AD7476AYRM 查看數據表（PDF） - Analog Devices
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AD7476AYRM Datasheet PDF : 24 Pages
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AD7476A/AD7477A/AD7478A
TERMINOLOGY
Integral Nonlinearity
This is the maximum deviation from a straight line passing through
the endpoints of the ADC transfer function. For the AD7476A/
AD7477A/AD7478A, the endpoints of the transfer function are
zero scale, a point 1 LSB below the first code transition, and full
scale, a point 1 LSB above the last code transition.
Differential Nonlinearity
This is the difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Offset Error
This is the deviation of the first code transition (00 . . . 000) to
(00 . . . 001) from the ideal, i.e., AGND + 1 LSB.
Gain Error
This is the deviation of the last code transition (111 . . . 110)
to (111 . . . 111) from the ideal, i.e., VREF – 1 LSB after the
offset error has been adjusted out.
Track-and-Hold Acquisition Time
The track-and-hold amplifier returns to track mode at the end
of conversion. The track-and-hold acquisition time is 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 conversion. See
the Serial Interface section for more details.
Signal-to-(Noise + Distortion) Ratio (SINAD)
This is the measured ratio of signal-to-(noise + distortion) at the
output of the A/D converter. The signal is the rms amplitude of
the fundamental. Noise is the sum of all nonfundamental signals
up to half the sampling frequency (fS/2), excluding dc. The ratio
is dependent on the number of quantization levels in the digiti-
zation process; the more levels, the smaller the quantization
noise. The theoretical signal-to-(noise + distortion) ratio for an
ideal N-bit converter with a sine wave input is given by
Signal-to-(Noise + Distortion) = (6.02 N + 1.76) dB
Thus, it is 74 dB for a 12-bit converter, 62 dB for a 10-bit con-
verter, and 50 dB for an 8-bit converter.
Total Unadjusted Error (TUE)
This is a comprehensive specification that includes the gain,
linearity, and offset errors.
Total Harmonic Distortion (THD)
Total harmonic distortion is the ratio of the rms sum of har-
monics to the fundamental. It is defined as
( ) THD dB = 20 log V22 + V3 2 + V4 2 + V5 2 + V62
V1
where V1 is the rms amplitude of the fundamental, and V2, V3,
V4, V5, and V6 are the rms amplitudes of the second through the
sixth harmonics.
Peak Harmonic or Spurious Noise (SFDR)
Peak harmonic or spurious noise is defined as the ratio of the
rms value of the next largest component in the ADC output
spectrum (up to fS/2 and excluding dc) to the rms value of the
fundamental. Normally, the value of this specification is deter-
mined by the largest harmonic in the spectrum. But for ADCs
where the harmonics are buried in the noise floor, it will be a
noise peak.
Intermodulation Distortion (IMD)
With inputs consisting of sine waves at two frequencies, fa and fb,
any active device with nonlinearities will create distortion products
at sum and difference frequencies of mfa ± nfb, where m and
n = 0, 1, 2, 3, and so on. 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), while the
third-order terms include (2fa + fb), (2fa – fb), (fa + 2fb), and
(fa – 2fb).
The AD7476A/AD7477A/AD7478A are tested using the CCIF
standard where two input frequencies are used (see fa and fb on
the specification pages). In this case, the second-order terms are
usually distanced in frequency from the original sine waves, while
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 dis-
tortion is 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 dBs.
REV. C
–11–
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