F is dominant - as I've
mentioned, followed by 2F, F and 4F. 6F and 7F are the next lowest peaks.

Of course I ran the FFT, and I looked at the sidebands. You're blithely
assuming everyone else is dumber than you.

That you can look at the spectrum and not see the problem is why I posted
an example (and description) in the time domain--to make it plain to every
'scope driver on the planet--but which so far only John has understood.

Just look at YOUR OWN CIRCUIT's zero-crossing spacings. They're AWFUL.

This may strike you as "spectrally dirty" and the zero crossings will
presumably be all over the shop, but an intelligent designer would have
tuned his tank circuit rather closer to a specific harmonic than you have.

Well that's been my whole bleeping point. The thing you said didn't
matter--tank-tuning--does matter, doesn't it?

Which now you admit, but suggest it's my fault for not tuning the tank
better? THAT WAS THE POINT. IF THE TANK IS OFF-TUNE, THE ZERO CROSSINGS
AREN'T *EXACTLY* WHERE YOU WANT THEM.

One thing I'm not clear about it that this tank circuit is a filter
right? I believe it could be called a linear filter, no? I believe by
definition a linear filter does not create new frequencies other than
what is in the input.

Do I misunderstand this?

The distortion in the zero crossings is because of the presence of the
harmonics. Your and John's comments seem to be saying the tuned filter
is not capable of passing a given frequency input without disrupting its
frequency. I'm pretty sure that is just plain wrong. It has nothing to
do with the tuning of the filter.

In particular, John seems to be unaware of the spectral content of a
square wave when he says,

If you ping a tank, it rings at its natural frequency. Period.
(So to speak.)

An L-C tank doesn't know or care when the next pulse is coming;
you're
implicitly arguing that it does.

The L-C tank does "know" the frequency of each harmonic within the
square wave and it responds to each of them independently, without
altering their frequencies. "Pinging" the tank is a bit of a shooting
from the hip comment and is not accurate for this discussion where the
tank is a filter with an input of various frequency sine waves.

--

Rick

 

[John Larkin]

On Mon, 29 Sep 2014 20:48:42 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

On Monday, September 29, 2014 10:48:38 PM UTC-4, Bill Sloman wrote:
On 30/09/2014 11:51 AM, dagmargoo...@yahoo.com wrote:
On Monday, September 29, 2014 11:54:17 AM UTC-4, John Larkin wrote:
On Mon, 29 Sep 2014 06:38:52 -0700 (PDT), dagmargoo...@yahoo.com
wrote:
On Sunday, September 28, 2014 10:21:28 PM UTC-4, Bill Sloman wrote:

The tank can only respond to the frequencies present in the output of the multiplier. It's essentially a linear
part, so can't do any kind of frequency multiplication or inter-modulation on its own.

The tank is typically driven with a rectangular wave or a pulse.
If you ping a tank, it rings at its natural frequency. Period. (So to speak.)

An L-C tank doesn't know or care when the next pulse is coming; you're
implicitly arguing that it does.

Imagine pinging an LC at, say, F, with its resonant frequency close
to, say 5F. In the time domain, after each ping it rings at its LC
resonant frequency, which is not precisely 5F. And it loses amplitude
between pings. Both make the ringing wobble and add jitter.

Yes, you've repeated my argument.

Bill doesn't get it. So I supplied a sim file, and he still doesn't get it.

The sim file simulates a a high-Q tank circuit whose natural resonance
is heavily damped by the forward impedance of the diode and the voltage
source for 20% of the time - the 0.5usec that the drive current is on in
the 2.5usec period.

It's not simulating anything useful.

Useful? For Pete's sake, it's pretty close to what people do in real life
multipliers.

Instead he posts a modified sim with horrible sidebands and phase noise,
as proof it doesn't happen.

Did you run an DFT on the stable output after it had settled down? I
didn't - it was after midnight and I wanted to go to bed.

I've now done it - a DFT on the stretch from 2msec to 10msec, with a
Blackman-Harris window.

The strongest line was at 1.2MHz (the third harmonic of the forcing
current) at -14dB, with 800kHz second at -22dB, 400kHz third at -32dB
and 1.6MHz fourth at -35dB.

There is a peak in the noise floor at 1.125MHz - the resonant frequency
of the tank circuit, but it's at -87dB - and it reflects the noise
injected by the rounding error in the numerical modelling. Real-life
noise levels would be rather lower.

You need to scrape the egg of your face and start thinking, rather than
banging kerosene cans against your chest.

Communicating with the written word is remarkably difficult. I don't think it
would be this hard in person.

Probably not. The phrase "let's see what it really looks like" does
avoid a lot of foolish posturing.

You're lecturing someone who has actually done this, and you don't know
what you're about.

