Datasheet LT1675-1, LT1675 Datasheet (Linear Technology)

LT1675/LT1675-1

250MHz, Triple and Single

RGB Multiplexer with Current Feedback Amplifiers

FEATURES

■

100MHz Pixel Switching

■

– 3dB Bandwidth: 250MHz

■

Small 16-Pin SSOP Package

■

Channel Switching Time: 2.5ns

■

Expandable to Larger Arrays

■

Drives Cables Directly

■

High Slew Rate: 1100V/µs

■

Low Switching Transient: 50mV

■

Shutdown Supply Current: 0mA

■

Output Short-Circuit Protected

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APPLICATIONS

■

RGB Switching

■

Workstation Graphics

■

Pixel Switching

■

Coaxial Cable Drivers

■

High Speed Signal Processing

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DESCRIPTION

The LT®1675 is a high speed RGB multiplexer designed for
pixel switching and fast workstation graphics.
Included on chip are three SPDT switches and three
current feedback amplifiers. The current feedback ampli­fiers drive double-terminated 50Ω or 75Ω cables and are

configured for a fixed gain of 2, eliminating six external
gain setting resistors. The SPDT switches are designed to
be break-before-make to minimize unwanted signals cou­pling to the input.

The LT1675-1 is a single version with two inputs, a single
output and is ideal for a single channel application such as
video sync.

The key to the LT1675 fast switching speed is Linear
Technology’s proprietary high speed bipolar process. This
MUX can toggle between sources in excess of 100MHz,
has a slew rate over 1000V/µs and has a –3dB bandwidth
of 250MHz. The speed and ease of use of the LT1675 make
it ideal for high performance PCs, workstations and pro­fessional video monitors. The input-referred switching
transient is only 50mV

and lasts just 5ns, making it

P-P

virtually undetectable. Power supply requirements are
±4V to ±6V and power dissipation is only 300mW on ±5V,
or 100mW for the LT1675-1. The expandable feature uses
the disable pin to reduce the power dissipation to near
0mW in the off parts.

Unlike competitive solutions that are in bulky high pin
count packages, the LT1675 is in a 16-lead narrow body
SSOP. This small footprint, the size of an SO-8, results in
a very clean high performance solution. The LT1675-1 is
available in the tiny MSOP and the SO-8.

, LTC and LT are registered trademarks of Linear Technology Corporation.

TYPICAL APPLICATION

High Speed RGB MUX

RED 1

75Ω

GREEN 1

75Ω

BLUE 1

75Ω

RED 2

75Ω

GREEN 2

75Ω

BLUE 2

75Ω

LT1675

+1

+1

+1

+1

+1

+1

+2

+2

+2

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75Ω

75Ω

75Ω

+

V

ENABLE

CABLE

CABLE

CABLE

–

V

SELECT RGB1/RGB2

V

75Ω

V

75Ω

V

75Ω

OUT RED

OUT GREEN

OUT BLUE

1675 TA01

Select Pin Switches Inputs at 100MHz

3V

SELECT

LOGIC

PIN 10

0V

1V
RED
OUT

0V

RED 1 = 0V, RED 2 = 1V, RL = 100Ω
MEASURED BETWEEN 50Ω BACK TERMINATION AND 50Ω LOAD

1V/DIV

500mV/DIV

1675 TA02

1

LT1675/LT1675-1

WW

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ABSOLUTE MAXIMUM RATINGS

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(Note 1)

Supply Voltage ..................................................... ±6.3V

Inputs, ENABLE and SELECT, Current ................ ±20mA

Output Short-Circuit Duration (Note 2).........Continuous

Specified Temperature Range (Note 3)....... 0°C to 70°C

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PACKAGE/ORDER INFORMATION

TOP VIEW

V

1

IN1

2

GND

3

V

IN2

–

4

V

MS8 PACKAGE

8-LEAD PLASTIC MSOP

T

= 150°C, θJA = 250°C/ W

JMAX

8

V

7

ENABLE

6

V

5

SELECT

+

OUT

V

IN1

GND
V

IN2

V

TOP VIEW

1

2

3

–

4

S8 PACKAGE

8-LEAD PLASTIC SO

T

= 150°C, θJA = 150°C/ W

JMAX

Operating Temperature Range ................ –40°C to 85°C

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

Junction Temperature (Note 4)............................ 150°C

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

TOP VIEW

8

7

6

5

+

V
ENABLE
V

OUT

SELECT

1

RED 1

GREEN 1

GREEN 2

2
3

BLUE 1

4

GND

5

GND

6

RED 2

7
8

BLUE 2

GN PACKAGE

16-LEAD PLASTIC SSOP NARROW

T

= 150°C, θJA = 120°C/W

JMAX

16
15
14
13
12
11
10

9

+

V
V

OUT RED

V

OUT GREEN

V

OUT BLUE
–

V

–

V
SELECT
ENABLE

ORDER PART

NUMBER

LT1675CMS8-1

MS8 PART

MARKING

LTGX

Consult factory for Industrial and Military grade parts.

