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PDF AD8174 Data sheet ( Hoja de datos )
| Número de pieza | AD8174 | |
| Descripción | Multiplexers w/Amplifier | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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a
250 MHz, 10 ns Switching
Multiplexers w/Amplifier
AD8170/AD8174
FEATURES
Fully Buffered Inputs and Outputs
Fast Channel Switching: 10 ns
Internal Current Feedback Output Amplifier
High Output Drive: 50 mA
Flexible Gain Setting via External Resistor(s)
High Speed
250 MHz Bandwidth, G = +2
1000 V/s Slew Rate
Fast Settling Time of 15 ns to 0.1%
Low Power: < 10 mA
Excellent Video Specifications (RL = 150 ⍀, G = +2)
Gain Flatness of 0.1 dB Beyond 80 MHz
0.02% Differential Gain Error
0.05؇ Differential Phase Error
Low Crosstalk of –78 dB @ 5 MHz
High Disable Isolation of –88 dB @ 5 MHz
High Shutdown Isolation of –92 dB @ 5 MHz
Low Cost
Fast Output Disable Feature for Connecting Multiple
Devices (AD8174 Only)
Shutdown Feature Reduces Power to 1.5 mA (AD8174 Only)
APPLICATIONS
Pixel Switching for “Picture-In-Picture”
LCD and Plasma Displays
Video Routers
PRODUCT DESCRIPTION
The AD8170(2:1) and AD8174(4:1) are very high speed
buffered multiplexers. These multiplexers offer an internal
current feedback output amplifier whose gain can be pro-
grammed via external resistors and is capable of delivering 50
mA of output current. They offer –3 dB signal bandwidth of
250 MHz and slew rate of greater than 1000 V/µs. Additionally,
the AD8170 and AD8174 have excellent video specifications
with low differential gain and differential phase error of 0.02%
and 0.05° and 0.1 dB flatness out to 80 MHz. With a low 78
dB of crosstalk and better than 88 dB isolation, these devices are
useful in many high speed applications. These are low power
devices consuming only 9.7 mA from a ± 5 V supply.
FUNCTIONAL BLOCK DIAGRAM
SELECT 1
GND 2
–VS 3
IN0 4
+1
AD8170
+1
8 VOUT
7 –VIN
6 +VS
5 IN1
IN0 1 +1
GND 2
IN1 3 +1
GND 4
IN2 5 +1
–VS 6
IN3 7
+1
2
AD8174
14 +VS
13 VOUT
12 –VIN
11 SD
10 ENABLE
9 A1
8 A0
2
The AD8174 offers a high speed disable feature allowing the
output to be put into a high impedance state for cascading
stages so that the off channels do not load the output bus.
Additionally, the AD8174 can be shut down (SD) when not in
use to minimize power consumption (IS = 1.5 mA). These
products will be offered in 8-lead and 14-lead PDIP and SOIC
packages.
VIN = 50mV rms
G = +2
RF = 499Ω (AD8170R)
RF = 549Ω (AD8174R)
0.1 RL = 100Ω
0
–0.1
–0.2
–0.3
–0.4
–0.5
1M
10M
100M
FREQUENCY – Hz
0
–1
–2
–3
–4
–5
–6
–7
–8
–9
1G
Figure 1. Small Signal Frequency Response
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700 World Wide Web Site: http://www.analog.com
Fax: 617/326-8703
© Analog Devices, Inc., 1996
1 page  
Typical Performance Characteristics – AD8170/AD8174
∆tFALL = 9.1ns ∆tRISE = 7.5ns
DUT
OUT
OUTPUT
IN0, IN2 =
+0.5V
IN1, IN3 =
+0.5V
G = +2
RF = RG = 499⍀
RL = 100⍀
SELECT
PULSE
0 TO +5V
5ns/DIV
Figure 4. Channel Switching Characteristics
OUTPUT (AD8170R) SEL SWITCHING
G = +2
RF = 499⍀
(AD8170R)
RF = 549⍀
(AD8174R)
RL = 100⍀
OUTPUT
(AD8174R)
A0 SWITCHING
A1 SWITCHING
SEL, A0, A1
PULSE
0 TO +5V
10ns/DIV
Figure 7. Switching Transient (Glitch) Response
AD8174R
OUTPUT
INØ = +0.5VDC
G = +2
RF = 549⍀
RL = 100⍀
∆tOFF = 120ns
∆tON = 17ns
ENABLE PULSE
0 TO +5V
(5nsec EDGES)
50ns/DIV
Figure 5. Enable and Disable Switching Characteristics
4
G = +2
3 RF = RG = 1kΩ
