AN1636 datasheet(13/42 Pages) STMICROELECTRONICS

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UNDERSTANDING AND MINIMISING ADC CONVERSION ERRORS

Hence an ADC which converts the analog signal to a 10-bit digital value, has a resolution of 10

bits.

The smallest incremental voltage that can be recognized is expressed in terms of LSB.

1LSB = (VAREF - VSSA)/2

where LSB = Least significant bit.

n = number of bits output by the ADC.

VAREF = Reference voltage

VSSA = Analog ground

An ADC which has ‘n’ bit digital output, provides 2n digital values. It includes both 0 and 2n-1.

With a 5V reference voltage, the resolution is 5 (volts) /210 = 5 (volts)/1024 = 4.88 mV.

This means that for a change in 4.88mV analog input the ADC converted digital value will

change by 1LSB.

In reality there are 2n-1 steps. So the actual resolution is 1LSB = (VAREF - VSSA)/(2

n -1). As in

practice there is very little difference between the two calculated values because ‘n’ is quite a

large number, both definitions are used.

Figure 11. Resolution representation

3.3 QUANTIZATION

In theory, the continuous analog signal can be broken into an infinite number of digital steps,

but the quantization of an analog signal by the ADC can be done only in the finite number of

steps which can be produced by the ADC.

Digital

Output

Analog

Input

00h

3FFh

VAREF

(n+1)

VAREF

N+1

Resolution

VAREF

AN1636 Datasheet(PDF) 13 Page - STMicroelectronics