LM7121
235 MHz Tiny Low Power Voltage Feedback Amplifier
General Description
The LM7121 is a high performance operational amplifier
which addresses the increasing AC performance needs of
video and imaging applications, and the size and power constraints of portable applications.
The LM7121 can operate over a wide dynamic range of supply voltages, from5V(singlesupply) up to
±
15V (see the Application Information section for more details). It offers an excellent speed-power product delivering 1300V/µs and 235
MHz Bandwidth (−3 dB,A
V
=
+1).Another key feature of this
operational amplifier is stability while driving unlimited capacitive loads.
Due to its Tiny SOT23-5 package, the LM7121 is ideal for
designs where space and weight are the critical parameters.
The benefits of the Tiny package are evident in small portable electronic devices, such as cameras, and PC video
cards. Tiny amplifiers are so small that they can be placed
anywhere on a board close to the signal source or near the
input to an A/D converter.
Features
(Typical unless otherwise noted) V
S
=
±
15V
n Easy to use voltage feedback topology
n Stable with unlimited capacitive loads
n Tiny SOT23-5 package—typical circuit layout takes half
the space of SO-8 designs
n Unity gain frequency: 175 MHz
n Bandwidth (−3 dB, A
V
=
+1, R
L
=
100Ω): 235 MHz
n Slew rate: 1300V/µs
n Supply Voltages SO-8: 5V to
±
15V
SOT23-5: 5V to
±
5V
n Characterized for: +5V,
±
5V,±15V
n Low supply current: 5.3 mA
Applications
n Scanners, color fax, digital copiers
n PC video cards
n Cable drivers
n Digital cameras
n ADC/DAC buffers
n Set-top boxes
Connection Diagrams
Ordering Information
Package Ordering Information NSC Drawing Package Supplied As
Number Marking
8-Pin SO-8 LM7121IM M08A LM7121IM Rails
LM7121IMX M08A LM7121IM 2.5k Tape and Reel
5-Pin SOT23-5 LM7121IM5 MA05A A03A 1k Tape and Reel
LM7121IM5X MA05A A03A 3k Tape and Reel
8-Pin SO-8
DS012348-2
Top View
5-Pin SOT23
DS012348-1
Top View
August 1999
LM7121 235 MHz Tiny Low Power Voltage Feedback Amplifier
© 1999 National Semiconductor Corporation DS012348 www.national.com
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ESD Tolerance (Note 2) 2000V
Differential Input Voltage (Note 7)
±
2V
Voltage at Input/Output Pin (V
+
)−1.4V, (V−)+1.4V
Supply Voltage (V
+–V−
) 36V
Output Short Circuit to Ground
(Note 3) Continuous
Lead Temperature 260˚C
(soldering, 10 sec) 260˚C
Storage Temperature Range −65˚C to +150˚C
Junction Temperature (Note 4) 150˚C
Operating Ratings (Note 1)
Supply Voltage: SO-8 4.5V ≤ V
S
≤ 33V
SOT23-5 4.5V ≤ V
S
≤ 11V
Junction Temperature Range −40˚C ≤ T
J
≤ +85˚C
Thermal Resistance (θ
JA
)
M Package, 8-pin Surface Mount 165˚C/W
SOT23-5 Package 325˚C/W
±
15V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=
25˚C, V
+
=
+15V, V
−
=
−15V, V
CM
=
V
O
=
0V and R
L
>
1MΩ.
Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LM7121I Units
Limit
(Note 6)
V
OS
Input Offset Voltage 0.9 8 mV
15 max
I
B
Input Bias Current 5.2 9.5 µA
12 max
I
OS
Input Offset Current 0.04 4.3 µA
7 max
R
IN
Input Resistance Common Mode 10 MΩ
Differential Mode 3.4 MΩ
C
IN
Input Capacitance Common Mode 2.3 pF
CMRR Common Mode −10V ≤ V
CM
≤ 10V 93 73 dB
Rejection Ratio 70 min
+PSRR Positive Power Supply 10V ≤ V
+
≤ 15V 86 70 dB
Rejection Ratio 68 min
−PSRR Negative Power Supply −15V ≤ V
−
≤ −10V 81 68 dB
Rejection Ratio 65 min
V
CM
Input Common-Mode CMRR ≥ 70 dB 13 11 V
Voltage Range min
−13 −11 V
max
A
V
Large Signal R
L
=
2kΩ,V
O
=
20 V
PP
72 65 dB
Voltage Gain 57 min
V
O
Output Swing R
L
=
2kΩ 13.4 11.1 V
10.8 min
−13.4 −11.2 V
−11.0 max
R
L
=
150Ω 10.2 7.75 V
7.0 min
−7.0 −5.0 V
−4.8 max
I
SC
Output Short Circuit Sourcing 71 54 mA
Current 44 min
Sinking 52 39 mA
34 min
www.national.com 2
±
15V DC Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for T
J
=
25˚C, V
+
=
+15V, V
−
=
−15V, V
CM
=
V
O
=
0V and R
L
>
1MΩ.
Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LM7121I Units
Limit
(Note 6)
I
S
Supply Current 5.3 6.6 mA
7.5 max
±
15V AC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=
25˚C, V
+
=
15V, V
−
=
−15V, V
CM
=
V
O
=
0V and R
L
>
1MΩ.Bold-
face limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LM7121I Units
Limit
(Note 6)
SR Slew Rate A
V
=
+2, R
L
=
1kΩ, 1300 V/µs
(Note 8) V
O
=
20 V
PP
GBW Unity Gain-Bandwidth R
L
=
1kΩ 175 MHz
φ
m
Phase Margin 63 Deg
f (−3 dB) Bandwidth R
L
=
100Ω,A
V
=
+1 235 MHz
(Notes 9, 10) R
L
=
100Ω,A
V
=
+2 50
t
s
Settling Time 10 VPPStep, to 0.1%,74 ns
R
L
=
500Ω
t
r,tf
Rise and Fall Time A
V
=
+2, R
L
=
100Ω, 5.3 ns
(Note 10) V
O
=
0.4 V
PP
A
D
Differential Gain A
V
=
+2, R
L
=
150Ω 0.3
%
φ
D
Differential Phase A
V
=
+2, R
L
=
150Ω 0.65 Deg
e
n
Input-Referred f=10 kHz
17
Voltage Noise
i
n
Input-Referred f=10 kHz
1.9
Current Noise
T.H.D. Total Harmonic Distortion 2 V
PP
Output, R
L
=
150Ω, 0.065
%
A
V
=
+2, f=1 MHz
2V
PP
Output, R
L
=
150Ω, 0.52
A
V
=
+2, f=5 MHz
±
5V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=
25˚C, V
+
=
5V, V
−
=
−5V, V
CM
=
V
O
=
0V and R
L
>
1MΩ.Bold-
face limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LM7121I Units
Limit
(Note 6)
V
OS
Input Offset Voltage 1.6 8 mV
15 max
I
B
Input Bias Current 5.5 9.5 µA
12 max
I
OS
Input Offset Current 0.07 4.3 µA
7.0 max
R
IN
Input Resistance Common Mode 6.8 MΩ
Differential Mode 3.4 MΩ
www.national.com3
±
5V DC Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for T
J
=
25˚C, V
+
=
5V, V
−
=
−5V, V
CM
=
V
O
=
0V and R
L
>
1MΩ.Bold-
face limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LM7121I Units
Limit
(Note 6)
C
IN
Input Capacitance Common Mode 2.3 pF
CMRR Common Mode −2V ≤ V
CM
≤ 2V 75 65 dB
Rejection Ratio 60 min
+PSRR Positive Power Supply 3V ≤ V
+
≤ 5V 89 65 dB
Rejection Ratio 60 min
−PSRR Negative Power Supply −5V ≤ V
−
≤ −3V 78 65 dB
Rejection Ratio 60 min
V
CM
Input Common Mode CMRR ≥ 60 dB 3 2.5 V
Voltage Range min
−3 −2.5 V
max
A
V
Large Signal R
L
=
2kΩ,V
O
=
3V
PP
66 60 dB
Voltage Gain 58 min
V
O
Output Swing R
L
=
2kΩ 3.62 3.0 V
2.75 min
−3.62 −3.0 V
−2.70 max
R
L
=
150Ω 3.1 2.5 V
2.3 min
−2.8 −2.15 V
−2.00 max
I
SC
Output Short Circuit Sourcing 53 38 mA
Current 33 min
Sinking 29 21 mA
19 min
I
S
Supply Current 5.1 6.4 mA
7.2 max
±
5V AC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=
25˚C, V
+
=
5V, V
−
=
−5V, V
CM
=
V
O
=
0V and R
L
>
1MΩ.Bold-
face limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LM7121I Units
Limit
(Note 6)
SR Slew Rate A
V
=
+2, R
L
=
1kΩ, 520 V/µs
(Note 8) V
O
=
6V
PP
GBW Unity Gain-Bandwidth R
L
=
