Table of Contents
Advertisement
AC75 Hardware Interface Description
Strictly confidential / Preliminary
3.15.2.1
Single-ended Microphone Input
Figure 24 as well as Figure 46 show an example of how to integrate a single-ended
microphone input.
R
R
A
C
V
Bias
R
Figure 24: Single ended microphone input
R
has to be chosen so that the DC voltage across the microphone falls into the bias voltage
A
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
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
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.
AC75_HD_V00.202
VMIC
R
VMIC
A
MICPx
F
MICNx
C
K
B
AGND
Page 65 of 120
R
= typ. 2k
A
R
= typ. 5k
B
R
VMIC
C
= typ. 100nF
k
C
= typ. 22µF
F
V
MIC
GSM module
V
bias
and C
).
VMIC
F
s
= typ. 470Ohm
= typ. 2.5V
= 1.0V ... 1.6V, typ. 1.5V
27.04.2006
K
Advertisement
Table of Contents