In the frequency domain, the LC lets some other harmonics leak through
(3F, 7F, maybe 4F and 6F if present) so the output is spectrally
dirty, ditto phase noise.

Run the simulation for yourself and do the DFT. 3F is dominant - as I've
mentioned, followed by 2F, F and 4F. 6F and 7F are the next lowest peaks.

Of course I ran the FFT, and I looked at the sidebands. You're blithely
assuming everyone else is dumber than you.

That you can look at the spectrum and not see the problem is why I posted
an example (and description) in the time domain--to make it plain to every
'scope driver on the planet--but which so far only John has understood.

Just look at YOUR OWN CIRCUIT's zero-crossing spacings. They're AWFUL.

This may strike you as "spectrally dirty" and the zero crossings will
presumably be all over the shop, but an intelligent designer would have
tuned his tank circuit rather closer to a specific harmonic than you have.

Well that's been my whole bleeping point. The thing you said didn't
matter--tank-tuning--does matter, doesn't it?

Which now you admit, but suggest it's my fault for not tuning the tank
better? THAT WAS THE POINT. IF THE TANK IS OFF-TUNE, THE ZERO CROSSINGS
AREN'T *EXACTLY* WHERE YOU WANT THEM.

Then you try to suggest it's okay. Tell that to John's customers when
they try firing their lasers off those zero-crossings!

I chose an exaggerated example, you quibbled about extraneous stuff, ran
your own sim, and still argue.

And presume to lecture. Simply amazing.


Cheers,
James Arthur

Ignore him. Your life will be slightly improved.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

David Platt <dplatt@coop.radagast.org> wrote:

In article <mlrj2a1r1h8kres22eqs2n0lssrnmocfq1@4ax.com>,
John Larkin <jlarkin@highlandtechnology.com> wrote:
Maynard A. Philbrook Jr. <jamie_ka1lpa@charter.net> wrote:

Anyway, I was wondering if you plan on maintaining the control loop
signal to the VXO at the current state if you lose the GPS for a
short time? or are you depending on the reference from the GPS
receiver to do that for you if signal is lost?

I can talk to the customer about this. Losing the 10 MHz and
especially the 1 PPS would be a big deal. I think they would suspend
operations until everything was fixed.

Ask them whose baby it is to figure out if GPS has gone... do you get
a TTL "GPS OK" line that you can believe, or do you have to decide on
your own?

What you hope is that the 1PPS and 10 MHz just stop coming if the GPS
receiver is "out of lock". Sometimes it's a configuration option to
the GPS receiver to stop sending these signals when in doubt. Sometimes
they just keep coming, and you need to look at some of the alarm flags
in the serial data output from the GPS receiver to know that their
accuracy is bad. (On the third hand, if you look at every single alarm
flag from the GPS receiver, you will sometimes decide that the world is
ending when things are really OK.)

Losing GPS lock is a not-uncommon occurrance, in industrial-timing
applications (e.g. cellphone tower timing controllers). It's quite
common to have a secondary or even tertiary timing source to "tide
you through" when the GPS signal and the resulting PPS go "off-line"
for a while.

Another vote for this. In your application it may or may not be
appropriate to "ride through"; maybe "stop the world" is OK. In the
system I worked on, we had to "ride through", but without the benefit
of a secondary reference; our timestamps were allowed to get less
precise if we were on "ride through" mode. It took a while but we made
it work.

What with random electronic noise, kids playing with "GPS jammers",
the occasional solar storm, and so forth, I think you're likely to
find the need for a local high-stability "holdover" time/PPS source
to be quite important in your application.

It's not always kids. A few years back the FAA installed some new air
traffic control hardware at Newark airport (IIRC). It had checked out
OK on the bench but started losing GPS more than it should when on
site. After ruling out the obvious stuff like hawks perching on the
antenna, they decided it was interference, and did a little direction-
finding. The signal was coming from the Interstate; a trucker was using
a GPS jammer to defeat his company's tracking of his truck.

Matt Roberds

 

[Bill Sloman]

On Tuesday, 30 September 2014 17:01:43 UTC+10, rickman wrote:

On 9/30/2014 1:15 AM, Bill Sloman wrote:



Kevin Alyward - who really does know about this stuff - talked about

double-tuned tank circuits, and Wenzel's gear fudges the multiplication

process to get reasonably pure harmonics. The crude example would be

exploiting the trignometric identity



cosx^2=cos2x/2-1



as a frequency doubler which you can realise with an AD834 multiplier.

More complicated schemes are possible.



I am not clear on your formula as the square notation is not clear what

you intend it to be applied to. Which of these did you mean?



cos^2(x) = cos(2x)/2 - 1 or

cos(x^2) = cos(2x)/2 - 1



I checked a few web sites and didn't find a formula for cos(x^2). In

context cos^2(x) makes more sense but I didn't find the identity you

provide.



