This is my cicuit diagram:
The ADC works in master mode , DAC works in slave mode, single-ended output. Master clock is 12.288MHz, the sampling clock is 48KHZ.
The following are my measured under different frequencies of input and output analog signals. Of which the yellow is the ADC input signal, the green signal is the DAC output. Followed by the input signal frequency: 100HZ, 1KHz, 3.4KHz, 5KHz, 6KHz, 10KHZ, 12KHZ, 15KH. Measurement, remove the 4.7uF dc blocking capacitors, that is the figure of C28, C32. In other words, measuring the DAC output without adding any load, is the direct measurement of the output waveform on the pin. Seen by the waveform, DAC output with the input signal frequency signal amplitude decreased significantly. I hope you can give me help to solve this problem. Or can point me in the circuit is unreasonable. Thank you!
I am not sure if this is the cause of your problem, but on the d/s on page 39, there is a note that VCOM needs the following capacitors on it:
C3: 0.1- F ceramic capacitor and 10- F electrolytic capacitor is recommended.
I notice you don't have any capacitance on VCOM. Perhaps this is the cause of your attenuation at higher frequencies.
Audio Applications Engineering Manager
Dallas, TX USA
Thanks for replying me.I am a Chinese,please forgive my poor English.
In the schematic,you may not not you may not notice that VCOM is connected between the GND and the two capacitors ,C31 and C29.And VCOM is connected with AGND through C31 and C29 by nets ta.I think my schematic meet the requirements of datasheet.
I want to know what led to the amplitude attenuation.And I have tried a higher sampling frequency ,setting SCK at 25MHz.,but attenuation still remains.
Thank you for you reply ,and I am looking forward to your next.
Happy new year!
Hi, Kui Xu,
Gong xi fa cai!!!
Did you make any progress in debugging this? I am not sure what might be causing this.
Thanks for your replying ! And happy Chinese New Year!
There was no progress in my project. And I will use a new chip replacing PCM3060.
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