ANALOG-TO-DIGITAL CONVERTER
M68HC16 Z SERIES
8-16
USER’S MANUAL
Figure 8-5 Errors Resulting from Clipping
8.8.3 Analog Supply Filtering and Grounding
Two important factors influencing performance in analog integrated circuits are supply
filtering and grounding. Generally, digital circuits use bypass capacitors on every V
DD
/
V
SS
pin pair. This applies to analog subsystems or submodules also. Equally important
as bypassing is the distribution of power and ground.
Analog supplies should be isolated from digital supplies as much as possible. This ne-
cessity stems from the higher performance requirements often associated with analog
circuits. Therefore, deriving an analog supply from a local digital supply is not recom-
mended. However, if for economic reasons digital and analog power are derived from
a common regulator, filtering of the analog power is recommended in addition to the
bypassing of the supplies already mentioned. For example, an RC low-pass filter could
be used to isolate the digital and analog supplies when generated by a common reg-
ulator. If multiple high precision analog circuits are locally employed (such as two A/D
converters), the analog supplies should be isolated from each other, as sharing sup-
plies introduces the potential for interference between analog circuits.
ADC CLIPPING
0
.020
5.100
5.110
INPUT IN VOLTS (V
RH
= 5.120 V, V
RL
= 0 V)
1
2
3
4
5
6
7
8
3FA
3FB
3FC
3FD
3FE
3FF
.010
.030
5.120
5.130
10-BIT RESULT
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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