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AS3418

Functional Description

Datasheet

• PUBLIC

DS000507

• v4-00 • 2020-Jan-23

│ 15

Microphone Gain

fcut-off

18dB

2795Ω

19405Ω

6.1Hz

21dB

1979Ω

20221Ω

8.4Hz

24dB

1400Ω

20800Ω

11.5Hz

27dB

992Ω

21208Ω

16.3Hz

30dB

702Ω

21498Ω

22.7Hz

It is important when doing the ANC filter simulations to include all microphone filter components to

incorporate the gain and phase influence of these components. In the cut-off frequency overview,

capacitor CAC was defined as 10µF which results in a rather low cut-off frequency for best ANC filter

design. If a different capacitor value is desired in the application, the following formula defines the

transfer function of the high pass circuit of the microphone preamplifier:

Equation 2:

|��| =

√4 ∗ ��

2 ∗ ��2 ∗ (��

1 + ��2)

2 ∗ ��2 + 1

√4 ∗ ��

2 ∗ ��2 ∗ ��

2 ∗ ��2 + 1

The simplified transfer function does not include the high pass filter defined by CMIC and RMICIN.

With the recommended values of 2.2µF for CMIC and 22kΩ for RMICIN this filter can be neglected

because of the very low cut-off frequency of 1.5Hz. The cut-off frequency for this filter can be

calculated with the following formula:

Equation 3:

��−�� =

2 ∗ �� ∗ �� ∗ ��

The simulated frequency response for the microphone preamplifier with the recommended component

values is shown in Figure 12.

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