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1-145

7470/7471/7477/7478 GROUP USER’S MANUAL

HARDWARE

1.14 A-D converter

1.14.4 References

2 Definition of A-D conversion precision

The definition of A-D conversion precision is described.

Refer to the definition of A-D conversion precision shown in Figure 1.14.3.

(1) Relative precision

q Zero transition error (VOT)

Deviation of the input voltage, at which A-D conversion output data changes from “0” to “1,” from

the ideal A-D conversion characteristics between 0 and VREF

VOT = (VO –

× V

REF

)/1LSB [LSB]

q Full-scale transition error (VFST)

Deviation of the ideal A-D conversion characteristics between 0 and VREF of the input voltage

when the A-D conversion output data changes from “255” to “254”.

VFST = {(VREF –

3 × VREF ) – V254}/1LSB [LSB]

q Non-linearity error

Deviation of the real A-D conversion characteristics from the ideal characteristics between V0 and V254

Non-linearity error = {Vn – (1LSB

× n + VO)}/1LSB [LSB]

q Differential non-linearity error

Deviation of the input voltage required to change output data by “1” from the ideal characteristics

between V0 and V254

Differential non-linearity error = {(Vn+1 – Vn) – 1LSB}/1LSB [LSB]

(2) Absolute precision

q Absolute precision

Deviation of the real A-D conversion characteristic from the ideal characteristics between 0 and

VREF.

Absolute precision = {Vn – 1LSB

× (n + 1

)}/1LSB [LSB]

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