1kΩ 105 MHz
φ
m
Phase Margin R
L
=
1kΩ 74 Deg
f (−3 dB) Bandwidth R
L
=
100Ω,A
V
=
+1 160 MHz
(Notes 9, 10) R
L
=
100Ω,A
V
=
+2 50
t
s
Settling Time 5 VPPStep, to 0.1%,65 ns
R
L
=
500Ω
t
r,tf
Rise and Fall Time A
V
=
+2, R
L
=
100Ω, 5.8 ns
(Note 10) V
O
=
0.4 V
PP
A
D
Differential Gain A
V
=
+2, R
L
=
150Ω 0.3
%
www.national.com 4
±
5V AC Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for T
J
=
25˚C, V
+
=
5V, V
−
=
−5V, V
CM
=
V
O
=
0V and R
L
>
1MΩ.Bold-
face limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LM7121I Units
Limit
(Note 6)
φ
D
Differential Phase A
V
=
+2, R
L
=
150Ω 0.65 Deg
e
n
Input-Referred f=10 kHz
17
Voltage Noise
i
n
Input-Referred f=10 kHz
2
Current Noise
T.H.D. Total Harmonic Distortion 2 V
PP
Output, R
L
=
150Ω, 0.1
%
A
V
=
+2, f=1 MHz
2V
PP
Output, R
L
=
150Ω, 0.6
A
V
=
+2, f=5 MHz
+5V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=
25˚C, V
+
=
+5V, V
−
=
0V, V
CM
=
V
O
=
V
+
/2 and R
L
>
1MΩ.Bold-
face limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LM7121I Units
Limit
(Note 6)
V
OS
Input Offset Voltage 2.4 mV
I
B
Input Bias Current 4 µA
I
OS
Input Offset Current 0.04 µA
R
IN
Input Resistance Common Mode 2.6 MΩ
Differential Mode 3.4 MΩ
C
IN
Input Capacitance Common Mode 2.3 pF
CMRR Common Mode 2V ≤ V
CM
≤ 3V 65 dB
Rejection Ratio
+PSRR Positive Power Supply 4.6V ≤ V
+
≤ 5V 85 dB
Rejection Ratio
−PSRR Negative Power Supply 0V ≤ V
−
≤ 0.4V 61 dB
Rejection Ratio
V
CM
Input Common-Mode CMRR ≥ 45 dB 3.5 V
Voltage Range min
1.5 V
max
A
V
Large Signal R
L
=
2kΩto V
+
/2 64 dB
Voltage Gain
V
O
Output Swing R
L
=
2kΩto V
+
/2, High 3.7 V
R
L
=
2kΩto V
+
/2, Low 1.3
R
L
=
150Ω to V
+
/2, High 3.48
R
L
=
150Ω to V
+
/2, Low 1.59
I
SC
Output Short Circuit Sourcing 33 mA
Current Sinking 20 mA
I
S
Supply Current 4.8 mA
www.national.com5
+5V AC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=
25˚C, V
+
=
+5V, V
−
=
0V, V
CM
=
V
O
=
V
+
/2 and R
L
>
1MΩ.Bold-
face limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LM7121I Units
Limit
(Note 6)
SR Slew Rate A
V
=
+2, R
L
=
1kΩto 145 V/µs
(Note 8) V
+
/2, V
O
=
1.8 V
PP
GBW Unity Gain-Bandwidth R
L
=
1k, to V
+
/2 80 MHz
φ
m
Phase Margin R
L
=
1k to V
+
/2 70 Deg
f (−3 dB) Bandwidth R
L
=
100Ω to V
+
/2, A
V
=
+1 200 MHz
(Notes 9, 10) R
L
=
100Ω to V
+
/2, A
V
=
+2 45
t
r,tf
Rise and Fall Time A
V
=
+2, R
L
=
100Ω,8 ns
(Note 10) V
O
=
0.2 V
PP
T.H.D. Total Harmonic Distortion 0.6 VPPOutput, R
L
=
150Ω, 0.067
%
A
V
=
+2, f=1 MHz
0.6 V
PP
Output, R
L
=
150Ω, 0.33
A
V
=
+2, f=5 MHz
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.
Note 2: Human body model, 1.5 kΩ in series with 100 pF.
