ADAU1701 Full Scale Output Voltage Slightly Low for Full Scale Input Voltage

Jesse4801 Question

Apr 26, 2018 00:00

Hi,

I am using the ADAU1701 DSP and I am passing a full scale input signal (2V RMS) directly through from the external 18k resistor on ADC0 (Pin2) to VOUT0 (Pin46). The issue is that I am finding that the output voltage is 35mV short of 0.9V RMS full scale output of the DAC.

The signal level detector is showing -4dB. If I put in an input signal slightly greater than 2V RMS, the signal meter will go to -3dB etc (see attached screenshot).

I've double checked the hardware. I am sampling at 48kHz. therefore ADC0 and ADC_RES are fitted with an 18k external resistor (+/-1% tolerance) as per the datasheet (see attached schematic snippet).

I’ve also double checked that I am initializing the DAC Setup Register as per page 44 of the datasheet.

That datasheet doesn't specify a tolerance on the full-scale output of the DAC but just states 0.9V RMS as the typical.

Just wondering if the 35mV error that I am getting is within tolerance of the chip or if it is large enough to warrant further investigation of my design?

Kind Regards,

Jesse

Audio Signal Processors

SigmaDSP Audio Processors

adau1701

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DaveThib Reply

Apr 30, 2018 00:00

Hello jesse4801,

It is within tolerance. The gain error on the ADC is +- 11% and for the DAC it is +- 10%. So you are well within the tolerance. Also, keep in mind that your test setup combines both tolerances. The key would be to measure one or the other. It is best to setup an internal oscillator to feed the DACs. Then you have a known full scale output. Then you can measure the gain error on the DACs and then offset that error when measuring the output from the data obtained by the ADC. The internal meters in SigmaStudio are not meant to be precise laboratory level meters but they do a decent job.

The gain error on these parts is wide to accommodate all silicon skews and temperature variations but the inter-channel gain error is quite good.