Gain Error; Figure 9. Positive Gain Error Representation - ST STM32 Application Note

ADC errors
2.1.2

Gain error

The gain error is the deviation between the last actual transition and the last ideal transition.
It is denoted by E
The last actual transition is the transition from 0xFFE to 0xFFF. Ideally, there should be a
transition from 0xFFE to 0xFFF when the analog input is equal to V
V = 3.3 V, the last ideal transition should occur at 3.299597 V.
REF+
If the ADC provides the 0xFFF reading for V
error is obtained.
Example
The gain error is obtained by the formula below:
E = Last actual transition – ideal transition
G
If V
REF+
E = 3.298435 V – 3.299597 V
G
= –1162 µV
E
G
= (–1162 µV / 805.6 V) LSB = –1.44 LSB
E
G
If a full scale reading (0xFFF) is not obtained for V
positive. This means that a voltage greater than V
shows a positive gain error while
1. The gain error, E
12/49
.
G
= 3.3 V and V = 3.298435 V generate a transition from 0xFFE to 0xFFF then:
AIN

Figure 9. Positive gain error representation

, is shown in magenta.
G
< V
AIN REF+
AIN
REF+
Figure 10 shows a a negative gain error.
DocID15067 Rev 3
– 0.5 LSB. So for
REF+
– 0.5 LSB, then a negative gain
equal to V , the gain error is
REF+
will cause the last transition.
AN2834
Figure 9