AN1636 datasheet(5/42 Pages) STMICROELECTRONICS

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UNDERSTANDING AND MINIMISING ADC CONVERSION ERRORS

VAREF is the reference voltage used by ADC for conversions. The details are mentioned in

Section 2.5

After this comparison is done, the next significant bit is set (=VAREF/4) and a comparison is

done again with the input voltage. The procedure is followed till all the bit positions are com-

pared.

At the end of all the bit comparisons we get the corresponding digital output for the analog

input.

The successive approximation steps are shown in Table 1. As you can see, the digital output

obtained from the ADC is B2h when the analog input is 3.5V.

Table 1. 8-bit ADC successive approximation steps

Steps

Vin = 3.5v, VAREF= 5V

Digital code

DAC output

Comparator

output

digital output

(for steps)

1000 0000

2.5v

1000 0000

1100 0000

3.76v

1000 0000

1010 0000

3.13v

1010 0000

1011 0000

3.45

1011 0000

1011 1000

3.6

1011 0000

1011 0100

3.52

1011 0000

1011 0010

3.49

1011 0010

1011 0011

3.509

1011 0010

Final output = B2h

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