Analog Devices AD8075ARU, AD8075, AD8074ARU, AD8074 Datasheet

500 MHz, G = +1 and +2 Triple

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 (R

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

APPLICATIONS
RGB Buffer in LCD and Plasma Displays
RGB Driver
Video Routers

= 150 ⍀):

L

Video Buffers with Disable

AD8074/AD8075

FUNCTIONAL BLOCK DIAGRAM

AD8074 /AD8075

OE

DGND

IN2

AGND

IN1

AGND

IN0

V

1

2

G =

3

+1/+2

4

G =

5

+1/+2

6

G =

7

+1/+2

8

EE

V

16

CC

V

15

CC

14

OUT2

13

V

EE

12

OUT1

V

11

CC

OUT0

10

V

9

EE

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.

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. A

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.

Table I. Truth Table

OE OUT0, 1, 2

0 IN0, IN1, IN2
1 High Z

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] © Analog Devices, Inc., 2001

AD8074/AD8075–SPECIFICATIONS

(TA = 25ⴗC, VS = ⴞ5 V, unless otherwise noted.)

Parameter Conditions Min Typ Max Unit

DYNAMIC PERFORMANCE

–3 dB Bandwidth (Small Signal) V

–3 dB Bandwidth (Large Signal) V

0.1 dB Bandwidth V

Slew Rate 2 V Step, R

= 200 mV p-p, CL = 5 pF 330/310 600/550 MHz

IN

V

= 200 mV p-p, RL = 150 Ω 250/230 400/400 MHz

IN

= 2 V p-p, CL = 5 pF 330/300 500/500 MHz

IN

V

= 2 V p-p, RL = 150 Ω 250/230 350/350 MHz

IN

= 200 mV p-p, CL = 5 pF 70/65 MHz

IN

V

= 200 mV p-p, RL = 150 Ω 70/65 MHz

IN

= 1 kΩ/150 Ω 1600/1350 V/µs

L

Settling Time to 0.1% 2 V Step, RL = 1 kΩ/150 Ω 4/7.5 ns

NOISE/DISTORTION PERFORMANCE

Differential Gain V = 3.58 MHz, 150 Ω 0.01 %
Differential Phase V = 3.58 MHz, 150 Ω 0.01 Degrees
All Hostile Crosstalk V = 10 MHz, R

V = 100 MHz, R

OFF Isolation V = 10 MHz, R

= 1 kΩ –80/–74 dB

L

= 1 kΩ –50/–44 dB

L

= 150 Ω 90 dB

L

Voltage Noise V = 10 kHz to 100 MHz 19.5/22 nV/√Hz

DC PERFORMANCE

Voltage Gain Error No Load ±0.1/±0.2 ±0.15/± 0.65 %
Input Offset Voltage 2.5 27/40 mV

to T

T

MIN

MAX

3mV

Input Offset Drift 10 µV/°C
Input Bias Current 5 9.5/10 µA

INPUT CHARACTERISTICS

Input Resistance 10 MΩ
Input Capacitance Channel Enabled 1.5 pF

Channel Disabled 1.5 pF

Input Voltage Range ±2.8/±1.4 V

OUTPUT CHARACTERISTICS

Output Voltage Swing R

= 1 kΩ +VS – 1.95 +VS – 1.8 V

L

R

= 150 Ω +VS – 2.35 +VS – 2.2 V

L

+ 2.1 –VS + 1.8 V

–V

S

+ 2.30 –VS + 2.2 V

–V

S

Short Circuit Current (Protected) 70 mA
Output Resistance Enabled 0.5 Ω

Disabled 3.5 7.5 MΩ

Output Capacitance Disabled 2.2 pF

POWER SUPPLY

Operating Range ±4.5 ±5.5 V
Power Supply Rejection Ratio +PSRR: +V

–PSRR: –V

= +4.5 V to +5.5 V, –VS = –5 V 60 74 dB

S

= –4.5 V to –5.5 V, +VS = +5 V 56 64 dB

S

Quiescent Current All Channels “ON” 21.5/24 30 mA

All Channels “OFF” 3/4 5.5 mA
T

MIN

to T

MAX

23/26 mA

DIGITAL INPUT

Logic “1” Voltage OE Input 2.0 V
Logic “0” Voltage OE Input 0.8 V
Logic “1” Input Current OE = 4 V 100 nA
Logic “0” Input Current OE = 0.4 V 1 µA

OPERATING TEMPERATURE RANGE

Temperature Range Operating (Still Air) –40 +85 °C

θ

JA

θ

JC

Specifications subject to change without notice.