Perhaps you meant

cos^2(x) = (1 + cos(2x))/2

In English, the square if the cosine of the angle x is equal to one half plus half the cosine of the angle two times x.

I thought that I'd transcribed the formula from a reliable web site, but I clearly wasn't thinking straight.

The basic array of trignometrical identities got drummed into my brain at secondary school in Tasmania in the late 1950's and I have had occasion to recall them since,but not all that often.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Tuesday, 30 September 2014 18:23:50 UTC+10, Gerhard Hoffmann wrote:

Am 30.09.2014 um 02:17 schrieb Bill Sloman:

Peltier junctions are expensive, but having the crystal at 25C means
that it won't age as fast.

If one needs a cold stage, Peltiers cannot be avoided.

But for crystal ovens, the most important thing is isolation.
Peltiers are a thermal highway and get only acceptable by
electronic regulation.

Too true. A heater behind good thermal isolation offers a lot more stability for the same amount of effort.

And below the dew point, they are a mess because of the water.
We ran our water-cooled mixed signal wafer probers at 38°C t
avoid that.

Dry nitrogen - boiled off liquid nitrogen - can prevent condensation in the lab.
Gets a bit messy in the field.

(50 KW for 4K channels in a few cubic-feet, with huge nekkid chips
between the boards & the cooling plates).

Sounds like fun. My electron-microscope based electron beam tester might eventually have needed that kind of test stage - cooling bare chips working in vacuum isn't trivial - if it had ever gotten into production and had had real users.

> SC crystals have their best operating point at 80° C or so,

I didn't know that. I thought that the optimal temperature could be chosen - at least to some extent.

more than one would like for the rest of the oscillator
electronics. They don't work w/o an oven.

The oven - or some sort of temperature control - is essential for serious stability. Laser diodes tend to have the same problem.

--
Bill Sloman, Sydney

 

[rickman]

On 9/30/2014 1:15 AM, Bill Sloman wrote:

Kevin Alyward - who really does know about this stuff - talked about
double-tuned tank circuits, and Wenzel's gear fudges the multiplication
process to get reasonably pure harmonics. The crude example would be
exploiting the trignometric identity

cosx^2=cos2x/2-1

as a frequency doubler which you can realise with an AD834 multiplier.
More complicated schemes are possible.

I am not clear on your formula as the square notation is not clear what
you intend it to be applied to. Which of these did you mean?

cos^2(x) = cos(2x)/2 - 1 or
cos(x^2) = cos(2x)/2 - 1

I checked a few web sites and didn't find a formula for cos(x^2). In
context cos^2(x) makes more sense but I didn't find the identity you
provide.

Perhaps you meant
cos^2(x) = (1 + cos(2x))/2

--

Rick

 

[Gerhard Hoffmann]

Am 30.09.2014 um 02:17 schrieb Bill Sloman:

Peltier junctions are expensive, but having the crystal at 25C means
that it won't age as fast.

If one needs a cold stage, Peltiers cannot be avoided.

But for crystal ovens, the most important thing is isolation.
Peltiers are a thermal highway and get only acceptable by
electronic regulation.

And below the dew point, they are a mess because of the water.
We ran our water-cooled mixed signal wafer probers at 38°C to
avoid that.
(50 KW for 4K channels in a few cubic-feet, with huge nekkid chips
between the boards & the cooling plates)

SC crystals have their best operating point at 80° C or so,
more than one would like for the rest of the oscillator
electronics. They don't work w/o an oven.

Gerhard

 

[Gerhard Hoffmann]

Am 26.09.2014 um 19:41 schrieb DecadentLinuxUserNumeroUno:

On Fri, 26 Sep 2014 18:52:30 +0200, Gerhard Hoffmann
ghf@hoffmann-hochfrequenz.de> Gave us:

Am 26.09.2014 um 18:34 schrieb rickman:

Why does it need to be a "reasonably big" Spartan 6? It can be a low
power iCE40 device and have tons of room left over.

I took spartan6 as an example because I used it to test some filters,
and my DDS with a huge sine table compiled to run > 200 MHz without
any effort.



Yes, but in that application, was jitter a concern?

Or better put: Is it not true that jitter was NO concern in that
application?

I do not understand the questions.
Please bear with me, I have to think in a foreign language.

That is a completely digital DDS in a purely digital environment.
The concept of time only appears as clock events. Where
could there be jitter?

Gerhard

 

[rickman]

On 9/30/2014 4:50 AM, Gerhard Hoffmann wrote:

Am 26.09.2014 um 19:41 schrieb DecadentLinuxUserNumeroUno:
On Fri, 26 Sep 2014 18:52:30 +0200, Gerhard Hoffmann
ghf@hoffmann-hochfrequenz.de> Gave us:

Am 26.09.2014 um 18:34 schrieb rickman:

Why does it need to be a "reasonably big" Spartan 6? It can be a low
power iCE40 device and have tons of room left over.

