The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator

[andrea_mori]

I will measure the phase noise of the TWTMC-STS-FSDO next week, in the meantime you can refer to this link
Phase Noise and other Measurements with a Timepod - KO4BB
where was measured the phase noise of the LTC6957.

 

[Thom]

Ah, great, thanks for the link!

 

[living sounds]

Hi,

I bought an old SAR ADC evaluation board to try out.

It uses a 16.9344 MHz crystal oscilllator.

Can someone recommend a low jitter/low phase noise (ideally drop in) replacement?

Thanks!

 

[marcus1]

I've ordered the following to get 25.0000 MHz:

1 x 6.2500 MHz AT-cut
1 x TWTMC-PXO-AIO-SF
1 x TWTMC-PXO-AIO-XFMR
1 x TWTMC-STS-FSDO-F

I've struggled to understand the figures relating to performance between the different crystals etc but now the 25.0000 MHz SC-cut crystal has reached the MOQ, could someone offer thoughts if the following components greatly exceeds my existing order performance-wise?

1 x 25.0000 MHz SC-cut
1 x TWTMC-DRIXO-SF
1 x TWTMC-DRIXO-XFMR 22-25 MHz
1 x TWTMC-STS-FSDO-F

I wouldn't cancel my order for the 6.2500 MHz AT-cut and associated parts but am considering getting the 25 MHz SC-cut, Drixo etc as well.

 

[living sounds]

What would be the recommended road to replace the 16.9344 MHz crystal oscilllator in my board?

I should be able to get a HC-49/U-SMD 3rd overtone AT cut special polished 16.9344 MHz crystal from Quarztechnik Daun.

The RutgerS clock achieves below 100 dB phase noise at a frequency of 11.288427 MHz with the aforementioned crystal.

Is this attainable with one of the boards availible here?

Thanks!

 

[Basillus]

The answer is no. See Andrea`s answer here: https://www.diyaudio.com/forums/dig...se-jitter-crystal-oscillator-post6430640.html

A 6.2500 MHz SC-cut and drixo will be the best.

I've ordered the following to get 25.0000 MHz:

1 x 6.2500 MHz AT-cut
1 x TWTMC-PXO-AIO-SF
1 x TWTMC-PXO-AIO-XFMR
1 x TWTMC-STS-FSDO-F

I've struggled to understand the figures relating to performance between the different crystals etc but now the 25.0000 MHz SC-cut crystal has reached the MOQ, could someone offer thoughts if the following components greatly exceeds my existing order performance-wise?

1 x 25.0000 MHz SC-cut
1 x TWTMC-DRIXO-SF
1 x TWTMC-DRIXO-XFMR 22-25 MHz
1 x TWTMC-STS-FSDO-F

I wouldn't cancel my order for the 6.2500 MHz AT-cut and associated parts but am considering getting the 25 MHz SC-cut, Drixo etc as well.

 

[andrea_mori]

What would be the recommended road to replace the 16.9344 MHz crystal oscilllator in my board?

I should be able to get a HC-49/U-SMD 3rd overtone AT cut special polished 16.9344 MHz crystal from Quarztechnik Daun.

The RutgerS clock achieves below 100 dB phase noise at a frequency of 11.288427 MHz with the aforementioned crystal.

Is this attainable with one of the boards availible here?

Thanks!

It's difficult to predict the phase noise performance of unknown crystals, so you can try the Quartztechnik crystal with the TWTMC-C oscillator but I cannot assure any good performance.

For sure you'll get better phase noise performance with the Driscoll oscillator with Sc-Cut 3rd overtone crystal at 16.9344 MHz.

 

[euro21]

A 6.2500 MHz SC-cut and drixo will be the best.

It's maybe a typo.
6.25 AT-cut+AIO has better PN than 25MHz SC-cut+Drixo oscillator, below 25Hz.

 

[Basillus]

Nope, a SC 6.25MHz, Drixo oscillator board followed by a couple of doubler is the best.
The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator

 

[living sounds]

It's difficult to predict the phase noise performance of unknown crystals, so you can try the Quartztechnik crystal with the TWTMC-C oscillator but I cannot assure any good performance.

