SPMCK16Z4MPV16 datasheet(202/500 Pages) FREESCALE

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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 VDD/

VSS 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

.020

5.100

5.110

INPUT IN VOLTS (VRH = 5.120 V, VRL = 0 V)

3FA

3FB

3FC

3FD

3FE

3FF

.010

.030

5.120

5.130

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