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Compiler/PCM1863: About PCM1863 input connection and SNR

user3680879
Intellectual 390 points
Part Number: PCM1863
Other Parts Discussed in Thread: PCM1803

Tool/software: TI C/C++ Compiler

Hi, Mr. Diego,

We got 2 questions about PCM1863

1. For the single end input connection, like the example design in TIDA-01470,  when the VINL1/R1 connecting to the ADC1/2 , must I connect the VINL2/R2 to GND, or just left it float ?  If so , it is just like the differential diagram.

2. For the SNR in D/S page 12, it is  about 110db in typical but 97db in MIN(SE will lower for 4db), so 13db variant. Comparing to the PCM1803, it is  about 103db in typical and 100db in MIN, so just 3db variant. Whcih one is the winner when more concern about the SNR or dynanmic range?

Best Regards,

James J.

  • 0
    TI__Guru 57800 points

    Hi, James,

    Please refer to below comments

    1- If the PCM1863 inputs are configured in Single-ended mode, you can keep both VINL2/R2 floating as they will not be used for this configuration.

    2- The PCM1803 is a quite old device,  so I would like to recommend to use the PCM1863. Overall, the performance of PCM1863 is better, you can compare the dynamic range of both parts on the  Typical characteristics plots of the datasheets.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Intellectual 390 points

    Hi, Mr. Diego,

    Thanks a lot for your so soon and professional  reply！

    1. We are still worry about the 13db deviation of the  SNR in MIN and typical case, versus the 3db in PCM1803 case. We can't image what is the condition for such huge deviation for PCM1863. Would you give us more detail about it? Actualy we worry about the final SNR performance deviation introduced by the ADC.

    2. About the THD , the number is -87db in PCM1863 case and -95db in PCM1803 case. And there have a sharp turnover point near 0db input in the THD plot for PCM1863, versus the flat  bottom in PCM1803 plot. Can we say the PCM1863 is more easy to degard its performance when in large signal input condition?

    3. Could your give us some advice on the detail to evaluate the SNR or THD in the practical way in our lab  without the special instrument?

    Best Regards,

    James j.

  • 0 in reply to user3680879
    TI__Guru 57800 points

    Hi, Jim

    The deviation for the SNR performance is result of the test solution, but all the ICs distributed should be at 110dB point. The PCM1863 supports wider input ranges than the PCM1803, which makes it flexible to support wider input signals, at expense of a degradation on the THD at higher input levels. As reference, the full-scale single-ended voltage for the PCM1803 is 3Vpp (1.06Vrms), while the PCM1863 supports 2.1Vrms(5.93V), which is about 6dBFS difference.

    Unfortunately, without proper test equipment it is complicated to measure THD, SNR and other important performance parameters. For THD, the only way I can imagine is to listen to the recording signal and determine if the performance is fine for the end-application. SNR may be determined by inputting a full-scale signal to the device under test, get the output value as reference and then remove the input and capture the "silence" output value, after that, compare it against the full-scale output. Please note that for certain results, it would be required to do tests with a proper audio analyzer. 

    Regards,

      -Diego Meléndez López
       Audio Applications Engineer