Operating (Still Air) 150.4 °C/W
Operating 27.6 °C/W

–2–

REV. A

AD8074/AD8075

AMBIENT TEMPERATURE – ⴗC

MAXIMUM POWER DISSIPATION – Watts

TJ = 150ⴗC

010 30 50

70

90

0

0.5

1.0

1.5

–50 –30 –10

ABSOLUTE MAXIMUM RATINGS

Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.0 V

Internal Power Dissipation

2, 3

1

AD8074/AD8075 16-Lead TSSOP (RU) . . . . . . . . . . . . . 1 W

Input Voltage

IN0, IN1, IN2 . . . . . . . . . . . . . . . . . . . . . . . . . VEE ≤ VIN ≤ V

OE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DGND ≤ VIN ≤ V

Output Short Circuit Duration . . . . . . . . . . . . . . . . . . Indefinite

CC

CC

3

Storage Temperature Range . . . . . . . . . . . . . . –65°C to +150°C

Lead Temperature Range (Soldering 10 sec) . . . . . . . . . . . 300°C

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 (TA = 25°C).

3

16-lead plastic TSSOP; θJA = 150.4°C/W. Maximum internal power dissipa­tion (P

) should be derated for ambient temperature (TA) such that

D

PD < (150°C – TA)/θJA.

ORDERING GUIDE

Temperature Package Package

Model Range Description Option

AD8074ARU –40°C to +85°C 16-Lead Plastic TSSOP RU-16
AD8075ARU –40°C to +85°C 16-Lead Plastic TSSOP RU-16
AD8074-EVAL Evaluation Board
AD8075-EVAL Evaluation Board

PIN CONFIGURATION

AD8074 /AD8075

OE

DGND

IN2

AGND

IN1

AGND

IN0

V

1

2

G =

3

+1/+2

4

G =

5

+1/+2

6

G =

7

+1/+2

8

EE

V

16

CC

V

15

CC

14

OUT2

13

V

EE

12

OUT1

V

11

CC

OUT0

10

V

9

EE

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

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.

Figure 1. Maximum Power Dissipation vs. Temperature

WARNING!

