INMP411

APPLICATIONS INFORMATION

CONNECTING TO AUDIO CODECS

The INMP411 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 inMP411 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 4.7 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 17 Hz. Figure 7 shows the INMP411 connected to an op amp

configured as a non-inverting preamplifier.

Figure 9. INMP411 Connected to a Codec

Figure 10. INMP411 Connected to an Op Amp

DYNAMIC RANGE CONSIDERATIONS

To fully utilize the 99 dB dynamic range of the INMP411 in a design, the preamp, ADC, or codec circuit following it must be chosen

and the ADC input of the codec, some gain must be added to the INMP411 output. For example, at the 131 dB SPL maximum acoustic

input, the INMP411 outputs a −13 dBV RMS signal. The full-scale input voltage of a codec may be 0 dBV; therefore, 13 dB of gain must be

added to the signal to match the dynamic range of the microphone with the dynamic range of the codec.

ADC

OR

CODEC

INMP411

GND

OUTPUT

INPUT

MICBIAS

2.2 µF

MINIMUM

0.1 µF

VDD

GAIN = (R1 + R2)/R1

INMP411

GND

OUTPUT

1µF

MINIMUM

0.1µF

10k

Ω

R1

R2

VDD

AMP

1.8-3.3 V

Page 8 of 14

Document Number: DS-INMP411-00

Revision: 1.0.