I2S slave mode w/o master clock to S/PDIF - diyAudio
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Old 12th August 2013, 12:46 PM   #1
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Join Date: Aug 2013
Default I2S slave mode w/o master clock to S/PDIF

In several occation I've had a I2S signal available inside equipment, where I wanted to pick up the I2S signal and send it outside the equipment as a S/PDIF signal.

Last case was my car radio.

In that case, as well as on some other cases there is no 128/256/512*Fs master clk. Only the 64*Fs bitclk. They probably sample rate convert the signal where it is recieved.

So we're talking a stand-alone slave mode S/PDIF modulator with a clock doubler.
I don't know of a S/PDIF modulator IC that can run in slave mode, and internally double the bitclk to make the double freq for the biphase coding.

I wouldn't make a birds nest construction in the enviroment of a car, and basicly it would be easier and cheaper if there's a small PCB for this for sale on the net.

Do you know a (small) board for this? Or maybe a single chip I've overseen, that can do it? I'm not looking for extreme quality and VCXO's..

Best Regards, Eskil
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Old 17th August 2013, 08:00 PM   #2
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Chip: WM8804 - MCLK source can be a 12-MHz xtal.
PCB: Twisted Pear S/PDIF Transceiver module.
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Old 17th August 2013, 08:13 PM   #3
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Thanks - I studied that one, prior to asking. As I read the datasheet, the 12MHz Xtal and PLL only works in master mode. The PLL does not sync to an incoming bitclk, only to an incoming S/PDIF. Is that a misunderstanding? Doesn't the MCLK have to be synchronous to the bitclk?
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Old 18th August 2013, 01:28 AM   #4
dmills is online now dmills  United Kingdom
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Join Date: Aug 2008
Location: High Wycombe
Xor gate and an RC network to double the clock, then whatever you normally use for a transmitter.

Use a picologic gate and a few 0603 parts, should be nearly trivial to throw together.

Regards, Dan.
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Old 18th August 2013, 08:53 AM   #5
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Hi Dan, thanks for your kind reply.
It's a good point that a XOR gate and a RC Network can make a clock doubler. It will add a lot of jitter to the spdif stream, but that's probably not a problem in my car.
I don't trust a birds nest construction in a car, for reliability/vibration reasons.
Basicly I'm asking if there's a small cheap PCB out there that does it. It seems like there isn't. Thanks everyone for the replies!
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