MCLK rate fluctuating
Hi there,
I'm running an ADAU1701 and have found that my MCLK frequency fluctuates.
Specifically, in master mode, the clock doesn't stay at one frequency. This is leading to a noisy I2S output. I've tried outputting a sine wave and the pitch changes, on top of having a high noise floor.
In master mode, I've also tried taking out the oscillator and used a function generator to generate the clock signal. Surprisingly, the result is the same. Scoping the generator output, I get a clean clock signal. But scoping MCLK from the chip, the frequency fluctuates.
Is this a known or common problem?
Thanks for any help or suggestions.
-- Garry
fluctuation
Audio Signal Processors
mclk
SigmaDSP Audio Processors
frequency
adau1701
Show More
About what percentage fluctuation are you seeing relative to the ideal rate?
It's about 10% to 20%. There is no voltage drift while this is happening.
Hmmmm... That's some pretty large deviation. Normally our devices operate with very low jitter and clock drift (i.e. only a couple of Hz for an MCLK rate of 12.288 MHz). Are you using one of our evaluation boards or your own prototype? If it's your own prototype, let's start looking at the schematic to see if we can find some clues for what might be causing the issue.
What is the source of the MCLK to the ADAU1701? Are you using the oscillator with a crystal resonator? If so, what type of crystal? Quartz crystals, like the ones we use on our boards, have a frequency tolerance of 0.001%. Piezoelectric ceramics like lead zirconium titanate (NOT recommended for use in audio systems) have much higher frequency tolerances of 0.5% or more.
This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.
Thank you,
EZ Admin
Please log in to reply.