dsp56167 Freescale Semiconductor, Inc, dsp56167 Datasheet - Page 80

• Manufacturer Part Number: dsp56167
• Description: Advance Information 16-bit Digital Signal Processor
• Manufacturer: Freescale Semiconductor, Inc

Design Considerations
Analog I/O Considerations
ANALOG I/O CONSIDERATIONS
4-4
This section discusses the requirements of the on-chip codec. The two analog inputs
(MIC and AUX) are electrically identical. When one is not used, it can be left floating.
When an input is used, an AC coupling capacitor is required. The value of the
capacitor combines with the input impedance of MIC or AUX to determine the cutoff
frequency of a high pass filter. The input impedance of MIC and AUX varies with
respect to the Microphone Gain Select value (MGS[1:0]). An AC coupling capacitor of
10 F defines a high pass filter pole of 3 Hz. A smaller capacitor value moves this pole
higher in frequency.
Figure 4-1 shows the recommended analog I/O and power supply configurations.
• If possible, do not have digital signals running over the analog V
• Do not route clock signal lines across multiple signal lines. Keep the clock
• Take special care to minimize noise levels on the PLL supply pins (both V
ground planes. Decouple analog V
to the DSP.
signals away from the analog power and ground lines and all analog signal
lines.
and V
SS
).
DSP56167/D, Rev. 1
DD
and ground planes as close as possible
MOTOROLA
DD
and
DD