WM7231

Pre-Production

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PP, Rev 3.0, January 2014

6

TERMINOLOGY

1.

Sensitivity (dBFS) – Sensitivity is a measure of the microphone output response to the acoustic pressure of a 1kHz

94dB SPL (1Pa RMS) sine wave. This is referenced to the output Full Scale Range (FSR) of the microphone.

2.

Full Scale Range (FSR) - Sensitivity, Electrical Noise Floor and Power Supply Rejection are measured with reference

to the output Full Scale Range (FSR) of the microphone. FSR is defined as the amplitude of a 1kHz sine wave output

whose positive peak value reaches 100% density of logic 1s and whose negative peak value reaches 0% density of

logic 1s. This is the largest undistorted 1kHz sine wave that will fit in the digital output numerical range. Note that,

because the definition of FSR is based on a sine wave, it is possible to support a square wave test signal output

whose level is +3dBFS.

3.

Signal-to-Noise Ratio (dB) – SNR is a measure of the difference in level between the output response of a 1kHz 94dB

SPL sine wave and the idle noise output.

4.

Total Harmonic Distortion (%) – THD is the ratio of the RMS sum of the harmonic distortion products in the specified

bandwidth (see note below) relative to the RMS amplitude of the fundamental (ie. test frequency) output.

5.

Dynamic Range (dB) – DR is the ratio of the 1% THD microphone output level (in response to a sine wave input) and

the idle noise output level.

6.

All performance measurements are carried out with 20kHz low pass ‘brick-wall’ filter and, where noted, an A-weighted

filter. Failure to use these filters will result in higher THD and lower SNR values than are found in the Acoustic and

Electrical Characteristics. The brick wall filter removes out of band noise.

7.

SLEEP Mode is enabled when the CLK input is below the CLK Sleep Frequency noted above. This is a power-saving

mode. Normal operation resumes automatically when the CLK input is above the CLK Sleep Frequency. Note that the

VDD supply is still required in SLEEP mode.