I took spartan6 as an example because I used it to test some filters,
and my DDS with a huge sine table compiled to run > 200 MHz without
any effort.



Yes, but in that application, was jitter a concern?

Or better put: Is it not true that jitter was NO concern in that
application?


I do not understand the questions.
Please bear with me, I have to think in a foreign language.

That is a completely digital DDS in a purely digital environment.
The concept of time only appears as clock events. Where
could there be jitter?

I think he was confused by your use of the term DDS which implies an
analog signal from an ADC. When the output of the sine table is used
digitally it is more often termed an NCO, numerically controlled
oscillator. The terms are often interchanged. I have not been able to
find any real definition of them, or I should say I can't find any
formal distinction. But this is the convention I have found.

Then there is the DCO and I think one more I can't remember.

--

Rick

 

Rick wrote:

On 9/29/2014 11:48 PM, dagmarg...@yahoo.com wrote:
On Monday, September 29, 2014 10:48:38 PM UTC-4, Bill Sloman wrote:
On 30/09/2014 11:51 AM, dagmargoo...@yahoo.com wrote:

Just look at YOUR OWN CIRCUIT's zero-crossing spacings. They're AWFUL.

This may strike you as "spectrally dirty" and the zero crossings will
presumably be all over the shop, but an intelligent designer would have
tuned his tank circuit rather closer to a specific harmonic than you have.

Well that's been my whole bleeping point. The thing you said didn't
matter--tank-tuning--does matter, doesn't it?

Which now you admit, but suggest it's my fault for not tuning the tank
better? THAT WAS THE POINT. IF THE TANK IS OFF-TUNE, THE ZERO CROSSINGS
AREN'T *EXACTLY* WHERE YOU WANT THEM.

One thing I'm not clear about it that this tank circuit is a filter
right? I believe it could be called a linear filter, no? I believe by
definition a linear filter does not create new frequencies other than
what is in the input.

Do I misunderstand this?

The distortion in the zero crossings is because of the presence of the
harmonics. Your and John's comments seem to be saying the tuned filter
is not capable of passing a given frequency input without disrupting its
frequency. I'm pretty sure that is just plain wrong. It has nothing to
do with the tuning of the filter.

In particular, John seems to be unaware of the spectral content of a
square wave when he says,

If you ping a tank, it rings at its natural frequency. Period.
(So to speak.)

An L-C tank doesn't know or care when the next pulse is coming;
you're
implicitly arguing that it does.

I wrote that, not John.

The L-C tank does "know" the frequency of each harmonic within the
square wave and it responds to each of them independently, without
altering their frequencies. "Pinging" the tank is a bit of a shooting
from the hip comment and is not accurate for this discussion where the
tank is a filter with an input of various frequency sine waves.

Let's dump the intellectual baggage.

John wants to produce *exact* zero-crossings. A frequency
multiplier has been suggested in the signal chain.

Simulate this better-than-life quasi-ideal frequency multiplier:

(10mA pulsed current source into 1nF + 22uH LC tank.
Pulse width=500nS, period=5.2uS.)

WIRE 96 16 0 16
WIRE 160 16 96 16
WIRE 96 32 96 16
WIRE 160 32 160 16
WIRE 96 128 96 96
WIRE 160 128 160 112
WIRE 160 128 96 128
WIRE 288 128 160 128
WIRE 304 128 288 128
WIRE 0 176 0 16
WIRE 160 176 160 128
WIRE 160 288 160 256
FLAG 160 288 0
FLAG 0 176 0
FLAG 288 128 out
SYMBOL current 160 176 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName I1
SYMATTR Value PULSE(10mA 0 0 20n 20n 500n 5.2u)
SYMBOL ind 144 16 R0
SYMATTR InstName L1
SYMATTR Value 22ľH
SYMATTR SpiceLine Rser=.2
SYMBOL cap 80 32 R0
SYMATTR InstName C1
SYMATTR Value 1n
TEXT -34 312 Left 2 !.tran 2mS

Look at the voltage waveform--are the zero-crossings uniform?
If the LC drifted or were mistuned, would the zero-crossings
stay fixed in time, or would they move?

That's the point.

Cheers,
James Arthur

 

[Gerhard Hoffmann]

Am 27.09.2014 um 01:58 schrieb Phil Hobbs:

On 9/26/2014 1:57 PM, rickman wrote:
....
155.52MHz and feeding a number cruncher embedded in a reasonably big
programmable logic device. He mentioned a Xilinx Spartan-6

http://www.xilinx.com/products/silicon-devices/fpga/spartan-6/

A pretty big hammer to replace a single D-flop!

