DSP56156FV40 MOTOROLA [Motorola, Inc], DSP56156FV40 Datasheet - Page 70

• Manufacturer Part Number: DSP56156FV40
• Description: 16-bit Digital Signal Processor
• Manufacturer: MOTOROLA [Motorola, Inc]

Analog I/O Considerations
Figure 44 describes the recommended analog I/O and power supply configurations. The two
analog inputs are electrically identical. When one is not used, it can be left floating. When
used, an AC coupling capacitor is required. The value of the capacitor along with the input
impedance of the pin determine the cut off frequency of a high pass filter. The input imped-
ance of the MIC and AUX varies as a function of the sigma-delta (²ý) modulator master clock.
78 k is a typical value at 2 MHz. An AC capacitor of 1µF defines a high pass filter pole of 2
Hz. A smaller capacitor value will move this pole higher in frequency.
MOTOROLA
digital GND
GND
External
GND
digital V
(to microphone)
0.01 F
220 F
15 F
CC
External Supply
1 F
1 F
+
GNDA
ð50 nF
+5 V
+
600
600
Single trace
0.001 F
R
0.001 F
Figure 44 Recommended Analog I/O Configuration
Š10 F
Bias
Freescale Semiconductor, Inc.
0.1 F
For More Information On This Product,
Š1 K
10 K
±1mA)
VREF
VREF
Single trace
Bias
MIC
AUX
VDIV
SPKP
Go to: www.freescale.com
VREF
SPKM
15 F
GNDA
V
DSP56156 Data Sheet
CCA
V
36 K
54 K
GNDA
CCA
VC3-VC0
+
0.1 F
Analog Decoupling
2.0 V 10%
INS bit
(2/5 V
GNDA
near DSP
3 POLE
2 ZERO
Low Pass
CC
Filter (LPF)
)
6 dB
17 dB
-6 dB
MGS1-0 bits
+5 dB
modulator
Analog I/O Considerations
Design Considerations
65