AD AD8074ARU 500 mhz, g = 1 and 2 triple video buffers with disable Datasheet

a
FEATURES
Dual Supply ⴞ5 V
High-Speed Fully Buffered Inputs and Outputs
600 MHz Bandwidth (–3 dB) 200 mV p-p
500 MHz Bandwidth (–3 dB) 2 V p-p
1600 V/␮s Slew Rate, G = +1
1350 V/␮s Slew Rate, G = +2
Fast Settling Time: 4 ns
Low Supply Current: <30 mA
Excellent Video Specifications (RL = 150 ⍀):
Gain Flatness of 0.1 dB to 50 MHz
0.01% Differential Gain Error
0.01ⴗ Differential Phase Error
“All Hostile“ Crosstalk
–80 dB @ 10 MHz
–50 dB @ 100 MHz
High “OFF” Isolation of 90 dB @ 10 MHz
Low Cost
Fast Output Disable Feature
500 MHz, G = +1 and +2 Triple
Video Buffers with Disable
AD8074/AD8075
FUNCTIONAL BLOCK DIAGRAM
AD8074 /AD8075
OE 1
16 VCC
15 VCC
DGND 2
IN2 3
G=
+1/+2
AGND 4
IN1 5
13 VEE
G=
+1/+2
VEE 8
12 OUT1
11 VCC
AGND 6
IN0 7
14 OUT2
G=
+1/+2
10 OUT0
9 VEE
APPLICATIONS
RGB Buffer in LCD and Plasma Displays
RGB Driver
Video Routers
Table I. Truth Table
PRODUCT DESCRIPTION
The AD8074/AD8075 are high-speed triple video buffers with
G = +1 and +2 respectively. They have a –3 dB full signal bandwidth in excess of 450 MHz, along with slew rates in excess of
1400 V/µs. With better than –80 dB of all hostile crosstalk and
90 dB isolation, they are useful in many high-speed applications. The differential gain and differential phase error are 0.01%
and 0.01°. Gain flatness of 0.1 dB up to 50 MHz makes the
AD8074/AD8075 ideal for RGB buffering or driving. They
consume less than 30 mA on a ± 5 V supply.
OE
OUT0, 1, 2
0
1
IN0, IN1, IN2
High Z
Both devices offer a high-speed disable feature that allows the
outputs to be put into a high impedance state. This allows the
building of larger input arrays while minimizing “OFF” channel output loading. The AD8074/AD8075 are offered in a
16-lead TSSOP package.
Rev. B
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 that
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.
www.analog.com
Tel: 781.329.4700
Fax: 781.461.3113
©2001–2011 Analog Devices, Inc. All rights reserved.
AD8074/AD8075–SPECIFICATIONS (T = 25ⴗC, V = ⴞ5 V, unless otherwise noted.)
A
Parameter
DYNAMIC PERFORMANCE
–3 dB Bandwidth (Small Signal)
–3 dB Bandwidth (Large Signal)
0.1 dB Bandwidth
Slew Rate
Settling Time to 0.1%
NOISE/DISTORTION PERFORMANCE
Differential Gain
Differential Phase
All Hostile Crosstalk
OFF Isolation
Voltage Noise
DC PERFORMANCE
Voltage Gain Error
Input Offset Voltage
S
Conditions
Min
Typ
VIN = 200 mV p-p, CL = 5 pF
VIN = 200 mV p-p, RL = 150 Ω
VIN = 2 V p-p, CL = 5 pF
VIN = 2 V p-p, RL = 150 Ω
VIN = 200 mV p-p, CL = 5 pF
VIN = 200 mV p-p, RL = 150 Ω
2 V Step, RL = 1 kΩ/150 Ω
2 V Step, RL = 1 kΩ/150 Ω
330/310
250/230
330/300
250/230
600/550
400/400
500/500
350/350
70/65
70/65
1600/1350
4/7.5
MHz
MHz
MHz
MHz
MHz
MHz
V/µs
ns
V = 3.58 MHz, 150 Ω
V = 3.58 MHz, 150 Ω
V = 10 MHz, RL = 1 kΩ
V = 100 MHz, RL = 1 kΩ
