AN1058 Freescale Semiconductor / Motorola, AN1058 Datasheet - Page 21

• Manufacturer Part Number: AN1058
• Description: Reducing A/D Errors in Microcontroller Applications
• Manufacturer: Freescale Semiconductor / Motorola

AN1058
MOTOROLA
At this point, only power distribution buses had been manipulated to
reduce ADC errors. Another part of the ADC circuit manipulated to yield
some improvement was the linear portion interfacing the MCU to the
various input signals. Consisting of 324-type opamps operated at unity
gain, this linear buffer provided a low-impedance source for the ADC
input multiplexer. Although not usually considered a wideband opamp, it
proved too wideband for this system. Most data coming from the devices
Note: Readings are rounded to nearest 1% value. Columns with 0% and a grey bar imply >0% and <0.5%.
Note: Readings are rounded to nearest 1% value. Columns with 0% and a grey bar imply >0% and <0.5%.
READ ING
READIN G
A1–A8
A9–B0
B1–B8
B9–C0
C1–FF
Freescale Semiconductor, Inc.
B9–C0
C1–FF
(H EX)
99–A0
(HEX)
99–A0
A1–A8
A9–B0
B1–B8
81–98
81–98
ADC
AD C
0–80
0–80
Figure 10. Separate MCU Power Supply with 0.1 F Bypass
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FREQ.
FREQ .
100 %
100 %
0 %
0 %
0 %
0 %
0 %
0 %
0 %
0 %
0 %
0 %
0 %
0 %
0 %
0 %
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EXPANDED SCALE
0
EXPANDED SCALE
0
C ON DITIO NS: SEPARATE M C U PO W ER SU PPLY
TOTAL SAM PLES = 16,384
CO NDITIO NS: SEPARATE M CU POW ER SUPPLY
TO TAL SAM PLES = 16,384
Figure 9. Separate MCU Power Supply
5
5
AN D BYPASS
10
10
20
20
30
30
PERCENT OCCURRENCE
PERCENT OCCURRENCE
40
40
50
50
60
60
M 68HC11 INDUSTR IAL
M 68HC11 INDU STRIAL
70
70
CO NTRO LLER
CO NTRO LLER
The Perfect Circuit
Application Note
80
80
90
90
100
100
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