In this test case, we add gain from the audio device to -1dBr of the device full-scale and check the performance. This -1dBr input is used to avoid clipping due to gain error. In the TAX5XXX device, the gain is set through Digital Volume (DVOL) and for ADC6120 device, the gain is set through the PGA register.

From the maximum input level of the microphone measured previously, we apply +31dB to increase the record audio path level to -1dBr of input full-scale.

Figure 3-8 TAA5212 Captured of Maximum mic Input With +31dB Gain

Figure 3-9 ADC6120 Captured of Maximum mic Input With +31dB Gain

Figure 3-10 ADC6120 Captured of Maximum mic Input With +31dB Gain and DRE Enable

In TAX5XXX, adding the DVOL gain to the input level does not change the THDN level, but in the ADC6120 device PGA gain improves THDN. This improvement is because the ADC noise is less dominant than the PGA thus THDN is better.