V = 10 MHz, RL = 150 Ω
V = 10 kHz to 100 MHz
0.01
0.01
–80/–74
–50/–44
90
19.5/22
%
Degrees
dB
dB
dB
nV/√Hz
No Load
± 0.1/± 0.2
2.5
3
10
5
TMIN to TMAX
Input Offset Drift
Input Bias Current
INPUT CHARACTERISTICS
Input Resistance
Input Capacitance
Channel Enabled
Channel Disabled
Input Voltage Range
OUTPUT CHARACTERISTICS
Output Voltage Swing
RL = 1 kΩ
+VS – 1.95
–VS + 2.1
+VS – 2.35
–VS + 2.30
RL = 150 Ω
Short Circuit Current (Protected)
Output Resistance
Output Capacitance
POWER SUPPLY
Operating Range
Power Supply Rejection Ratio
Quiescent Current
Enabled
Disabled
Disabled
3.5
+PSRR: +VS = +4.5 V to +5.5 V, –VS = –5 V
–PSRR: –VS = –4.5 V to –5.5 V, +VS = +5 V
All Channels “ON”
All Channels “OFF”
TMIN to TMAX
± 4.5
60
56
DIGITAL INPUT
Logic “1” Voltage
Logic “0” Voltage
Logic “1” Input Current
Logic “0” Input Current
OE Input
OE Input
OE = 4 V
OE = 0.4 V
2.0
OPERATING TEMPERATURE RANGE
Temperature Range
θJA
θJC
Operating (Still Air)
Operating (Still Air)
Operating
–40
Max
± 0.15/± 0.65
27/40
9.5/10
Unit
%
mV
mV
µV/°C
µA
10
1.5
1.5
± 2.8/± 1.4
MΩ
pF
pF
V
+VS – 1.8
–VS + 1.8
+VS – 2.2
–VS + 2.2
70
0.5
7.5
2.2
V
V
V
V
mA
Ω
MΩ
pF
± 5.5
74
64
21.5/24
3/4
23/26
30
5.5
0.8
100
1
+85
150.4
27.6
V
dB
dB
mA
mA
mA
V
V
nA
µA
°C
°C/W
°C/W
Specifications subject to change without notice.
–2–
Rev. B
AD8074/AD8075
ABSOLUTE MAXIMUM RATINGS 1
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.0 V
Internal Power Dissipation 2, 3
AD8074/AD8075 16-Lead TSSOP (RU) . . . . . . . . . . . . . 1 W
Input Voltage
IN0, IN1, IN2 . . . . . . . . . . . . . . . . . . . . . . . . . VEE ≤ VIN ≤ VCC
OE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DGND ≤ VIN ≤ VCC
Output Short Circuit Duration . . . . . . . . . . . . . . . . . . Indefinite3
Storage Temperature Range . . . . . . . . . . . . . . –65°C to +150°C
Lead Temperature Range (Soldering 10 sec) . . . . . . . . . . . 300°C
PIN CONFIGURATION
NOTES
1
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
2
Specification is for device in free air (T A = 25°C).
3
16-lead plastic TSSOP; θJA = 150.4°C/W. Maximum internal power dissipation (P D) should be derated for ambient temperature (T A ) such that
PD < (150°C – T A)/θJA.
AD8074 /AD8075
OE 1
16 VCC
15 VCC
DGND 2
IN2 3
G=
+1/+2
14 OUT2
AGND 4
IN1 5
13 VEE
G=
+1/+2
12 OUT1
11 VCC
AGND 6
IN0 7
G=
+1/+2
10 OUT0
9 VEE
VEE 8
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD8074/AD8075 features proprietary ESD protection circuitry, permanent damage may occur
on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions
are recommended to avoid performance degradation or loss of functionality.
MAXIMUM POWER DISSIPATION
WARNING!
ESD SENSITIVE DEVICE
1.5
TJ = 150ⴗC
MAXIMUM POWER DISSIPATION – Watts
The maximum power that can be safely dissipated by the AD8074/
AD8075 is limited by the associated rise in junction temperature.
