LINER LT1675 250mhz, triple and single rgb multiplexer with amplifier Datasheet

LT1675/LT1675-1
250MHz, Triple and Single
RGB Multiplexer with Amplifiers
FEATURES
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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.
100MHz Pixel Switching
– 3dB Bandwidth: 250MHz
Channel Switching Time: 2.5ns
Expandable to Larger Arrays
Drives Cables Directly
High Slew Rate: 1100V/µs
Low Switching Transient: 50mV
Shutdown Supply Current: 100µA
Output Short-Circuit Protected
Available in Small 16-Pin SSOP Package
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. 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.
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APPLICATIO S
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RGB Switching
Workstation Graphics
Pixel Switching
Coaxial Cable Drivers
High Speed Signal Processing
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DESCRIPTIO
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
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.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
High Speed RGB MUX
Clocking Between 2 DC Levels at 100MHz
LT1675
RED 1
3V
V+
+1
75Ω
75Ω CABLE
+2
VOUT RED
+1
GREEN 1
LOGIC
INPUT
PIN 10
75Ω
0V
75Ω
75Ω
+1
BLUE 1
CABLE
+2
1V/DIV
1V
VOUT GREEN
RED
OUT
500mV/DIV
75Ω
75Ω
+1
RED 2
75Ω CABLE
VOUT BLUE
+2
75Ω
GREEN 2
0V
RED INPUT 1 = 0VDC, RED INPUT 2 = 1VDC
MEASURED BETWEEN 50Ω BACK TERMINATION AND 50Ω LOAD
75Ω
+1
V–
+1
ENABLE
1675 TA02
75Ω
SELECT RGB1/RGB2
BLUE 2
75Ω
1675 TA01
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LT1675/LT1675-1
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ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage ..................................................... ±6.3V
Inputs, ENABLE and SELECT, Current ................ ±20mA
Output Short-Circuit Duration (Note 2) ......... Continuous
Specified Temperature Range ..................... 0°C to 70°C
Operating Temperature Range (Note 3) .. – 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
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PACKAGE/ORDER INFORMATION
VIN1
GND
VIN2
V–
1
2
3
4
TOP VIEW
TOP VIEW
TOP VIEW
8
7
6
5
V+
ENABLE
VOUT
SELECT
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 250°C/ W
RED 1
1
16 V +
GREEN 1
2
15 VOUT RED
BLUE 1
3
14 VOUT GREEN
VOUT
GND
4
13 VOUT BLUE
SELECT
GND
5
12 V –
RED 2
6
11 V –
GREEN 2
7
10 SELECT
BLUE 2
8
9
VIN1 1
8
V+
GND 2
7
ENABLE
VIN2 3
6
V– 4
5
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 150°C/ W
ENABLE
GN PACKAGE
16-LEAD PLASTIC SSOP NARROW
TJMAX = 150°C, θJA = 120°C/ W
ORDER PART
NUMBER
LT1675CMS8-1
MS8 PART
MARKING
LTGX
ORDER PART
NUMBER
LT1675CS8-1
S8 PART
MARKING
16751
ORDER PART
NUMBER
LT1675CGN
GN PART
MARKING
1675
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF, Lead Free Tape and Reel: Add #TRPBF, Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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LT1675/LT1675-1
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the specified
temperature range, otherwise specifications are at TA = 25°C. VS = ±5V, RL = ∞, VIN = 0V LT1675 (Pins 1, 2, 3, 6, 7, 8),
LT1675-1 (Pins 1, 3), ENABLE = 0V, unless otherwise specified.
