Low Jitter 20MHz oscillator

[hbv]

Hi all,

We need a low jitter clock generator ( 3v3 or 1v8 CMOS output single
ended ), 20Mhz (+-few percent...) and most important a low jitter on
this output (few ps).

Any ideas are welcomed. Habib.

 

[Spehro Pefhany]

Hi all,

We need a low jitter clock generator ( 3v3 or 1v8 CMOS output single
ended ), 20Mhz (+-few percent...) and most important a low jitter on
this output (few ps).

Any ideas are welcomed. Habib.

Conner-Winfield DV75C series has maximum integrated phase jitter 1ps
RMS over 12kHz to 20MHz. Period jitter 5ps RMS maximum. Also very good
temperature stability for a low-power non-ovenized oscillator (which I
happen to need).

Some info on jitter specs:-
http://www.silabs.com/Support Documents/TechnicalDocs/AN256.pdf

 

[Jeroen]

You can easily slap one together with a 74HCU04. Just make sure it's
the "U" version.

Making an oscillator is easy. Making a low jitter oscillator isn't.
A few uV of power supply noise would mess up the jitter specs of
a 74HCU04 based oscillator. Minuscule temperature variations would
probably do the same.

Jeroen Belleman

 

[Jamie]

Hi all,

We need a low jitter clock generator ( 3v3 or 1v8 CMOS output single
ended ), 20Mhz (+-few percent...) and most important a low jitter on
this output (few ps).

Any ideas are welcomed. Habib.

Xtal base clock for 20 mhz should be ok..

Digikey has lots of XC type osc that are surface
mount that fits your needs.

Jamie

 

[Habib Bouaziz-Viallet]

You can easily slap one together with a 74HCU04. Just make sure it's
the "U" version.

Hello Jim,

What do you mean with "slap together with a U version" ? I believe an
integrated oscillator will not gain benefit with an additional U version
of anything.

Best regards, Habib

 

[Habib Bouaziz-Viallet]

How do you plan to measure the jitter?

Why does it matter?

John,

Measuring jitter is really the point (method based on something which
ressemble on eye diag or something like that ... i don't know at the
moment) the best is that i would not measure anything like that, just
based on component spec.

I need a CMOS low jitter oscillator (few ps in absolute way) only on
specs for feeding the clock input of an16bits AD converter (is that so
hard ?)

Some guys said that a basic 74HCU would be sufficient ... i did'nt read
anything such a thing on any 74HCUxx datasheet.

I remember i had used IDT chips feeding a 100MHz PLL clock input for a
PPC (AMCC PPC440) with something like 1 or 2 ps absolute jitter. I'm
expecting that it's not so hard to find the equivalent on 20MHz.

I will manage the point this week.

Thx anyway for the topic. Habib

 

[[email protected]]

On 01/03/2013 18:07, Jim Thompson wrote:> You can easily slap one together with a 74HCU04.  Just make sure it's

Hello Jim,

What do you mean with "slap together with a U version" ? I believe an
integrated oscillator will not gain benefit with an additional U version
of anything.

Best regards, Habib

A 74HCU04,an xtal, 2 caps, 2 resistors and you have a very nice
oscillator

-Lasse

 

[Habib Bouaziz-Viallet]

Conner-Winfield DV75C series has maximum integrated phase jitter 1ps
RMS over 12kHz to 20MHz

Really good point, thank you. But for the silabs solutions i think these
guys are too obfuscated ... and i'm too in a hurry.

Best Regards, Habib.

 

[Habib Bouaziz-Viallet]

A 74HCU04,an xtal, 2 caps, 2 resistors and you have a very nice
oscillator

-Lasse

Ahh ok a simple RC oscillator on 20MHz ! mmhhh ... i would not
experiment such a basic thing when stable, cheap and reliable integrated
oscillators exits for years with a jitter as low as 1ps.

Thank anyway, Habib.

 

[[email protected]]

Ahh ok a simple RC oscillator on 20MHz ! mmhhh ... i would not
experiment such a basic thing when stable, cheap and reliable integrated
oscillators exits for years with a jitter as low as 1ps.

Thank anyway, Habib.

not an RC oscillator a crystal oscillator, the R's are for bias and
drive
the C's for the xtal

-Lasse

 

[Habib Bouaziz-Viallet]

You're French... what can you say ?>:-}

...Jim Thompson

Jim,

I will never experiment a RC or Quartz + 74HCU or anything like that to
achieve a low jitter oscillator. I leave this sort of thing to some
flashers beginners. No offense.

And the fact is i'm French has nothing to do with this.

Habib.

 

[Habib Bouaziz-Viallet]

Habib, haboom...;-)

my turn : Jim tom tom tom ... -D

 

[George Herold]

Habib, Your debut if off to a very shaky start.  Most of the world
uses 74HCU04 as the core of their crystal oscillators.  And those
two-pin ports on Microchip's uP's... guess what's inside ?

