Specifications

AC65/AC75 Hardware Interface Description
3.15 Audio Interfaces
s
AC65_AC75_HD_v01.002 Page 59 of 117 2006-10-30
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3.15.2.1 Single-ended Microphone Input
Figure 24 as well as Figure 47 show an example of how to integrate a single-ended microphone input.
R
A
has to be chosen so that the DC voltage across the microphone falls into the bias voltage range of 1.0V to
1.6V and the microphone feeding current meets its specification.
The MICNx input is automatically self biased to the MICPx DC level. It is AC coupled via C
K
to a resistive divider
which is used to optimize supply noise cancellation by the differential microphone amplifier in the module.
The VMIC voltage should be filtered if gains larger than 20dB are used. The filter can be attached as a simple
first order RC-network (R
VMIC
and C
F
).
This circuit is well suited if the distance between microphone and module is kept short. Due to good grounding
the microphone can be easily ESD protected as its housing usually connects to the negative terminal.
R
A
= typ. 2k
R
B
= typ. 5k
R
VMIC
= typ. 470Ohm
C
k
= typ. 100nF
C
F
= typ. 22µF
V
MIC
= typ. 2.5V
V
bias
= 1.0V … 1.6V, typ. 1.5V
Figure 24: Single ended microphone input