12
LTC1654
1654fb
Figure 3. Effect of Negative Offset
Least Significant Bit (LSB): One LSB is the ideal voltage
difference between two successive codes.
LSB = (V
FS
– V
OS
)/(2
n
– 1) = (V
FS
– V
OS
)/16383
Nominal LSBs:
LTC1654 LSB = 4.09575V/16383 = 250µV
Zero-Scale Error (ZSE): The output voltage when the
DAC is loaded with all zeros. Since this is a single supply
part, this value cannot be less than 0V.
Integral Nonlinearity (INL): End-point INL is the maxi-
mum deviation from a straight line passing through the
end points of the DAC transfer curve. Because the part
operates from a single supply and the output cannot go
below zero, the linearity is measured between low code
k
L
and full scale. The INL error at a given input code is
calculated as follows:
INL = [V
OUT
– V
OS
– (V
FS
– V
OS
)(code/16383)]/LSB
V
OUT
= The output voltage of the DAC measured at the
given input code
Differential Nonlinearity (DNL): DNL is the difference
between the measured change and the ideal one LSB
change between any two adjacent codes. The DNL error
between any two codes is calculated as follows:
DNL = (∆V
OUT
– LSB)/LSB
∆V
OUT
= The measured voltage difference between
two adjacent codes
Digital Feedthrough: The glitch that appears at the analog
output caused by AC coupling from the digital inputs when
they change state. The area of the glitch is specified in
nV • s.
Resolution (n): Resolution is defined as the number of
digital input bits (n). It is also the number of DAC output
states (2
n
) that divide the full-scale range. Resolution does
not imply linearity.
Full-Scale Voltage (V
FS
): This is the output of the DAC
when all bits are set to 1.
Voltage Offset Error (V
OS
): Normally, DAC offset is the
voltage at the output when the DAC is loaded with all zeros.
The DAC can have a true negative offset, but because the
part is operated from a single supply, the output cannot go
below 0V. If the offset is negative, the output will remain
near 0V resulting in the transfer curve shown in Figure 3.
Therefore, the offset of the part is measured at low code k
L
:
V
Vk
kV
k
OS
OUT
L
L
FS
n
L
n
=
⎛
⎝
⎜
⎞
⎠
⎟
()–
()( )
–
–
–
21
1
21
DAC CODE
1654 F01
OUTPUT
VOLTAGE
NEGATIVE
OFFSET
0V
DEFI ITIO S
UU
