AN2834 datasheet(11/45 Pages) STMICROELECTRONICS

11 / 45 page

DocID15067 Rev 2

11/45

AN2834

ADC errors

2.1.2

Gain error

Gain error is defined as the deviation between the last actual transition and the last ideal

transition. Gain error is represented as EG.

The last actual transition is the transition from FFEh to FFFh. Ideally, there should be a

transition from FFEh to FFFh, when the analog input is equal to VREF+ – 0.5LSB. So for

VREF+= 3.3 V, the last ideal transition should be at 3.299597 V.

If the ADC provides the FFFh reading for VAIN < VREF+ – 0.5LSB, then we have a negative

gain error.

Example

Gain error EG = Last actual transition – ideal transition

If VREF+ = 3.3 V and VAIN = 3.298435 V generates a transition from FFE to FFF then,

EG = 3.298435 V – 3.299597 V

EG = –1162 µV

EG = (–1162 µV / 805.6 µV) LSB = –1.44 LSB

If we do not get a full scale reading (FFFh) for VAIN equal to VREF+, the gain error is positive.

This means that a voltage greater than VREF+ will cause the last transition. Figure 9 shows a

positive gain error and Figure 10, a negative gain error.

Figure 9. Positive gain error representation

Figure 10. Negative gain error representation

VAIN

Digital output

ai15477

Ideal transfer curve

Actual transfer curve

EG > 0

4095

4094.5

LSB

VAIN

Digital output

ai15478

Ideal transfer curve

Actual transfer curve

EG < 0

4095

4094.5

LSB

AN2834 Datasheet(PDF) 11 Page - STMicroelectronics

AN2834 Datasheet(HTML) 11 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

Datasheet Download

Link URL