The maximum safe junction temperature for plastic encapsulated
devices is determined by the glass transition temperature of the
plastic, approximately 150°C. Temporarily exceeding this limit
may cause a shift in parametric performance due to a change in
the stresses exerted on the die by the package. Exceeding a junction temperature of 175°C for an extended period can result in
device failure.
While the AD8074/AD8075 is internally short circuit protected,
this may not be sufficient to guarantee that the maximum junction
temperature (150°C) is not exceeded under all conditions. To
ensure proper operation, it is necessary to observe the maximum
power derating curves shown in Figure 1.
1.0
0.5
0
–50
–30
–10
0
10
30
50
70
90
AMBIENT TEMPERATURE – ⴗC
Figure 1. Maximum Power Dissipation vs. Temperature
Rev. B
–3–
AD8074/AD8075–Typical Performance Characteristics
1
0.4
GAIN
0.3
0
–1
0.2
–1
–2
0.1
–4
–0.1
–5
–0.2
2V p-p
0.3
0.2
2V p-p
–2
0.1
FLATNESS
–3
200mV p-p
0
–4
–0.1
–5
–0.2
–6
–0.3
–7
–0.4
–7
–0.4
–8
–0.5
–8
–0.5
–9
0.1
1
10
FREQUENCY – MHz
–6
100
–9
0.1
2
0.5
1
0.4
0
–1
0.3
–1
–2
0.2
2V p-p
–3
FLATNESS
0.1
0
–0.1
–5
200mV p-p
2V p-p
–0.2
200mV p-p
–7
FLATNESS – dB
GAIN
NORMALIZED GAIN – dB
0.6
–6
10
100
–0.6
1000
TPC 4. AD8075 Frequency Response; RL = 150 Ω
1
–4
1
FREQUENCY – MHz
2
0
–0.3
2V p-p
–0.6
1000
TPC 1. AD8074 Frequency Response; RL = 150 Ω
GAIN – dB
GAIN
–0.3
0.6
0.5
GAIN
0.4
0.3
2V p-p
–2
2V p-p
–4
0.2
0.1
–3
FLATNESS
0
–0.1
–5
–0.2
–6
–7
200mV p-p
–0.3
–8
–0.4
–8
–0.4
–9
–0.5
–9
–0.5
–10
0.1
1
10
FREQUENCY – MHz
100
–0.6
1000
–10
0.1
TPC 2. AD8074 Frequency Response; RL = 1 kΩ, CL = 5 pF
1
GAIN – dB
NORMALIZED GAIN – dB
0
–1
CL = 0pF
–2
CL = 5pF
–3
–4
VIN
VOUT
CL
75⍀
1k⍀
–7
0
–1
CL = 0pF
–2
CL = 5pF
–3
–4
–5
–6
VIN
VOUT
CL
75⍀
150k⍀
–7
–8
–10
0.1
CL = 10pF
2
1
–9
–0.6
1000
3
CL = 10pF
2
–6
10
100
FREQUENCY – MHz
TPC 5. AD8075 Frequency Response; RL = 1 kΩ, CL = 5 pF
3
–5
1
NORMALIZED FLATNESS – dB
GAIN – dB
0
FLATNESS – dB
200mV p-p
FLATNESS
–3
NORMALIZED GAIN – dB
0
NORMALIZED FLATNESS – dB
0.4
1
–8
VOUT = 2V p-p
1
–9
10
FREQUENCY – MHz
100
–10
0.1
1000
TPC 3. AD8074 Frequency Response vs. Capacitive Load
VOUT = 2V p-p
1
10
FREQUENCY – MHz
100
1000
TPC 6. AD8075 Frequency Response vs. Capacitive Load
–4–
Rev. B
AD8074/AD8075
0
0
VOUT = 2V p-p (ACTIVE CHANNEL(s))
RL = 1k⍀
RT = 37.5⍀
–10
–20
–20
–30
CROSSTALK – dB
–30
CROSSTALK – dB
VOUT = 2V p-p (ACTIVE CHANNEL(s))
RL = 150⍀
RT = 37.5⍀
–10
–40
–50
–60
ALL-HOSTILE
–70
–40
–50
ALL-HOSTILE
–60
–70
–80
–80
ADJACENT
ADJACENT
–90
–90
–100
–100
–110
–110
0.1
1
10
100
0.1
1000
1
TPC 7. AD8074 Crosstalk vs. Frequency (All Hostile and
Adjacent RL = 1 kΩ)
1000
0
VOUT = 2V p-p
RL = 150⍀
RT = 37.5⍀
–10
–20
–20
–30
–40
–50
SECOND
HARMONIC
–60
VOUT = 2V p-p
RL = 150⍀
RT = 37.5⍀
–10
DISTORTION – dBc
DISTORTION – dBc
100
TPC 9. AD8075 Crosstalk vs. Frequency (All Hostile and
Adjacent RL = 150 Ω)
0
–70
–80
–30
–40
SECOND
HARMONIC
–50
–60
–70
THIRD
HARMONIC
–80
THIRD
HARMONIC
