EM785830AA

8-bit Micro-controller

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* This specification is subject to be changed without notice.

37

12/1/2004

V1.6

EM785830AA’s 10 bit ADC characteristic

EM785830AA build in 10 bit resolution, multi channel ADC function. In ideal, if ADC’s reference voltage is 5V,

the ADC’s LSB will be 5V/1024. But in practical, for some physics or circuit’s character, some un-ideal will effect the

converter result. As the next figure, offset voltage will reduce AD’s converter range. If AD’s input voltage less than VOFL,

ADC will output 0; in opposition, if input voltage is larger than (VDD-VOFH), ADC will output 1023. That is to say the

physics AD converter range will replace by (VDD-VOFH+LSB-VOFL+LSB). If we defined that VRB = VOFL – LSB and

VRT = VDD-VOFH+LSB, the physics LSB is:

LSB = (VRT - VRB) / 1024

= (VDD – (VOFH+VOFL) ) / 1022

For real operating, please think about the effect of AD’s offset voltage. If converter the range of (VRT - VRB), the AD

converter’s opposite result will be précised.

0V

VDD

Min. input for ADC output = 1023

10-bit ADC

(For 10-bit ADC, internally it takes this range to

average 1024 steps)

VOFL

VOFH

VRB

VRT

Min. input for ADC output = 1

Fig.16

The relative between ADC and offset voltage