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RF Attenuators = Jitter Reducers
RF Attenuators = Jitter Reducers
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View Poll Results: Do you have a SPDIF transformer in your Digital Device
Yes 40 71.43%
No 16 28.57%
Voters: 56. You may not vote on this poll

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Old 28th June 2010, 07:06 PM   #171
jkeny is offline jkeny  Ireland
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Originally Posted by infinia View Post
Maybe the only way to find out out about the SC part is to spend the extra $12 here and let your ears tell you. LOL
No I've already got a Newava 1:1 XFMR

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Well let's just say that by only showing time plots of NOT random data proving a case for clock recovery improvement does not help my confidence in someones testing ability. If he showed a phase noise plot with a block diagram I'd be really impressed.
As he said already - got a Wavecrest to loan him?
 
Old 28th June 2010, 07:11 PM   #172
stormsonic is offline stormsonic  Slovenia
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Originally Posted by infinia View Post
Hi George or Joe K
In my experience common mode interference of PC audio using single ended connections can do much greater damage to a Rx clock than Tx poor return loss ever can, so yes pulse XFMR/s with greater isolation ie less inter-winding capacitance is the right approach.
Disagree. Low interwinding capacitance=wrong approach.
Connect low-interwinding-capacitance-high-leakage-inductance-low-bandwith-pulse-transformer to TDR.
 
Old 28th June 2010, 07:17 PM   #173
infinia is offline infinia  United States
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Originally Posted by stormsonic View Post
Disagree. Low interwinding capacitance=wrong approach.
Connect low-interwinding-capacitance-high-leakage-inductance-low-bandwith-pulse-transformer to TDR.
yes wrong approach for return loss, but quite right approach for noisy PCs SMPS, USB power on Tx clocks and using singled ended connections. Get a spectrum analyzer or BER tester.
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Old 28th June 2010, 07:36 PM   #174
stormsonic is offline stormsonic  Slovenia
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Originally Posted by wakibaki View Post
RF Attenuators = Jitter Reducers

So we can mark this one as not demonstrated except maybe in the case of the Hiface?

You guys have signally failed to make your case for the generality, in particular, rkeny your insistence that receive impedance could not be determined with a DMM is debunked, and you, Joseph K, have retreated from your insistence that your plots showed anything of significance and are now groping to retrieve some credibility in the case of one device, the Hiface.
@wakibaki

bellow is digital input of actual product. What can be measured with DMM?
75R resistor? Is everything OK or something wrong with this circuit?

Please teach me, how to measure this with DMM.
My DMM will go only to 10, maybe your DMM can go to 11?
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Old 28th June 2010, 07:38 PM   #175
infinia is offline infinia  United States
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No I've already got a Newava 1:1 XFMR
That IMO will unlikely be an improvement,
the TI chip mostly won't like driving that low of impedance also making Rds (a variable) more of an influence on Zo, also increases CMOS ground bounce it's the whole reason for using a XFMR in the first place (CMRR ie reducing ground noise).
Why would you expect this approach to be better than the TI reference design?
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Old 28th June 2010, 07:47 PM   #176
wakibaki is offline wakibaki  United Kingdom
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Nothing wrong here stormsonic, just measure with the DMM. The capacitor isolates the rest of the circuit at DC and the 75R will swamp everything else. You put one probe of the DMM on the centre conductor and the other on the outer. If your DMM only goes to 10, time to get a new one.

w

Ask me a hard one...
 
Old 28th June 2010, 07:49 PM   #177
wakibaki is offline wakibaki  United Kingdom
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Sure I understand what you're saying.

'Hence they can only be used on a cable where the SPDIF signal is higher than normal & can bear some reduction & not drop below SPDIF spec.'

But this would still only make them useful in the case where reflections had been demonstrated to be degrading the reception.

Recall that transformers are not normally employed in consumer SPDIF equipment and that co-ax cables are commonly specified to +-3 ohms or better.

Let's suppose that the terminating resistor at the receive end is a 1% with an unfavourable coincidence with the cable; i.e the cable is 72 ohms (to get the worst case at the transmit end) and the resistor 76 ohms. The coefficient of reflection is (76-72)/(76+72) (just taking the absolute value) or 4/148 = 0.027027.