–90
–90
–100
–100
1
10
100
1
1000
10
100
1000
FUNDAMENTAL FREQUENCY – MHz
FUNDAMENTAL FREQUENCY – MHz
TPC 8. AD8074 Distortion vs. Frequency
Rev. B
10
FREQUENCY – MHz
FREQUENCY – MHz
TPC 10. AD8075 Distortion vs. Frequency
–5–
–20
–20
–30
–30
–40
–40
OFF ISOLATION – dB
OFF ISOLATION – dB
AD8074/AD8075
–50
–60
–70
RL = 1k⍀
–80
–90
–50
–60
RL = 1k⍀
–70
–80
RL = 150⍀
–90
RL = 150⍀
–100
–100
–110
–110
0.1
1
10
100
1000
1
0.1
1000
TPC 14. AD8075 Off Isolation vs. Frequency
10
20
0
10
0
–PSRR
–10
PSRR – dB
–20
PSRR – dB
100
TPC 11. AD8074 Off Isolation vs. Frequency
–10
–30
+PSRR
–40
+PSRR
–20
–PSRR
–30
–50
–40
–60
–50
–70
–60
–80
–70
1
0.1
10
100
1000
0.1
1
FREQUENCY – MHz
100
1000
TPC 15. AD8075 PSRR vs. Frequency
400
300
350
VOLTAGE NOISE – nV/ Hz
350
250
200
150
100
50
0
10
FREQUENCY – MHz
TPC 12. AD8074 PSRR vs. Frequency
VOLTAGE NOISE – nV/ Hz
10
FREQUENCY – MHz
FREQUENCY – MHz
300
250
200
150
100
50
10
100
1k
10k
FREQUENCY – Hz
100k
0
10
1M
100
1k
10k
FREQUENCY – Hz
100k
1M
TPC 16. AD8075 Voltage Noise vs. Frequency
TPC 13. AD8074 Voltage Noise vs. Frequency
–6–
Rev. B
AD8074/AD8075
1000
1000
INPUT IMPEDANCE – k⍀
10000
INPUT IMPEDANCE – k⍀
10000
100
10
1
100
10
1
0.1
0.1
0.01
0.01
0.1
1
10
100
1000
0.1
1
FREQUENCY – MHz
100
100
OUTPUT IMPEDANCE – ⍀
1000
OUTPUT IMPEDANCE – ⍀
1000
10
1
1000
10
1
0.1
0.1
0.1
1
10
100
0.1
1000
1
10
100
1000
FREQUENCY – MHz
FREQUENCY – MHz
TPC 21. AD8075 Output Impedance vs. Frequency;
Enabled
TPC 18. AD8074 Output Impedance vs. Frequency;
Enabled
1000
100
100
OUTPUT IMPEDANCE – k⍀
1000
OUTPUT IMPEDANCE – k⍀
100
TPC 20. AD8075 Input Impedance vs. Frequency
TPC 17. AD8074 Input Impedance vs. Frequency
10
1
0.1
10
1
0.1
0.01
0.01
0.001
0.001
0.1
1
10
100
0.1
1000
1
10
100
1000
FREQUENCY – MHz
FREQUENCY – MHz
TPC 22. AD8075 Output Impedance vs. Frequency;
Disabled
TPC 19. AD8074 Output Impedance vs. Frequency;
Disabled
Rev. B
10
FREQUENCY – MHz
–7–
AD8074/AD8075
0.15
0.15
VO = 200mV STEP
VO = 200mV STEP
0.10
0.10
0.05
0.05
0
0
–0.05
–0.05
–0.10
–0.10
2ns
2ns
–0.15
–0.15
TPC 23. AD8074 Small Signal Pulse Response (RL = 1 kΩ,
CL = 5 pF)
TPC 26. AD8075 Small Signal Pulse Response (RL = 150 kΩ)
0.8
0.8
0.7
0.7
VO = 700mV STEP
0.6
VO = 700mV STEP
0.6
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0
2ns
–0.1
0
–0.2
–0.1
2ns
TPC 24. AD8074 Video Amplitude Pulse Response
(RL = 1 kΩ, CL = 5 pF)
TPC 27. AD8075 Video Amplitude Pulse Response
(RL = 150 Ω)
1.5
1.5
VO = 2V STEP
VO = 2V STEP
1.0
1.0
0.5
0.5
0
0
–0.5
–0.5
–1.0
–1.0
2ns
2ns
–1.5
–1.5
TPC 28. AD8075 Large Signal Pulse Response (RL = 150 Ω)
TPC 25. AD8074 Large Signal Pulse Response
(RL = 1 kΩ, CL = 5 pF)
–8–
Rev. B
AD8074/AD8075
THEORY OF OPERATION
The AD8074 (G = +1) and AD8075 (G = +2) are triple-channel,
high-speed buffers with TTL-compatible output enable control.
Optimized for buffering RGB (red, green, blue) video sources,
the devices have high peak slew rates, maintaining their bandwidth for large signals. Additionally, the buffers are compensated