I could have sworn there was some other stuff in that design... another
d-flop to start (fancy ECL stuff, and expensive)... a rather tricky
filter and bunches more. Most of that gets replaced with logic in the
FPGA, the ADC and a DAC.

man-with-only-a-hammer-alert

The D-flop costs about $5 in unit quantity, which is pretty cheap for an
FPGA, especially since all the programming effort would be amortized
over 8 whole units.

As for the rest, the 10 MHz will have to be cleaned up in analogue
somehow, because otherwise its jitter will show up in the FPGA's
output--the analogy between DSP and real genuine analogue signal
processing stands or falls by the samples being evenly spaced. Most of
the time that's not such a worry, but for 1 ps timing accuracy, it most
emphatically is.

I'm definitely not a man with only a hammer.


I have designed transmitters with tubes when I was 17, ultrasonics for
measurements on the inner enclosure of nuclear rectors, signal averagers
in Schottky TTL when TRW's 20 MHz 8 bit ADC was the best one available,
with a fingernail-sized chip inside. The same in 10KH ECL when a 200 MHz
ADC became available, another iteration with the first Xilinx XC3020,
Unix workstations, laser drivers for 10GB/s fiber
optics, precision oscillators, low phase noise synthesizers for
avionics, cell phone base station (and yes, at 10 Mio systems over the
system livetime Xilinx gets flexible wrt prices, a large Spartan 3A was
wayyyy below $5. )

I'm currently working on a system that does sth. similar like JL's, with
similar numbers, but over ground/space/ground to compare atomic clocks.
We'll also fly a maser and a Cs and I did the analog circuitry to
compare them.

You can get around as a consultant.

Ger - The Engineering Flash Mob - hard

 

On Tuesday, September 30, 2014 3:01:43 AM UTC-4, rickman wrote:

On 9/30/2014 1:15 AM, Bill Sloman wrote:

Kevin Alyward - who really does know about this stuff - talked about
double-tuned tank circuits, and Wenzel's gear fudges the multiplication
process to get reasonably pure harmonics. The crude example would be
exploiting the trignometric identity

cosx^2=cos2x/2-1

as a frequency doubler which you can realise with an AD834 multiplier.
More complicated schemes are possible.

I am not clear on your formula as the square notation is not clear what
you intend it to be applied to. Which of these did you mean?

cos^2(x) = cos(2x)/2 - 1 or
cos(x^2) = cos(2x)/2 - 1

I checked a few web sites and didn't find a formula for cos(x^2). In
context cos^2(x) makes more sense but I didn't find the identity you
provide.

Perhaps you meant
cos^2(x) = (1 + cos(2x))/2

Bill's just throwing out buzzwords.

Of course you can use a more complicated filter and get a cleaner
waveform, that's obvious.

But that's changing the question from whether a pulsed LC tank has a
certain behavior, into whether a sufficiently elaborate filter can
select a particular component.

I've personally designed and used double- and triple-tuned multiplier
tanks. The Efratom rubidium standard John posted uses a multiplier
quite close to my sim (that Bill carped about), followed by ~6(*) tuned
stages for filtering.

See pg. 69.
https://dl.dropboxusercontent.com/u/53724080/Gear/Efratom.pdf

(*) Can't tell exactly how many tuned stages count without knowing
the transformer coupling factors, but T1, at a minimum, appears
to be double-tuned.

Less obvious is that the result has ppm phase stability w.r.t. to
the excitation when the filter is detuned or drifts.

But I've already surmised, days ago, that Wenzel and others can use
low-order multipliers with special topologies to excite their filters
with unusually pure excitations, minimizing and avoiding most of those
considerations. Oh, and put 'em in ovens.

Cheers,
James Arthur

 

[John Larkin]

On Tue, 30 Sep 2014 06:39:11 +0000 (UTC), mroberds@att.net wrote:

David Platt <dplatt@coop.radagast.org> wrote:
In article <mlrj2a1r1h8kres22eqs2n0lssrnmocfq1@4ax.com>,
John Larkin <jlarkin@highlandtechnology.com> wrote:
Maynard A. Philbrook Jr. <jamie_ka1lpa@charter.net> wrote:

Anyway, I was wondering if you plan on maintaining the control loop
signal to the VXO at the current state if you lose the GPS for a
short time? or are you depending on the reference from the GPS
receiver to do that for you if signal is lost?

I can talk to the customer about this. Losing the 10 MHz and
especially the 1 PPS would be a big deal. I think they would suspend
operations until everything was fixed.

Ask them whose baby it is to figure out if GPS has gone... do you get
a TTL "GPS OK" line that you can believe, or do you have to decide on
your own?