RL = 150Ω
2
1
0
–1
–2
–3
–4
–3 –2 –1
0
1
2
3
VIN – Volts
Figure 8. Output Voltage vs. Input Voltage, G = +2
OUTPUT
AD8174R
INØ = +0.5VDC
G = +2
RF = 549⍀
RL = 100⍀
∆tON = 20ns
∆tOFF = 115ns
SHUTDOWN PULSE
0 TO +5V
(5nsec EDGES)
50ns/DIV
Figure 6. Shutdown Switching Characteristics
9
6
3
0
–3
–6
–9
–12
–15
–18
–21
1M
VIN = 1.0V rms
VIN = 0.5V rms
VIN = 0.25V rms
VIN = 125mV rms
VIN = 625mV rms
10M 100M
FREQUENCY – Hz
G = +2
RF = 549Ω
RL = 100Ω
9
0
–3
–6
–9
–12
–15
–18
–21
–24
–27
1G
Figure 9. Large Signal Frequency Response
REV. 0
–5–
5 Page 
AD8170/AD8174
IN0
75Ω
1 +1
AD8174
+VS 14
0.1µF
+
10µF
+5V
IN1
75Ω
2 GND
3 +1
IN2
75Ω
0.1µF
4 GND 2
5 +1
–5V +
6 –VS
10µF
7 +1
2
IN3
75Ω
13
549Ω
12
SD
11 +5V
ENABLE
10
A1
9
A0
8
549Ω
RBT
75Ω
VOUT
A2
RT*
A1
RT*
IN4
75Ω
1 +1
AD8174
+VS 14
0.1µF
+
10µF
+5V
IN5
75Ω
2 GND
3 +1
IN6
75Ω
0.1µF
4 GND 2
5 +1
–5V +
6 –VS
10µF
7 +1
2
IN7
75Ω
13
549Ω
12
SD
11 +5V
ENABLE
10
A1
9
A0
8
549Ω
*OPTIONAL
A0
RT*
Figure 26. 8-to-1 Multiplexer
Color Document Scanner
Charge Coupled Devices (CCDs) find widespread use in
scanner applications. A monochrome CCD delivers a serial
stream of voltage levels, each level being proportional to the
light shining on that cell. In the case of the color image scanner
shown, there are three output streams, representing red, green
and blue. Interlaced with the stream of voltage levels is a voltage
representing the reset level (or black level) of each cell. A
Correlated Double Sampler (CDS) subtracts these two voltages
from each other in order to eliminate the relatively large offsets
which are common with CCDs.
The next step in the data acquisition process involves digitizing
the three signal streams. Assuming that the analog to digital
converter chosen has a fast enough sample rate, multiplexing the
three streams into a single ADC is generally more economic
than using one ADC per channel. In the example shown, the
AD8174 is used to multiplex the red, green and blue channels
into the AD876, an 8- or 10-bit 20 MSPS ADC. Because of its
high bandwidth, the AD8174 is capable of driving the switched
capacitor input stage of the AD876 without additional buffering.
In addition to the bandwidth, it is necessary to consider the
settling time of the multiplexer. In this case, the ADC has a
sample rate of 20 MHz which corresponds to a sampling
period of 50 ns. Typically, one phase of the sampling clock is
used for conversion (i.e., all levels are held steady) and the other
phase is used for switching and settling to the next channel.
Assuming a 50% duty cycle, the signal chain must settle within
25 ns. With a settling time to 0.1% of 15 ns, the multiplexer
easily satisfies this criterion.
In the example shown, the fourth (spare) channel of the
AD8174 is used to measure a reference voltage. This voltage
would probably be measured less frequently than the R, G and
B signals. Multiplexing a reference voltage offers the advantage
that any temperature drift effects caused by the multiplexer will
equally impact the reference voltage and the to-be-measured
signals. If the fourth channel is unused, it is good design
practice to tie the input permanently to ground.
CONTROL AND TIMING
R
G
CCD
B
CDS
CDS
CDS
REFERENCE
A0 A1 SD ENABLE
IN0
AD8174
IN1
VOUT
IN2
IN3 –VIN
1kΩ
(G = +1)
AD876
8/10-BIT
20MSPS
A/D
Figure 27. Color Document Scanner
REV. 0
–11–
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet AD8174.PDF ] | |
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