ORDER PART

NUMBER

LT1675CS8-1

S8 PART

MARKING

16751

ORDER PART

NUMBER

LT1675CGN

GN PART

MARKING

1675

2

LT1675/LT1675-1

ELECTRICAL CHARACTERISTICS

0°C ≤ TA ≤ 70°C, VS = ±5V, RL = ∞

= 0V LT1675 (Pins 1, 2, 3, 6, 7, 8),

, VIN

LT1675-1 (Pins 1, 3), ENABLE = 0V, unless otherwise specified.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Output Offset Voltage Any Input Selected ● 20 40 mV
Output Offset Matching Between Outputs R1 to R2, G1 to G2, B1 to B2 ● 520 mV
Input Current Any Input Selected ● –12 –30 µA
Input Resistance VIN = ±1V ● 100 700 kΩ
PSRR VS =±2.6V to ±6V, Measured at Output ● 38 50 dB
DC Gain Error 0V to 1V VIN = 1V, R

V

= 1V, RL = 150Ω ● 48 %

IN

= 1V, RL = 75Ω ● 510 %

V

IN

DC Gain Error 0V to –1V VIN = –1V, R

= –1V, RL = 150Ω ● 48 %

V

IN

V

= –1V, RL = 75Ω ● 820 %

IN

Output Voltage VIN = 2V, R

V

= 2V, RL = 150Ω ● 2.8 3.0 V

IN

= 2V, RL = 75Ω ● 2.4 2.8 V

V

IN

VIN = –2V, R

= –2V, RL = 150Ω ● –2.7 – 3.0 V

V

IN

V

= –2V, RL = 75Ω ● – 2.3 – 2.6 V

IN

Disabled Output Impedance ENABLE Open ● 1.1 1.5 2.0 kΩ
Maximum Output Current VIN = ±1V, VO = 0V ● 50 70 mA
Supply Current LT1675 ENABLE = 0V ● 25 33 42 mA

ENABLE = 4.7V

LT1675-1 ENABLE = 0V ● 81114 mA

ENABLE = 4.7V

ENABLE Pin Current LT1675 ENABLE= 0V ● 450 600 µA

LT1675-1 ENABLE= 0V ● 150 200 µA

SELECT Pin Current LT1675 SELECT = 0V ● 90 180 µA

LT1675-1 SELECT = 0V ● 30 60 µA

SELECT Low SELECT (See Truth Table) ● 0.8 V
SELECT High SELECT (See Truth Table) ● 2V

= ∞ ● 36 %

L

= ∞ ● 36 %

L

= ∞ ● 3.1 3.4 V

L

= ∞ ● –3.1 –3.3 V

L

● 1 100 µA

● 0.3 33 µA

3

LT1675/LT1675-1

AC CHARACTERISTICS

0°C ≤ TA ≤ 70°C, VS = ±5V, RL = 150Ω

= 0V LT1675 (Pins 1, 2, 3, 6, 7, 8),

, VIN

LT1675-1 (Pins 1, 3), ENABLE = 0V, unless otherwise specified.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Slew Rate V
Full Power Bandwidth (Note 5) V
Small-Signal –3dB Bandwidth Less Than 1dB Peaking 250 MHz
Gain Flatness Less Than 0.1dB 70 MHz
Gain Matching R to G to B 0.10 dB

Channel-to-Channel Select Time R1 = 0V, R2 = 1V

Delay Time Measured from Time SELECT Pin Crosses Logic Threshold 5.0 ns

Switching Time Time for V
Enable Time 10 ns
Disable Time 100 ns
Input Pin Capacitance 2pF
SELECT Pin Capacitance LT1675 2.2 pF

LT1675-1 1.5 pF

ENABLE Pin Capacitance LT1675 2.1 pF

LT1675-1 1.5 pF
Output Pin Capacitance (Disabled) ENABLE Open 4.4 pF
Small-Signal Rise Time VIN = 300mV
Propagation Delay VIN = 300mV
Overshoot VIN = 300mV
On-Channel to Off-Channel Crosstalk Measured at 10MHz 60 dB
Chip Disable Crosstalk Measured at 10MHz, ENABLE Open 90 dB
Channel Select Output Transient Measured Between Back Termination and Load 50 mV
Differential Gain (Note 6) 0.07 %
Differential Phase (Note 6) 0.05 DEG

