CHAPTER 11 A/D CONVERTER
User’s Manual U13850EJ4V0UM
357
(4) Countermeasures against noise
To keep the resolution of 10 bits, prevent noise from being superimposed on the AV
REF
and ANI0 to ANI11 pins.
The higher the output impedance of the analog input source, the heavier the influence of noise. To lower noise,
connecting an external capacitor as shown in Figure 11-9 is recommended.
Figure 11-9. Handling of Analog Input Pin
AV
REF
V
DD
V
SS
AV
DD
AV
SS
Reference voltage input
Clamp with diode with a low V
F
(0.3 V MAX.) if noise higher than
AV
REF
or lower than AV
SS
may be generated.
C = 100 to 1000 pF
(5) ANI0 to ANI11
The analog input (ANI0 to ANI11) pins are multiplexed with port pins.
To execute A/D conversion with any of ANI0 to ANI11 selected, do not execute an instruction that inputs data to
the port during conversion; otherwise, the resolution may drop.
If a digital pulse is applied to pins adjacent to the pin whose input signal is converted into a digital signal, the
expected A/D conversion result may not be obtained because of the influence of coupling noise. Therefore, do
not apply a pulse to the adjacent pins.
(6) Input impedance of AV
REF
pin
A series resistor string is connected between the AV
REF
and AV
SS
pins.
If the output impedance of the reference voltage source is too high, the series resistor string between the AV
REF
and AV
SS
pins are connected in series, increasing the error of the reference voltage.
Содержание MPD703030A
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