I just posted an FAQ about some questions we commonly receive on the TPA3100D2 about its MASTER/SLAVE and SYNC functionality.
We have done some studies on these parts, and put in different SYNC frequencies into two parts and looked for beat noise. We never did find any, so we came to the conclusion that it's not different clocks that cause beat noise, but rather, the amount that leaks thru via poor power supply rejection. Our class-D amps have pretty good PSRR, so we don't see problems with beat noise.
I would be interested in hearing about others beliefs/experiences with beat noise in systems running several class-D amps, or being powered from SMPS. We just don't see it as being a problem with our devices.
Audio Applications Engineering Manager
Dallas, TX USA
One case may cause beat noise: The input signal pick up switching signal of different frequency and amplified by following amplifier. 1) the input amplify stage is non-linear at high frequency, beat frequency is generated. 2) the modulation stage is non-linear, beat frequency is generated. Since the TPA3100D2 is designed with input at one side, and output at the other side, the input is away from output, it should not cause such problems (except very careless PCB layout).
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