= 5V

OUT

P-P

=6V

OUT

P-P

R1 to R2, G1 to G2, B1 to B2, LT1675-1 V

to Go from 0V to 1V 2.5 ns

OUT

, RL = 100Ω 1.85 ns

P-P

, RL = 100Ω 3ns

P-P

, RL = 100Ω 10 %

P-P

IN1

to V

IN2

1100 V/µs

58 MHz

0.01 dB

P-P

The

● denotes specifications that apply over the specified temperature

range.
Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

Note 2: May require a heat sink.
Note 3: The LT1675/LT1675-1 are guaranteed to meet specified

performance from 0°C to 70°C and are designed, characterized and
expected to meet these extended temperature limits, but are not tested at
–40°C and 85°C. Guaranteed I grade parts are available; consult factory.

Truth Table

SELECT ENABLE RED OUT GREEN OUT BLUE OUT VOUT

1 0 RED 1 GREEN 1 BLUE 1 VIN1
0 0 RED 2 GREEN 2 BLUE 2 VIN2
X 1 OFF OFF OFF OFF

4

Note 4: TJ is calculated from the ambient temperature TA and power
dissipation P

LT1675CGN: T
LT1675CMS8-1: T
LT1675CS8-1: T

Note 5: Full power bandwidth is calculated from the slew rate
measurement:

FPBW = SR/2πV

Note 6: Differential Gain and Phase are measured using a Tektronix
TSG120 YC/NTSC signal generator and a Tektronix 1780R Video
Measurement Set. The resolution of this equipment is 0.1% and 0.1°. Nine
identical MUXs were cascaded giving an effective resolution of 0.011%
and 0.011°.

LT1675 LT1675-1

according to the following formula:

D

= TA + (PD)(120°C/W)

J

= TA + (PD)(250°C/W)

J

= TA + (PD)(150°C/W)

J

.

PEAK

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TYPICAL PERFORMANCE CHARACTERISTICS

LT1675/LT1675-1

Gain and Phase vs
Frequency

5
4
3
2
1
0

GAIN (dB)

–1
–2
–3

CL = 0pF

–4

R

L

–5

100k 10M 100M 1G

GAIN

= 150Ω

1M

FREQUENCY (Hz)

PHASE

–3dB Bandwidth vs
Supply Voltage

300

RL = 150Ω

280
260
240
220
200
180

FREQUENCY (MHz)

160
140
120
100

2

3

SUPPLY VOLTAGE (±V)

4

5

1675 G01

1675 G04

0
–20
–40
–60

PHASE (DEG)

–80
–100
–120
–140
–160
–180
–200

GAIN (dB)

Crosstalk Rejection vs Frequency

–30
–40
–50
–60
–70
–80
–90

–100

CROSSTALK REJECTION (dB)

–110
–120
–130

6

100k 10M 100M 1G

Frequency Response with
Capacitive Loads

6

RL = 150Ω

5
4
3
2
1

0
–1
–2
–3
–4

100k 10M 100M 1G

RS = 75Ω
R
R1 DRIVEN
R2 SELECTED

= 150Ω

L

1M

1M

FREQUENCY (Hz)

CL = 10pF

CL = 5pF

CL = 3pF

CL = 0pF

FREQUENCY (Hz)

1675 G02

1675 G05

Gain vs Frequency

6.5
RL = 100Ω

6.4

6.3

6.2

6.1

6.0

GAIN (dB)

5.9

5.8

5.7

5.6

5.5

10k 1M 10M 100M

100k

FREQUENCY (Hz)

R

Crosstalk Rejection vs Frequency

20

RS = 75Ω

10

= 150Ω

R

L

G1 DRIVEN

0

R1 SELECTED

–10
–20
–30
–40
–50

CROSSTALK REJECTION (dB)

–60
–70
–80

100k 10M 100M 1G

1M

FREQUENCY (Hz)

G

B

1675 G03

1675 G23

Crosstalk Rejection vs Frequency
(Disabled)

–10

RS = 75Ω

–20

= 150Ω

R

L

–30
–40
–50
–60
–70
–80

CROSSTALK REJECTION (dB)

–90
–100
–110

100k 10M 100M 1G

1M

FREQUENCY (Hz)

1675 G06

Power Supply Rejection Ratio
vs Frequency

70
60
50
40
30
20
10

0
–10
–20

POWER SUPPLY REJECTION RATIO (dB)

–30

100k 10M 100M 1G

–PSRR

1M

FREQUENCY (Hz)

