Other Parts Discussed in Thread: PCM1792
Hello,
First of all, the LMK04803 is a fantastic chip! Lock and holdover work very well to get a consistent signal with very little jitter at the CLKout ports. Even if the reference signal at CLKin has terrible jitter and frequently initiates holdover.
The jitter of the output signal is very low, but unfortunately there are no clean square wave signals. At 2.8224 MHz the signal at CLKOUT_2 is somewhat ok, but with the rising edge at the top and the falling edge at the bottom, it has an obliquely flattened area (please note blue circles). The oblique flattened area extends with increasing frequency, 12.288 MHz. At 24,576MHz, it is an ugly sawtooth signal.
Due to the subsequent circuits, the CLKout ports are operated in LVCMOS mode. The trace of the measured signals CLKOUT_2 lies on the top of the board, the trace lengths are very short and there are no Vias. Therefore, I suspect a faulty termination of the CLKout ports. But you may also know other reasons.
Unfortunately, the LMK04803 datasheet gives no recommendation regarding the termination of the CLKout port in LVCMOS mode and my schematic looks as follows:
Best regards
Andreas Nicklas