for high phase margin, minimizing overshoot for good pixel
resolution. The buffers also have video specifications that are
suitable for buffering NTSC or PAL composite signals.
The buffers are organized as three independent channels, each
with an input transconductance stage and an output transimpedance stage. Each channel is characterized by low input
capacitance and high input impedance. The transconductance
stages, NPN differential pairs, source signal current into the folded
cascode output stages. Each output stage contains a compensating network and emitter follower output buffer. Internal voltage
feedback sets the gain, the AD8074 being configured as a unity
gain follower, and the AD8075 as a gain-of-two amplifier with a
feedback network. The architecture provides drive for a reverseterminated video load (150 Ω) with low differential gain and
phase error for relatively low power consumption. Careful chip
design and layout allow excellent crosstalk isolation between
channels.
One logic pin, OE, controls whether the three outputs are
enabled, or disabled to a high-impedance state. The high impedance disable allows larger matrices to be built when busing the
outputs together. When disabled, the AD8074 and AD8075 consume a fifth the power as when enabled. In the case of the
AD8075 (G = +2), a feedback isolation scheme is used so that
the impedance of the gain-of-two feedback network does not
load the output.
Full power bandwidth for an undistorted sinusoid is often calculated using peak slew rate from the equation:
Full Power Bandwidth =
Peak Slew Rate
2 × π × Sinusoidal Amplitude
Peak slew rate is not the same as average slew rate (25% to
75%) which is typically specified. For a natural response, peak
slew rate may be 2.7 times larger than average slew rate. Therefore, calculating a full power bandwidth with a specified average
slew rate will give a pessimistic result.
The primary cause of overshoot in these amplifiers is the presence of large reactive loads at the output and insufficient series
isolation of the load. However, it is possible to overdrive these
amplifiers with 1 V, subnanosecond input-pulse edges. The
ensuing dynamics may give rise to subnanosecond overshoot. To
reduce these effects, an edge-rate limiting network at the input
should be considered for input transition times less than 0.5 ns.
Rev. B
APPLICATIONS
Response Tuning
It has been mentioned in passing that the primary cause of overshoot for the AD8074 and AD8075 is the presence of large
reactive loads at the output. If the system exhibits excessive
ringing while settling, a 10 Ω–50 Ω series resistor may be used
at the output to isolate the emitter-follower output buffer from
the reactive load. If the output exhibits an overdamped response,
the system designer may add a few pF shunt capacitance at the
output to tune for a faster edge transition. A system with a small
degree of overshoot will settle faster than an overdamped system.
