ISD3900
Publication Release Date: Dec 10, 2013
- 17 -
Revision 1.5
in
f
v
R
R
A
.
ANAIN supports gain settings from 1 to 100 according to
in
f
v
R
R
A
.
f
R
should satisfy
k
Rf
k
100
40
. To achieve a gain of 100,
f
R
can be set to 100
k
, and
in
R
set to 1
k
.
coup
C
AC couples signals into the ISD3900, forming a single pole high pass filter. The 3dB frequency
is given by:
coup
in
pass
C
R
f
2
1
For
F
C
coup
1
,
k
R
in
1
, signals above 160Hz will be fed into the audio path.
Differential MICIN Input
Figure 7-4 Differential MIC Input Amplifier
The ISD3900 allows the use of pins ANAIN and ANAOUT as differential MIC inputs. In this mode, the
ANAIN and ANAOUT pins become MIC+ and MIC- and allow a differential input to be applied to the
ADC. This configuration is designed to be used in conjunction with the AGC to amplify microphone
signals while achieving good common mode rejection of supply noise. No mixing with AUXIN is
possible in this mode.
7.1.2
AUX Analog Input
The AUX Analog Input amplifies input signals with a fixed gain of 0dB, 3dB, 6dB, or 9dB, selectable
via SPI command. Similar to ANAIN, the gain setting should be configured so that the output signal
has a 1Vpp swing.
