Data Sheet

ADMP411

Rev. 0 | Page 7 of 12

APPLICATIONS INFORMATION

CODEC CONNECTIONS

The ADMP411 output can be connected to a dedicated codec

microphone input (see Figure 11) or to a high input impedance

gain stage (see Figure 12). A 0.1 µF ceramic capacitor placed

close to the ADMP411 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 11

because the ADAU1761/ADAU1361 input impedance 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 12 shows the ADMP411 connected to an ADA4075-2

op amp configured as a noninverting preamplifier. The

AN-1165 Application Note describes using op amps for

microphone preamp circuits and includes a list of

recommended Analog Devices, Inc., op amps.

Figure 11. ADMP411 Connected to the Analog Devices ADAU1761 or

ADAU1361 Codec

Figure 12. ADMP411 Connected to the ADA4075-2 Op Amp

DYNAMIC RANGE CONSIDERATIONS

To fully utilize the 99 dB dynamic range of the ADMP411 in

a design, the preamp, ADC, or codec circuit following it must

be chosen carefully. For example, the ADAU1761 has a 98 dB

between the microphone and the ADC input of the codec, some

gain must be added to the ADMP411 output. For example, at

the 131 dB SPL maximum acoustic input, the ADMP411 outputs a

−13 dBV rms signal. The full-scale input voltage of the ADAU1761

ADC is 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.

SUPPORTING DOCUMENTS

Evaluation Board User Guide

UG-445, EVAL-ADMP411Z-FLEX: Bottom-Ported Analog

Output MEMS Microphone Evaluation Board

Application Notes

AN-1003, Recommendations for Mounting and Connecting

Analog Devices, Inc., Bottom-Ported MEMS Microphones

AN-1068, Reflow Soldering of the MEMS Microphone

AN-1112, Microphone Specifications Explained

AN-1124, Recommendations for Sealing Analog Devices, Inc.,

Bottom-Port MEMS Microphones from Dust and Liquid

Ingress

AN-1140, Microphone Array Beamforming

AN-1165, Op Amps for MEMS Microphone Preamp Circuits

AN-1181, Using a MEMS Microphone in a 2-Wire Microphone

Circuit

ADAU1761

OR

ADAU1361

ADMP411

GND

OUTPUT

LINN

LINP

MICBIAS

CM

4.7µF

MINIMUM

0.1µF

GAIN = (R1 + R2)/R1

ADMP411

GND

OUTPUT

1µF

MINIMUM

0.1µF

10kΩ

R1

R2

ADA4075-2

1.8V TO 3.3V