AD7866(Rev0) 查看數據表（PDF） - Analog Devices
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AD7866 Datasheet PDF : 20 Pages
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AD7866
TERMINOLOGY
Integral Nonlinearity
This is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function. The end-
points 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 applies when using Straight Binary output coding. It is the
deviation of the first code transition (00 . . . 000) to (00 . . . 001)
from the ideal, i.e., AGND + 1 LSB.
Offset Error Match
This is the difference in Offset Error between the two channels.
Gain Error
This applies when using Straight Binary output coding. It 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.
Gain Error Match
This is the difference in Gain Error between the two channels.
Zero Code Error
This applies when using the two’s complement output coding option,
in particular with the 2 × VREF input range as –VREF to +VREF biased
about the VREF point. It is the deviation of the midscale transition
(all 1s to all 0s) from the ideal VIN voltage, i.e., VREF – 1 LSB.
Zero Code Error Match
This is the difference in Zero Code Error between the two
channels.
Positive Gain Error
This applies when using the two’s complement output coding
option, in particular with the 2 × VREF input range as –VREF to
+VREF biased about the VREF point. It is the deviation of the
last code transition (011 . . . 110) to (011 . . . 111) from the
ideal (i.e., +VREF – 1 LSB) after the Zero Code Error has
been adjusted out.
Negative Gain Error
This applies when using the two’s complement output coding
option, in particular with the 2 × VREF input range as –VREF to
+VREF biased about the VREF point. It is the deviation of the first
code transition (100 . . . 000) to (100 . . . 001) from the ideal
(i.e., –VREF + 1 LSB) after the Zero Code Error error has been
adjusted out.
Track/Hold Acquisition Time
The track/hold amplifier returns into track mode after the end
of conversion. Track/Hold acquisition time is the time required
for the output of the track/hold amplifier to reach its final value,
within ± 1/2 LSB, after the end of conversion.
Signal to (Noise + Distortion) Ratio
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 for a 12-bit converter, this is 74 dB.
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the rms sum of
harmonics to the fundamental. For the AD7866, it is defined as:
THD (dB) = 20 log V22 + V32 + V42 + V52 + 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
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
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, n = 0,
1, 2, 3, etc. 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 AD7866 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
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 dB.
Channel-to-Channel Isolation
Channel-to-channel isolation is a measure of the level of crosstalk
between channels. It is measured by applying a full-scale (2 × VREF),
455 kHz sine wave signal to all non selected input channels and
determining how much that signal is attenuated in the selected
channel with a 10 kHz signal (0 V to VREF). The figure given is
the worst-case across all four channels for the AD7866.
PSR (Power Supply Rejection)
See Performance Curves section.
REV. 0
–7–
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