EM785830AA
8-bit Micro-controller
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.
10-bit ADC
VDD
VRT
VOFH
Min. input for ADC output = 1023
(For 10-bit ADC, internally it takes this range to
average 1024 steps)
Min. input for ADC output = 1
VOFL
VRB
0V
Fig.16 The relative between ADC and offset voltage
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* This specification is subject to be changed without notice.
37
12/1/2004 V1.6
ELAN [ ELAN MICROELECTRONICS CORP ]
