DocID026988 Rev 1

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AN4598

Designing the circuit

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Designing the circuit

A typical pre-amplification circuit is shown in Figure 2.

Figure 2. MEMS microphone amplification circuit

R4 and R5 are used to generate a voltage reference to bias the input common mode voltage

of the op amp at Vcc/2.

C5 allows the noise of the power supply (and of the equivalent R4 and R5 resistors) to be

reduced. Generally, this noise would be amplified by the op amp.

R6 and C6 create a low pass filter which also helps to reduce noise, resulting in an overall

second order, low-pass filtering.

R1 and C1 allow AC coupling of the microphone signal. The op amp is DC biased by Vcc/2

and in AC i.e. above ~1/2π R1C1 (16 Hz) its input receives the microphone signal.

Note that if the op amp is used with a dual supply configuration, ground is used as the input

common mode voltage (R1 is directly connected to ground).

R2 and C2 create a high-pass gain so as not to amplify the DC biasing of the op amp