AD7846
TERMINOLOGY
Offset Error
Least Significant Bit
This is the error present at the device output with all 0s loaded
in the DAC. It is due to op amp input offset voltage and bias
current and the DAC leakage current.
This is the analog weighting of 1 bit of the digital word in a
DAC. For the AD7846, 1 LSB = (VREF+ − VREF−)/216.
Relative Accuracy
Bipolar Zero Error
Relative accuracy or endpoint nonlinearity is a measure of the
maximum deviation from a straight line passing through the
endpoints of the DAC transfer function. It is measured after
adjusting for both endpoints (that is, offset and gain errors are
adjusted out) and is normally expressed in least significant bits
or as a percentage of full-scale range.
When the AD7846 is connected for bipolar output and 10…000
is loaded to the DAC, the deviation of the analog output from
the ideal midscale of 0 V is called the bipolar zero error.
Digital-to-Analog Glitch Impulse
This is the amount of charge injected from the digital inputs to
the analog output when the inputs change state. This is normally
specified as the area of the glitch in either pA-sec or nV-sec
depending upon whether the glitch is measured as a current or
a voltage.
Differential Nonlinearity
Differential nonlinearity is the difference between the measured
change and the ideal change between any two adjacent codes. A
specified differential nonlinearity of 1 LSB over the operating
temperature range ensures monotonicity.
Multiplying Feedthrough Error
This is an ac error due to capacitive feedthrough from either of
the VREF terminals to VOUT when the DAC is loaded with all 0s.
Gain Error
Gain error is a measure of the output error between an ideal
DAC and the actual device output with all 1s loaded after offset
error has been adjusted out. Gain error is adjustable to zero
with an external potentiometer.
Digital Feedthrough
CS
When the DAC is not selected (that is,
is held high), high
frequency logic activity on the digital inputs is capacitively
coupled through the device to show up as noise on the VOUT pin.
This noise is digital feedthrough.
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