I get 10 MHz and 1 PPS. I assume that the customer can talk directly
to the SyncServer and observe its status.

Not my problem!

What you hope is that the 1PPS and 10 MHz just stop coming if the GPS
receiver is "out of lock". Sometimes it's a configuration option to
the GPS receiver to stop sending these signals when in doubt. Sometimes
they just keep coming, and you need to look at some of the alarm flags
in the serial data output from the GPS receiver to know that their
accuracy is bad. (On the third hand, if you look at every single alarm
flag from the GPS receiver, you will sometimes decide that the world is
ending when things are really OK.)

Losing GPS lock is a not-uncommon occurrance, in industrial-timing
applications (e.g. cellphone tower timing controllers). It's quite
common to have a secondary or even tertiary timing source to "tide
you through" when the GPS signal and the resulting PPS go "off-line"
for a while.

Another vote for this. In your application it may or may not be
appropriate to "ride through"; maybe "stop the world" is OK. In the
system I worked on, we had to "ride through", but without the benefit
of a secondary reference; our timestamps were allowed to get less
precise if we were on "ride through" mode. It took a while but we made
it work.

What with random electronic noise, kids playing with "GPS jammers",
the occasional solar storm, and so forth, I think you're likely to
find the need for a local high-stability "holdover" time/PPS source
to be quite important in your application.

It's not always kids. A few years back the FAA installed some new air
traffic control hardware at Newark airport (IIRC). It had checked out
OK on the bench but started losing GPS more than it should when on
site. After ruling out the obvious stuff like hawks perching on the
antenna, they decided it was interference, and did a little direction-
finding. The signal was coming from the Interstate; a trucker was using
a GPS jammer to defeat his company's tracking of his truck.

Matt Roberds

--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

On Tuesday, September 30, 2014 11:38:06 AM UTC-4, John Larkin wrote:

On Tue, 30 Sep 2014 06:31:54 -0700 (PDT), dagmargoo...@yahoo.com
wrote:

John wants to produce *exact* zero-crossings. A frequency
multiplier has been suggested in the signal chain.

Simulate this better-than-life quasi-ideal frequency multiplier:

(10mA pulsed current source into 1nF + 22uH LC tank.
Pulse width=500nS, period=5.2uS.)

<snip LTSpice >

Look at the voltage waveform--are the zero-crossings uniform?
If the LC drifted or were mistuned, would the zero-crossings
stay fixed in time, or would they move?

That's the point.

1) It looks more sinusoidal if the pulse frequency is exactly a
fraction of the LC resonant frequency, say 1/5, but it still wobbles.

The fix for that is normally an excitation pulsewidth significantly less
than 1/2 cycle of the output frequency.

That still perturbs the LC phase with every impulse, though.

The 3rd and 7th harmonics are only 10 dB down. Of course the LC
doesn't create new frequencies; the multiple frequencies are already
present in the driving current.

Yes, and more are created by a real transistor's non-linearities,
then the intermodulation products thereof can produce every product
imaginable.

The HP5370A counter needed to make a low-jitter 200 MHz clock from 10
MHz, and they used a multiplier chain. The first section was X5:
https://dl.dropboxusercontent.com/u/53724080/Circuits/Filters/5370A_X5_Mult.jpg

A stock x5.

It took 6 trimmed LC resonators to get the desired spectral purity/low
jitter.

It's a wonder that doesn't drift. Low-Q stages would help, but I have to
wonder if the phase-purity business and the phase-absolute-accuracy
business are two somewhat different animals.

2) When dealing with these two idiots, there's not much reward in
being right.

It had the benefit of me answering my own question, but it sure wasn't
easy.

Here's the easy answer:
http://www.wenzel.com/documents/2diomult.html

"It is often necessary to multiply the frequency of low noise oscillators without significantly degrading the phase noise beyond the theoretical 20 log (N)." ...

Cheers,
James Arthur

 

On Tuesday, September 30, 2014 1:22:16 PM UTC-4, John Larkin wrote:

On Tue, 30 Sep 2014 10:07:01 -0700 (PDT), dagmargoo...@yahoo.com wrote:
On Tuesday, September 30, 2014 11:38:06 AM UTC-4, John Larkin wrote:
On Tue, 30 Sep 2014 06:31:54 -0700 (PDT), dagmargoo...@yahoo.com
wrote:

John wants to produce *exact* zero-crossings. A frequency
multiplier has been suggested in the signal chain.

Simulate this better-than-life quasi-ideal frequency multiplier:

(10mA pulsed current source into 1nF + 22uH LC tank.
Pulse width=500nS, period=5.2uS.)

snip LTSpice

Look at the voltage waveform--are the zero-crossings uniform?
If the LC drifted or were mistuned, would the zero-crossings
stay fixed in time, or would they move?

That's the point.

