AN2834 datasheet(12/45 Pages) STMICROELECTRONICS

12 / 45 page

ADC errors

AN2834

12/45

DocID15067 Rev 2

2.1.3

Differential linearity error

The differential linearity error (DLE) is defined as the maximum deviation between the actual

and ideal steps. Here ‘ideal’ is not used for the ideal transfer curve but for the resolution of

the ADC. The DLE is denoted by ED. It is represented in Figure 11.

ED = Actual step width – 1LSB

Ideally, an analog input voltage change of 1LSB should cause a change in the digital code. If

an analog input voltage greater than 1LSB is required for a change in digital code, the ADC

has a differential linearity error. The DLE therefore corresponds to the maximum additional

voltage that is required to change from one digital code to the next.

The DLE is also known as the differential non-linearity (DNL) error.

Example

A given digital output should correspond to an analog input range. Ideally, the step width

should be 1LSB. Let us assume that we get the same digital output over an analog input

voltage range of 1.9998 V to 2.0014 V, the step width will be 2.0014 V – 1.9998 V = 1.6 mV.

ED is thus the voltage difference between the higher (2.0014 V) and lower (1.9998 V)

analog voltages less the voltage corresponding to 1LSB.

Figure 11. Differential linearity error representation

If VREF+ = 3.3 V, an analog input of 1.9998 V (9B1h) can provide results varying between

9B0h and 9B2h. Similarly, for an input of 2.0014 V (9B3h), the results may vary between

9B2h and 9B4h.



Thus, the total voltage variation corresponding to the 9B2h step is:

9B3h – 9B1h, that is, 2.0014 V – 1.9998V = 1.6 mV (1660 µV)

ED= 1660 µV – 805.6 µV

ED= 854.4 µV

ED= (854.4 µV/805.6 µV) LSB

ED= 1.06 LSB

Let us assume that no voltage greater than 2.0014 V will result in the 9B2h digital code.

When the step width is less than 1LSB, ED is negative.

VAIN

Digital output

Ideal transfer curve

Actual transfer curve

Actual

step

width

Actual

step

width

1LSB

ED > 0

1LSB

ED < 0

ai15479

AN2834 Datasheet(PDF) 12 Page - STMicroelectronics

AN2834 Datasheet(HTML) 12 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