Measuring Digital MEMS Microphones: Frequency, Sensitivity and Power Supply Rejection (PSR) Performance
This test suite contains 3 sequences to enable comprehensive testing of digital MEMS microphones.
The first measures the frequency and sensitivity and displays two graphs: absolute level in dBFS, and the same response curve but normalized to 0 dB at 1 kHz.
The second sequence uses the substitution method to test a digital MEMS microphone frequency response with a source speaker that is not or cannot be equalized. The MEMS microphone is simultaneously measuring with a reference microphone , and by subtracting the response of the reference microphone from the DUT microphone the response and sensitivity of the device under test is revealed.
Measuring Digital Microphone PSR (Power Supply Rejection)
The third sequence demonstrates a method for measuring a digital MEMS microphone’s power supply rejection performance (PSR). This sequence measures PSR at 217 Hz (the 217 Hz GSM TDM pulse often of concern) but is easy to modify to test at any frequency. A DC supply with a calibrated AC signal, simulating electrical interference is applied to the MEMS microphone. SoundCheck then records the audio from the DUT, analyzes it with a spectrum analyzer and extracts the RMS energy at the specific frequency of the simulated electrical interference and returns the PSR value. The setting of frequency, waveform type and amplitude of the simulated electrical interference is controlled entirely from within SoundCheck.
