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ADAU1979 Output Data Format

Question asked by analog123 on Jul 13, 2018
Latest reply on Jul 16, 2018 by analog123

Can you please provide a description of the output data format for the ADAU1979? In this post, it specifies that data is two's complement, and I do not see anything in the datasheet regarding the format. We cannot seem to calculate the appropriate voltage output based on the data read from the ADC, which we calculate as:


Vout = ADC_data * 3 / 2^23 + 1.5


We assume 3 V as the full scale voltage given the bias at 1.5 V, but could you please verify 3 V vs 3.3 V?



In particular, our output is gained by ~0.47. This appears to match the gain of the internal input circuit, which is set at 0.4445 (Fig. 16). Is this input stage gain not accounted for by the chip before outputting the data or do you suspect we have some other issue? We verified that the Post ADC Gain is 0 dB. 


Lastly, could you provide a description of the signal path internally? Does it follow:


input circuit (gain = 0.4445, instrumentation amplifier?) --> anti-aliasing low pass filter --> ADC conversion --> Post ADC gain (i.e., multiplication and not some other hardware gain)