PARAMETER
CONDITIONS
Output Offset Voltage
Any Input Selected
●
20
50
mV
Output Offset Matching
Between Outputs R1 to R2, G1 to G2, B1 to B2
●
5
20
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, RL = ∞
VIN = 1V, RL = 150Ω
VIN = 1V, RL = 75Ω
●
●
3
4
5
6
8
10
%
%
%
DC Gain Error 0V to –1V
VIN = –1V, RL = ∞
VIN = –1V, RL = 150Ω
VIN = –1V, RL = 75Ω
●
●
3
4
8
6
8
20
%
%
%
Output Voltage
VIN = 2V, RL = ∞
VIN = 2V, RL = 150Ω
VIN = 2V, RL = 75Ω
●
●
●
3.1
2.7
2.4
3.4
3.0
2.8
V
V
V
VIN = – 2V, RL = ∞
VIN = – 2V, RL = 150Ω
VIN = – 2V, RL = 75Ω
●
●
●
– 3.1
– 2.6
– 2.3
– 3.3
– 3.0
– 2.6
V
V
V
Disabled Output Impedance
ENABLE Open
●
1.1
1.5
Maximum Output Current
VIN = ±1V, VO = 0V
●
50
70
LT1675
ENABLE = 0V
ENABLE = 4.7V
●
●
25
33
1
42
100
mA
µA
LT1675-1
ENABLE = 0V
ENABLE = 4.7V
●
●
8
11
0.3
14
33
mA
µA
LT1675
ENABLE= 0V
●
450
600
µA
LT1675-1
ENABLE= 0V
●
150
200
µA
LT1675
SELECT = 0V
●
90
180
µA
LT1675-1
SELECT = 0V
●
30
60
µA
SELECT Low
SELECT (See Truth Table)
●
SELECT High
SELECT (See Truth Table)
●
Supply Current
ENABLE Pin Current
SELECT Pin Current
MIN
TYP
MAX
2.0
kΩ
mA
0.8
2
UNITS
V
V
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LT1675/LT1675-1
AC CHARACTERISTICS
TA = 25°C. VS = ±5V, RL = 150Ω, VIN = 0V LT1675 (Pins 1, 2, 3, 6, 7, 8),
LT1675-1 (Pins 1, 3), ENABLE = 0V, unless otherwise specified.
PARAMETER
CONDITIONS
Slew Rate
VOUT = 5VP-P
Full Power Bandwidth (Note 5)
Small-Signal –3dB Bandwidth
MIN
TYP
MAX
UNITS
1100
V/µs
VOUT =6VP-P
58
MHz
Less Than 1dB Peaking
250
MHz
Gain Flatness
Less Than 0.1dB
70
MHz
Gain Matching
R to G to B
R1 to R2, G1 to G2, B1 to B2, LT1675-1 VIN1 to VIN2
0.10
0.01
dB
dB
Channel-to-Channel Select Time
Delay Time
Switching Time
R1 = 0V, R2 = 1V
Measured from Time SELECT Pin Crosses Logic Threshold
Time for VOUT to Go from 0V to 1V
5.0
2.5
ns
ns
Enable Time
10
ns
Disable Time
100
ns
Input Pin Capacitance
2
pF
LT1675
2.2
pF
LT1675-1
1.5
pF
LT1675
2.1
pF
LT1675-1
1.5
pF
ENABLE Open
4.4
pF
Small-Signal Rise Time
VIN = 300mVP-P, RL = 100Ω
1.85
ns
Propagation Delay
VIN = 300mVP-P, RL = 100Ω
3
ns
Overshoot
VIN = 300mVP-P, RL = 100Ω
10
%
SELECT Pin Capacitance
ENABLE Pin Capacitance
Output Pin Capacitance (Disabled)
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
mVP-P
Differential Gain (Note 6)
0.07
%
Differential Phase (Note 6)
0.05
DEG
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.
Note 4: TJ is calculated from the ambient temperature TA and power
dissipation PD according to the following formula:
LT1675CGN: TJ = TA + (PD)(120°C/W)
LT1675CMS8-1: TJ = TA + (PD)(250°C/W)
LT1675CS8-1: TJ = TA + (PD)(150°C/W)
Note 5: Full power bandwidth is calculated from the slew rate
measurement:
FPBW = SR/2πVPEAK.
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°.