ESD SENSITIVE DEVICE

REV. A

–3–

AD8074/AD8075–Typical Performance Characteristics

FLATNESS

GAIN

2V p-p

200mV p-p

2V p-p

FREQUENCY – MHz

0.1 10001 10 100

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

0.4

0.3

0.2

0.1

0

–0.1

–0.2

–0.3

–0.4

–0.5

–0.6

NORMALIZED FLATNESS – dB

NORMALIZED GAIN – dB

0.1 10001 10 100

2

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

–10

0.6

0.5

0.4

0.3

0.2

0.1

0

–0.1

–0.2

–0.3

–0.4

–0.5

–0.6

2V p-p

GAIN

FLATNESS

NORMALIZED FLATNESS – dB

NORMALIZED GAIN – dB

200mV p-p

FREQUENCY – MHz

2V p-p

1

GAIN

0

–1

–2

FLATNESS

–3

–4

GAIN – dB

–5

–6

–7

–8

–9

0.1 10001 10 100
FREQUENCY – MHz

200mV p-p

2V p-p

TPC 1. AD8074 Frequency Response; RL = 150

2

1

GAIN

0

–1

–2

–3

FLATNESS

–4

–5

GAIN – dB

–6

–7

–8

–9

–10

0.1 10001 10 100

200mV p-p
2V p-p

FREQUENCY – MHz

2V p-p

200mV p-p

0.4

0.3

0.2

0.1

0

–0.1

–0.2

–0.3

–0.4

–0.5

–0.6

Ω

0.6

0.5

0.4

0.3

0.2

0.1

0

–0.1

–0.2

–0.3

–0.4

–0.5

–0.6

FLATNESS – dB

FLATNESS – dB

TPC 4. AD8075 Frequency Response; RL = 150

Ω

TPC 2. AD8074 Frequency Response; RL = 1 kΩ, CL = 5 pF

3

2

1

0

–1

–2

–3

–4

GAIN – dB

V

–5

IN

75

–6

–7

–8

TPC 3. AD8074 Frequency Response vs. Capacitive Load

–9

–10

0.1 1 10 100 1000

⍀

V

= 2V p-p

OUT

CL = 10pF

CL = 0pF

CL = 5pF

C

FREQUENCY – MHz

L

1k

TPC 5. AD8075 Frequency Response; RL = 1 kΩ, CL = 5 pF

3

2

1

0

–1

–2

–3

–4

V

OUT

⍀

–4–

–5

V

IN

NORMALIZED GAIN – dB

–10

–6

–7

–8

–9

75⍀

V

= 2V p-p

OUT

0.1 1 10 100 1000
FREQUENCY – MHz

TPC 6. AD8075 Frequency Response vs. Capacitive Load

CL = 10pF

CL = 0pF

CL = 5pF

V

C

L

150k⍀

OUT

REV. A

0

FREQUENCY – MHz

0

0.1 1000

1 10 100

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

V

OUT

= 2V p-p (ACTIVE CHANNEL(s))

R

L

= 150⍀

R

T

= 37.5⍀

ALL-HOSTILE

ADJACENT

CROSSTALK – dB

V

= 2V p-p (ACTIVE CHANNEL(s))

OUT

–10

= 1k⍀

R

L

= 37.5⍀

R

T

–20

–30

–40

–50

–60

ALL-HOSTILE

ADJACENT

1 10 100

FREQUENCY – MHz

–70

CROSSTALK – dB

–80

–90

–100

–110

0.1 1000

TPC 7. AD8074 Crosstalk vs. Frequency (All Hostile and
Adjacent R

= 1 kΩ)

L

AD8074/AD8075

TPC 9. AD8075 Crosstalk vs. Frequency (All Hostile and
Adjacent R

= 150 Ω)

