SLAU213A Datasheet, PDF (9/19 Pages) Texas Instruments – MSP430FG4618/F2013 Experimenter’s Board

6.3.1 Microphone
The microphone is connected to the MSP430FG4618 and may be used
for various applications. The microphone is enabled/disabled via a port pin
connected to the MSP430FG4618.
6.3.2 Analog Filters
An active first order high-pass filter (HPF) with a cut-off frequency set at
approximately 340Hz follows the microphone to eliminate extremely low
input frequencies. An optional 2^nd order Sallen-Key active low-pass filter
(LPF) with a cut-off frequency set to approximately 4 kHz removes the
high-frequency noise on the analog output of the 12-bit DAC. The filter
setup is shown in Figure 5. These filters use the integrated Op-Amps of
the MSP430. The Op-Amps OA0 & OA1 facilitate the filtering processes.
The grayed dashed blocks in Figure 5 identify those elements which are
internal to the MSP430FG4618.
C18
470nF
R29
1K
MIC
C21 15pF
R30 150K
1^st Order
Active HPF
-
OA0I0 _OA0
12-bit
+ OA0OOA0OADC12
OA0I1
MSP430
Internal
12-bit
DAC12
R24
1.4K
C17
3.3nF
R25 C16
15.4K 22nF
-
OA1I1
OA1O
OA1
+
OA1I0
SALLEN-KEY 2^nd
Order Active LPF
-
OA2I1
OA2
+
OA2O
OA2I0
Unity Gain
Buffer
Figure 5: Active Analog Filter setup
6.3.3 Analog Output
Analog output can be brought out of the board via a mono 3.5mm jack
connected to the integrated Op-Amp OA2. The input to this amplifier can
be internally connected to the DAC12 output of the MSP430FG4618.
Several attenuation options are provided internally and in hardware using
jumper JP4.
6