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參數(shù)資料
| 型號： | AD8186-EVAL |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 480 MHz Single-Supply (5 V) Triple 2:1 Multiplexers |
| 中文描述： | 480兆赫單電源（5V）的三重2:1多路復(fù)用器 |
| 文件頁數(shù)： | 13/20頁 |
| 文件大小： | 474K |
| 代理商： | AD8186-EVAL |
REV. A
AD8186/AD8187
–13–
The AD8187
The AD8187 uses on-chip feedback resistors to realize the gain-
of-two function. To provide low crosstalk and a high output
impedance when disabled, each set of 500
feedback resistors is
terminated by a dedicated reference buffer. A reference buffer is
a high speed op amp configured as a unity-gain follower. The
three reference buffers, one for each channel, share a single, high
impedance input, the V
REF
pin (see Figure 4). V
REF
input bias
current is typically less than 2
μ
A.
A0
B0
V
REF
5V
5V
5V
GBUF 0
5V
GBUF 1
5V
GBUF 2
500
500
OUT 0
500
500
500
500
VF-1
VF-2
1
VFO
OUT1
OUT2
Figure 4. Conceptual Diagram of a Single
Multiplexer Channel, G = +2
This configuration has a few implications for single-supply
operation:
1) On the AD8187, V
REF
may not be tied to the most negative
analog supply, V
EE
.
Limits on Reference Voltage (AD8187, see Figure 5):
V
1 3
.
V
V
<
V
V
V
V
V on V / V Supplies
0
5
EE
REF
3 4
.
CC
REF
+
<
<
<
1 3
.
–1 6
A0
V
REF
5V
5V
OUT 0
5V
5V
1.3V
1.3V
1.6V
1.3V
V
OUT
V
O_MAX
= 3.7V
V
O_MAX
= 3.4V
V
O_MIN
= 1.3V
V
O_MIN
= 1.3V
V
REF
GND
GND
Figure 5. Output Compliance of Main Amplifier
Channel and Ground Buffer
2) Signal at the V
REF
pin appears at each output. Therefore,
V
REF
should be tied to a well bypassed, low impedance source.
Using superposition, it is easily shown that
V
V
V
OUT
IN
REF
=
×
2
–
3) To maximize the output dynamic range, the reference voltage
should be chosen with some care.
For example, consider amplifying a 700 mV video signal with a
sync pulse 300 mV below black level. The user might decide to set
V
REF
at black level to preferentially run video signals on the faster
NPN transistor path. The AD8186 would, in this case, allow a
reference voltage as low as 1.3 V + 300 mV = 1.6 V. If the AD8187
is used, the sync pulse would be amplified to 600 mV. Therefore,
the lower limit on V
REF
becomes 1.3 V + 600 mV = 1.9 V. For
routing RGB video, an advantageous configuration would be to
employ +3 V and –2 V supplies, in which case V
REF
could be
tied to ground.
If system considerations prevent running the multiplexer on split
supplies, a false ground reference should be employed. A low
impedance reference may be synthesized with a second opera-
tional amplifier. Alternately, a well bypassed resistor divider
may serve. Refer to the Application section for further explana-
tion
and more examples.
V
REF
1 F
5V
GND
OP21
100k
10k
0.022 F
100
1 F
FROM 1992 ADI AMPLIFIER
APPLICATIONS GUIDE
Figure 6a. Synthesis of a False Ground Reference
V
REF
1 F
5V
10k
10k
CAP MUST BE LARGE
ENOUGH TO ABSORB
TRANSIENT CURRENTS
WITH MINIMUM BOUNCE.
Figure 6b. Alternate Method for Synthesis of a
False Ground Reference
High Impedance Disable
Both the AD8186 and the AD8187 may have their outputs
disabled to a high impedance state. In the case of the AD8187,
the reference buffers also disable to a state of high output
impedance. This feature prevents the feedback network of a
disabled channel from loading the output, which is valuable
when busing together the outputs of several muxes.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD8187 | 制造商:AD 制造商全稱:Analog Devices 功能描述:480 MHz Single-Supply (5 V) Triple 2:1 Multiplexers |
| AD8187ARU | 制造商:Analog Devices 功能描述:Analog Multiplexer Triple 2:1 24-Pin TSSOP 制造商:Rochester Electronics LLC 功能描述:TSSOP TRIPLE 2:1 G=+2 SINGLE SUPPLY MUX - Bulk |
| AD8187ARU-REEL | 制造商:Analog Devices 功能描述:Analog Multiplexer Triple 2:1 24-Pin TSSOP T/R |
| AD8187ARU-REEL7 | 制造商:Analog Devices 功能描述:Analog Multiplexer Triple 2:1 24-Pin TSSOP T/R 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
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