L

0

V

= 2V p-p

OUT

–10

= 150⍀

R

L

= 37.5⍀

R

T

–20

–30

–40

–50

–60

DISTORTION – dBc

–70

–80

–90

–100

1 100010 100

SECOND

HARMONIC

THIRD

HARMONIC

FUNDAMENTAL FREQUENCY – MHz

TPC 8. AD8074 Distortion vs. Frequency

0

V

= 2V p-p

OUT

–10

–20

–30

–40

–50

–60

DISTORTION – dBc

–70

–80

–90

–100

= 150⍀

R

L

= 37.5⍀

R

T

SECOND

HARMONIC

THIRD

HARMONIC

1 100010 100

FUNDAMENTAL FREQUENCY – MHz

TPC 10. AD8075 Distortion vs. Frequency

REV. A

–5–

AD8074/AD8075

–20

–30

–40

–50

–60

–70

–80

OFF ISOLATION – dB

–90

–100

–110

0.1 1000

RL = 1k⍀

RL = 150⍀

1 10 100

FREQUENCY – MHz

TPC 11. AD8074 Off Isolation vs. Frequency

10

0

–10

–20

–30

–40

PSRR – dB

–50

–60

–70

–80

0.1 1000

1 10 100

–PSRR

+PSRR

FREQUENCY – MHz

–20

–30

–40

–50

–60

–70

–80

OFF ISOLATION – dB

–90

–100

–110

0.1 10001 10 100

FREQUENCY – MHz

RL = 1k⍀

RL = 150⍀

TPC 14. AD8075 Off Isolation vs. Frequency

20

10

0

–10

–20

–30

PSRR – dB

–40

–50

–60

–70

0.1 1000

1 10 100

+PSRR

–PSRR

FREQUENCY – MHz

TPC 12. AD8074 PSRR vs. Frequency

350

300

250

200

150

100

VOLTAGE NOISE – nV/ Hz

50

0

10 100 1M1k 10k 100k

FREQUENCY – Hz

TPC 13. AD8074 Voltage Noise vs. Frequency

TPC 15. AD8075 PSRR vs. Frequency

400

350

300

250

200

150

VOLTAGE NOISE – nV/ Hz

100

50

0

10 100 1M1k 10k 100k

FREQUENCY – Hz

TPC 16. AD8075 Voltage Noise vs. Frequency

–6–

REV. A

AD8074/AD8075

10000

1000

100

10

1

INPUT IMPEDANCE – k⍀

0.1

0.01

0.1 1000

1 10 100

FREQUENCY – MHz

TPC 17. AD8074 Input Impedance vs. Frequency

1000

100

10

10000

1000

100

10

1

INPUT IMPEDANCE – k⍀

0.1

0.01

0.1 10001 10 100

FREQUENCY – MHz

TPC 20. AD8075 Input Impedance vs. Frequency

1000

100

10

OUTPUT IMPEDANCE – ⍀

1

0.1

0.1 1000

1 10 100

FREQUENCY – MHz

TPC 18. AD8074 Output Impedance vs. Frequency;
Enabled

1000

100

10

1

0.1

OUTPUT IMPEDANCE – k⍀

0.01

0.001

0.1 1000

1 10 100

FREQUENCY – MHz

OUTPUT IMPEDANCE – ⍀

1

0.1

0.1 10001 10 100

FREQUENCY – MHz

TPC 21. AD8075 Output Impedance vs. Frequency;
Enabled

1000

100

10

1

0.1

OUTPUT IMPEDANCE – k⍀

0.01

0.001

0.1 1000

1 10 100

FREQUENCY – MHz

TPC 19. AD8074 Output Impedance vs. Frequency;
Disabled

REV. A

TPC 22. AD8075 Output Impedance vs. Frequency;
Disabled

–7–

AD8074/AD8075

0.15

VO = 200mV STEP

0.10

0.05

0

–0.05

–0.10

–0.15

2ns

TPC 23. AD8074 Small Signal Pulse Response (RL = 1 kΩ,

= 5 pF)

C

L

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

–0.1

–0.2

VO = 700mV STEP

2ns

TPC 24. AD8074 Video Amplitude Pulse Response
(R

= 1 kΩ, CL = 5 pF)

L

0.15

VO = 200mV STEP

0.10

0.05

0

–0.05

–0.10

–0.15

2ns

TPC 26. AD8075 Small Signal Pulse Response (RL = 150 kΩ)

0.8

0.7

V

0.6

0.5

0.4

0.3

0.2

0.1

0

–0.1

= 700mV STEP

O

2ns

TPC 27. AD8075 Video Amplitude Pulse Response
(R

= 150 Ω)

L

1.5

VO= 2V STEP

1.0

0.5

0

–0.5

–1.0

–1.5

2ns

TPC 25. AD8074 Large Signal Pulse Response
(R

= 1 kΩ, CL = 5 pF)

L

1.5

VO = 2V STEP

1.0

0.5

0

–0.5

–1.0

2ns

–1.5

TPC 28. AD8075 Large Signal Pulse Response (RL = 150 Ω)

–8–

REV. A

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

Sinusoidal Amplitude

××2 π

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.

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

1.5

1.0

0.5

–0.5

–1.0

–1.5

–2.0

0

RS = 0⍀

= 5pF

C

L

V

IN

75⍀

RS = 10⍀

= 10pF

C

L

RS = 20⍀

= 15pF

C

L

R

S

C

L

1k⍀

V

OUT

2ns

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 V
V

OE

< V

+ 0.8 V. TTL logic levels are expected. The fol-

DGND

OE

> V

+ ~2.0 V and enabled for

DGND

lowing restrictions are placed upon the digital ground potential:

35 12. –VV V V

≤≤

AVCC DGND

V

≥ V

DGND

AVEE

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.

REV. A

–9–

AD8074/AD8075

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 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

PC GRAPHICS IC

R

75⍀

CURRENT SOURCE

OUTPUT DRIVERS

G

75⍀

B

75⍀

can be connected to the same signal, as is done in some studio­type TV monitors.

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.

MONITOR #1

75⍀

INTERNAL

75⍀

TERMINATIONS

75⍀

25␮F

0.1␮F

+5V

0.1␮F

MONITOR #2

75⍀

75⍀

+5V

+

+5V

0.1␮F

AD8075

75⍀

INTERNAL

75⍀

TERMINATIONS

75⍀

75⍀

25␮F

+

0.1␮F

–5V

0.1␮F

–5V

0.1␮F

–5V

Figure 3. Buffer

–10–

REV. A

AD8074/AD8075

Triple Video Multiplexer

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.