+PSRR

VS = ±5V

= 25°C

T

A

= 150Ω

R

L

1675 G07

Undistorted Output Swing
vs Frequency

8

VS = ±5V

= 150Ω

R

L

7

)

P-P

6

5

4

OUTPUT VOLTAGE (V

3

2

1M

10M 100M 1G

FREQUENCY (Hz)

1675 G08

5

LT1675/LT1675-1

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TYPICAL PERFORMANCE CHARACTERISTICS

Output Impedance vs Frequency

10k

DISABLED

1k

100

10

OUTPUT IMPEDANCE (Ω)

ENABLED

1
100k 10M 100M 1G

1M

FREQUENCY (Hz)

Output Short-Circuit Current
vs Temperature

90

VS = ±5V

85

80

75

70

65

60

55

OUTPUT SHORT-CIRCUIT CURRENT (mA)

50

–50

050

–25 25 75 125

TEMPERATURE (°C)

SOURCING
V

IN

SINKING

= –1V

V

IN

= 1V

100

1675 G09

1675 G13

2nd and 3rd Harmonic Distortion
vs Frequency

–30

RL = 150Ω

= 2V

V

O

–40

–50

–60

DISTORTION (dBc)

–70

–80

1

P-P

2ND

3RD

10 100

FREQUENCY (MHz)

Positive DC Gain Error vs
Temperature

4

VS = ±5V

= 1V

V

IN

3

2

GAIN ERROR (%)

1

0

–25 25 75 125

–50

RL = 75Ω

RL = 150Ω

050

TEMPERATURE (°C)

LTXXXX 1675 G10

100

1675 G14

Input Bias Current vs
Input Voltage

15

VS = ±5V

10

5

0

–5

–10

–15

INPUT BIAS CURRENT (µA)

–20

–25

–30

–3 –2 0 2

INPUT VOLTAGE (V)

125°C

–1 3

Negative DC Gain Error vs
Temperature

12

VS = ±5V

= –1V

V

IN

10

8

6

GAIN ERROR (%)

4

2

0

–50

RL = 75Ω

RL = 150Ω

–25 0

50 100 125

25 75

TEMPERATURE (°C)

–55°C

25°C

1

1675 G12

1675 G15

Output Voltage vs Input Voltage

4

VS = ±5V

3

T

= 25°C

A

2

1

0

–1

OUTPUT VOLTAGE (V)

–2

–3

–4

–2

–1

INPUT VOLTAGE (V)

RL = 75Ω

0

6

RL =

1

∞

RL = 150Ω

2

1675 G16

Supply Current vs Supply Voltage

40

RL =

35

30

25

20

15

SUPPLY CURRENT (mA)

10

∞

5

0

01

125°C

243

SUPPLY VOLTAGE (±V)

25°C

–55°C

5

1675 G11

LT1675-1 Supply Current vs
Supply Voltage

14

RL =

∞

12

10

8

6

4

SUPPLY CURRENT (mA)

2

6

0

01

SUPPLY VOLTAGE (±V)

243

125°C

25°C

–55°C

5

6

1675 G24

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TYPICAL PERFORMANCE CHARACTERISTICS

LT1675/LT1675-1

INPUT BIAS CURRENT (µA)

SELECT

PIN 10

RED OUT

PIN 15

Input Bias Current vs
Temperature

–10

VS = ±5V

= 0V

V

IN

–11

–12

–13

–50

–25 0

25 75

TEMPERATURE (°C)

Toggling RED 2 to RED 1

3V

0V

50 100 125

1675 G17

1V/DIV

1V/DIV

Output Offset Voltage vs
Temperature

20

VS = ±5V

15

10

5

OUTPUT OFFSET VOLTAGE (mV)

0

–50 25 75

–25 0

TEMPERATURE (°C)

Slew Rate

RED 1 IN

RED OUT

PIN 15

50 100 125

1675 G18

1V/DIV

2V/DIV

RED 1 = 0V
RED 2 = UNCORRELATED SINEWAVE

= 150Ω, 10pF SCOPE PROBE 1675 G19

R

L

Small-Signal Rise Time

V

GEN

V

OUT

0V

RL = 100Ω
MEASURED WITH FET PROBES

1675 G21

50mV/DIV

50mV/DIV

ENABLE

PIN 9

RED OUT

PIN 15

MEASURED AT PIN 15
R

= 150Ω, 10pF SCOPE PROBE

L

SR = 1100V/µs

Enable and Disable

5V

0V

0V

ENABLE AND DISABLE OF UNCORRELATED
SINEWAVE

= 150Ω 1675 G22

R

L

1675 G20

2V/DIV

2V/DIV

7

LT1675/LT1675-1

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PIN FUNCTIONS

LT1675

RED 1 (Pin 1): Red 1 Input. The 1V video input signal to be

switched is applied to this pin. If 2V are applied to this pin,
V

OUT RED

will clip. The input must be terminated.

