S/PDIF to SPORT receiver PCB - diyAudio
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Old 11th September 2008, 04:43 AM   #1
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Default S/PDIF to SPORT receiver PCB

I'm looking to add a S/PDIF receiver to my blackfin DSP kit and I'm not finding anything that fits. There's some well designed S/PDIF DACs but that's more than I need. If anyone knows of a good quality module please let me know before I waste too many hours duplicating.

Anyway, I working up a CS8416 receiver into a 2" x 4" PCB that will plug onto the Blackfin EZKIT expansion bus. Essentially a fully featured S/PDIF input with an I2S bus programmable by SPI.
A few of my pet must-haves: individual regulators for every IC power pin. (If the chip designer bothered to give us multiple pins, we shouldn't tie them together) complete ground plane, controlled impedance connection for high speed buses with proper drive & termination, surface mount, consideration of EMI issues.

I'm going to build a small number for my own needs but would be willing to share if there's any interest in peer/design review. Quantity discount brings the PCB cost down.
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Old 11th September 2008, 12:01 PM   #2
gmarsh is offline gmarsh  Canada
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Sounds like a good idea. I don't have a huge need for a board like this, but I'll certainly throw a bit of help your way. What layout program are you using? If you're using Eagle, I've got part libraries for the Samtec headers and a couple example boards created which use the BF533 expansion headers.

A couple of suggestions:

- Add DIP switches which allow you to connect the CS8416 bit clock and FS outputs individually to the TSCLK0/TSCLK1/RSCLK0/RSCLK1 and TFS0/TFS1/RFS0/RFS1 signals.

- Perhaps even have DIP switches selecting whether the CS8416 drives DR0PRI or DR1PRI.

- Add a spot for a wire, so you can take RMCK from the CS8416 and bring it up to the EZKIT's main board and use it as the MCLK input for the AD1836 chip.

These changes will let you run the onboard codec synchronously with the CS8416's audio input source.
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Old 11th September 2008, 05:29 PM   #3
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Good call on the RMCLK pad - added that.

The DIP switch selector is a great idea! - that'll certainly make it useful to more people.

So it looks something like this:
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Old 11th September 2008, 05:30 PM   #4
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and this.....
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Old 11th September 2008, 05:37 PM   #5
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A couple of things I need to research unless anyone knows:

Do the GPO pins have enough drive to source 5mA for the LEDs? I see the logic level specs rated at 3mA but there's no spec for current limits.

Spec says you can either float the unused S/PDIF lines or tie to ground. Has anyone seen any performance difference? Thoughts?

OK to float OMCLK?

Anyway, thanks gmarsh for some good comments. Oh and BTW, I'm using Orcad.
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Old 11th September 2008, 06:45 PM   #6
Johnix is offline Johnix  France
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My 2 cents,

Cirrus CS8416 has a very bad behaviour with unlocks on input streams with unstable pll. (recovered master clock glitching from ex 256fs nominal value to undetermined one => DACs loves that )

I do not recommend to use this chip at all for this kind of application.
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Old 11th September 2008, 07:01 PM   #7
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That's strange. The CS8416 is the ONLY receiver Cirrus currently makes. I find it hard to believe they obsoleted the only ones that worked.

Can you elaborate a bit?
What connection were you using - RCA/XLR/optical?
Was this a DIY board or a store bought product?
What was the source?

I'm not connecting to a DAC so I'm not using RMCLK but I assume that if RMCLK is broke then the SDAT/BCLK/LRCLK lines are broke too?
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Old 11th September 2008, 10:29 PM   #8
gmarsh is offline gmarsh  Canada
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On the schematic...

The way you've got the AES/EBU input set up, the input signal level can't be greater than 3.3Vpp. Most AES/EBU sources I've seen are 5Vpp square wave (loaded with 110 ohms) and bandwidth limiting pushes the edges up higher than that, to 6-7Vpp. You'll want to divide that down or you might pop the '8416.

I've never encountered any disconnected-input-weirdness problems with a CS8416, though I've never actually designed anything where the input wasn't directly fed into a SRC chip.

If you want to move away from the '8416, I recently used the DIX4192 transceiver from TI and I can't say anything bad about it. It has four real, actual differential inputs. And a transmitter (heh). It does require a +1.8V supply, but in your application I don't think that's a problem
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Old 12th September 2008, 02:16 AM   #9
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more good stuff.
So a Pi network on the front end should provide infinite balanced adjustability. I'm going optical so I hadn't thoroughly flushed out the transformer input. I set it for just over 13dB attenuation (seeing as you get 6dB for an impedance matched connection) with standard resistors.

Talking of impedance matched - what do you think about 192KS/s (6MB/s+) through a DIP switch - not exactly impedance controlled. Is this a jitter nightmare about to happen or is 6MHz sufficiently slow?


Anyone else had lock problems with the CS8416? Any votes to abort?
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Old 12th September 2008, 11:16 AM   #10
gmarsh is offline gmarsh  Canada
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You could use 74**125 chips with the outputs enabled/disabled by DIP switches, instead of dip switches directly - however, the additive jitter of the gate would probably be more than anything caused by an impedance mismatch through a DIP switch.

The SMT slide types like those on the EZKIT itself are pretty low inductance. IIRC, the EZKIT actually runs a couple of memory interface signals through DIP switches..
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