PXD10 Datasheet, PDF (95/130 Pages) Lumins Inc. – 4” Dia.X 6” extruded aluminum step poles

Electrical characteristics
1023
1022
1021
1020
1019
1018
Offset Error OSE
Gain Error GE
1 LSB ideal = V_DDA / 1024
(2)
code out
7
6
5
(5)
4
(4)
3
2
(3)
1
1 LSB (ideal)
0
1 23 45 67
Offset Error OSE
(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
1017 1018 1019 1020 1021 1022 1023
V_in(A) (LSB_ideal)
Figure 17. ADC Characteristics and Error Definitions
3.17.1 Input impedance and ADC accuracy
In the following analysis, the input circuit corresponding to the precise channels is considered.
To preserve 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; furthermore, it sources charge during the sampling phase,
when the analog signal source is a high-impedance source.
A real filter can typically be obtained by using a series resistance with a capacitor on the input pin (simple
RC filter). The RC filtering may be limited according to the value of source impedance of the transducer
PXD10 Microcontroller Data Sheet, Rev. 1
Freescale Semiconductor
95