参数资料
型号: AD871
厂商: Analog Devices, Inc.
英文描述: Complete 12-Bit 5 MSPS Monolithic A/D Converter(12位5MSPS单片A/D转换器)
中文描述: 完整的12位5 MSPS的单片的A / D转换器(12位5MSPS单片的A / D转换器)
文件页数: 15/16页
文件大小: 319K
代理商: AD871
AD871
REV. A
–15–
1
2
V
INA
V
INB
AD871
V
IN
IBPO
IOUT
RL
ACOM
LCOM
REF COM
AD568
74
HC
574
74
HC
574
8
8
4
4
DIGITAL
OFFSET
WORD
Figure 32. Offset Correction Using the AD568
UNDERSAMPLING USING THE AD871 AND AD9100
The AD871’s on-chip THA optimizes transient response while
maintaining low noise performance. For super-Nyquist (under-
sampling) applications it may be necessary to use an external
THA with fast track-mode slew rate and hold mode settling
time. An excellent choice for this application is the AD9100, an
ultrahigh speed track-and-hold amplifier.
In order to maximize the spurious free dynamic range of the cir-
cuit in Figure 33, it is advantageous to present a small signal to
the input of the AD9100 and then amplify the output to the
AD871’s full-scale input range. This can be accomplished with
a low distortion, wide bandwidth amplifier such as the AD9617.
The circuit uses a gain of 3.5 to optimize S/(N+D).
The peak performance of this circuit is obtained by driving the
AD871 + AD9100 combination with a full-scale input. For
small scale input signals (–20 dB, –40 dB), the AD871 performs
better without the track-and-hold because slew-limiting effects
are no longer dominant. To gain the advantages of the added
track-and-hold, it is important to give the AD871 a full-scale
input.
An alternative to the configuration presented above is to use the
AD9101 track-and-hold amplifier. The AD9101 provides a
built-in post amplifier with a gain of 4, providing excellent ac
characteristics in conjunction with a high level of integration.
As illustrated in Figure 33, it is necessary to skew the AD871
sample clock and the AD9100 sample/hold control. Clock skew
(t
S
) is defined as the time starting at the AD9100’s transition
into hold mode and ending at the moment the AD871 samples.
The AD871 samples on the rising edge of the sample clock, and
the AD9100 samples on the falling edge of the sample/hold con-
trol. The choice of t
S
is primarily determined by the settling
time of the AD9100. The droop rate of the AD9100 must also
be taken into consideration. Using these values, the ideal t
S
is
17 ns. When choosing clock sources, it is extremely important
that the front end track-and-hold sample/hold control is given a
very low jitter clock source. This is not as crucial for the AD871
sample clock, because it is sampling a dc signal.
AD96685
R
T
CLOCK 1
IN
Q
Q
+V
S
–V
S
510
V
510
V
–V
S
R
T
V
IN
10
m
F
442
V
0.1
m
F
0.1
m
F
3.3
m
F
+5V
0.1
m
F
*
AD9617
*
0.1
m
F
3.3
m
F
–5V
10
m
F
–V
S
–V
S
+V
S
A
IN
AD871
EB
CLOCK 2
IN
*OPTIONAL, SEE
AD9617 DATA SHEET
+V
S
= 5.0V
–V
S
= –5.2V
ALL CAPACITORS ARE 0.01
m
F
(LOW INDUCTANCE - DECOUPLING)
UNLESS OTHERWISE NOTED.
0V
T = 200ns
+5V
+1V
–1V
T = 200ns
t
S
CLOCK 1
CLOCK 2
t
S
= 17ns
AD9100
127
V
Figure 33. Undersampling Using the AD871 and AD9100
相关PDF资料
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