THS4281_14 Datasheet, PDF (18/38 Pages) Texas Instruments – VERY LOW-POWER, HIGH-SPEED, RAIL-TO-RAIL INPUT AND OUTPUT VOLTAGE-FEEDBACK OPERATIONAL AMPLIFIER

THS4281
SLOS432A – APRIL 2004 – REVISED NOVEMBER 2009
APPLICATION INFORMATION
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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
decrease loading of the feedback network on the
output of the amplifier, but may cause peaking and
instability. 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
increases, at the expense of bandwidth. Figure 69
and Figure 70 show the THS4281 using feedback
resistors 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
printed circuit board (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
18
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