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Part Number: PCM4204
We observe that the THD vs. frequency performance varies between channels while SNR stays the same. Is this expected, and if so, what influences the variations in THD performance?
Regards,Collin WellsPrecision ADC Applications
The large signal THD+N matching for the PCM4204 is limited. There is always a several dB difference between the channels, even with a careful PCB layout and good reference decoupling. The PCM4204 includes two separate reference circuits, one for Channels 1 and 2, and one for Channels 3 and 4. Matching the absolute accuracy between the two references is difficult.
The best way to guarantee good THD+N performance (understanding that matching all four channels is near impossible) is to use low ESR capacitors for the reference decoupling caps and to reduce the area of the reference return loop to a minimum. We use low ESR tantalum and X7R ceramic chip caps on the PCM4204EVM board.
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