For sure you'll get better phase noise performance with the Driscoll oscillator with Sc-Cut 3rd overtone crystal at 16.9344 MHz.

Thanks!

I just realized that the decimation filter of the ADC allows to be set to accept a 256fs input, which translates to 11.2896 MHz.

Currently there is an oscillator installed, but either an external clock (applied to Pin XTI) or crystal oscillator (Pins XTI and XTO) can be employed. AC coupling is required for an external clock.

What would be the best solution in this case? I think for this value a group buy oscillator is availible, right?

Sorry for the basic questions and thanks again.

 

[andrea_mori]

BOM update

I attach the Mouser BOMs for the new DRIXO semi-finished boards at 24 and 25 MHz.
Please note that C38 is a parallel of two capacitors to reach the correct value (you have to piggyback them).

I also attach a revision for the DRIXO semi-finished board at 16.9344 MHz, there was an error in C28).

 

[andrea_mori]

Thanks!

I just realized that the decimation filter of the ADC allows to be set to accept a 256fs input, which translates to 11.2896 MHz.

Currently there is an oscillator installed, but either an external clock (applied to Pin XTI) or crystal oscillator (Pins XTI and XTO) can be employed. AC coupling is required for an external clock.

What would be the best solution in this case? I think for this value a group buy oscillator is availible, right?

Sorry for the basic questions and thanks again.

Well, at 11.2896 MHz you have 4 options, I attach the phase noise comparison:

- the TWTMC-PXO is the worst performer and the cheaper option
- the other 3 options have similar state of the art performance (almost -145 dBc at 10Hz and almost -120 dBc at 1Hz from the carrier), so I suggest the TWTMC-DRIXO with SC-Cut crystal at 11.2896 MHz

 

[living sounds]

Thanks!

So I need a TWTMC-DRIXO-SF, the crystal, the parts from the mouser BOM and well-regulated 12-16V DC power?

How does it connect to the input of my converter's decimation filter (see attached drawing)? I want to put the device right next to the DAC PCB (in the same box).

According to the manual "an external clock (applied to Pin XTI) or crystal oscillator (Pins XTI and XTO) can be employed. AC coupling is required for an external clock."

I guess a sinewave is still an oscillator but the squarewave makes it a clock? So do I need the squarewave board? And for AC coupling - what would be the recommended capacitor?

 

[andrea_mori]

It's not clear to me what they mean with external clock and external oscillator, can you please provide a link to the datasheet?

 

[living sounds]

Sure:

DF1750 Datasheet pdf - DISCONTINUED PRODUCT. No longer recommended for new design. - Burr Brown

 

[andrea_mori]

I don't think the DF 1750 accepts sine wave, it looks like it requires CMOS clock, so you also need the TWTMC-STS sine to square converter.

Then you can use a C0G 10nF to decouple the XTI pin of the DF1750 from the output of the TWTMC-STS.

 

[anhton82]

Hi, I just consider about 24MHz, 25MHz clock for my Sotm Sms-200. Anyone help me to chose the best option on group buy. Thanks a lot.

 

[andrea_mori]

You have 2 options for each frequency:
- 6.00 and 6.25 MHz AT-cut crystals and TWTMC-PXO-AIO (more expensive)
- 24 and 25 MHz Sc-cut crystals and TWTMC-DRIXO (cheaper)

Both options have similar and very good phase noise performance.

Both frequencies with DRIXO options looks like they meet the Crystals MOQ.
While the 24 MHz with PXO-AIO option looks like that will not meet the crystals MOQ.

 

[anhton82]

Thanks Andrea !
So maybe I will order cheaper option. Do you have any instruction for it.

 

[andrea_mori]

Please, look at the first post of the GB thread
The Well Tempered Master Clock - Group buy

There you can find the links to the order form, to the guide of all the devices and to the shared spreadsheet where you can find MOQ and ordered quantity for each device.