ST10F271 datasheet(135/173 Pages) STMICROELECTRONICS

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ST10F271

Electrical characteristics

135/173

Note:

Bisector characteristic is obtained drawing a line from 1/2 LSB before the first step of the

real characteristic, and 1/2 LSB after the last step again of the real characteristic.

24.7.3

Total unadjusted error

The Total Unadjusted Error specifies the maximum deviation from the ideal characteristic:

the number provided in the Data Sheet represents the maximum error with respect to the

entire characteristic. It is a combination of the Offset, Gain and Integral Linearity errors. The

different errors may compensate each other depending on the relative sign of the Offset and

Gain errors. Refer to Figure 39, see TUE.

Figure 39.

A/D conversion characteristic

24.7.4

Analog reference pins

The accuracy of the A/D converter depends on how accurate is 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 VAREF and VAGND), is recommended

in order to clean the signal, minimizing the noise. A simple capacitive bypassing may be

sufficient in most of the cases; in presence of high RF noise energy, inductors or ferrite

beads may be necessary.

In this architecture, VAREF and VAGND pins represents also the power supply of the analog

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.

(2)

(1)

(3)

(4)

(5)

Offset Error OFS

Gain Error GE

1 LSB (ideal)

VAIN (LSBIDEAL)

[LSBIDEAL = VAREF / 1024]

Digital

Out

(HEX)

3FF

3FE

3FD

3FC

3FB

3FA

005

004

003

002

001

000

007

006

(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)

1024

1022

1020

1018

(6)

(7)

Bisector Characteristic

Ideal Characteristic

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