14
Definition of Specifications
Integral Linearity Error, INL, is the measure of the worst
case point that deviates from a best fit straight line of data
values along the transfer curve.
Differential Linearity Error, DNL, is the measure of the
step size output deviation from code to code. Ideally the step
size should be 1 LSB. A DNL specification of 1 LSB or less
guarantees monotonicity.
Output Settlin g Ti me , is the time required for the output
voltage to settle to within a specified erro r band measured
from the beginning of the output transition. In the case of the
HI5760, the measurement was done by switching from code
0 to 256, or quarter scale. Termination impedance was 25Ω
due to the parallel resistance of the output 50Ω and the
oscilloscope’s 50Ω input. This also aids the ability to resolve
the specified error band without overdriving the oscilloscope.
Singlet Glitch Area, is the switching transient appearing on
the output during a code transition . It is measured as the
area under the overshoot po rtion of the curve and is
expressed as a Volt-Time specification.
Full Scale Gain Error, is the error from an ideal ratio of 32
between the output current and the full scale ad just current
(through RSET).
Full Scale Gain Drift, is measured by setting the data inputs
to all ones and measuring the output voltage through a
known resistance as the temperature is varied from TMIN to
TMAX. It is defined as the maximum deviation from the value
measured at room temperature to the value measured at
either TMIN or TMAX. The units are ppm of FSR (full scale
range) per degree C.
Total Harmonic Distortion, THD, is the ratio of the DAC
output fundamental to the RMS sum of the first five
harmonics.
Spurious Free Dynamic Range, SFDR, is the amplitude
difference from the fundamental to the largest harmonica lly or
non-harmonically related spur within th e speci fied wi ndow.
Output Voltage Compliance Ran ge, is the voltage limit
imposed on the output. The output impe dance load should
be chosen such that the voltage devel oped does not violate
the compliance range.
Offset Error, is measured by setting the data inputs to all
zeros and measuring the output voltage through a known
resistance. Offset error is defined as the maximum deviation
of the output current from a value of 0mA.
Offset Drift, is measured by setting the data inputs to all
zeros and measuring the output voltage through a known
resistance as the temperature is varied from TMIN to TMAX.
It is defined as the maxi mu m deviation from the value
measured at room temperature to the value measured at
either TMIN or TMAX. The units are ppm of FSR (full scale
range) per degree C.
Power Supply Rejection, is measured using a single power
supply. Its nominal +5V is varied ±10% and the change in
the DAC full scale output is noted.
Reference Input Multiplying Bandwidth, is defined as the
3dB bandwidth of the voltage reference input. It is measured
by using a sinusoidal waveform as the external reference
with the digital inputs set to all 1s. The frequency is
increased until the amplitude of the output waveform is
0.707 of its original value.
Internal Reference Voltage Drift, is defined as the
maximum deviation from the value measured at room
temperature to the value measured at either Tmin or Tmax.
The units are ppm per degree C.
Detailed Description
The HI5760 is a 10-bit, current out, CMOS, digital to analog
converter. Its maximum update rate is 125MSPS and can be
powered by either single or dual power supplies in the
recommended range of +3V to +5V. It consumes less than
165mW of power when using a +5V supply with the data
switching at 100MSPS. The architecture is based on a
segmented current source arrangement that reduces glitch
by reducing the amount of current switching at any one time.
The five MSBs are represented by 31 major current sources
of equivalent current. The five LSBs are comprised of binary
weighted current sources. Consider an input waveform to
the converter which is ramped through all the codes from 0
to 1023. The five LSB current sources would be gin to count
up. When they reached the all high state (decimal value of
31) and needed to count to the next code, they would all turn
off and the first major current source would turn on. To
continue counting upward, t he 5 LSBs would count up
another 31 codes, and then the next major curren t source
would turn on and the five LSBs would all turn off. The
process of the single, equivalent, major current source
turning on and the five LSBs turning off each time the
converter reaches another 31 codes greatly reduce s the
glitch at any one switching point. In previous architectures
that contained all binary weighted current sources or a
binary weighted resistor ladder, the converter might have a
substantially larger amount of current turning on and off at
certain, worst-case transition points such as mid-scale and
quarter scale transitions. By greatly redu cing the amount of
current switching at certain ‘major’ transitions, the overall
glitch of the converter is dramatically reduced, improving
settling times and transient problems.
HI5760