INMP404

APPLICATION INFORMATION

CONNECTING TO AUDIO CODECS

The INMP404 output can be connected to a dedicated codec microphone input (see Figure 6) or to a high input impedance gain

stage (see Figure 7.) A 0.1 µF ceramic capacitor placed close to the INMP404 supply pin is used for testing and is recommended to

adequately decouple the microphone from noise on the power supply. A DC-blocking capacitor is required at the output of the

microphone. This capacitor creates a high-pass filter with a corner frequency at

where R is the input impedance of the codec.

A minimum value of 2.2 µF is recommended in Figure 6 because the input impedance of codecs can be as low as 2 kΩ at its highest

PGA gain setting, which results in a high-pass filter corner frequency at about 37 Hz. Figure 7 shows the INMP404 connected to an op

amp configured as a non-inverting preamplifier.

Figure 6. INMP404 Connected to a Codec

Figure 7. INMP404 Connected to an Op Amp

GAIN = (R1 + R2)/R1

INMP404

GND

OUTPUT

1µF

MINIMUM

0.1µF

10k

Ω

R1

R2

VDD

AMP

1.8-3.3 V

CODEC

INMP404

VDD

GND

OUTPUT

LINN

LINP

MICBIAS

CM

2.2µF

MINIMUM

0.1µF

Page 8 of 13

Document Number: DS-INMP404-00

Revision: 1.0.