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Optical Digital Output Signal Quality Check

Created 30 Oct 2009

Question:

We have a device that takes an S/PDIF signal from its TOSLINK input and converts it to I2S. When we connect the optical digital output port of the SYS-2722 to the DUT and set the generator to produce walking zeros, they aren’t seen on the I2S output. How can I verify the quality of signal at the TOSLINK output of the SYS-2722?

Answer:

You can easily check the quality of the signal on the TOSLINK output by looping a cable from the optical digital output back to the optical digital input. To observe, for example, a walking zeros pattern, set the Digital Generator and Digital I/O panels as shown below. With an output sample rate of 48 kHz and the Samples/Step control set to 48 k, the zeros will “walk” at the rate of once per second.

The SYS-2722 has built-in loopback capability for the analog and AES digital outputs. This internal loopback is fundamentally the same as connecting an external cable. In the case though of the TOSLINK optical digital connections, the internal loopback signal is taken before the optical transmitter and returned after the optical receiver. Therefore, connecting an external cable is necessary to include the optical transmitter and receiver in the loop and verify the quality of the optical signal.

DGEN panel; set for Special Walking Zeros waveform at 48k steps.