2.0
RS = 10⍀
CL = 10pF
1.5
1.0
RS = 0⍀
CL = 5pF
0.5
RS = 20⍀
CL = 15pF
0
–0.5
–1.0
RS
VIN
–1.5
75⍀
CL
VOUT
1k⍀
2ns
–2.0
Figure 2. Driving Capacitive Loads
Single Supply Operation
The AD8074 and AD8075 may be operated from a single 10 V
supply. In this configuration, the AD8075’s AGND pins must
be tied near midsupply, as AGND provides the reference for the
ground buffer, to which the internal gain network is terminated.
Logic is referenced to DGND. The buffers are disabled in single
supply operation for VOE > V DGND + ~2.0 V and enabled for
VOE < VDGND + 0.8 V. TTL logic levels are expected. The following restrictions are placed upon the digital ground potential:
3.5 V ≤ VAVCC – VDGND ≤ 12 V
VDGND ≥ VAVEE
The architecture of the output buffer is such that the output
voltage can swing to within ~2.3 V of either rail. For example, if
the output need swing only 2 V, then the buffers could be operated on dual 3.5 V or single 7 V supplies. It is cautioned that
saturation effects may become noticeable when the output swings
within 2.6 V of either rail. The system designer may opt to
use this characteristic to his or her advantage by using the
soft-saturation regime, (2.2 V–2.6 V from the supply rails), to
tame excessive overshoot. The designer is cautioned that a
charge storage associated time delay of several nanoseconds is
incurred when recovering from soft-saturation. This effect
results in longer settling tails.
–9–
AD8074/AD8075
can be connected to the same signal, as is done in some studiotype TV monitors.
RGB Buffer for Second Monitor
The RGB signals for PC monitors are driven through coax
cables whose characteristic impedance is 75 Ω. The graphics
chip will generally have current-source output drivers that should
be double terminated with a 75 Ω shunt termination at each end.
On the transmit end, the shunt terminations are provided to
ground close to the graphics IC, while the monitor terminates
its end via internal termination resistors. While this scheme works
well and is virtually foolproof for a single monitor, it leaves no
means for passively connecting a second monitor to the same source.
A way around this problem is to connect the first monitor to the
RGB channels in the standard fashion, and then to provide a
triple gain-of-two buffer to drive the second monitor. The AD8075
is designed to provide this function and also provide excellent
high-frequency performance for high-resolution graphics signals.
Figure 3 shows a schematic of this circuit.
The outputs of the AD8075 are low impedance voltage sources
and are therefore series-terminated with 75 Ω resistors. The
internal resistors in Monitor #2 provide the terminations at its
end. The overall effect of this type of termination scheme is to
divide the signal amplitude by two. This is compensated by the
gain of two provided by the AD8075.
A second monitor that is connected simply in parallel will provide an extra set of terminations that will upset the signal levels.
To keep costs low, most computer monitors do not have the ability
to open-circuit the terminations in order that an additional monitor
MONITOR #1
PC GRAPHICS IC
R
CURRENT SOURCE
OUTPUT DRIVERS
75⍀
75⍀
75⍀
75⍀
75⍀
75⍀
G
INTERNAL
TERMINATIONS
B
+5V
25␮F
+
+5V
0.1␮F
+5V
0.1␮F
0.1␮F
MONITOR #2
75⍀
75⍀
AD8075
75⍀
75⍀
INTERNAL
TERMINATIONS
75⍀
75⍀
25␮F
0.1␮F
+
–5V
0.1␮F
–5V
0.1␮F
–5V
Figure 3. Buffer
–10–
Rev. B
AD8074/AD8075
Triple Video Multiplexer
and the amplifier output are disabled to a high impedance to
provide a high-impedance disabled state.
