EVAL-AD7291SDZ(Rev0) 데이터 시트보기 (PDF) - Analog Devices
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EVAL-AD7291SDZ Datasheet PDF : 28 Pages
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TERMINOLOGY
Signal-to-Noise and Distortion Ratio (SINAD)
The measured ratio of signal-to-noise and distortion at the
output of the ADC. 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
digitization process; the more levels, the smaller the quantization
noise. The theoretical signal-to-noise and 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, the SINAD is 74 dB for an ideal 12-bit converter.
Total Harmonic Distortion (THD)
The ratio of the rms sum of harmonics to the fundamental. For
the AD7291, it is defined as
THD (dB) = 20 log V22 +V32 + V4 2 + V52 +V6 2
V1
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 and excluding dc) to the rms
value of the fundamental. Typically, the value of this specification
is determined by the largest harmonic in the spectrum, but for
ADCs where the harmonics are buried in the noise floor, it is 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, n = 0, 1, 2, 3, and so on. Intermodulation distortion terms
are those for which neither m nor n equals zero. For example,
second-order terms include (fa + fb) and (fa − fb), while third-
order terms include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa − 2fb).
The AD7291 is tested using the CCIF standard where two input
frequencies near the top end of the input bandwidth are used.
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 intermodulation distortion is,
like the THD specification, the ratio of the rms sum of the
individual distortion products to the rms amplitude of the sum
of the fundamentals, expressed in dB.
AD7291
Aperture Delay
The measured interval between the sampling clock’s leading
edge and the point at which the ADC takes the sample.
Aperture Jitter
This is the sample-to-sample variation in the effective point in
time at which the sample is taken.
Full-Power Bandwidth
The input frequency at which the amplitude of the recon-
structed fundamental is reduced by 0.1 dB or 3 dB for a
full-scale input.
Power Supply Rejection Ratio (PSRR)
PSRR is defined as 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 VDD supply of frequency, fS. The frequency
of the input varies from 5 kHz to 25 MHz.
PSRR (dB) = 10 log(Pf/PfS)
where:
Pf is the power at frequency, f, in the ADC output.
PfS is the power at frequency, fS, in the ADC output.
Integral Nonlinearity
The maximum deviation from a straight line passing through
the endpoints of the ADC transfer function. The endpoints 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
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, GND1 + 1 LSB.
Offset Error Match
The difference in offset error between any two channels.
Gain Error
The deviation of the last code transition (111…110) to
(111…111) from the ideal (that is, VREF − 1 LSB) after the offset
error has been adjusted out.
Gain Error Match
The difference in gain error between any two channels.
Track-and-Hold Acquisition Time
The track-and-hold amplifier returns to track mode at the end
of conversion. Track-and-hold acquisition time is the time
required for the output of the track-and-hold amplifier to reach
its final value, within ±1 LSB, after the end of conversion.
Rev. 0 | Page 11 of 28
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