SPDIF output impedance of PCM2704C

Hi, Ben,

Welcome to e2e!!!

I am going to move your post to the Audio Converter forum.

-d2

Ben,

Usually some impedance matching is needed along with a transformer, the SRC4392 EVM User Guide shows an example in the schematic.  (http://proddms.itg.ti.com/stage/lit/ug/sbou038/sbou038.pdf)

Commercial S/PDIF connector (cinch) use lower voltage than TTL. Usually about 1V and impedance 75R. I use 75176 RS422 driver with voltage divider. For DC current isolation you can use serial capacitor. For galvanic isolation you can use pulse transformer. You can inspire on my page: http://www.pavouk.org/hw/modulardac/en_pcm2706i2s.html

Dear Pavel,

I am trying to design an S/PDIF interface for a Class D amplifier in which Modulation is done with a Digital Signal Processor. I found you design. I wish to know why u added the 75176 IC in your design. I wish to also use the 24.576MHz crystal as indicated in the Datasheet for DIR9001

Any advice?

Hi Sydney, I used SN75176B for conversion of voltage levels. Pin RXIN of DIR9001 accept TTL level. This level is usually used only internally like CDROM S/PDIF output. For external use is used optical S/PDIF usually called TOSLINK or consumer S/PDIF which is unbalanced, use CINCH connector and have impedance 75R and voltage 0.6V p-p. Professional S/PDIF sometimes called AES3 is balanced, use XLR connector and have impedance 110R and voltage 2-7V p-p. Optical receiver from TOSHIBA or SHARP can be directly connected to RXIN pin, because it has TTL level output. DIR9001 accept 3.3V and 5V TTL level on this pin. For electrical input is needed some voltage level converter. I used SN75176B because it was for me available and it is cheap. It accept on the input voltage from -7V to 12V and it has sensitivity 200mV. Output is in TTL level. S/PDIF is electrically very similar to RS422/RS485 bus. Why not to use chip, which is specialized for this use :-)

About crystal. I didn't use them, because I used clock signals reconstructed from S/PDIF by internal PLL. If I remember that if clock from S/PDIF source differ with clock from crystal, that there will be "slip". Sometimes lost sample or doubled sample. I don't remember exactly how is solved data buffer in DIR9001. Maybe some other tell you more.

Best regards, Pavel.

Hello Pavel,

Thanks for your reply. It is really helpful. As for the Pulse Transformer, I am thinking of using just one DA102C since I can easily get it. Will it work exactly as the one you used in your design? Also, I can see that you didn't use PIN9 (CLKST) any reason for that because in the Datasheet for DIR9001 it is being used.

I am using only the S/PDIF (AES3) input.  I have attached an adapted form of your schematic here.1411.SCHEMATIC.docx

Thanks once more for the tips while looking forward to read from you.

Kind regards

Sidney

Hello Sidney,

if you mean this project: http://www.pavouk.org/hw/modulardac/en_dir9001spdif.html that it will work with DA102C.

CLKST output is not useful for me.

If you will use S/PDIF (AES3) XLR input that you must use other value of termination resistor. 110R instead 75R.

Best regards, Pavel.

Hello Pavel,

Thanks for your mail. In my design, I am using S/PDIF digital Audio and Analog audio inputs. I have to convert the Analog input  to Digital using ADC and the S/PDIF Digital input is sent to DIR9001 through I2S.  My ADC has a maximum Sampling Frequency of 192KHz, so I want to convert the Sampling frequency of 96KHz of DIR9001 to 192 KHz. I intend to use the Sampling Rate Converter SCR4190. I have attached here a Block Architecture of my Design.

I would appreciate if you can give me some advice

Kind regards

Sidney

6201.ARCHITECTURE FOR INTERFACE.pdf

Helo Sidney,

I haven't experience with sampling rate converters because I am not fan of resampling. I usually want to play data how they are. Also I2S bus is universal and for example DAC with I2S input accept samples in wide range. Standard I2S can have 16bits to 32bits and 22.050kHz to 384kHz. From your project I don't know what you plan to do with I2S bus signal and if resampling is really needed.

Hi Sidney,

You have two options. You can use other S/PDIF receiver like CS8416 or WM8804 which support 192kHz. For 192kHz is usually not possible to use optical S/PDIF, because it is not fast enough. Electrical input can be used.

Second option is to use 96kHz also for ADC.

Hello Pavel,

I wish to find out if this projects

http://www.pavouk.org/hw/modulardac/en_cs8416spdif.html

Can the SPDIF input accept both CD player (44.1kHz)  and   Digital audio tape DAT  (48 kHz) signal as inputs. Because from my understanding of SPDIF, it allows the data to be run at any rate, and encoding the clock and the data together using Bi-Phase Mark Coding.

Kind regards

Hello Sidney,

There is only one transformer in circuit, but I created PCB universal, because there are two transformer pinouts. It depends on you which transformer is available for you.

Best regards. Pavel.

Yes, you are right. S/PDIF receiver accept signal in a wide range of sample frequencies. DIR9001 up to 96kHz and CS8416 with worse jitter up to 192kHz. Also CS8416 doesn't need external bus receiver, because it is embedded in a chip.

Thanks Pavel, I am designing a Class D amplifier with S/PDIF input and DSP for modulation. So I want to use part of your design so I wanted to know if your design can accept but 44.1KHz and 48 KHz as inputs without making any changes. The maximum sampling rate is 192KHz

Kind regards

Yes, it accept both frequencies. Data are sent with same frequency to the I2S bus output.

Best regards, Pavel.

Hi Sidney,

I haven't experience with sample rate converters.

About I2C versus SPI. In my opinion it doesn't matter if you will use I2C bus or SPI bus. In both cases you will get same functionality. It depend mainly on used processor and neighbour chips which must be driven.

Best regards, Pavel

Hi Sidney,

for reset of CS8416 you need MCP130T, not MCP120T because pull-up resistor.

Solution with CS8416 and SRC4190 probably will work.

You can in Eagle create your own parts library, copy to them part with same package and edit pin names.

I found that Eagle drawing of SRC4190 is available at http://www.farnell.com

Best regards, Pavel

Hi Sidney,

For 3.3V supply voltage you need to use other version of MCP130T-300 or -315.

You can't connect crystal directly to the RCKI input. It has LVTTL input. You must use Crystal oscillator with LVTTL output or you can use system clock from I2S input.

Best regards,

Pavel

Hello Pavel,

Please I would like to know how you tested your design for the project "CS8415 S/PDIF Decoder" to check if it fulfilled the requirements for the Sampling Frequency and number of bits. 

Kind regards

Sidney

Hello Sidney,

I don't know what exactly you mean. I tested CS8416 decoder with S/PDIF signal from computer and connected DAC via I2S. When It works that I verified frequency of SCK, LRCK and BCK output if it is corresponding to expectation. For example for 16bits/44.1kHz LRCK will be 44.1kHz, BCK 2.8224MHz and SCK 5.6448MHz or 11.2896MHz depend on RMCK (SCK) setting.

Best regards, Pavel

Thanks Pavel, You have given the answer I expected.

Kind regards

Sidney