                                        ...Jim Thompson
--
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I love to cook with wine.     Sometimes I even put it in the food.

Hi Jim, What's the advantage of the U version for xtal drive?

Thanks,
George H.

 

[Tim Williams]

Hi Jim, What's the advantage of the U version for xtal drive?

Standard HC is buffered (one on the front, one on the back, plus whatever
logic lies inbetween, so an HC04 is actually three inverters), which
doesn't bias well. HCU is unbuffered, so it makes linear amps just as
well as the old CD4000s did.

Tim

 

[Habib Bouaziz-Viallet]

make sure it and the ADC have very quiet,
well bypassed power

Ok my first plan was to power the analog card with a 3V6 battery.

I realize that driving modern ADC clock input is not so trivial (like
LTC2203)

the oscillator supply and the ADC
logic supply are the same rail
Ok.

If your oscillator slews at
a volt per ns, a millivolt of equivalent noise is a picosecond

Thx, Habib.

 

[Habib Bouaziz-Viallet]

He's a redneck, and at the low end of that scale.

Jim is a little bit condescendant with French guys like me but he must
not as an analog innovatOR and as a good wines amatOR. I guess he spent
too a long time in the cellar and returning here afterwards pissing on
my shoes.

These old men are incorrigible!

Habib.

 

[[email protected]]

Hi all,



We need a low jitter clock generator ( 3v3 or 1v8 CMOS output single

ended ), 20Mhz (+-few percent...) and most important a low jitter on

this output (few ps).



Any ideas are welcomed. Habib.

Jitter is a function of the phase noise profile.

Set your jitter spec., calculate your jitter from the phase noise

of your chosen oscillator.

Then you don't need to argue with anybody.

It's not difficult.

 

[Habib Bouaziz-Viallet]

We did a box that uses an LTC2242-12, a 12-bit ADC running at 250 MHz. The clock
is AC-coupled differential, which makes it pretty much immune to low frequency
and common-mode noise.

Yes surely the single ended input clock requires more attention by us
(PCB stack up issues, Power supplies and signal integrity) thank you for
pointing these topics and we have been some experience on that subjects.

https://dl.dropbox.com/u/53724080/Circuits/ESM/ESM_rev_B.jpg

Seems to be such a thing approching what we plan to do. Great piece of
electronics design.

Often, maybe usually, picosecond jitter is caused by*low* frequency effects:
power supply ripple, ground loops, switcher noise, cmos analog noise,
temperature fluctuations, clock 1/f phase noise.

That is always the same guys, Spehro, you and a few others who are
speaking about electronics designs down here.

Recently someone tells me to not question anything about electronics and
just let some guys like Jim Thompson the great guru analog innovaTOR
pissing me off.

What a pity !

Habib.

 

[George Herold]

09, [email protected] wrote:
A 74HCU04,an xtal, 2 caps, 2 resistors and you have a very nice
oscillator
-Lasse
Ahh ok a simple RC oscillator on 20MHz ! mmhhh ... i would not
experiment such a basic thing when stable, cheap and reliable integrated
oscillators exits for years with a jitter as low as 1ps.
Thank anyway, Habib.
Habib, Your debut if off to a very shaky start.  Most of the world
uses 74HCU04 as the core of their crystal oscillators.  And those
two-pin ports on Microchip's uP's... guess what's inside ?
                                        ...Jim Thompson

[snip]

Hi Jim, What's the advantage of the U version for xtal drive?

Thanks,
George H.

The "U" stands for "unbuffered".

A standard 74HC04 (no "U") inverter is actually 3 inverters in series,
to scale up the power gain.

The "U" version is just a single (2-transistor) inverter, so it's
simply a transconductance device... in other words, an amplifier ;-)

Most crystal oscillators use some variation of the 'HCU04
configuration.  In more critical applications, AGC is applied to...
guess what?... the 'HCU04 configuration... to make it a completely
linear amplifier, with good spectral characteristics.

My MC1648 (circa 1968) is a bipolar example of an AGC'd oscillator to
get good spectral characteristics.

                                        ...Jim Thompson
--
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon athttp://www.analog-innovations.com|    1962     |

I love to cook with wine.     Sometimes I even put it in the food.- Hide quoted text -

- Show quoted text -

Got it, thanks Jim (and Tim)

George H.

 

[[email protected]]

On Sun, 03 Mar 2013 10:01:34 +0100, Habib Bouaziz-Viallet





Often, maybe usually, picosecond jitter is caused by *low* frequency effects:

power supply ripple, ground loops, switcher noise, cmos analog noise,

temperature fluctuations, clock 1/f phase noise.

you're talking about correlated system issues. goes without saying those components have to be dealt with. you don't want them setting your overall system spec. again, those contributions can be calculated.

but ultimately timing systems specs starts with a master clock phase noise profile. in the case of downconverter all sources have to be considered.

then it becomes obvious that spectral profiles can be shaped to maintain jitter, (time domain), specs.