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參數(shù)資料
| 型號： | EVAL-AD7887CB |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | +2.7 V to +5.25 V, Micropower, 2-Channel, 125 kSPS, 12-Bit ADC in 8-Lead uSOIC |
| 中文描述： | 2.7 V至5.25 V，微功耗，2通道，125 kSPS的，12位ADC的8引腳uSOIC |
| 文件頁數(shù)： | 6/16頁 |
| 文件大?。?/td> | 133K |
| 代理商： | EVAL-AD7887CB |
REV. B
AD7887
–6–
T E RMINOLOGY
Integral Nonlinearity
T his is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function. T he end-
points of the transfer function are zero scale, a point 1/2 LSB
below the first code transition, and full scale, a point 1/2 LSB
above the last code transition.
Differential Nonlinearity
T his is the difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Offset E rror
T his is the deviation of the first code transition (00 . . . 000) to
(00 . . . 001) from the ideal, i.e., AGND + 0.5 LSB.
Offset E rror Match
T his is the difference in Offset Error between any two channels.
Gain E rror
T his is the deviation of the last code transition (111 . . . 110) to
(111 . . . 111) from the ideal (i.e., V
REF
– 1.5 LSB) after the
offset error has been adjusted out.
Gain E rror Match
T his is the difference in Gain Error between any two channels.
T rack/Hold Acquisition T ime
T he track/hold amplifier returns into track mode at the end of
conversion. T rack/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
T his is the measured ratio of signal to (noise + distortion) at the
output of the A/D converter. T he signal is the rms amplitude of
the fundamental. Noise is the sum of all nonfundamental sig-
nals up to half the sampling frequency (f
S
/2), excluding dc. T he
ratio is dependent on the number of quantization levels in the
digitization process; the more levels, the smaller the quantiza-
tion noise. T he 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
T hus for a 12-bit converter, this is 74 dB.
T otal Harmonic Distortion
T otal harmonic distortion (T HD) is the ratio of the rms sum of
harmonics to the fundamental. For the AD7887, it is defined
as:
THD dB
V
V
V
V
V
V
(
)
log
=
+
+
+
+
20
2
2
3
2
4
2
5
2
6
2
1
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
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 f
S
/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).
T he AD7887 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 sepa-
rately. T he calculation of the intermodulation distortion is as
per the T HD 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.
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 25 kHz sine wave signal to the nonselected input channel
and determining how much that signal is attenuated in the se-
lected channel. T he figure given is the worst case across both
channels for the AD7887.
PSR (Power Supply Rejection)
Variations in power supply will affect the full-scale transition,
but not the converter’s linearity. Power Supply Rejection is the
maximum change in the full-scale transition point due to a
change in power-supply voltage from the nominal value.
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相關(guān)代理商/技術(shù)參數(shù) |
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| EVAL-AD7887CB4 | 制造商:AD 制造商全稱:Analog Devices 功能描述:2.7 V to 5.25 V, Micropower, 2-Channel, 125 kSPS, 12-Bit ADC in 8-Lead MSOP |
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