st10f273m STMicroelectronics, st10f273m Datasheet - Page 141

• Manufacturer Part Number: st10f273m
• Description: 16-bit Mcu With 512 Kbyte Flash Memory And 36 Kbyte Ram
• Manufacturer: STMicroelectronics

ST10F273M
24.7.4
Figure 40. A/D conversion characteristics
Analog reference pins
The accuracy of the A/D converter depends on the accuracy of its analog reference: A noise
in the reference results in at least that much error in a conversion. A low pass filter on the
A/D converter reference source (supplied through pins V
in order to clean the signal, minimizing the noise. A simple capacitive bypass may be
sufficient in most cases; in presence of high RF noise energy, inductors or ferrite beads may
be necessary.
In this architecture, V
circuitry of the A/D converter: There is an effective DC current requirement from the
reference voltage by the internal resistor string in the R-C DAC array and by the rest of the
analog circuitry.
An external resistance on V
reason, series resistance is not advisable, and more in general any series devices in the
filter network should be designed to minimize the DC resistance.
Analog input pins
To improve the accuracy of the A/D converter, it is necessary that analog input pins have low
AC impedance. Placing a capacitor with good high frequency characteristics at the input pin
of the device can be effective: The capacitor should be as large as possible, ideally infinite.
This capacitor contributes to attenuating the noise present on the input pin; moreover, it
sources charge during the sampling phase, when the analog signal source is a high-
impedance source.
Digital
Out
(HEX)
Offset Error OFS
3FE
3FD
3FC
3FB
3FA
3FF
007
006
005
004
003
002
001
000
1
2
AREF
3
Ideal Characteristic
4
and V
1 LSB (ideal)
AREF
5
AGND
could introduce error under certain conditions: For this
(7)
6
V
[LSB
AIN
(4)
(3)
IDEAL
7
(LSB
(2)
(5)
pins also represent the power supply of the analog
IDEAL
= V
AREF
)
1018
/ 1024]
(6)
1020
(1)
(1) Example of an actual transfer curve
(2) The ideal transfer curve
(3) Differential non-linearity error (DNL)
(4) Integral non-linearity error (INL)
(5) Center of a step of the actual transfer curve
(6) Quantization error (1/2 LSB)
(7) Total unadjusted error (TUE)
Offset Error OFS
AREF
1022
and V
Electrical characteristics
AGND
1024
Bisector Characteristic
Gain Error GE
) is recommended
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