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EtherREGEN: The long development thread. [Some Gen2 dev. pics and update starting on page 92.]


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Thanks John,

 

Also is the masterclock input 50 or 75 ohm per Silabs specifications?

 

Does the clock input accept any other frequency besides 10mhz. For example 5mhz, 25mhz?

 

Having considered the technicals and purpose of the isolator between  A and B ports,

Is the 10m also isolated by the moat if the clock input is also linked to the dac, this might cause a common ground contamination.

 

 

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1 hour ago, Superdad said:

I’m Alex, not John.

 

We are choosing to use a 75ohm BNC and approriate termination resistors (50ohm will be available as special order).  Specifications of the clock synthesizer have nothing to do with the input impedance of the external clock connection.

 

No, we are programming it for 10MHz as that is the frequency of virtually every available external reference clock. To set it for some other frequency would not make any sense.

 

Interesting question. John might have some other thoughts on this but I can state what I know:

 

We have positioned the clock synth (and the Crystek 575 which for 95%+ of EtherREGEN users will be the internal reference clock driving it) on the ‘B’ side (the one with the lone port). The external BNC port also comes in on the ‘B’ side of the moat. 

 

So while the clocking to ‘A’ and ‘B’ sides is equally ultra-low-jitter on both sides (remember all clocking runs on very tightly controlled differential lines), the power/ground domain the external clock connects to is the ‘B’ side (refer to the board photo I posted).

Thus if using an external reference clock it is probably better to also be using—as most people will typically—the ‘B’ side port for connection to the furthest downstream, DAC-attached renderer/endpoint.  Otherwise there is a chance the galvanic isolation will be defeated. It depends.

 

Thinking about this makes me wonder about external reference clocks which typically have multiple ports (I sure can’t imagine someone buying a $3,500 ref clock just for an EtherREGEN!).  Are the output grounds of those ports common to each other? This is an area I don’t yet know much about.

 

I suppose if common ground domains (and possible power supply loops between a clock and upstream gear) are an issue, it is possible that performance may be better just using the EtherREGEN’s internal reference clock. 

[That may be the case anyway since jitter/phase-noise at the end of a long clock cable may be worse than from the internal clock.]

 

Please be careful about getting too hung up on ultimate clocking—whch in fact our circuitry is already very close to.  We think the “magic” of the EtherREGEN’s performance will come from the total leakage blocking of the active-isolated, dual data/power/clock domains—plus all the care we put into choosing magnetics, voltage regulators, logic chips and all the differential signaling.

As I’ve said, this is an Ethernet switch unlike ANY other. 9_9

Hi Alex,

 

Sorry for the mixup.

 

Yes, i will check, but am quite sure the Mutecs ar3 common. It will possibly defeat the fibre isolation as it will still be grounded to the sitry network side. Ismthe grounds of the B side totally isolated from the A and power ground. Somehow, with a Mutec clock this may not work out so well form the total isololation point of view.

 

There are clock like the new Cybershaft and Esoteric master clock which can have individual outputs ground lifted.

 

The cchd 575 have excellent phase noise, but theres also the non techinal specs of clocks that no one understands affects the sonis largely as well.

 

The reason is if the input master clock can be specified when  ordering? This will allow also the use of say the Mutec mc3+ reclocker for those who have that piece to utilise together with the etherregen.

 

 

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