GREEN 1 (Pin 2): Green 1 Input. The 1V video input signal
to be switched is applied to this pin. If 2V are applied to this
pin, V

OUT GREEN

will clip. The input must be terminated.

BLUE 1 (Pin 3): Blue 1 Input. The 1V video input signal to
be switched is applied to this pin. If 2V are applied to this
pin, V

OUT BLUE

will clip. The input must be terminated.

GND (Pins 4, 5): Signal Ground. Connect to ground plane.
RED 2 (Pin 6): Red 2 Input. The 1V video input signal to be

switched is applied to this pin. If 2V are applied to this pin,
V

OUT RED

will clip. The input must be terminated.

GREEN 2 (Pin 7): Green 2 Input. The 1V video input signal
to be switched is applied to this pin. If 2V are applied to this
pin, V

OUT GREEN

will clip. The input must be terminated.

BLUE 2 (Pin 8): Blue 2 Input. The 1V video input signal to
be switched is applied to this pin. If 2V are applied to this
pin, V

OUT BLUE

will clip. The input must be terminated.

ENABLE (Pin 9): Chip Enable. Ground this pin for normal
operation. Take this pin to within 300mV of V+, or open to
shut down the part. This pin is also used for router
applications. When the part is disabled, the supply current
is 1µA.

SELECT (Pin 10): Channel Select. Use this pin to select
between RGB1 inputs and RGB2 inputs. Use this pin for
fast toggling. HIGH Selects RGB1.

V– (Pins 11, 12): Negative Power Supply. Connect these
pins to –5V and bypass with good tantalum capacitor

(4.7µF). The pin may also require a 0.1µF or 0.01µF
depending on layout.

V

OUT BLUE

2 depending on which channel is selected by Pin 10. V

BLUE

(Pin 13): Blue Output. It is twice BLUE 1 or BLUE

OUT

drives 50Ω or 75Ω double-terminated cables. Do not

add capacitance to this pin.

V

OUT GREEN

(Pin 14): Green Output. It is twice GREEN 1 or

GREEN 2 depending on which channel is selected by Pin

10. V

OUT GREEN

drives 50Ω or 75Ω double-terminated

cables. Do not add capacitance to this pin.

V

OUT RED

depending on which channel is selected by Pin 10. V

RED

(Pin 15): Red Output. It is twice RED 1 or RED 2

OUT

drives 50Ω or 75Ω double-terminated cables. Do not

add capacitance to this pin.

V+ (Pin 16): Positive Power Supply. Connect this pin to 5V

and bypass with good tantalum capacitor (4.7µF). The pin
may also require a 0.1µF or 0.01µF depending on layout.

LT1675-1

V

(Pin 1): The 1V video input signal to be switched is

IN1

applied to this pin. If 2V are applied to this pin, V

OUT

will

clip. The input must be terminated.

GND (Pin 2): Signal Ground. Connect to ground plane.

V

(Pin 3): The 1V video input signal to be switched is

IN2

applied to this pin. If 2V are applied to this pin, V

OUT

will

clip. The input must be terminated.

V– (Pin 4): Connect this pin to –5V and bypass with good

tantalum capacitor (4.7µF). The pin may also require a

0.1µF or 0.01µF depending on layout.
SELECT (Pin 5): Use this pin to select V

pin for fast toggling. HIGH Selects V

IN1

IN1

.

or V

. Use this

IN2

8

V

(Pin 6): It is twice V

OUT

channel is selected by Pin 5. V

IN1

or V

depending on which

IN2

drives 50Ω or 75Ω

OUT

double-terminated cables. Do not add capacitance to this
pin.

ENABLE (Pin 7): Ground this pin for normal operation.
Take this pin to within 300mV of V+, or open to shut down
the part. This pin is also used for router applications. When
the part is disabled, the supply current is 0.3µA.

V+ (Pin 8): Connect this pin to 5V and bypass with good

tantalum capacitor (4.7µF). The pin may also require a

0.1µF or 0.01µF depending on layout.

LT1675/LT1675-1

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APPLICATIONS INFORMATION

Power Supplies

The LT1675 will function with supply voltages below ±2V
(4V total), however, to ensure a full 1V
(2V

at the output pins), the power supply voltage

P-P

should be between ±4V to ±6V. The LT1675 is designed
to operate on ±5V, and at no time should the supplies
exceed ±6V. The power supplies should be bypassed with
quality tantalum capacitors. It may be necessary to add

0.01µF or 0.1µF in parallel with the tantalum capacitors if
there is excessive ringing on the output waveform. Even
though the LT1675 is well behaved, bypass capacitors
should be placed as close to the LT1675 as possible.

