LQFP176 datasheet(97/133 Pages) STMICROELECTRONICS

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DocID15131 Rev 9

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SPC560B54x/6x

Electrical characteristics

132

Figure 16. ADC_0 characteristic and error definitions

4.17.2

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

(2)

(1)

(3)

(4)

(5)

Offset Error (EO)

Gain Error (EG)

1 LSB (ideal)

1023

1022

1021

1020

1019

1018

1017 1018 1019 1020 1021 1022 1023

(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

1 LSB ideal = VDD_ADC / 1024

Vin(A) (LSBideal)

code out

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