Datasheet

DAC7678
www.ti.com SBAS493B –FEBRUARY 2010–REVISED JULY 2012
PARAMETER DEFINITIONS
With the increased complexity of many different Full-Scale Error
specifications listed in product data sheets, this
Full-scale error is defined as the deviation of the real
section summarizes selected specifications related to
full-scale output voltage from the ideal output voltage
digital-to-analog converters.
while the DAC register is loaded with the full-scale
code (0xFFF). Ideally, the output should be AVDD – 1
STATIC PERFORMANCE
LSB. The full-scale error is expressed in percent of
full-scale range (%FSR).
Static performance parameters are specifications
such as differential nonlinearity (DNL) or integral
Offset Error
nonlinearity (INL). These are dc specifications and
The offset error is defined as the difference between
provide information on the accuracy of the DAC. They
actual output voltage and the ideal output voltage in
are most important in applications where the signal
the linear region of the transfer function. This
changes slowly and accuracy is required.
difference is calculated by using a straight line
defined by two codes (code 30 and 4050). Since the
Resolution
offset error is defined by a straight line, it can have a
Generally, the DAC resolution can be expressed in
negative or positive value. Offset error is measured in
different forms. Specifications such as IEC 60748-4
mV.
recognize the numerical, analog, and relative
resolution. The numerical resolution is defined as the
Zero-Code Error
number of digits in the chosen numbering system
The zero-code error is defined as the DAC output
necessary to express the total number of steps of the
voltage, when all '0's are loaded into the DAC
transfer characteristic, where a step represents both
register. Zero-scale error is a measure of the
a digital input code and the corresponding discrete
difference between actual output voltage and ideal
analogue output value. The most commonly-used
output voltage (0V). It is expressed in mV. It is
definition of resolution provided in data sheets is the
primarily caused by offsets in the output amplifier.
numerical resolution expressed in bits.
Gain Error
Least Significant Bit (LSB)
Gain error is defined as the deviation in the slope of
The least significant bit (LSB) is defined as the
the real DAC transfer characteristic from the ideal
smallest value in a binary coded system. The value of
transfer function. Gain error is expressed as a
the LSB can be calculated by dividing the full-scale
percentage of full-scale range (%FSR).
output voltage by 2
n
, where n is the resolution of the
Full-Scale Error Drift
converter.
Full-scale error drift is defined as the change in full-
Most Significant Bit (MSB)
scale error with a change in temperature. Full-scale
The most significant bit (MSB) is defined as the
error drift is expressed in units of µV/°C.
largest value in a binary coded system. The value of
Offset Error Drift
the MSB can be calculated by dividing the full-scale
Offset error drift is defined as the change in offset
output voltage by 2. Its value is one-half of full-scale.
error with a change in temperature. Offset error drift
Relative Accuracy or Integral Nonlinearity (INL)
is expressed in µV/°C.
Relative accuracy or integral nonlinearity (INL) is
Zero-Code Error Drift
defined as the maximum deviation between the real
Zero-code error drift is defined as the change in zero-
transfer function and a straight line passing through
code error with a change in temperature. Zero-code
the endpoints of the ideal DAC transfer function. INL
error drift is expressed in µV/°C.
is measured in LSBs.
Gain Temperature Coefficient
Differential Nonlinearity (DNL)
The gain temperature coefficient is defined as the
Differential nonlinearity (DNL) is defined as the
change in gain error with changes in temperature.
maximum deviation of the real LSB step from the
The gain temperature coefficient is expressed in ppm
ideal 1LSB step. Ideally, any two adjacent digital
of FSR/°C.
codes correspond to output analog voltages that are
exactly one LSB apart. If the DNL is less than 1LSB,
the DAC is said to be monotonic.
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