Note 3: Applies to both single-supply and split-supply operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the
maximum allowed junction temperature of 150˚C.
Note 4: The maximum power dissipation is a function of T
J(max)
, θJA, and TA. The maximum allowable power dissipation at any ambient temperature is P
D
=
(T
J(max)–TA
)/θJA. All numbers apply for packages soldered directly into a PC board.
Note 5: Typical Values represent the most likely parametric norm.
Note 6: All limits are guaranteed by testing or statistical analysis.
Note 7: Differential input voltage is measured at V
S
=
±
15V.
Note 8: Slew rate is the average of the rising and fallng slew rates.
Note 9: Unity gain operation for
±
5V and±15V supplies is with a feedback network of 510Ω and 3 pF in parallel (see the Application Information section). For +5V
single supply operation, feedback is a direct short from the output to the inverting input.
Note 10: A
V
=
+2 operation with 2 kΩ resistors and 2 pF capacitor from summing node to ground.
Typical Performance Characteristics T
A
=
25˚C, R
L
=
1MΩ. unless otherwise specified
Supply Current vs
Supply Voltage
DS012348-66
Supply Current vs
Temperature
DS012348-67
Input Offset Voltage
vs Temperature
DS012348-68
www.national.com 6
Typical Performance Characteristics T
A
=
25˚C, R
L
=
1MΩ. unless otherwise specified (Continued)
Input Bias Current
vs Temperature
DS012348-69
Input Offset Voltage vs
Common Mode Voltage
@
V
S
=
±
15V
DS012348-76
Input Offset Voltage vs
Common Mode Voltage
@
V
S
=
±
5V
DS012348-77
Short Circuit Current
vs Temperature (Sourcing)
DS012348-78
Short Circuit Current
vs Temperature (Sinking)
DS012348-79
Output Voltage vs Output
Current (I
SINK,VS
=
±
15V)
DS012348-70
Output Voltage vs Output
Current (I
SOURCE,VS
=
±
15V)
DS012348-71
Output Voltage vs Output
Current (I
SOURCE,VS
=
±
5V)
DS012348-72
Output Voltage vs Output
Current (I
SINK,VS
=
±
5V)
DS012348-73
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Typical Performance Characteristics T
A
=
25˚C, R
L
=
1MΩ. unless otherwise specified (Continued)
Output Voltage vs Output
Current (I
SOURCE,VS
=
+5V)
DS012348-74
Output Voltage vs Output
Current (I
SINK,VS
=
+5V)
DS012348-75
CMRR vs Frequency
DS012348-3
PSRR vs Frequency
DS012348-4
PSRR vs Frequency
DS012348-5
Open Loop Frequency
Response
DS012348-88
Open Loop Frequency
Response
DS012348-89
Open Loop Frequency
Response
DS012348-90
Unity Gain Frequency vs
Supply Voltage
DS012348-24
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Typical Performance Characteristics T
A
=
25˚C, R
L
=
1MΩ. unless otherwise specified (Continued)
GBWP
@
10 MHz
vs Supply Voltage
DS012348-25
Large Signal Voltage Gain
vs Load, V
S
=
±
15V
DS012348-96
Large Signal Voltage Gain
vs Load, V
S
=
±
5V
DS012348-97
Input Voltage
Noise vs Frequency
DS012348-27
Input Current
Noise vs Frequency
DS012348-28
Input Voltage
Noise vs Frequency
DS012348-29
Input Current
Noise vs Frequency
DS012348-30
Slew Rate vs Supply Voltage
DS012348-31
Slew Rate vs Input Voltage
DS012348-32
www.national.com9
Typical Performance Characteristics T
A
=
25˚C, R
L
=
1MΩ. unless otherwise specified (Continued)
Slew Rate vs Input Voltage
DS012348-33
Slew Rate vs
Load Capacitance
DS012348-34
Large Signal Pulse Response,
A
V
=
−1, V
S
=
±
15V
DS012348-35
Large Signal Pulse Response,
A
V
=
−1, V
S
=
±
5V
DS012348-36
Large Signal Pulse Response,
A
V
=
−1, V
S
=
+5V
DS012348-37
Large Signal Pulse Response,
A
V
=
+1, V
S
=
±
15V
DS012348-38
Large Signal Pulse Response,
A
V
=
+1, V
S
=
±
5V
DS012348-39