1) It looks more sinusoidal if the pulse frequency is exactly a
fraction of the LC resonant frequency, say 1/5, but it still wobbles.

The fix for that is normally an excitation pulsewidth significantly less
than 1/2 cycle of the output frequency.

That still perturbs the LC phase with every impulse, though.

The 3rd and 7th harmonics are only 10 dB down. Of course the LC
doesn't create new frequencies; the multiple frequencies are already
present in the driving current.

Yes, and more are created by a real transistor's non-linearities,
then the intermodulation products thereof can produce every product
imaginable.

The HP5370A counter needed to make a low-jitter 200 MHz clock from 10
MHz, and they used a multiplier chain. The first section was X5:
https://dl.dropboxusercontent.com/u/53724080/Circuits/Filters/5370A_X5_Mult.jpg

A stock x5.

It took 6 trimmed LC resonators to get the desired spectral purity/low
jitter.

It's a wonder that doesn't drift. Low-Q stages would help, but I have to
wonder if the phase-purity business and the phase-absolute-accuracy
business are two somewhat different animals.

They didn't care about slow phase drift from the 10MHz reference up to
the 200 MHz clock. I do.

2) When dealing with these two idiots, there's not much reward in
being right.

It had the benefit of me answering my own question, but it sure wasn't
easy.

If people want to fling around personal insults, and call other people
incompetent, you'd think they would make some effort to be right.

Here's the easy answer:
http://www.wenzel.com/documents/2diomult.html

"It is often necessary to multiply the frequency of low noise oscillators without significantly degrading the phase noise beyond the theoretical 20 log (N)." ...

x2 is a nice special case, because pumping a sine wave through an
analog squaring circuit does, in theory, make a clean 2F sine wave.

There's a trig identity about that.

You can also do a pretty clean x2 from a sine with a bridge rectifier,
and a decent odd-order exciter with a schottky diode-quad clamp.

Both are lossy, so it surprised me (without calculating) that the several
gain stages needed don't add significantly to the oscillator's phase
noise, but both Kevin and Wenzel--and several other mfrs--are pretty
clear testimonials for that practice.

Cheers,
James Arthur

 

[whit3rd]

On Tuesday, September 30, 2014 1:23:50 AM UTC-7, Gerhard Hoffmann wrote:

Am 30.09.2014 um 02:17 schrieb Bill Sloman:



Peltier junctions are expensive, but having the crystal at 25C means
that it won't age as fast.

If one needs a cold stage, Peltiers cannot be avoided.

...And below the dew point, they are a mess because of the water.

SC crystals have their best operating point at 80° C or so,
more than one would like for the rest of the oscillator
electronics. They don't work w/o an oven.

AT crystals likewise have improved performance at elevated
temperature (there is a hydroxyl-ion contaminant that creates damping
at lower temperatures). Probably the rock (the crystal) isn't at
risk of aging at any paltry 80C temperature, unless the packaging
and leadwires are an issue.

 

[John Larkin]

On Tue, 30 Sep 2014 06:31:54 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

Rick wrote:
On 9/29/2014 11:48 PM, dagmarg...@yahoo.com wrote:
On Monday, September 29, 2014 10:48:38 PM UTC-4, Bill Sloman wrote:
On 30/09/2014 11:51 AM, dagmargoo...@yahoo.com wrote:

Just look at YOUR OWN CIRCUIT's zero-crossing spacings. They're AWFUL.

This may strike you as "spectrally dirty" and the zero crossings will
presumably be all over the shop, but an intelligent designer would have
tuned his tank circuit rather closer to a specific harmonic than you have.

Well that's been my whole bleeping point. The thing you said didn't
matter--tank-tuning--does matter, doesn't it?

Which now you admit, but suggest it's my fault for not tuning the tank
better? THAT WAS THE POINT. IF THE TANK IS OFF-TUNE, THE ZERO CROSSINGS
AREN'T *EXACTLY* WHERE YOU WANT THEM.

One thing I'm not clear about it that this tank circuit is a filter
right? I believe it could be called a linear filter, no? I believe by
definition a linear filter does not create new frequencies other than
what is in the input.

Do I misunderstand this?

The distortion in the zero crossings is because of the presence of the
harmonics. Your and John's comments seem to be saying the tuned filter
is not capable of passing a given frequency input without disrupting its
frequency. I'm pretty sure that is just plain wrong. It has nothing to
do with the tuning of the filter.

In particular, John seems to be unaware of the spectral content of a
square wave when he says,

If you ping a tank, it rings at its natural frequency. Period.
(So to speak.)

An L-C tank doesn't know or care when the next pulse is coming;
you're
implicitly arguing that it does.

I wrote that, not John.