The AD8074 and AD8075 each have an output-enable function
that can be used to disable the outputs and put them in a highimpedance state. Usually, for a unity-gain device, it is relatively
easy to provide high disabled impedance, because the feedback
path is from the output to a high-impedance input. However, for a
non-unity-gain part, the feedback provides a resistive path to
ground. This will usually dominate the disabled output impedance, and make it a much lower value than the unity-gain device.
To construct a multiplexer, the outputs from one or more devices
are connected in parallel and only one device is enabled at a
time while all of the others are disabled. The two sets of inputs
are applied individually to each of the separate device inputs.
Figure 4 shows the circuit details for this function. The first RGB
Source 1 is input to the first AD8075. Each of the individual
signals is terminated to ground with 75 Ω to provide proper
termination for the input cables. In a similar fashion, the Source
2 signals are input to the second AD8075.
The AD8075 has an internal buffer that provides a low-impedance,
ground level output that terminates the feedback path during
enabled operation. In the disabled state, both this buffer output
+5V
25␮F
+
+5V
0.1␮F
+5V
0.1␮F
0.1␮F
75⍀
R
R
75⍀
AD8075
75⍀
SOURCE 1
G
G
75⍀
75⍀
B
B
75⍀
OE
25␮F
0.1␮F
+
–5V
0.1␮F
–5V
0.1␮F
–5V
SEL1/SEL2
+5V
25␮F
+
+5V
0.1␮F
+5V
0.1␮F
0.1␮F
OE
75⍀
R
75⍀
AD8075
75⍀
SOURCE 2
G
75⍀
75⍀
B
75⍀
25␮F
0.1␮F
+
–5V
0.1␮F
–5V
Figure 4. Mux
Rev. B
–11–
0.1␮F
–5V
OUTPUT
AD8074/AD8075
Each of the six outputs has a 75 Ω series resistor that is used to
reverse-terminate the output transmission line. The corresponding outputs are then wired in parallel and delivered to the output
cable. The termination resistors in this position help to isolate
the off capacitance of the disabled device’s outputs from loading
the enabled device’s outputs. The gain-of-two of the AD8075
compensates for the signal halving that occurs as a result of the
output terminations.
A select signal is provided directly to the OE of the second
AD8075 and an inverted version is used to drive the other device’s
OE. This will ensure that only one device is active at a time. Since
there is a total of 150 Ω in series between any two outputs, it is
not essential to be overly concerned about the exact timing of
the making and breaking of the enable signals.
A major area of focus should be the power distribution system.
There should be a full ground plane that provides the reference
and return paths for both the inputs and outputs. The ground
also provides isolation between the input signals to minimize the
crosstalk. This ground plane should cover as wide an area as
possible and be minimally interrupted in order to keep its
impedance to a minimum.
The power planes should also be as broad as possible to provide
minimal inductance, which is required for high-slew-rate signals. These power planes layers should be spaced closely to the
ground plane to increase the interplane capacitance between the
supplies and ground.
Each supply pin should be bypassed with a low inductance
0.1 µF ceramic capacitance with minimal excess circuit length
to minimize the series impedance. A 25 µF tantalum electrolytic capacitor will supply a charge reservoir for lower frequency,
high-amplitude transitions.
Additional inputs can easily be added to the circuit shown to
make wider multiplexers. The outputs of all of the devices will
be wired in parallel, and the logic must allow that only one output
be enabled at a time.
If it is desired to make a triple 3:1 multiplexer, a triple 2:1 multiplexer, like the AD8185 can be used along with the AD8075.
The same general guidelines for input and output treatment
should be followed and the logic must perform the proper function.
If it is desired to design such a multiplexer at unity gain, the
AD8074 should be used. For a triple 3:1 multiplexer, an
AD8183 (triple 2:1 mux) can be combined with an AD8074 to
provide this function.
Layout and Grounding
The AD8074 and AD8075 are extreme bandwidth, high-slew-rate
devices that are designed to drive up to the highest resolution
monitors and provide excellent resolution. To realize their full
performance potential, it is essential to adhere to the best practices of high-speed PCB layout.
The input and output signals should be run as directly as possible in order to minimize the effects of parasitics. If they must
run over a longer distance of more than a few centimeters, controlled impedance PCB traces should be used to minimize the
effect of reflections due to mismatches in impedance and the
proper termination should be provided.
