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參數資料
| 型號： | AD871JE |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | Complete 12-Bit 5 MSPS Monolithic A/D Converter |
| 中文描述： | 1-CH 12-BIT FLASH METHOD ADC, PARALLEL ACCESS, CQCC44 |
| 封裝： | CERAMIC, LCC-44 |
| 文件頁數： | 11/16頁 |
| 文件大小： | 378K |
| 代理商： | AD871JE |
AD871
REV. A
–11–
The wide input bandwidth and superior dynamic performance of
the input THA make the AD871 suitable for sampling inputs at
frequencies up to the Nyquist Rate. The input THA is designed
to recover rapidly from input overdrive conditions, returning
from a 50% overdrive in less than 100 ns.
Because of the THA’s exceptionally wide input bandwidth, some
users may find the AD871 is sensitive to noise at frequencies
from 10 MHz to 50 MHz that other converters are incapable of
responding to. This sensitivity can be mitigated by careful use of
the differential inputs (see previous paragraphs). Additionally,
Figure 18 shows how a small capacitor (10 pF – 20 pF for 50
terminated inputs) may be placed between V
INA
and V
INB
to help
reduce high frequency noise in applications where limiting the
input bandwidth is acceptable.
1
2
V
INA
V
INB
AD871
6
1V
10 OR 20pF
Figure 18. Optional High Frequency Noise Reduction
The AD871 will contribute its own wideband thermal noise. As
a result of the integrated wideband noise (0.17 LSB rms,
referred-to-input), applying a dc analog input may produce more
than one code at the output. A histogram of the ADC output
codes, for a dc input voltage, will be between 1 and 3 codes
wide, depending on how well the input is centered on a given
code and how many samples are taken. Figure 8 shows a typical
AD871 code histogram, and Figure 9 illustrates the AD871’s
transition noise.
REFERENCE INPUT
The nominal reference input should be 2.5 V, taken with respect
to REFERENCE GROUND (REF GND). Figure 19 illustrates
the equivalent model for the reference input: there is no clock or
signal-dependent activity associated with the reference input cir-
cuitry, therefore no “kickback” into the reference.
1
2
REF IN
REF GND
AD871
5k
V
(
6
20%)
AV
SS
Figure 19. Equivalent Reference Input Circuit
However, in order to realize the lowest noise performance of the
AD871, care should be taken to minimize noise at the reference
input.
The AD871’s reference input impedance is equal to 5 k
(
±
20%),
and its effective noise bandwidth is 10 MHz, with a referred-
to-input noise gain of 0.8. For example, the internal reference,
with an rms noise of 28
μ
V (using an external 1
μ
F capacitor),
contributes 24
μ
V (0.05 LSB) of noise to the transfer function
of the AD871.
The full-scale peak-to-peak input voltage is a function of the ref-
erence voltage, according to the equation:
(V
INA
– V
INB
) Full Scale =
0.8
×
(V
REF
– REF GND
)
Note that the AD871’s performance was optimized for a 2.5 V
reference input: performance may degrade somewhat for other
reference voltages. Figure 20 illustrates the S/(N+D) perfor-
mance vs. reference voltage for a 1 MHz, –0.5 dB input signal.
Note also that if the reference is changed during a conversion,
all three conversions in the pipeline will be invalidated.
1.5
2
3.5
3
2.5
70
60
50
REFERENCE INPUT VOLTAGE – Volts
S
Figure 20. S/(N+D) vs. Reference Input Voltage,
f
IN
= 1 MHz, FS = 5 MHz
Table II summarizes various 2.5 V references suitable for use
with the AD871, including the onboard bandgap reference (see
REFERENCE OUTPUT section).
Table II. Suitable 2.5 V References
Drift (PPM/
8
C)
Initial Accuracy %
REF-43B
AD680JN
Internal
6 (max)
10 (max)
30 (typ)
0.2
0.4
0.4
If an external reference is connected to REF IN, REF OUT
must be connected to +5 V. This should lower the current in
REF GND to less than 350
μ
A and eliminate the need for a
1
μ
F capacitor, although decoupling the reference for noise
reduction purposes is recommended.
Alternatively, Figure 21 shows how the AD871 may be driven
from other references by use of an external resistor. The exter-
nal resistor forms a resistor divider with the on-chip 5 k
resis-
tor to realize 2.5 V at the reference input pin (REF IN). A trim
potentiometer is needed to accommodate the tolerance of the
AD871’s 5 k
resistor.
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相關代理商/技術參數 |
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|---|---|
| AD871SD | 制造商:Analog Devices 功能描述: 制造商:Rochester Electronics LLC 功能描述:IC, 12-BIT 5 MSPS ADC IC - Bulk |
| AD871SD/883B | 制造商:Rochester Electronics LLC 功能描述:IC, 12-BIT 5MSPS ADC IC - Bulk 制造商:Analog Devices 功能描述: |
| AD871SD883B | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:MICROCIRCUIT, LINEAR, A/D CONVERTER, 12-BIT, 5 MSPS, MONOLITHIC SILICON |
| AD871SE | 制造商:AD 制造商全稱:Analog Devices 功能描述:Complete 12-Bit 5 MSPS Monolithic A/D Converter |
| AD871SE/883B | 制造商:Rochester Electronics LLC 功能描述:IC, 12-BIT 5MSPS ADC IC - Bulk 制造商:Analog Devices 功能描述: |
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