Truth Table
LT1675
SELECT
LT1675-1
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
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LT1675/LT1675-1
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TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Response with
Capacitive Loads
Gain and Phase vs
Frequency
5
4
PHASE
6
–20
5
Gain vs Frequency
6.5
RL = 150Ω
4
–60
3
CL = 5pF
6.2
1
–80
2
CL = 3pF
6.1
6.3
GAIN (dB)
–100
GAIN (dB)
0
PHASE (DEG)
–40
GAIN
1
0
–120
–2
–140
–1
5.8
–160
–2
5.7
–180
–3
5.6
CL = 0pF
RL = 150Ω
–4
–5
100k
1M
10M
100M
FREQUENCY (Hz)
CL = 0pF
–4
100k
–200
1G
1M
10M
100M
FREQUENCY (Hz)
– 3dB Bandwidth vs
Supply Voltage
–40
CROSSTALK REJECTION (dB)
220
200
180
160
140
–50
–60
–80
–90
–100
–110
–130
100k
1M
10M
100M
FREQUENCY (Hz)
–30
–40
–50
–60
–80
100k
1G
70
–10
POWER SUPPLY REJECTION RATIO (dB)
–30
–40
–50
–60
–70
–80
–90
–100
1G
1675 G06
1M
10M
100M
FREQUENCY (Hz)
Undistorted Output Swing
vs Frequency
8
VS = ±5V
TA = 25°C
RL = 150Ω
60
50
40
VS = ±5V
RL = 150Ω
7
+PSRR
30
1G
1675 G23
Power Supply Rejection Ratio
vs Frequency
Crosstalk Rejection vs Frequency
(Disabled)
10M
100M
FREQUENCY (Hz)
–20
1675 G05
1675 G04
1M
0
–10
–70
100
RS = 75Ω
RL = 150Ω
RS = 75Ω
RL = 150Ω
G1 DRIVEN
R1 SELECTED
10
–70
–120
6
100M
Crosstalk Rejection vs Frequency
RS = 75Ω
RL = 150Ω
R1 DRIVEN
R2 SELECTED
120
–110
100k
1M
10M
FREQUENCY (Hz)
20
OUTPUT VOLTAGE (VP-P)
FREQUENCY (MHz)
240
5
4
3
SUPPLY VOLTAGE (±V)
100k
1675 G03
CROSSTALK REJECTION (dB)
RL = 150Ω
260
–20
B
5.5
10k
1G
–30
2
R G
Crosstalk Rejection vs Frequency
300
280
5.9
1675 G02
1675 G01
CROSSTALK REJECTION (dB)
6.0
–1
–3
RL = 100Ω
6.4
CL = 10pF
2
3
GAIN (dB)
0
–PSRR
20
10
0
–10
6
5
4
3
–20
–30
100k
1M
10M
100M
FREQUENCY (Hz)
1G
1675 G07
2
1M
10M
100M
FREQUENCY (Hz)
1G
1675 G08
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LT1675/LT1675-1
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TYPICAL PERFORMANCE CHARACTERISTICS
10k
15
–30
RL = 150Ω
VO = 2VP-P
DISABLED
INPUT BIAS CURRENT (µA)
100
2ND
–50
3RD
–60
10
–70
10M
100M
FREQUENCY (Hz)
10
FREQUENCY (MHz)
1
1G
–3
SINKING
VIN = –1V
60
VS = ±5V
VIN = –1V
10
RL = 75Ω
GAIN ERROR (%)
70
3
2
Negative DC Gain Error vs
Temperature
12
3
SOURCING
VIN = 1V
75
–1
0
1
INPUT VOLTAGE (V)
–2
1675 G12
VS = ±5V
VIN = 1V
80
RL = 150Ω
2
8
RL = 75Ω
6
4
1
2
55
RL = 150Ω
0
25
50
75
100
0
–50 –25
125
TEMPERATURE (°C)
0
25
50
75
100
40
0
–1
–2
SUPPLY CURRENT (mA)
1
14
30
125°C
25
–55°C
20
25°C
15
10
0
–4
–2
–1
1
0
INPUT VOLTAGE (V)
2
1675 G16
RL = ∞
12
10
125°C
8
–55°C
25°C
6
4
2
5
–3
125
LT1675-1 Supply Current vs
Supply Voltage
RL = ∞
35
RL = 75Ω
RL = 150Ω
100
1675 G15
Supply Current vs Supply Voltage
RL = ∞
2
50
25
75
0
TEMPERATURE (°C)
1675 G14
Output Voltage vs Input Voltage
VS = ±5V
TA = 25°C
125
TEMPERATURE (°C)
1675 G13
4
0
–50 –25
SUPPLY CURRENT (mA)
50
–50 –25
OUTPUT VOLTAGE (V)
–55°C
25°C
–20
100
4
VS = ±5V
GAIN ERROR (%)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
90
3
125°C
–15
Positive DC Gain Error vs
Temperature
Output Short-Circuit Current
vs Temperature
65
–5
–10
LTXXXX 1675 G10
1675 G09
85
0
–30
–80
1M
5
–25
ENABLED
1
100k
VS = ±5V
10
–40
1k
DISTORTION (dBc)
OUTPUT IMPEDANCE (Ω)
Input Bias Current vs
Input Voltage
