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PCM3168A: Differential input voltage rms vs single-ended signal rms

Shifali N
Expert 2040 points
Part Number: PCM3168A

Hi ,

I am using PCM3168PAP in my design. I am using audio input signals in balanced mode.

1. Table 8.3 of datasheet shows Differential input signal rms value and single-ended input signal rms value. What is the difference between them.

2. Whether Analog Output Voltage =8Vpp same as differential output voltage swing.

3. What is  Digital filter roll-off control. What is the use of the same.

4. What is the maximum rms analog input value that can be given to Audio Codec after which distortion can be observed in Audio output.

5. During my testing with Audio Codec, I am observing that distortion happens when turning audio input signal beyond 1.5V rms then goes away when turning the generator down to 1.5V RMS. What may be the reason for the same.

  • 0
    TI__Mastermind 23015 points

    Hi Shifali,

    1) A single ended input has the signal pass to the positive input while the negative input is ground. A differential signal has an inverted copy of the original signal sent to the negative terminal. This results in double the voltage scale while each pin still sees the same original voltage i.e. each pin only sees 1Vrms but the resulting measurement is 2Vrms.

    2) Yes those are the same

    3) The DAC has a digital filter to remove quantization noise. You can see in section 8.15.2 that the filter curves have two options: slow or steep, depending on your needs. Each filter has different trade offs, such as a wider passband but a worse ripple for the steep filter.

    4) The full-scale input voltage is typically 0.2*VCCAD1 for single ended inputs and 0.4*VCCAD1 for differential inputs.

    5) 1.5Vrms might happen to be the level that distortion begins to appear. That specifically depends on your physical set up, but it is tied to the full scale voltage.

    Best regards,

    Jeff

  • 0 in reply to Jeff McPherson
    Expert 2040 points

    Hi Jeff,

    In continuation to the above query, what is the difference between Analog Input level and Full scale input voltage. 

    2. What will happen if we give input voltage beyond the full-scale input voltage level.

  • 0 in reply to Shifali N
    TI__Mastermind 23015 points

    Hi Shifali,

    The analog input level is the voltage value of the analog signal applied at the input, while full scale input voltage is the largest signal amplitude that can be delivered to the analog to digital converter before the signal is clipped in its digital output representation. Therefore, if we apply input voltage past the full scale input voltage level, the output signal will be clipped.

    Best regards,

    Jeff