Large Signal Pulse Response,
A
V
=
+1, V
S
=
+5V
DS012348-40
Large Signal Pulse Response,
A
V
=
+2, V
S
=
±
15V
DS012348-41
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Typical Performance Characteristics T
A
=
25˚C, R
L
=
1MΩ. unless otherwise specified (Continued)
Large Signal Pulse Response,
A
V
=
+2, V
S
=
±
5V
DS012348-42
Large Signal Pulse Response,
A
V
=
+2, V
S
=
+5V
DS012348-43
Small Signal Pulse Response,
A
V
=
−1, V
S
=
±
15V, R
L
=
100Ω
DS012348-44
Small Signal Pulse Response,
A
V
=
−1, V
S
=
±
5V,
R
L
=
100Ω
DS012348-45
Small Signal Pulse Response,
A
V
=
−1, V
S
=
+5V,
R
L
=
100Ω
DS012348-46
Small Signal Pulse Response,
A
V
=
+1, V
S
=
±
15V,
R
L
=
100Ω
DS012348-47
Small Signal Pulse Response,
A
V
=
+1, V
S
=
±
5V,
R
L
=
100Ω
DS012348-48
Small Signal Pulse Response,
A
V
=
+1, V
S
=
+5V,
R
L
=
100Ω
DS012348-49
Small Signal Pulse Response,
A
V
=
+2, V
S
=
±
15V,
R
L
=
100Ω
DS012348-50
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Typical Performance Characteristics T
A
=
25˚C, R
L
=
1MΩ. unless otherwise specified (Continued)
Small Signal Pulse Response,
A
V
=
+2, V
S
=
±
5V,
R
L
=
100Ω
DS012348-51
Small Signal Pulse Response,
A
V
=
+2, V
S
=
+5V,
R
L
=
100Ω
DS012348-52
Closed Loop Frequency
Response vs Temperature
V
S
=
±
15V, A
V
=
+1, R
L
=
100Ω
DS012348-53
Closed Loop Frequency
Response vs Temperature
V
S
=
±
5V, A
V
=
+1, R
L
=
100Ω
DS012348-54
Closed Loop Frequency
Response vs Temperature
V
S
=
+5V, A
V
=
+1, R
L
=
100Ω
DS012348-55
Closed Loop Frequency
Response vs Temperature
V
S
=
±
15V, A
V
=
+2, R
L
=
100Ω
DS012348-58
Closed Loop Frequency
Response vs Temperature
V
S
=
±
5V, A
V
=
+2, R
L
=
100Ω
DS012348-59
Closed Loop Frequency
Response vs Temperature
V
S
=
+5V, A
V
=
+2, R
L
=
100Ω
DS012348-60
Closed Loop Frequency
Response vs Capacitive
Load (A
V
=
+1, V
S
=
±
15V)
DS012348-61
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Typical Performance Characteristics T
A
=
25˚C, R
L
=
1MΩ. unless otherwise specified (Continued)
Closed Loop Frequency
Response vs Capacitive
Load (A
V
=
+1, V
S
=
±
5V)
DS012348-62
Closed Loop Frequency
Response vs Capacitive
Load (A
V
=
+2, V
S
=
±
15V)
DS012348-63
Closed Loop Frequency
Response vs Capacitive
Load (A
V
=
+2, V
S
=
±
5V)
DS012348-64
Total Harmonic Distortion
vs Frequency
DS012348-80
Total Harmonic Distortion
vs Frequency
DS012348-81
Total Harmonic Distortion
vs Frequency
DS012348-83
Total Harmonic Distortion
vs Frequency
DS012348-82
Undistorted Output Swing
vs Frequency
DS012348-85
Undistorted Output Swing
vs Frequency
DS012348-84
www.national.com13
Typical Performance Characteristics T
A
=
25˚C, R
L
=
1MΩ. unless otherwise specified (Continued)
Application Information
The table below,depicts the maximum operating supply voltage for each package type:
TABLE 1. Maximum Supply Voltage Values
SOT23-5 SO-8
Single Supply 10V 30V
Dual Supplies
±
5V
±
15V
Stable unity gain operation is possible with supply voltage of
5V for all capacitive loads. This allows the possibility of using
the device in portable applications with low supply voltages
with minimum components around it.
Above a supply voltage of 6V (
±
3V Dual supplies), an additional resistor and capacitor (shown below) should be placed
in the feedback path to achieve stability at unity gain over the
full temperature range.
The package power dissipation should be taken into account
when operating at high ambient temperatures and/or high
power dissipative conditions. Refer to the power derating
curves in the data sheet for each type of package.