Smallest Package and PC Board Space

The LT1675 has the internal gain set for +2V/V or 6dB,
because it is designed to drive a double-terminated 50Ω or
75Ω cable that has an inherent 6dB loss. There are several
advantages to setting the gain internally. This topology
eliminates six gain set resistors, reduces the pin count of
the package and eliminates stray capacitance on the
sensitivity feedback node. The LT1675 fits into the small

video signal

P-P

SSOP package, and these advantages lead to the smallest
PC board footprint with enhanced performance. The
LT1675-1 eliminates two gain set resistors and is available
in the tiny MSOP package and the cost-effective SO-8
package.

Fast Switching

The key to the LT1675 fast switching speed is Linear
Technology’s proprietary high speed bipolar process.
Internal switches can change state in less than 1ns, but the
output of the MUX switches in about 2.5ns, as shown in
Figure 1. The additional delay is due to the finite bandwidth
and the slew rate of the current feedback amplifier that
drives the cable.

For minimum ringing, it is important to minimize the load
capacitance on the output of the part. This is normally not
a problem in a controlled impedance environment, but
stray PC board capacitance and scope probe capacitance
can degrade the pulse fidelity. Figure 2 shows the
response of the output to various capacitive loads mea­sured with a 10pF scope probe.

SELECT

PIN 10

RED OUT

PIN 15

3V

0V

RED 1 = 1V, RED 2 = 0V
MEASURED BETWEEN 75Ω BACK TERMINATION

AND 75Ω LOAD

Figure 1. Toggling at 25MHz

1675 F01

1V/DIV

500mV/DIV

CL = 20pF

C

= 10pF

L

C

= 0pF

L

MEASURED AT PIN 15

= 150Ω, 10pF SCOPE PROBE 1675 F02

R

L

Figure 2. Response to Capacitive Loads

2V/DIV

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LT1675/LT1675-1

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APPLICATIONS INFORMATION

Switching Transients

This MUX includes fast current steering break-before­make SPDT switches that minimize switching glitches.
The switching transients of Figure 3 are input-referred
(measured between 75Ω back termination and the 75Ω
load). The glitch is only 50mV
5ns. This transient is small and fast enough to not be
visible on quality graphics terminals. Additionally, the
break-before-make SPDT switch is open before the alter­nate channel is connected. This means there is no input
feedthrough during switching. Figure 4 shows the amount
of alternate channel that is coupled at the input.

Expanding Inputs

In video routing applications where the ultimate speed is
not mandatory, as it is in pixel switching, it is possible to
expand the number of MUX inputs by shorting the
LT1675 outputs together and switching with the
ENABLE pins. The internal gain set resistors have a nomi­nal value of 750Ω and cause a 1500Ω shunt across the
75Ω cable termination. Figure 5 shows schematically the
effect of expanding the number of inputs. The effect of this
loading is to cause a gain error that can be calculated by
the following formula:

and the duration is just

P-P

Ω

75

Ω




dB Error (dB)= 6dB+20log





Gain








157575Ω

75+

n

–1

1575

Ω

n

–1

where n is total number of LT1675s. For example, using
ten LT1675s (20 Red, 20 Green and 20 Blue) the Gain Error
is only –1.7dB per channel.

Figure 6 shows a 4-input RGB router. The response from
RED 1 Input to Red Output is shown in Figure 7 for a
25MHz square wave with Chip Select = 0V. In this case the
Gain Error is –0.23dB. Toggling with Chip Select between
IC #1 and IC #2 is shown in Figure 8. In this case RED 1
Input is connected to 0V and RED 3 Input is connected to
an uncorrelated sinewave.

SELECT

PIN 10

RED OUT

PIN 15

10

3V

1V/DIV

0V

0V

= 150Ω, 10pF SCOPE PROBE 1675 F03

R

L

Figure 3. Input-Referred Switching Transient

50mV/DIV

3V

SELECT

PIN 10

0V

RED 1 IN

0V

PIN 1

RS = 75Ω 1675 F04

Figure 4. Switching Transient at RED 1 (Pin 1)

1V/DIV

20mV/DIV

LT1675/LT1675-1

U

WUU

APPLICATIONS INFORMATION

n

.

.

.

