What is a digital microphone?

A digital microphone needs to receive analog audio data and convert it to digital data, which is usable for digital electronics. Let’s look at how we can accomplish this using Pulse-Density Modulation (PDM).

What is PDM?

A PDM signal is captured by a 1-bit analog-to-digital converter (ADC) that receives an analog waveform and encodes its output as a string of digital pulses, as shown in Figure 6.1. When the pulses are denser over a period of time, they represent larger values. In Figure 6.1, we see a signal from the testbench as a sine wave. The following signal shows an example of what a PDM form of that waveform might look like:

Figure 6.1: PDM waveform example

The advantage of this type of signal is that we only need a single wire to transmit the information since audio is limited to about 24 kHz and our clock rate will be orders of magnitude above this.

With the basics of digital microphones and PDM, let’s now...