In determining maximum operable temperature of the device, make sure the total power dissipation of the device is
considered; this includes the power dissipated in the device
with a load connected to the output as well as the nominal
dissipation of the op amp.
The device is capable of tolerating momentary short circits
from its output to ground but prolonged operation in this
mode will damage the device, if the maximum allowed junction temperation is exceeded.
APPLICATION CIRCUITS
Current Boost Circuit
The circuit in
Figure 2
can be used to achieve good linearity
along with high output current capability.
By proper choice of R
3
, the LM7121 output can be set to
supply a minimal amount of current, thereby improving its
output linearity.
R
3
can be adjusted to allow for different loads:
R
3
=
0.1 R
L
The circuit above has been set for a load of 100Ω.
Reasonable speeds (
<
30 ns rise and fall times) can be ex-
pected up to 120 mA
PP
of load current (see
Figure 3
for step
response across the load).
Undistorted Output Swing
vs Frequency
DS012348-86
Total Power Dissipation
vs Ambient Temperature
DS012348-65
DS012348-87
FIGURE 1. Typical Circuit for A
V
=
+1
Operation (V
S
≥ 6V)
DS012348-92
FIGURE 2. Simple Circuit to Improve Linearity
and Output Drive Current
www.national.com 14
Application Information (Continued)
It is very important to keep the lead lengths to a minimum
and to provide a low impedance current path by using a
ground-plane on the board.
Caution: If R
L
is removed, the current balance at the output
of LM7121 would be disturbed and it would have to supply
the full amount of load current. This might damage the part if
power dissipation limit is exceeded.
Color Video on Twisted Pairs Using Single Supply
The circuit shown in
Figure 4
can be used to drive in excess
of 25 meters length of twisted pair cable with no loss of resolution or picture definition when driving a NTSC monitor at
the load end.
DS012348-93
FIGURE 3. Waveform across a 100Ω Load
www.national.com15
Application Information (Continued)
Differential Gain and Differential Phase errors measured at
the load are less than 1%and 1˚ respectively.
R
G
and CCcan be adjusted for various cable lengths to compensate for the line losses and for proper response at the
output. Values shown correspond to a twisted pair cable
length of 25 meters with about 3 turns/inch (see
Figure 5
for
step response).
The supply voltage can vary from 8.5V up to 30V with the
output rise and fall times under 12 ns. With the component
values shown, the overall gain from the input to the output is
about 1.
Even though the transmission line is not terminated in its
nominal characteristic impedance of about 600Ω, the resulting reflection at the load is only about 5%of the total signal
and in most cases can be neglected. Using 75Ω termination
instead, has the advantage of operating at a low impedance
and results in a higher realizable bandwidth and signal
fidelity.
DS012348-94
Note:
Pin numbers shown are for SO-8 package.
*
Input termination of NTSC monitor.
FIGURE 4. Single Supply Differential Twister Pair Cable Transmitter/Receiver
8.5V ≤ V
CC
≤ 30V
www.national.com 16
Application Information (Continued)
DS012348-95
FIGURE 5. Step Response toa1VPPInput Signal Measured across the 75Ω Load
DS012348-98
(a) A
V
=
−1
DS012348-99
C
C
=
2 pF for R
L
=
100Ω
C
C
=
Open for R
L
=
Open
(b) A
V
=
+2
DS012348-A0
(c) A
V
=
+2, Capacitive Load
DS012348-A1
R
F
=
0Ω,C
C
=
Open for V
S
<
6V
R
F
=
510Ω,C
C
=
3 pF for V
S
≥ 6V
(d) A
V
=
+1
DS012348-A2
(e) A
V
=
+1, V
S
=
+5V, Single Supply Operation
FIGURE 6. Application Test Circuits
www.national.com17
Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead (0.150" Wide) Small Outline Package, JEDEC
Order Number LM7121IM or LM7121IMX
NS Package Number M08A
www.national.com 18
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
National Semiconductor
Europe
Fax: +49 (0) 1 80-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 1 80-530 85 85
English Tel: +49 (0) 1 80-532 78 32
Français Tel: +49 (0) 1 80-532 93 58
Italiano Tel: +49 (0) 1 80-534 16 80
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: sea.support@nsc.com
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
www.national.com
5-Lead Molded SOT23-5
Order Number LM7121IM5 or LM7121IM5X
NS Package Number MA05A
LM7121 235 MHz Tiny Low Power Voltage Feedback Amplifier
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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