2nd and 3rd Harmonic Distortion
vs Frequency
Output Impedance vs Frequency
0
1
2
3
4
SUPPLY VOLTAGE (±V)
5
6
1675 G11
0
0
1
2
3
4
SUPPLY VOLTAGE (±V)
5
6
1675 G24
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LT1675/LT1675-1
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TYPICAL PERFORMANCE CHARACTERISTICS
Input Bias Current vs
Temperature
Output Offset Voltage vs
Temperature
–10
20
VS = ±5V
OUTPUT OFFSET VOLTAGE (mV)
INPUT BIAS CURRENT (µA)
VS = ±5V
VIN = 0V
–11
–12
–13
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
15
10
5
0
–50 –25
125
50
25
75
0
TEMPERATURE (°C)
1675 G17
100
125
1675 G18
Slew Rate
Toggling RED 2 to RED 1
3V
SELECT
PIN 10
RED 1 IN
1V/DIV
RED OUT
PIN 15
2V/DIV
1V/DIV
0V
RED OUT
PIN 15
1V/DIV
RED 1 = 0V
RED 2 = UNCORRELATED SINEWAVE
RL = 150Ω, 10pF SCOPE PROBE
MEASURED AT PIN 15
RL = 150Ω, 10pF SCOPE PROBE
SR = 1100V/µs
1675 G19
Small-Signal Rise Time
1675 G20
Enable and Disable
50mV/DIV
VGEN
5V
2V/DIV
ENABLE
PIN 9
0V
VOUT
50mV/DIV
RED OUT 0V
PIN 15
2V/DIV
0V
RL = 100Ω
MEASURED WITH FET PROBES
1675 G21
ENABLE AND DISABLE OF UNCORRELATED
SINEWAVE
1675 G22
RL = 150Ω
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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 is applied to this pin,
VOUT RED will clip. The input must be terminated.
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.
GREEN 1 (Pin 2): Green 1 Input. The 1V video input signal
to be switched is applied to this pin. If 2V is applied to this
pin, VOUT GREEN will clip. The input must be terminated.
V – (Pins 11, 12): Negative Power Supply. Connect these
pins to – 5V and bypass with a good tantalum capacitor
(4.7µF). The pin may also require a 0.1µF or 0.01µF
depending on layout.
BLUE 1 (Pin 3): Blue 1 Input. The 1V video input signal to
be switched is applied to this pin. If 2V is applied to this pin,
VOUT 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 is applied to this pin,
VOUT 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 is applied to this
pin, VOUT 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 is applied to this pin,
VOUT 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.
VOUT BLUE (Pin 13): Blue Output. It is twice BLUE 1 or BLUE
2 depending on which channel is selected by Pin 10. VOUT
BLUE drives 50Ω or 75Ω double-terminated cables. Do not
add capacitance to this pin.
VOUT GREEN (Pin 14): Green Output. It is twice GREEN 1 or
GREEN 2 depending on which channel is selected by Pin
10. VOUT GREEN drives 50Ω or 75Ω double-terminated
cables. Do not add capacitance to this pin.
VOUT RED (Pin 15): Red Output. It is twice RED 1 or RED 2
depending on which channel is selected by Pin 10. VOUT
RED 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 a good tantalum capacitor (4.7µF). The
pin may also require a 0.1µF or 0.01µF depending on
layout.
LT1675-1
VIN1 (Pin 1): The 1V video input signal to be switched is
applied to this pin. If 2V is applied to this pin, VOUT will clip.
The input must be terminated.
GND (Pin 2): Signal Ground. Connect to ground plane.
VIN2 (Pin 3): The 1V video input signal to be switched is
applied to this pin. If 2V is applied to this pin, VOUT 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.
