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Old 7th August 2010, 02:45 PM   #121
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Quote:
Onboard, fixed oscillators, with on board mini shunt ps regulation (has to be near the clocks, not running through a bunch of wire to get there)
Could you please tell me to which type of shunt implementations are you referring to? ... or which PSU you consider it would be appropriate for this task?
I'm in process of designing such an application and, for now, I'm stuck in finding a valid source for on-board oscillators. So far, I've tried NDKs but without success (unless I'll buy 1k units) and I'm looking to IQD... my next alternative. It seems that it's hard to find good crystal-based oscillators in Europe at a fair price. Crystek is an alternative but Mouser don't offer 22.5792 MHz parts in small Q (up to 100 pcs.); they hunts me down with 360 pcs minimum / order
Any help from you guys will be very appreciated!
L

Last edited by Lorien; 7th August 2010 at 02:48 PM.
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Old 7th August 2010, 03:04 PM   #122
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Default I am

not an ee, and I cannot design the circuits in question. I was listing my requirements for such a device. For oscillators, is there a Crystek distributor in the EU? Perhaps you could obtain samples? Hear in the US parts can be gotten from Mouser. Maybe not cheap, but I believe there is Tent Labs in Europe, and they distribute high precision XOs. I suggested on board ps regulation, because such regulation needs to be close to the clock to be effective. I still believe that that the raw power from the USB bus can be used, as long as the requirements are around 300 mA or less, and a combination of filtering and regulating the supply is used to reduce the noise from the computer (Ayre successfully utilizes USB power).
If one was designing a module to be sold as a diy board to add to DACs, it would seem to be relatively simple to power it from the USB bus, and to have pads with jumpers on the board to allow the end user to add a dedicated ps if they wanted to.
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Old 7th August 2010, 03:29 PM   #123
jcx is offline jcx  United States
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I've used Analog Devices adum34xx digital isolators between Cypress fx2 USB uC (usb powered) and the ADC data collection SciLab uC (external ps)

likely the USB ULPI byte wide phy interface could be isolated the same way

the hardware effort was relatively low compared to the ~2 man-years of programming time the project has soaked up for drivers and instrument UI and data acquisition/control code spread across 3 processors (PC, Cypress USB controller and SciLab instrument data acquisition controller)

this only works if there is a external digital bus between system parts the only solution for single chips would be serial audio stream digital isolation


the I2C could be isolated with the adum devices but they would introduce some jitter - maybe not a problem with ess Sabre DAC or similar jitter reduction in the audio DAC path

some claim sub nS jitter isolation is practical - http://www.nve.com/Downloads/ab17.pdf claims 30pS jitter
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Old 7th August 2010, 06:37 PM   #124
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Default maybe I

am confused, so experts please correct me if I am wrong:
If one chooses to isolate the incoming USB data, jitter (at that point) should not matter, all that matters is having sufficient bandwidth to transmit the data:
Asynchronous transfer is managed by code, that prompts the computer when to send data, in order to keep the on chip buffer from over or under running its output. The XO(s) are only relevant on the output of the USB receiver, as long as one uses fixed high precision XO(s) at the output of the receiver, the jitter at that point will be as low as is allowed by the XO. The control code manages the buffer, and assures data in the buffer keeps "in time" with the output.
So there should be no additional jitter caused by the isolation scheme, the isolators just have to have sufficient bandwidth to transfer the data.
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Old 7th August 2010, 11:09 PM   #125
jcx is offline jcx  United States
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sure, if the isolation is between the usb and the digital audio output hardware
currently there are no isolation chips for high speed 480 Mbuad usb signals

In the I2S isolation case the isolator would be after you have properly clocked the audio data stream for the DAC and so could add jitter
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Old 10th August 2010, 03:06 PM   #126
UnixMan is offline UnixMan  Europe
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Quote:
Originally Posted by jcx View Post
In the I2S isolation case the isolator would be after you have properly clocked the audio data stream for the DAC and so could add jitter
couldn't one reclock the I2S after the isolation? I mean putting the clock on the "clean side" and sending it back to the "dirty side" trough isolation as well?
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Old 10th August 2010, 03:08 PM   #127
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Quote:
Originally Posted by Lorien View Post
Could you please tell me to which type of shunt implementations are you referring to? ... or which PSU you consider it would be appropriate for this task?
I'm in process of designing such an application and, for now, I'm stuck in finding a valid source for on-board oscillators. So far, I've tried NDKs but without success (unless I'll buy 1k units) and I'm looking to IQD... my next alternative. It seems that it's hard to find good crystal-based oscillators in Europe at a fair price. Crystek is an alternative but Mouser don't offer 22.5792 MHz parts in small Q (up to 100 pcs.); they hunts me down with 360 pcs minimum / order
Any help from you guys will be very appreciated!
L
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Old 12th August 2010, 12:26 PM   #128
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Thanx Guido, I'll look into your offer!
L
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Old 18th August 2010, 07:37 AM   #129
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I just wanted to say that I am going to be following this thread regularly in hopes of a solution.

Thanks everyone for your contributions.
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Old 18th September 2010, 09:15 PM   #130
SunRa is offline SunRa  Romania
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Take a look at this Rigisystems Interface.

Supported audio sample rates: 32KHz - 192KHz
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16 x 16 channelKanal audio @ 96KHz
additional 2 x 2 channels for digital S/PDIF audio @ 96KHz
8 x 8 channels audio @ 192KHzTransparent 32bit S/PDIF out
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Inclusing complete channel mixer
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36x36 audio channel USBMLINK
USB bus powered option


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