I was hoping to get a sanity check on a design I'm doing. I'm trying to build an digital input stage for an amplifier I've been tinkering with the last few years. I want it to be able to read 192kHz/24 bit audio over SPDIF. I'm using the CS8416 chip, but I'm unsure exactly how to connect the SPDIF through it.
I've currently designed it using a 1:1 pulse transformer - the electrical ground in my flat is very noisy, so I feel like this is a good idea. But I'm unsure about the 75R resistor position and the caps on the ground and inputs at the CS8416 (As per the schematic, but the schematic doesn't have an isolation transformer.
If anyone can provide any guidance, please let me know! Thanks. The transformer I'm hoping to use is the DA101C - I'm having a hard time determining if it can do 192kHz though (which I think is 12Mb/s of bandwidth). But it seems to be one a lot of people have used.
Thanks
I've currently designed it using a 1:1 pulse transformer - the electrical ground in my flat is very noisy, so I feel like this is a good idea. But I'm unsure about the 75R resistor position and the caps on the ground and inputs at the CS8416 (As per the schematic, but the schematic doesn't have an isolation transformer.
If anyone can provide any guidance, please let me know! Thanks. The transformer I'm hoping to use is the DA101C - I'm having a hard time determining if it can do 192kHz though (which I think is 12Mb/s of bandwidth). But it seems to be one a lot of people have used.
Thanks
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What @uriy-ch has shown in the first picture is a 110ohm AES/EBU professional interface. If you need 75 ohms (consumer interface), there's no transformer. You could add one if you want, the termiination would be on the secondary side in place of the 110 ohms.
You could use a TOSLINK receiver like PLR135 (16Mbps).
https://www.mouser.com/datasheet/2/143/EVER_S_A0003539347_1-2548683.pdf
Toslink is optical, that won't help for an SPDIF.
Just use the schematic in your post at "figure. 26", connect the center of your coax to the capacitor and the shield to the other side of the primary. No need to connect your coax to ground as the transformer is taking care of that. Replace the 110 Ohm by 75 Ohm.
The transformer doesn't care about your signal being differential or not, it only cares about the voltage difference between both sides of its winding. And it reflects that to the secondary side. As you are using a 1:1 transformer, the impedance at the secondary is reflected 1:1 to the primary.
Just use the schematic in your post at "figure. 26", connect the center of your coax to the capacitor and the shield to the other side of the primary. No need to connect your coax to ground as the transformer is taking care of that. Replace the 110 Ohm by 75 Ohm.
The transformer doesn't care about your signal being differential or not, it only cares about the voltage difference between both sides of its winding. And it reflects that to the secondary side. As you are using a 1:1 transformer, the impedance at the secondary is reflected 1:1 to the primary.
In the PCB layout AGND is to be tied to the system common GND plane (on the opposite side of the PCB) at CS8416 pin-7 with a via, and that via would be the one and only place where AGND and GND join.
Place that via close to the pin-7.
I made a little sketch and hopefully it explains. The four traces leading out to the transformers can be 10 or 20 inches long as long as they are sized to have 75R impedance. And yes, the DA101C is more than capable of 192Khz/24bit S/PDIF.
Edit: the 3 SMD components off pin 6 are, from right to left, C 100n, C 1uF, L ferrite bead.
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