To avoid excess crosstalk, the above recommendations should
be followed carefully. The power system and signal routing are
the most important aspects of preventing excess crosstalk.
Beyond these techniques, shielding can be provided by ground
traces between adjacent signals, especially those that travel
parallel over long distances.
–12–
Rev. B
AD8074/AD8075
TP2
VEE
P1
DO NOT INSTALL
VEE
VEE
50⍀ IMPEDANCE LINE
1
C2
10␮F
+
TP3
TP4
AGND
AGND
AGND
VCC
AGND
AGND
R16
20k⍀
P1
AGND
2
TP1
W2
VCC
TP5
P1
3
DO NOT INSTALL
VCC
+
C1
10␮F
AGND
VCC
50⍀ IMPEDANCE LINE
50⍀ IMPEDANCE LINE
DISOUT
AGND
DISOUT
R11
50⍀
DO NOT INSTALL
AGND
IN2
75⍀ IMPEDANCE LINE
IN2
C3
0.1␮F
DO NOT INSTALL
R1
75⍀
AGND
DUT
AGND
IN1
75⍀ IMPEDANCE LINE
AGND
AGND
R2
75⍀
AGND
AGND
IN0
75⍀ IMPEDANCE LINE
IN0
AGND
3 IN2
C13
0.01␮F
C6
0.1␮F
AGND
C8
0.01␮F
VCC 15
R6
150⍀
DO NOT INSTALL
AGND
R8
75⍀
VEE 13
OUT1 12
6 AGND
VCC 11
AGND
AGND
VEE
C11
0.01␮F
AGND
C12
0.01␮F
75⍀ IMPEDANCE LINE
OUT1
DO NOT INSTALL
AGND
AGND
R9
75⍀
75⍀ IMPEDANCE LINE
OUT0
DO NOT INSTALL
AGND
Figure 5. Evaluation Board Schematic
–13–
OUT1
AGND
R12
150⍀
Rev. B
OUT2
R10
150⍀
VCC
OUT0 10
VEE 9
AD8074
75⍀ IMPEDANCE LINE
OUT2
AGND
OUT2 14
5 IN1
R7
75⍀
VEE
VCC 16
4 AGND
7 IN0
8 VEE
VEE
R3
75⍀
1 OE
2 DGND
AGND
C7
0.1␮F
AGND
IN1
VCC
C14
0.01␮F
C15
0.01␮F
AGND
OUT0
AD8074/AD8075
Figure 6. Component Side
Figure 8. Silkscreen Top
Figure 7. Circuit Side
Figure 9. Silkscreen Bottom
Figure 10. Internal 2
–14–
Rev. B
AD8074/AD8075
OUTLINE DIMENSIONS
5.10
5.00
4.90
16
9
4.50
4.40
4.30
6.40
BSC
1
8
PIN 1
1.20
MAX
0.15
0.05
0.20
0.09
0.30
0.19
0.65
BSC
COPLANARITY
0.10
SEATING
PLANE
8°
0°
0.75
0.60
0.45
COMPLIANT TO JEDEC STANDARDS MO-153-AB
Figure 1. 16-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-16)
Dimensions shown in millimeters
ORDERING GUIDE
Model1
AD8074ARU
AD8074ARUZ
AD8074ARUZ-REEL
AD8074ARUZ-REEL7
AD8075ARUZ
AD8075ARUZ-REEL
AD8075ARUZ-REEL7
AD8074Z-EVAL
AD8075Z-EVAL
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
Package Description
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
16-Lead Thin Shrink Small Outline Package [TSSOP]
Evaluation Board
Evaluation Board
Z = RoHS Compliant Part.
REVISION HISTORY
10/11—Rev. A to Rev. B
Changes to Ordering Guide ...........................................................15
10/01—Rev. 0 to Rev. A
Changes to Single-Supply Operation Section................................ 9
©2001–2011 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D02391-0-10/11(B)
Rev. B
-15-
Package Option
RU-16
RU-16
RU-16
RU-16
RU-16
RU-16
RU-16