The L-C tank does "know" the frequency of each harmonic within the
square wave and it responds to each of them independently, without
altering their frequencies. "Pinging" the tank is a bit of a shooting
from the hip comment and is not accurate for this discussion where the
tank is a filter with an input of various frequency sine waves.

Let's dump the intellectual baggage.

John wants to produce *exact* zero-crossings. A frequency
multiplier has been suggested in the signal chain.

Simulate this better-than-life quasi-ideal frequency multiplier:

(10mA pulsed current source into 1nF + 22uH LC tank.
Pulse width=500nS, period=5.2uS.)

WIRE 96 16 0 16
WIRE 160 16 96 16
WIRE 96 32 96 16
WIRE 160 32 160 16
WIRE 96 128 96 96
WIRE 160 128 160 112
WIRE 160 128 96 128
WIRE 288 128 160 128
WIRE 304 128 288 128
WIRE 0 176 0 16
WIRE 160 176 160 128
WIRE 160 288 160 256
FLAG 160 288 0
FLAG 0 176 0
FLAG 288 128 out
SYMBOL current 160 176 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName I1
SYMATTR Value PULSE(10mA 0 0 20n 20n 500n 5.2u)
SYMBOL ind 144 16 R0
SYMATTR InstName L1
SYMATTR Value 22ľH
SYMATTR SpiceLine Rser=.2
SYMBOL cap 80 32 R0
SYMATTR InstName C1
SYMATTR Value 1n
TEXT -34 312 Left 2 !.tran 2mS

Look at the voltage waveform--are the zero-crossings uniform?
If the LC drifted or were mistuned, would the zero-crossings
stay fixed in time, or would they move?

That's the point.

Cheers,
James Arthur

1) It looks more sinusoidal if the pulse frequency is exactly a
fraction of the LC resonant frequency, say 1/5, but it still wobbles.
The 3rd and 7th harmonics are only 10 dB down. Of course the LC
doesn't create new frequencies; the multiple frequencies are already
present in the driving current.

The HP5370A counter needed to make a low-jitter 200 MHz clock from 10
MHz, and they used a multiplier chain. The first section was X5:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Filters/5370A_X5_Mult.jpg

It took 6 trimmed LC resonators to get the desired spectral purity/low
jitter.

2) When dealing with these two idiots, there's not much reward in
being right.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Tue, 30 Sep 2014 10:07:01 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

On Tuesday, September 30, 2014 11:38:06 AM UTC-4, John Larkin wrote:
On Tue, 30 Sep 2014 06:31:54 -0700 (PDT), dagmargoo...@yahoo.com
wrote:

John wants to produce *exact* zero-crossings. A frequency
multiplier has been suggested in the signal chain.

Simulate this better-than-life quasi-ideal frequency multiplier:

(10mA pulsed current source into 1nF + 22uH LC tank.
Pulse width=500nS, period=5.2uS.)

snip LTSpice

Look at the voltage waveform--are the zero-crossings uniform?
If the LC drifted or were mistuned, would the zero-crossings
stay fixed in time, or would they move?

That's the point.

1) It looks more sinusoidal if the pulse frequency is exactly a
fraction of the LC resonant frequency, say 1/5, but it still wobbles.

The fix for that is normally an excitation pulsewidth significantly less
than 1/2 cycle of the output frequency.

That still perturbs the LC phase with every impulse, though.

The 3rd and 7th harmonics are only 10 dB down. Of course the LC
doesn't create new frequencies; the multiple frequencies are already
present in the driving current.

Yes, and more are created by a real transistor's non-linearities,
then the intermodulation products thereof can produce every product
imaginable.

The HP5370A counter needed to make a low-jitter 200 MHz clock from 10
MHz, and they used a multiplier chain. The first section was X5:
https://dl.dropboxusercontent.com/u/53724080/Circuits/Filters/5370A_X5_Mult.jpg

A stock x5.

It took 6 trimmed LC resonators to get the desired spectral purity/low
jitter.

It's a wonder that doesn't drift. Low-Q stages would help, but I have to
wonder if the phase-purity business and the phase-absolute-accuracy
business are two somewhat different animals.

They didn't care about slow phase drift from the 10MHz reference up to
the 200 MHz clock. I do.

2) When dealing with these two idiots, there's not much reward in
being right.

It had the benefit of me answering my own question, but it sure wasn't
easy.

If people want to fling around personal insults, and call other people
incompetent, you'd think they would make some effort to be right.

Here's the easy answer:
http://www.wenzel.com/documents/2diomult.html

"It is often necessary to multiply the frequency of low noise oscillators without significantly degrading the phase noise beyond the theoretical 20 log (N)." ...

Cheers,
James Arthur

x2 is a nice special case, because pumping a sine wave through an
analog squaring circuit does, in theory, make a clean 2F sine wave.
There's a trig identity about that.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com