How The Cdb-Hdr-Meas Works - Cirrus Logic CDB43131-GBK Manual

CDB43131-GBK

4.2 How the CDB-HDR-MEAS Works

Since the noise floor of the APx555 is around –124 dB, and the CS43131 has a DNR of 130 dB, the signal needs to be
amplified to make it measurable. The following image illustrates this issue. In an ideal situation, the –60 dB signal during
DNR tests would yield a total dynamic range of 130 dB. However, due to a higher noise floor of the measurement
equipment, the difference results in a measurement error that hampers performance.
Figure 16 Testing Without CDB-HDR-MEAS
To rectify this issue, the input signal can be amplified (in this case by 13.3 dB). This will also amplify the noise floor;
however, since the noise floor is small compared to the signal, the signal will dominate the amplification. In the figure
below, the signal and noise floor have been shifted up to be at least on par with the noise floor of the measurement
equipment. Now when using the –60 dB signal for the DNR measurement, the full range of 130 dB can be measured.
Figure 17 Testing With CDB-HDR-MEAS
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