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| 型号： | AD872AJD |
| 厂商： | ANALOG DEVICES INC |
| 元件分类： | ADC |
| 英文描述： | Complete 12-Bit 10 MSPS Monolithic A/D Converter |
| 中文描述： | 1-CH 12-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, CDIP28 |
| 封装： | SIDE BRAZED, CERAMIC, DIP-28 |
| 文件页数： | 11/20页 |
| 文件大小： | 330K |
| 代理商： | AD872AJD |
REV. A
–11–
AD872A
T he wide input bandwidth and superior dynamic performance
of the input T HA make the AD872A suitable for undersam-
pling applications where the input frequency exceeds half the
sample frequency. T he input T HA is designed to recover rap-
idly from input overdrive conditions, returning from a 50%
overdrive in less than 40 ns.
Because of the T HA’s exceptionally wide input bandwidth,
some users may find the AD872A is sensitive to noise at fre-
quencies from 10 MHz to 50 MHz that other converters are
incapable of responding to. T his 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
AD872A
6
1V
10 OR 20pF
Figure 18. Optional High Frequency Noise Reduction
T he AD872A will contribute its own wideband thermal noise.
As a result of the integrated wideband noise (0.26 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 one and
three 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 AD872A code histogram, and Figure 9 illus-
trates the AD872A’s transition noise.
RE FE RE NCE INPUT
T he nominal reference input should be 2.5 V, taken with re-
spect to REFERENCE GROUND (REF GND). Figure 19 il-
lustrates the equivalent model for the reference input: there is
no clock or signal-dependent activity associated with the refer-
ence input circuitry, therefore, no “kickback” into the reference.
1
2
REF IN
REF GND
AD872A
5k
V
(
6
20%)
AV
SS
Figure 19. Equivalent Reference Input Circuit
However, in order to realize the lowest noise performance of the
AD872A, care should be taken to minimize noise at the refer-
ence input.
T he AD872A’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 AD872A.
T he full-scale peak-to-peak input voltage is a function of the
reference voltage, according to the equation:
(
V
INA
=
V
INB
)
Full Scale
=
0.8
×
(
V
REF
±
REF GND
)
Note that the AD872A’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 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.5
REFERENCE INPUT VOLTAGE – V
75
70
65
60
55
50
S
Figure 20. S/(N+D) vs. Reference Input Voltage,
f
IN
= 1 MHz, FS = 10 MHz
T able II summarizes various 2.5 V references suitable for use
with the AD872A, including the onboard bandgap reference
(see REFERENCE OUT PUT section).
T able II. Suitable 2.5 V References
Drift (ppm/
8
C)
Initial Accuracy %
REF43B
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. T his 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 AD872A may be driven
from other references by use of an external resistor. T he 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
AD872A’s 5 k
resistor.
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相关代理商/技术参数 |
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|---|---|
| AD872AJE | 制造商:Rochester Electronics LLC 功能描述:IC, 12-BIT 10 MSPS ADC - Bulk |
| AD872ASD | 制造商:AD 制造商全称:Analog Devices 功能描述:Complete 12-Bit 10 MSPS Monolithic A/D Converter |
| AD872ASD/883B | 制造商:Analog Devices 功能描述:ADC Single Pipelined 10Msps 12-bit Parallel 28-Pin CDIP 制造商:Analog Devices 功能描述:ADC SGL PIPELINED 10MSPS 12-BIT PARALLEL 28CDIP - Rail/Tube 制造商:Rochester Electronics LLC 功能描述:IC, 12-BIT 10 MSPS ADC - Bulk 制造商:Analog Devices 功能描述:CONVERTER - ADC |
| AD872ASE | 制造商:AD 制造商全称:Analog Devices 功能描述:Complete 12-Bit 10 MSPS Monolithic A/D Converter |
| AD872ASE/883B | 制造商:Analog Devices 功能描述:ADC Single Pipelined 10Msps 12-bit Parallel 44-Pin LCC 制造商:Rochester Electronics LLC 功能描述:IC, 12-BIT 10 MSPS ADC - Bulk |
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