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PCM1809: My customer has some Questions

R.Fukunaga
Expert 2485 points
Part Number: PCM1809

Tool/software:

Hi all,
I have the following questions about using the PCM1809.

I am currently using the PCM1809 with the following configuration to check the output data.

1) It takes about 185 ms from the input of the BCLK and FSYNC waveform to the value I want to output. Is this normal?

2) Why does this happen? Is there a way to reduce it?

3) Can the CR filter miniature version used in SAR be used to improve it? Or can the decision filter be used?

4) Is there a disadvantage as a side effect of filtering? (Effect on gain, effect on DC offset, etc.)

5) If there is an effect on DC offset, can it be removed by High Pass Filter?

6) The Vref value is set at 2.75v.
When collecting the dump data of PCM1809, it seems that the output is about 10% lower than the sensor output. There is a cable in the middle, so it attenuates slightly (2~3%). What is the cause?
Also, when Vref=2.75v and a sine wave of 3v is input from FG, the dump data shows a sine wave of 3v. What does this Vref mean?

Best Regards,

Ryusuke

  • 0
    TI__Mastermind 27280 points

    Hi Ryusuke,

    1/2. Each device in your signal chain has some degree of latency. 185ms is the total time between sensor input and TDM/I2S output. Since this device is hardware controlled, the ability to optimize latency is very limited. You can either operate in linear phase mode or low-latency mode and note the difference in time.

    3/4. Decimation filter enabling does have an effect. Your trading speed for phase accuracy (some phase distortion) and slightly more passband ripple as shown in section 6.3.6.2 of the datasheet.

    5. Yes, see section 6.3.6.1

    5. Vref if the internal voltage reference that allows the ADC to function/convert data. Section 6.3.5 of the datasheet explains further