4 Quantization Noise Density for Each Microphone

The 1-bit modulator in the digital PDM microphone has architecturally high quantization noise that limits the PDM microphone SNR and dynamic range compared to what can be achieved with an analog microphone along with multi-bit ADC. The TLV320ADC51x0/PCM51x0-Q1 uses a multi-bit modulator which has in-band quantization noise up to 15 times lower, and better, than the typical 1-bit modulator. Moreover, the total quantization noise of the TLV320ADC51x0/PCM51x0-Q1 multi-bit modulator is 30 times lower than the total typical quantization noise of a 1-bit PDM modulator. The high quantization noise in in-band has worse voice recognition, and every 6 dB improvement in microphone and system performance can be improved by the record distance and doubled sensitivity.

The higher total quantization noise of a 1-bit PDM modulator drastically limits the maximum high amplitude signal that it can record with low distortion compared to a multi-bit ADC. This limitation makes the digital microphone the incorrect choice to be used for sound bars, HDTVs, professional speakers, and so forth, where the microphone is required to record very loud speaker output with low distortion so that the echo cancellation can be achieved with good quality, and voice command detection successfully is enabled.

Figure 4-1 shows the typical quantization noise density difference in all bands for the 1-bit PDM modulator and multi-bit analog modulator.

Figure 4-1 Quantization Noise Density