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AD7278BUJZ-500RL7 Datasheet(PDF) 15 Page - Analog Devices

Part No. AD7278BUJZ-500RL7
Description  3 MSPS, 12-/10-/8-Bit ADCs in 6-Lead TSOT
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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AD7278BUJZ-500RL7 Datasheet(HTML) 15 Page - Analog Devices

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Data Sheet
AD7276/AD7277/AD7278
Rev. D | Page 15 of 28
TERMINOLOGY
Integral Nonlinearity
The maximum deviation from a straight line passing through
the endpoints of the ADC transfer function. For the AD7276/
AD7277/AD7278, 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
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 after adjusting for the offset error,
that is, VREF − 1.5 LSB.
Total Unadjusted Error
A comprehensive specification that includes gain, linearity, and
offset errors.
Track-and-Hold Acquisition Time
The time required after the conversion for the output of the
track-and-hold amplifier to reach its final value within ±0.5 LSB.
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 (fS/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 defined as
dB
76
.
1
02
.
6
+
=
N
SINAD
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
log
20
dB
V
V
V
V
V
V
THD
+
+
+
+
=
where:
V1 is the rms amplitude of the fundamental.
V2, V3, V4, V5, and V6 are the rms amplitudes of the second
through sixth harmonics.
Peak Harmonic or Spurious Noise
The ratio of the rms value of the next largest component in the
ADC output spectrum (up to fS/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 determined
by a noise peak.
Intermodulation Distortion
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 AD7276/AD7277/AD7278 are tested using the CCIF
standard in which two input frequencies are used (see fa and fb
in the specifications). 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 intermodulation distortion is
calculated in a similar manner to the THD specification, that 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.
Aperture Delay
The measured interval between the leading edge of the sampling
clock and the point at which the ADC takes the sample.
Aperture Jitter
The sample-to-sample variation when the sample is taken.


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