VOUT (Pin 6): It is twice VIN1 or VIN2 depending on which
channel is selected by Pin 5. VOUT drives 50Ω or 75Ω
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 a 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 VIN1 or VIN2. Use this
pin for fast toggling. HIGH Selects VIN1.
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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 1VP-P video signal
(2VP-P at the output pins), the power supply voltage
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 a
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.
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
Smallest Package and PC Board Space
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.
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
sensitive feedback node. The LT1675 fits into the small
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.
3V
1V/DIV
SELECT
PIN 10
CL = 20pF
2V/DIV
CL = 10pF
0V
RED OUT
PIN 15
500mV/DIV
CL = 0pF
RED 1 = 1V, RED 2 = 0V
MEASURED BETWEEN 75Ω BACK TERMINATION
AND 75Ω LOAD
Figure 1. Toggling at 25MHz
MEASURED AT PIN 15
RL = 150Ω, 10pF SCOPE PROBE
1675 F02
1675 F01
Figure 2. Response to Capacitive Loads
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9
LT1675/LT1675-1
U
W
U
U
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 50mVP-P and the duration is just
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:
⎞
⎛ 1575Ω
75
Ω
⎟
⎜
Gain Error (dB) = 6dB + 20log ⎜ n – 1
⎟ dB
1575
Ω
⎜ 75 +
75Ω⎟
⎠
⎝
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.
3V
3V
1V/DIV
SELECT
PIN 10
1V/DIV
SELECT
PIN 10
0V
0V
RED OUT
PIN 15 0V
50mV/DIV
RL = 150Ω, 10pF SCOPE PROBE
1675 F03
Figure 3. Input-Referred Switching Transient
RED 1 IN 0V
PIN 1
20mV/DIV
RS = 75Ω
1675 F04
Figure 4. Switching Transient at RED 1 (Pin 1)
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10
LT1675/LT1675-1
U
U
W
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APPLICATIONS INFORMATION
n
.
.
.
750Ω
R1
75Ω
AV = 2
OFF
75Ω
750Ω
⇒
75Ω
750Ω
OFF
75Ω
1575
n–1
750Ω
R2
R2
75Ω
ENABLE
LT1675 #1
R1
75Ω
750Ω
CABLE
n = NUMBER OF LT1675s
IN PARALLEL
ON
750Ω
75Ω
1675 F05
R3
AV = +2
Figure 5. Off Channels Load the Cable Termination
with 1575Ω Each
75Ω
RED
OUT
75Ω
R4
ENABLE
LT1675 #2
CHIP
SELECT
1675 F06
74HC04
Figure 6. Two LT1675s Build a 4-Input RGB Router
CHIP 5V
SELECT
0V
1V
RED 1
INPUT
5V/DIV
500mV/DIV
0V
RED 0V
OUTPUT
1V
RED
OUTPUT
1V/DIV
500mV/DIV
0V
CHIP SELECT = 0V, IC #2 DISABLED
Figure 7. 4-Input Router Response
1675 F07
RED 1 INPUT = 0V
RED 3 INPUT = UNCORRELATED SINEWAVE
1675 F08
Figure 8. 4-Input Router Toggling
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11
LT1675/LT1675-1
U
TYPICAL APPLICATIO S
RGB Video Inverter
LT1675
RED
V+
+1
97.6Ω
75Ω CABLE
+2
VIDEO IN
VOUT RED
+1
GREEN
75Ω
97.6Ω
75Ω
+1
BLUE
CABLE
+2
VOUT GREEN
75Ω
97.6Ω
332Ω
75Ω CABLE
332Ω
+1
VOUT BLUE
+2
75Ω
–
+
332Ω
V–
+1
332Ω
–
SELECT
+1
ENABLE
+
5V
332Ω
10k
332Ω
1.25V
–
LT1634
10k
0.714V
+
COMPOSITE
BLANKING
1675 TA03
LT1399
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.