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

0.1␮F

+5V

0.1␮F

+5V

+

25␮F

R

75⍀

AD8075

SOURCE 1

G

B

75⍀

75⍀

and the amplifier output are disabled to a high impedance to
provide a high-impedance disabled state.

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.

+5V

0.1␮F

75⍀

75⍀

75⍀

OE

R

G

B

OUTPUT

SEL1/SEL2

SOURCE 2

25␮F

+

+5V

+

25␮F

R

75⍀

0.1␮F

0.1␮F

–5V

+5V

0.1␮F

–5V

+5V

0.1␮F

0.1␮F

–5V

0.1␮F

OE

75⍀

AD8075

G

B

75⍀

75⍀

25␮F

+

0.1␮F

0.1␮F

75⍀

75⍀

0.1␮F

REV. A

–5V

–5V

Figure 4. Mux

–11–

–5V

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.

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.

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 electro-
lytic capacitor will supply a charge reservoir for lower frequency,
high-amplitude transitions.

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. A

AD8074/AD8075

IN2

IN1

IN0

DISOUT

IN2

AGND

IN1

AGND

IN0

AGND

75⍀

R2

75⍀

R3

75⍀

TP5

DISOUT

R1

V

CC

R16

20k⍀

W2

AGND

50⍀ IMPEDANCE LINE

DO NOT INSTALL

75⍀ IMPEDANCE LINE

75⍀ IMPEDANCE LINE

75⍀ IMPEDANCE LINE

TP2

V

1P1

EE

AGND

V

CC

R11

50⍀

AGND

1

OE

AGND

DGND

2

3

IN2

AGND

4

AGND

5

IN1

AGND

6

AGND

IN0

7

V

EE

AGND

C6

0.1␮F

AGND

C8

0.01␮F

V

8

EE

2P1

TP1

3P1

DUT

AD8074

C2
10␮F

+

AGND

AGND

+

C1
10␮F

AGND

DO NOT INSTALL

AGND

V

16

CC

V

15

CC

OUT2

14

V

13

EE

OUT1

12

V

11

CC

OUT0

10

V

EE

9

DO NOT INSTALL

V

EE

50⍀ IMPEDANCE LINE

AGND

DO NOT INSTALL

V

CC

50⍀ IMPEDANCE LINE

C3

0.1␮F

C7

0.1␮F

C11

0.01␮F

AGND

V

EE

V

CC

AGND AGND

V

EE

C15

0.01␮F

AGND

AGND

C13

0.01␮F

C12

0.01␮F

AGND AGND

V

CC

C14

0.01␮F

V

EE

DO NOT INSTALL

V

CC

DO NOT INSTALL

TP4TP3

75⍀ IMPEDANCE LINE

R7

75⍀

R6

150⍀

75⍀ IMPEDANCE LINE

R8

75⍀

R10

150⍀

R9

75⍀ IMPEDANCE LINE

75⍀

R12

DO NOT INSTALL

150⍀

AGND

AGND

AGND

OUT2

OUT1

OUT0

OUT2

AGND

OUT1

AGND

OUT0

AGND

Figure 5. Evaluation Board Schematic

REV. A

–13–

AD8074/AD8075

Figure 6. Component Side

Figure 7. Circuit Side

Figure 8. Silkscreen Top

Figure 9. Silkscreen Bottom

Figure 10. Internal 2

–14–

REV. A

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

Controlling Dimension: Metric, shown in parentheses.

16-Lead TSSOP

(RU-16)

0.201 (5.10)

0.193 (4.90)

AD8074/AD8075

PIN 1

0.006 (0.15)

0.002 (0.05)

SEATING

PLANE

16

0.0256 (0.65)
BSC

9

0.177 (4.50)

0.169 (4.30)

81

0.0433 (1.10)
MAX

0.0118 (0.30)

0.0075 (0.19)

0.256 (6.50)

0.246 (6.25)

0.0079 (0.20)

0.0035 (0.090)

8ⴗ
0ⴗ

0.028 (0.70)

0.020 (0.50)

REV. A

–15–

AD8074/AD8075

Revision History

Location Page

Data Sheet changed from REV. 0 to REV. A.

Addition to equation in SINGLE SUPPLY OPERATION section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

C02391–0–10/01(A)

–16–

–16–

PRINTED IN U.S.A.

REV. A