Specification Definitions
APERTURE (SAMPLING) DELAY is that time required after
the fall of the clock input for the sampling switch to open. The
Sample/Hold circuit effectively stops capturing the input sig-
nal and goes into the “hold” mode the aperture delay time
(tAD) after the clock goes low.
APERTURE JITTER (tAJ) is the variation in aperture delay
from sample to sample. Aperture jitter shows up as input
noise.
CLOCK DUTY CYCLE is the ratio of the time that the clock
wave form is at a logic high to the total time of one clock
period.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of
the maximum deviation from the ideal step size of 1 LSB.
Measured at 1 GSPS with a ramp input.
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE
BITS) is another method of specifying Signal-to-Noise and
Distortion Ratio, or SINAD. ENOB is defined as (SINAD −
1.76) / 6.02 and says that the converter is equivalent to a
perfect ADC of this (ENOB) number of bits.
FULL POWER BANDWIDTH (FPBW) is a measure of the
frequency at which the reconstructed output fundamental
drops 3 dB below its low frequency value for a full scale
input.
GAIN ERROR is the deviation from the ideal slope of the
transfer function. It can be calculated from Offset and Full-
Scale Errors:
– PGE = OE − PFSE
– NGE = −(OE − NFSE) = NFSE − OE
– Gain Error = NFSE − PFSE = PGE + NGE
where PGE is Positive Gain Error, NGE is Negative Gain
Error, OE is Offset Error, PFSE is Positive Full-Scale Error
and NFSE is Negative Full-Scale Error.
INTEGRAL NON-LINEARITY (INL) is a measure of the
deviation of each individual code from a straight line through
the input to output transfer function. The deviation of any
given code from this straight line is measured from the
center of that code value. The best fit method is used.
INTERMODULATION DISTORTION (IMD) is the creation of
additional spectral components as a result of two sinusoidal
frequencies being applied to the ADC input at the same time.
it is defined as the ratio of the power in the second and third
order intermodulation products to the power in one of the
original frequencies. IMD is usually expressed in dBFS.
LSB (LEAST SIGNIFICANT BIT) is the bit that has the
smallest value or weight of all bits. This value is
VFS / 2n
where VFS is the differential full-scale amplitude of 600 mV
or 800 mV as set by the FSR input and "n" is the ADC
resolution in bits, which is 8 for the ADC081000.
LVDS DIFFERENTIAL OUTPUT VOLTAGE (VOD) is this
absolute value of the difference between the VD+ and VD−
outputs, each measured with respect to Ground.
LVDS OUTPUT OFFSET VOLTAGE (VOS) is the midpoint
between the the D+ and D− pins’ output voltages; i.e.,
[ (VD+) + (VD−) ] / 2.
20068190
FIGURE 1.
MISSING CODES are those output codes that are skipped
and will never appear at the ADC outputs. These codes
cannot be reached with any input value.
MSB (MOST SIGNIFICANT BIT) is the bit that has the
largest value or weight. Its value is one half of full scale.
NEGATIVE FULL-SCALE ERROR is a measure of how far
the last code transition is from the ideal 1/2 LSB above a
differential −800 mV with the FSR pin high, or 1/2 LSB above
a differential −600 mV with the FSR pin low. For the
ADC081000 the reference voltage is assumed to be ideal, so
this error is a combination of full-scale error and reference
voltage error.
OFFSET ERROR (VOFF) is a measure of how far the mid-
scale point is from the ideal zero voltage differential input.
OUTPUT DELAY (tOD) is the time delay after the falling edge
of the DCLK before the data update is present at the output
pins.
OVER-RANGE RECOVERY TIME is the time required after
the differential input voltages goes from ±1.2V to 0V for the
converter to recover and make a conversion with its rated
accuracy.
PIPELINE DELAY (LATENCY) is the number of clock cycles
between initiation of conversion and when that data is pre-
sented to the output driver stage. New data is available at
every clock cycle, but the data lags the conversion by the
Pipeline Delay plus the tOD.
POSITIVE FULL-SCALE ERROR (PFSE) is a measure of
how far the last code transition is from the ideal 1-1/2 LSB
below a differential +800 mV with the FSR pin high, or 1-1/2
LSB below a differential +600 mV with the FSR pin low. For
the ADC081000 the reference voltage is assumed to be
ideal, so this error is a combination of full-scale error and
reference voltage error.
POWER SUPPLY REJECTION RATIO (PSRR) can be one
of two specifications. PSRR1 (DC PSRR) is the ratio of the
change in offset error that results from a power supply
voltage change from 1.8V to 2.0V. PSRR2 (AC PSRR) is a
measure of how well an a.c. signal riding upon the power
supply is rejected from the output and is measured with a
248 MHz, 50 mVP-P signal riding upon the power supply. It is
the ratio of the output amplitude of that signal at the output to
its amplitude on the power supply pin. PSRR is expressed in
dB.
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