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12
LT1675/LT1675-1
U
TYPICAL APPLICATIO S
Logo or “Bug” Inserter
LT1675
RED
V+
+1
75Ω
CABLE
113Ω
+2
VIDEO IN
VOUT RED
+1
GREEN
75Ω
75Ω
CABLE
113Ω
+2
+1
BLUE
VOUT GREEN
75Ω
75Ω
CABLE
113Ω
+1
VOUT BLUE
+2
75Ω
SELECT A
0
0
1
1
SELECT B
0
1
0
1
V–
+1
OUTPUT
NO VIDEO, 100% WHITE
VIDEO PLUS 66% WHITE
VIDEO PLUS 33% WHITE
VIDEO, NO WHITE
SELECT
+1
ENABLE
A
SELECT A
SELECT B
B
LT1675
V+
+1
226Ω
+2
+1
226Ω
+1
+2
+1
+2
226Ω
5V
+1
10k
1.25V
LT1634
10k
V–
SELECT
0.714V
+1
ENABLE
1675 TA05
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
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.
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13
LT1675/LT1675-1
W
W
SI PLIFIED SCHE ATIC
(LT1675-1, LT1675 One Channel)
V+
V–
RED 1
OFF
RED 2
V–
+
V+
–
RED
VOUT
750Ω
750Ω
ENABLE
LOGIC
V+
SELECT
GND
V–
1675 SS
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14
LT1675/LT1675-1
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PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
GN Package
16-Lead Plastic SSOP (Narrow 0.150)
(LTC DWG # 05-08-1641)
0.189 – 0.196*
(4.801 – 4.978)
0.015 ± 0.004
× 45°
(0.38 ± 0.10)
0.007 – 0.0098
(0.178 – 0.249)
0.053 – 0.068
(1.351 – 1.727)
0.009
(0.229)
REF
16 15 14 13 12 11 10 9
0.004 – 0.0098
(0.102 – 0.249)
0° – 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.008 – 0.012
(0.203 – 0.305)
0.229 – 0.244
(5.817 – 6.198)
0.025
(0.635)
BSC
* 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
0.150 – 0.157**
(3.810 – 3.988)
1
2 3
4
7 6
5
5 6
7
8
GN16 (SSOP) 0398
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.118 ± 0.004*
(3.00 ± 0.102)
0.040 ± 0.006
(1.02 ± 0.15)
0.007
(0.18)
0.034 ± 0.004
(0.86 ± 0.102)
8
0° – 6° TYP
0.021 ± 0.006
(0.53 ± 0.015)
SEATING
PLANE 0.012
(0.30)
0.0256
REF
(0.65)
TYP
0.006 ± 0.004
(0.15 ± 0.102)
0.118 ± 0.004**
(3.00 ± 0.102)
0.192 ± 0.004
(4.88 ± 0.10)
MSOP (MS8) 1197
1
* 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" (0.152mm) PER SIDE
4
2 3
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
8
7
6
5
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
*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
0.050
(1.270)
TYP
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
SO8 0996
1
2
3
4
16751fb
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.
15
LT1675/LT1675-1
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TYPICAL APPLICATION
NTSC-Related Color Bar Generator
5V
74ACT04
CLOCK IS
SUBCARRIER × 4
DIVIDED BY 91
OR 157.343kHz
CLR ENP ENT
CLK
5V
A
LT1675
B
6.04k
QA
V+
+1
1k
74LS163
6.04k
75Ω CABLE
+2
R
VOUT BLUE
+1
QB
B
75Ω
1k
C
6.04k
75Ω
G
+1
QC
D
CABLE
+2
VOUT RED
75Ω
1k
LOAD
COMPOSITE
BLANKING
+1
75Ω CABLE
VOUT GREEN
+2
BLACK
RED
BLUE
MAGENTA
CYAN
GREEN
WHITE
YELLOW
75Ω
–5V
V–
+1
SELECT
10k
–0.285V
0.714V
B
+1
ENABLE
640Ω
0
0.714V
R
COMPOSITE
SYNC
0
1675 TA04
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, red and green signals, respectively. This
timing gives eight bars including white and black that fill
the 52.6µs active video time. The digital signals are run
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.
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT6555
650 MHz RGB Multiplexing Amplifier
2200V/µs Slew Rate, 2:1 Input MUX
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
with Shutdown
Drives Cables, Wide Supply Range, 0µA Shutdown Current
LT1398/LT1399
Low Cost Dual and Triple 300MHz Current Feedback Amp
with Shutdown
Performance Upgrade for the LT1259/LT1260
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16
Linear Technology Corporation
LT/LT 0605 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 1998