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12-15
ANALOG-TO-DIGITAL (A/D) CONVERTER
Figure 12-9. Ideal A/D Conversion Characteristic
Note that the ideal characteristic possesses unique qualities:
• its first code transition occurs when the input voltage is 0.5 LSB;
• its full-scale code transition occurs when the input voltage equals the full-scale reference
voltage minus 1.5 LSB (V
REF
– 1.5LSB); and
• its code widths are all exactly one LSB.
These qualities result in a digitization without zero-offset, full-scale, or linearity errors; in other
words, a perfect conversion.
FINAL CODE TRANSITION OCCURS
WHEN THE APPLIED VOLTAGE IS
EQUAL TO (Vref – 1.5 (LSB)).
ACTUAL CHARACTERISTIC OF
AN IDEAL A/D CONVERTER
FIRST CODE TRANSITION OCCURS
WHEN THE APPLIED VOLTAGE IS
EQUAL TO 1/2 LSB.
THE VOLTAGE CHANGE
BETWEEN THE ADJACENT CODE
TRANSITIONS (THE “CODE
WIDTH”) IS = 1 LSB.
1/2123456786 1/2
0
1
2
3
4
5
6
7
INPUT VOLTAGE (LSBs)
Ø OUTPUT CODE, Q
A0083-01