AD7273/AD7274
Rev. 0 | Page 14 of 28
TERMINOLOGY
Integral Nonlinearity (INL)
The maximum deviation from a straight line passing through
the endpoints of the ADC transfer function. For the AD7273/
AD7274, the endpoints of the transfer function are zero scale at
0.5 LSB below the first code transition and full scale at 0.5 LSB
above the last code transition.
Differential Nonlinearity (DNL)
The difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Offset Error
The deviation of the first code transition (00 . . . 000) to (00 . . .
001) from the ideal, that is, AGND + 0.5 LSB.
Gain Error
The deviation of the last code transition (111 . . . 110) to
(111 . . . 111) from the ideal, that is, VREF – 1.5 LSB, after
adjusting for the offset error.
Tota l Unadjuste d Error ( TUE)
A comprehensive specification that includes gain, linearity, and
offset errors.
Track-and-Hold Acquisition Time
The time required for the output of the track-and-hold amplifier
to reach its final value, within ±0.5 LSB, after the end of the
conversion. See the
Serial Interface section for more details.
Signal-to-Noise + Distortion Ratio (SINAD)
The measured ratio of signal to noise plus distortion at the
output of the ADC. The signal is the rms amplitude of the
fundamental, and noise is the rms sum of all nonfundamental
signals up to half the sampling frequency (f
S
/2), including
harmonics but excluding dc. The ratio is dependent on the
number of quantization levels in the digitization process: the
more levels, the smaller the quantization noise. For an ideal N-bit
converter, the SINAD is
dB76.102.6 += NSINAD
According to this equation, the SINAD is 74 dB for a 12-bit
converter and 62 dB for a 10-bit converter. However, various
error sources in the ADC, including integral and differential
nonlinearities and internal ac noise sources, cause the measured
SINAD to be less than its theoretical value.
Total Harmonic Distortion (THD)
The ratio of the rms sum of harmonics to the fundamental. It is
defined as:
()
1
2
6
2
5
2
4
2
3
2
2
log20dB
V
VVVVV
THD
++++
=
where
V
1
is the rms amplitude of the fundamental, and V
2
, V
3
,
V
4
, V
5
, and V
6
are the rms amplitudes of the second through the
sixth harmonics.
Peak Harmonic or Spurious Noise (SFDR)
The ratio of the rms value of the next largest component in the
ADC output spectrum (up to f /2, excluding dc) to the rms value
of the fundamental. Normally, the value of this specification is
determined by the largest harmonic in the spectrum; however,
for ADCs with harmonics buried in the noise floor, it is deter-
mined by a noise peak.
S
Intermodulation Distortion (IMD)
With inputs consisting of sine waves at two frequencies, fa and fb,
any active device with nonlinearities creates distortion products
at sum and difference frequencies of mfa ± nfb, where m and
n = 0, 1, 2, 3, …. Intermodulation distortion terms are those for
which neither m nor n are equal to zero. For example, the second-
order terms include (fa + fb) and (fa − fb), and the third-order
terms include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa − 2fb).
The AD7273/AD7274 are tested using the CCIF standard in
which two input frequencies are used (see fa and fb in the
Specifications section). In this case, the second-order terms are
usually distanced in frequency from the original sine waves, and
the third-order terms are usually at a frequency close to the input
frequencies. As a result, the second- and third-order terms are
specified separately. The calculation of the intermodulation
distortion is as per the THD specification, where it is the ratio
of the rms sum of the individual distortion products to the rms
amplitude of the sum of the fundamentals expressed in decibels.
Power Supply Rejection Ratio (PSRR)
The ratio of the power in the ADC output at full-scale
frequency, f, to the power of a 100 mV p-p sine wave applied to
the ADC V supply of frequency f .
DD S
)
S
PfPfPSRR log10dB
where
Pf is the power at frequency f in the ADC output; Pf
S
is
the power at frequency
f
S
coupled onto the ADC V
DD
supply.
Aperture Delay
The measured interval between the leading edge of the sampling
clock and the point at which the ADC actually takes the sample.
Aperture Jitter
The sample-to-sample variation in the effective point in time at
which the sample is taken.
