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PCM1808-Q1: THD+N, Power on reset, Antialiasing filter questions

Yuta Kurimoto
Expert 8280 points
Part Number: PCM1808-Q1

Hello Team,

I got some question from customer. Can you please confirm them?

Q1. Datasheet says

THD+N=-93dB at the condition of VIN=-0.5dB, fs=48kHz, Ta=-40C~125C

How much is the THD+N for below condition?

THD+N= ?? dB at the condition of VIN=-1.0dB, fs=48kHz, Ta=-40C~125C

 

Q2. Please tell me the behavior of internal reset when VDD = less than 2.2V.

* I would like to confirm if there are any concerns when the power up timing between PCM1808-Q1 and the other devices shift

 

Q3. For Pin.13 and 14, The datasheet says there generally used antialiasing low pass filter (100 Ω and 0.01 μF to 1 kΩ and 1000 pF) for the pins. Can you let me know the input condition?

If the filter is 100Ω, 0.01uF, the fc will be 159kHz.

For example, if fs = 48kHz, we should cuts 24kHz or more.

It seems that there is no effect at fc = 159kHz.

Should the filter value be selected according to the input conditions?

 

thanks,

Yuta Kurimoto

  • 0
    TI__Mastermind 23050 points

    Hi Yuta-san,

    We don't provide specs across all operating conditions but the THD+N would be very similar with only a 0.5dB difference in the input signal. 

    When VDD is less than 2.2V the internal power on reset keeps the device in reset.

    The purpose of an anti-aliasing filter is to filter out higher frequency signal components that might alias back into the audio band since the decimation filter response repeats at multiples of the modulator frequency. If for example the modulator runs at 6.144MHz with a 48kHz sample rate there is another passband around 12.288MHz to 12.309MHz. Your goal is to filter out any noise that might be in that higher frequency band. Lower frequency content above 24kHz will be filtered out by the decimation filter, so it is not necessary to design the anti-alias filter for such low frequency.

    Best,

    Zak