THS4281 Datasheet, PDF (19/31 Pages) Texas Instruments – VERY LOW-POWER, HIGH-SPEED, RAIL-TO-RAIL INPUT AND OUTPUT VOLTAGE-FEEDBACK OPERATIONAL AMPLIFIER

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APPLICATION INFORMATION
THS4281
SLOS432 – APRIL 2004
HIGH-SPEED OPERATIONAL AMPLIFIERS
The THS4281 is a unity gain stable rail-to-rail input
and output voltage feedback operational amplifier
designed to operate from a single 2.7-V to 16.5-V
power supply.
Applications Section Contents
• Wideband, Noninverting Operation
• Wideband, Inverting Gain Operation
• Video Drive Circuits
• Single-Supply Operation
• Power Supply Decoupling Techniques and
Recommendations
• Active Filtering With the THS4281
• Driving Capacitive Loads
• Board Layout
• Thermal Analysis
• Additional Reference Material
• Mechanical Package Drawings
WIDEBAND, NONINVERTING OPERATION
Figure 68 shows the noninverting gain configuration
of 2 V/V used to demonstrate the typical performance
curves.
Voltage feedback amplifiers can use a wide range of
resistors values to set their gain with minimal impact
on frequency response. Larger-valued resistors de-
crease loading of the feedback network on the output
of the amplifier, but may cause peaking and insta-
bility. For a gain of +2, feedback resistor values
between 1 kΩ and 4 kΩ are recommended for most
applications. However, as the gain increases, the use
of even higher feedback resistors can be used to
conserve power. This is due to the inherent nature of
amplifiers becoming more stable as the gain in-
creases, at the expense of bandwidth. Figure 69 and
Figure 70 show the THS4281 using feedback re-
sistors of 10 kΩ and 100 kΩ. Be cautioned that using
such high values with high-speed amplifiers is not
typically recommended, but under certain conditions,
such as high gain and good high-speed-PCB layout
practices, such resistances can be used.
+V_S
50-Ω Source
V_I
+
49.9 Ω
_
2.49 kΩ R_g
R_f
2.49 kΩ
+
0.1 µF 6.8 µF
V_O
To Load
0.1 µF 6.8 µF
+
−V_S
Figure 68. Wideband, Noninverting Gain
Configuration
24
20
R_F = 100 kΩ
16
R_F = 1.65 kΩ
and 10 kΩ
12
8
V_S = 3 V
4 Gain = 10,
R_L = 1 kΩ,
V_O = 0.1 V_PP
0
0.1
1
10
100
f − Frequency − MHz
Figure 69. Signal Gain vs
Frequency, V_S = 3 V
24
20
R_F = 100 kΩ
16
R_F = 2.5 kΩ
and 10 kΩ
12
8
V_S = ±5 V
4 Gain = 10,
R_L = 1 kΩ,
V_O = 0.1 V_PP
0
0.1
1
10
100
f − Frequency − MHz
Figure 70. Signal Gain vs
Frequency, V_S = ±5 V
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