73
MB90210 Series
6. A/D Converter Glossary
Resolution: Analog changes that are identifiable with the A/D converter
When the number of bits is 10, analog voltage can be divided into 210 = 1024.
Total error: Difference between actual and logical values. This error is caused by a zero transition error,
full-scale transition error, linearity error, differential linearity error, or by noise.
Linearity error: The deviation of the straight line connecting the zero transition point (“00 0000 0000”
“00
0000 0001”) with the full-scale transition point (“11 1111 1111”
“11 1111 1110”) from actual
conversion characteristics
Differential linearity error: The deviation of input voltage needed to change the output code by 1 LSB from the
theoretical value.
Equivalent Circuit of Analog Input Circuit
Note: The values shown here are reference values.
Analog input
Comparator
C1
C0
R ON2
R ON1
RON1: Approx. 1.5 k
RON2: Approx. 1.5 k
C0: Approx. 60 pF
C1: Approx. 4 pF
External impedance
Digital output
11 1111 1111
11 1111 1110
11 1111 1101
N + 1
N
N – 1
00 0000 0010
00 0000 0001
00 0000 0000
1LSB
VFST – V0T
1022
=
AVRH – AVRL
1022
=
Linearity error
1LSB theoretical value
VNT– (N
× 1LSB + V0T)
=
1LSB
N = 0 to 1022
VNT (N = 0) = V0T
VNT (N = 1022) = VFST
Differential linearity error
VNT – V(N – 1) T
=
1LSB
– 1
N = 1 to 1022
Total error
VNT – { ( N + 0.5 )
× 1LSB theoretical value }
=
1LSB theoretical value
N = 0 to 1022
V FST
V 0T
V(N–1)T
Theoretical value
Actual conversion value
Total error
Linerity error
V 1T
V 2T
V(N+1)T
V NT
AVRH (V)
AVRL
N
× 1LSB + V 0T
Theoretical value V NT