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AIC3204 Quantization

Martin Hofmann
Prodigy 80 points
Other Parts Discussed in Thread: TLV320AIC3204

Hello

I have a question concerning the TLV320AIC3204 codec on the eZdsp C5515. I use the codecs' ADC to measure amplitues of an audio signal in 16-bit mode. This is part of a simple dual phase lock-in amplifier for testing reasons.

When I draw a graph showing the average values of different amplitudes I see a linear relation. That is what I expected. However, the standard deviation increases linearly with higher amplitudes of the input signal.

Are the quantization steps getting larger with larger amplitudes or is there some kind of non-uniform coding of the AIC3204 codec? I couldn't find anything in the datasheet and I just want to be sure. Thank you for your help.

Regards,

Martin

  • 0
    TI__Mastermind 46195 points

    Hello Martin,

    The coding for AIC3204 is linear. In portable audio applications, performance is measured with THD+N/SNR parameters, while an FFT shows the amplitude an associated harmonics. DNL and INL errors are not directly specified. As the amplitude reaches 0dBFS and beyond, a sinusoidal input will start distorting up to ~3dBFS, which is the max amplitude possible (e.g. square wave), assuming 0dBFS is referenced to a full-scale sinusoid (by definition). In the AIC3204, the 0dBFS input limit is associated with a full-scale sinusoid at ~500mVrms, assuming a single-ended configuration, 10kohm input resistor and 0dB MicPGA gain.

    Regards,

    J-

  • 0 in reply to J-
    Prodigy 80 points

    Hello J,

    thanks for your reply. My input signal was a noise-free sinusoid with a frequency of 4 kHz from a function generator. I varied the amplitude of this signal from 0 to 200 mVrms. How can I interpret the THD to my varied input signal?

    I also changed the function generator  and I get little bit smaller errors.

    Regards, Martin

  • 0 in reply to Martin Hofmann
    TI__Mastermind 46195 points

    Hello Martin,

    Audio is typically analyzed with an audio analyzer, such as an Audio Precision.

    Depending on the signal generator, it might be possible that the amplitude steps degrade with amplitude. Perhaps close to 10mV, the error might be +/-0.1mV and close to 200 mV the error might be +/- 1mV, as an example.

    Regards,

    J-