Now suppose the termination at the transmitting end, taking your own value for Rds(on) of 18 ohms, plus a 1% resistor of 303R, thru a 2:1 transformer is 80.25ohms. This gives a coefficient of reflection of (80.25-72)/(80.25+72) = 0.0541.

So that by the time the reflection has returned to the receiving end its value is 0.00146 of the amplitude of the original incident edge, or 1.5 thousandths worst case, to put it in round numbers.

Of course this could still be causing jitter. Without measurement of the received clock jitter both in the presence of this level of reflection and without, it is impossible to say. On the other hand, it seems extremely unlikely, and against that we have the assertions of a guy who didn't know that you could measure the receive termination with a DMM.

So we can mark this one as not demonstrated except maybe in the case of the Hiface?

Perhaps you know some other equipments where the SPDIF signal is higher than normal?

w

As I told Joseph K, it's not necessary to SHOUT and doing so does nothing for your credibility.
 
Old 28th June 2010, 07:56 PM   #178
jan.didden is offline jan.didden  Europe
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Originally Posted by wakibaki View Post
Nothing wrong here stormsonic, just measure with the DMM. The capacitor isolates the rest of the circuit at DC and the 75R will swamp everything else. You put one probe of the DMM on the centre conductor and the other on the outer. If your DMM only goes to 10, time to get a new one.

w

Ask me a hard one...
I think this WAS a hard one
No offense, but I believe that the 100 ohms series resistor is effectively in parallel with the 75 ohms. The inverter creates a sort of virtual earth at it's input so the 100 ohms is effectively terminated at a virtual gnd.....
No?

jd
 
Old 28th June 2010, 08:01 PM   #179
jkeny is offline jkeny  Ireland
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Originally Posted by wakibaki View Post
Sure I understand what you're saying.

'Hence they can only be used on a cable where the SPDIF signal is higher than normal & can bear some reduction & not drop below SPDIF spec.'

But this would still only make them useful in the case where reflections had been demonstrated to be degrading the reception.

Recall that transformers are not normally employed in consumer SPDIF equipment and that co-ax cables are commonly specified to +-3 ohms or better.

Let's suppose that the terminating resistor at the receive end is a 1% with an unfavourable coincidence with the cable; i.e the cable is 72 ohms (to get the worst case at the transmit end) and the resistor 76 ohms. The coefficient of reflection is (76-72)/(76+72) (just taking the absolute value) or 4/148 = 0.027027.

Now suppose the termination at the transmitting end, taking your own value for Rds(on) of 18 ohms, plus a 1% resistor of 303R, thru a 2:1 transformer is 80.25ohms. This gives a coefficient of reflection of (80.25-72)/(80.25+72) = 0.0541.

So that by the time the reflection has returned to the receiving end its value is 0.00146 of the amplitude of the original incident edge, or 1.5 thousandths worst case, to put it in round numbers.

Of course this could still be causing jitter.
Ah, a breakthrough - you've opened your mind up to the possibility - this is a great leap forward
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Without measurement of the received clock jitter both in the presence of this level of reflection and without, it is impossible to say. On the other hand, it seems extremely unlikely,
Oops, I sopke too soon - that crack of light only shone for a millisecond - ah well! keep exercising those muscles that open minds & you'll get there
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and against that we have the assertions of a guy who didn't know that you could measure the receive termination with a DMM
QED, waki - go back to the books! Throw away your shovel now - the hole is getting too deep!

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So we can mark this one as not demonstrated except maybe in the case of the Hiface?
Did I ever say anything else?

Quote:
Perhaps you know some other equipments where the SPDIF signal is higher than normal?
Did I say I did?
Quote:

w

As I told Joseph K, it's not necessary to SHOUT and doing so does nothing for your credibility.

Last edited by jkeny; 28th June 2010 at 08:06 PM.
 
Old 28th June 2010, 08:06 PM   #180
wakibaki is offline wakibaki  United Kingdom
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Originally Posted by janneman View Post
The inverter creates a sort of virtual earth at it's input
You're thinking of opamps.

w
 

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