AS3415 datasheet(22/102 Pages) AMSCO

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AS3415/AS3435 – 22

ams Datasheet, Confidential: 2014-Jun-13 [v1-30]

De tail ed De sc rip t ion

Figure 21:

Microphone Cut-Off Frequency Overview

Microphone Cut-Off frequency overview: This table shows an overview of the different cut-off frequencies with

CAC=10μF, CMIC= 2.2μF and RMICIN=22kΩ of the microphone preamplifier.

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:

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:

The simulated frequency response for the microphone

preamplifier with the recommended component values is

shown in Figure 22.

Microphone Gain

Fcut-off

0dB

22.2kΩ

0Ω

1.7Hz

3dB

15716Ω

6484Ω

1.9Hz

6dB

11126Ω

11074Ω

2.2Hz

9dB

7877Ω

14323Ω

2.7Hz

12dB

5576Ω

16623Ω

3.5Hz

15dB

3948Ω

18252Ω

4.5Hz

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

Filter Simulations:

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.

4 C

()

⋅⋅ ⋅

⋅

4 C

⋅⋅ ⋅

⋅

---------------------------------------------------------------------------------

cut

off

–

π R

MICIN

MIC

⋅⋅

⋅

---------------------------------------------------

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