750Ω

750Ω

750Ω

OFF

750Ω

OFF

750Ω

ON

750Ω

Figure 5. Off Channels Load the Cable Termination

with 1575Ω Each

75Ω

75Ω

R1

75Ω

CABLE

75Ω

⇒

n = NUMBER OF LT1675s
IN PARALLEL

75Ω

1575
n – 1

1675 F05

R2
75Ω

RED 1
INPUT

RED

OUTPUT

1V

0V

1V

0V

CHIP SELECT = 0V, IC #2 DISABLED

Figure 7. 4-Input Router Response

500mV/DIV

500mV/DIV

1675 F07

R1

AV = 2

75Ω

R2

ENABLE

LT1675 #1

R3

AV = +2

75Ω

R4

ENABLE

LT1675 #2

CHIP

SELECT

74HC04

Figure 6. Two LT1675s Build a 4-Input RGB Router

1675 F06

75Ω

RED
OUT

CHIP

SELECT

RED

OUTPUT

5V

0V

0V

RED 1 INPUT = 0V
RED 3 INPUT = UNCORRELATED SINEWAVE

Figure 8. 4-Input Router Toggling

5V/DIV

1V/DIV

1675 F08

11

LT1675/LT1675-1

U

TYPICAL APPLICATIO S

RGB Video Inverter

RED

VIDEO IN GREEN

BLUE

LT1634

10k

LT1675

+1

97.6Ω

+1

97.6Ω

+1

97.6Ω
332Ω 332Ω

–
+

332Ω 332Ω

–

5V

332Ω

1.25V

0.714V

10k

+

332Ω

–
+

LT1399

+1

+1

+1

+2

+2

+2

COMPOSITE

BLANKING

75Ω

75Ω

75Ω

+

V

CABLE

CABLE

CABLE

–

V

SELECT

ENABLE

75Ω

75Ω

75Ω

V

OUT RED

V

OUT GREEN

V

OUT BLUE

1675 TA03

This circuit is useful for viewing photographic negatives
on video. A single channel can be used for composite or
monochrome video. The inverting amplifier stages are
only switched in during active video so the blanking, sync

and color burst (if present) are not disturbed. To prevent
video from swinging negative, a voltage offset equal to the
peak video signal is added to the inverted signal.

12

U

TYPICAL APPLICATIO S

LT1675/LT1675-1

Logo or “Bug” Inserter

SELECT A

0
0
1
1

RED

VIDEO IN GREEN

BLUE

SELECT B

OUTPUT

0

NO VIDEO, 100% WHITE

1

VIDEO PLUS 66% WHITE

0

VIDEO PLUS 33% WHITE

1

VIDEO, NO WHITE

SELECT A
SELECT B

75Ω

75Ω

75Ω

LT1675

+1

+1

+1

+1

+1

+1

A

B

LT1675

+1

+1

+2

+2

+2

+2

113Ω

113Ω

113Ω

226Ω

+

V

–

V

SELECT

ENABLE

+

V

CABLE

CABLE

CABLE

75Ω

75Ω

75Ω

V

OUT RED

V

OUT GREEN

V

OUT BLUE

+1

+1

5V

+1

+1

LT1634

10k

1.25V

10k

0.714V

This circuit highlights a section of the picture under
control of a synchronous key signal. It can be used for
adding the logo (also called a “bug”) you see in the bottom
corner of commercial television pictures or any sort of
overlay signal, such as a crosshair or a reticule. The key
signal has 2 bits of control so there can be four levels of
highlighting: unmodified video, video plus 33% white,
video plus 66% white and 100% white. The two LT1675s
are configured as a 2-bit DAC. The resistors on the outputs

226Ω

+2

226Ω

+2

–

V

SELECT

ENABLE

1675 TA05

set the relative bit weights. The output of the LT1675
labeled B in the schematic is one half the weight of the A
device. To properly match the 75Ω video cable, the output
resistors are selected so the parallel combination of the
two is 75 ohms. The output will never exceed peak white,
which is 0.714V for this NTSC-related RGB video. The
reference white signal is adjustable to lower than peak
white to make the effect less intrusive, if desired.

13

LT1675/LT1675-1

WW

SI PLIFIED SCHE ATIC

(LT1675-1, LT1675 One Channel)

+

V

–

V

ENABLE

SELECT

LOGIC

GND

OFF

RED 1

RED 2

–

V

+

V

+

V

750Ω

750Ω

V

+
–

–

1675 SS

RED
V

OUT

14

PACKAGE DESCRIPTION

(

0.015

± 0.004

(0.38 ± 0.10)

0.007 – 0.0098
(0.178 – 0.249)

0.016 – 0.050

(0.406 – 1.270)

* DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD

FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

0.007

(0.18)

* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,

PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.

INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006"

0° – 8° TYP

0.021

± 0.006

(0.53 ± 0.015)

° – 6° TYP

0

LT1675/LT1675-1

U

Dimensions in inches (millimeters) unless otherwise noted.

