32186 datasheet(541/1032 Pages) RENESAS

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A/D CONVERTER

11-43

32185/32186 Group Hardware Manual

Rev.1.10 REJ09B0235-0110 May 15, 07

11.3.5 Accuracy of A/D Conversion

The accuracy of the A/D Converter is indicated by an absolute accuracy. The absolute accuracy refers to

a difference expressed by LSB between the output code obtained by A/D converting the analog input

voltages and the output code expected for an A/D converter with ideal characteristics. The analog input

voltages used during accuracy measurement are the midpoint values of the voltage width in which an A/D

converter with ideal characteristics produces the same output code. If VREF0 = 5.12 V, for example, the

width of 1 LSB for a 10-bit A/D converter is 5 mV, so that 0 mV, 5 mV, 10 mV, 15 mV, 20 mV, 25 mV and so

on are selected as midpoints of the analog input voltage.

If an A/D converter is said to have the absolute accuracy of ±2 LSB, it means that if the input voltage is 25

mV, for example, the output code expected for an A/D converter with ideal characteristics is H’005, and the

actual A/D conversion result is in the range of H’003 to H’007. Note that the absolute accuracy includes

zero and full-scale errors.

When actually using the A/D Converter, the analog input voltages are in the range of AVSS0 to VREF0.

Note, however, that low VREF0 voltages result in a poor resolution. Note also that output codes for the

analog input voltages from VREF0 to AVCC0 are always H’3FF.

H'000

H'001

H'002

H'003

H'3FE

H'3FF

→ Analog input voltage [V]

VREF0

1024

× 1

Ideal A/D conversion characteristics

A/D conversion characteristics with infinite resolution

VREF0

1024

× 2

VREF0

1024

× 3

VREF0

1024

× 1022

VREF0

1024

× 1023

VREF0

1024

× 1024

Figure 11.3.7 Ideal A/D Conversion Characteristics Relative to the 10-bit A/D Converter’s Analog Input Voltages

11.3 Functional Description of A/D Converter

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