GN Package

16-Lead Plastic SSOP (Narrow 0.150)

(LTC DWG # 05-08-1641)

× 45°

0.053 – 0.068

(1.351 – 1.727)

0.008 – 0.012

(0.203 – 0.305)

SEATING

PLANE

MS8 Package

8-Lead Plastic MSOP

(LTC DWG # 05-08-1660)

0.040

± 0.006

(1.02 ± 0.15)

0.012

(0.30)

0.0256

REF

(0.65)

TYP

0.152mm) PER SIDE

0.034 ± 0.004

(0.86 ± 0.102)

0.004 – 0.0098
(0.102 – 0.249)

0.025

(0.635)

BSC

0.006 ± 0.004

(0.15 ± 0.102)

0.229 – 0.244

(5.817 – 6.198)

0.118 ± 0.004*
(3.00 ± 0.102)

0.192 ± 0.004
(4.88 ± 0.10)

16

12

8

12

0.189 – 0.196*
(4.801 – 4.978)

15

14

13

4

3

7

6

5

4

3

5

678

(3.00 ± 0.102)

MSOP (MS8) 1197

9

12 11 10

0.118 ± 0.004**

0.009

(0.229)

REF

0.150 – 0.157**
(3.810 – 3.988)

GN16 (SSOP) 0398

8-Lead Plastic Small Outline (Narrow 0.150)

0.010 – 0.020

(0.254 – 0.508)

0.008 – 0.010

(0.203 – 0.254)

*

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

**

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

× 45°

0.016 – 0.050

0.406 – 1.270

0.053 – 0.069

(1.346 – 1.752)

0°– 8° TYP

0.014 – 0.019

(0.355 – 0.483)

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

S8 Package

(LTC DWG # 05-08-1610)

0.004 – 0.010

(0.101 – 0.254)

0.050

(1.270)

TYP

0.228 – 0.244

(5.791 – 6.197)

0.189 – 0.197*
(4.801 – 5.004)

8

1

7

2

5

6

0.150 – 0.157**
(3.810 – 3.988)

SO8 0996

3

4

15

LT1675/LT1675-1

TYPICAL APPLICATION

CLOCK IS

SUBCARRIER × 4

DIVIDED BY 91

OR 157.343kHz

0.714V

B

0

COMPOSITE

BLANKING

WHITE

YELLOW

CYAN

CLR
CLK

A5V

B

C

D

LOAD

GREEN

MAGENTA

ENP5VENT

74LS163

RED

BLUE

BLACK

QA

QB

QC

U

NTSC-Related Color Bar Generator

74ACT04

6.04k

1k

6.04k R

1k

6.04kBG

1k

–5V

10k

–0.285V

640Ω

+1

+1

+1

+1

+1

+1

LT1675

+

V

CABLE

+2

+2

+2

75Ω

75Ω

75Ω

CABLE

CABLE

–

V

SELECT

ENABLE

75Ω

75Ω

75Ω

V

OUT BLUE

V

OUT RED

V

OUT GREEN

0.714V

R

0

0.714V

G

0

An RGB color bar test pattern is easily generated by
dividing down a suitable clock. To form a stable pattern,
the clock must be synchronous with the horizontal scan
rate. Four times subcarrier, or 14.318MHz, is a readily
available frequency, which when divided by 91, gives

157.343KHz. Dividing this signal by two, four and eight,
gives the blue, read and green signals, respectively. This
timing gives eight bars including white and black that fill

COMPOSITE

SYNC

through a 74ACT04 inverter because the CMOS output
swings rail-to-rail. The inverter output is scaled to make
video (0.714V peak, for NTSC-related RGB). The LT1675
drives the cable and adds sync to the RGB signals by
switching in –0.286V. If no sync is required, this voltage
can be set to zero and composite blanking can be used to
drive the select pin of the LT1675 in order to provide a
more precise blanking level.

1675 TA04

the 52.6µs active video time. The digital signals are run

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT1203/LT1205 150MHz Video MUX 2-Input and 4-Input, 90dB Channel Separation, Wide Supply Range
LT1204 4-Input Video MUX with 75MHz Current Feedback Amp Drives Cables, Adjustable Gain, 90dB Channel Separation
LT1260 Low Cost Dual and Triple 130MHz Current Feedback Amp Drives Cables, Wide Supply Range, 0µA Shutdown Current

with Shutdown

LT1398/LT1399 Low Cost Dual and Triple 300MHz Current Feedback Amp Performance Upgrade for the LT1259/LT1260

with Shutdown

16

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com

16751fs, sn16751 LT/TP 0199 4K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1998