THS4271_16 Datasheet, PDF (20/50 Pages) Texas Instruments – LOW NOISE, HIGH SLEW RATE, UNITY GAIN STABLE VOLTAGE FEEDBACK AMPLIFIER

THS4271
THS4275
SLOS397F – JULY 2002 – REVISED OCTOBER 2009
HIGH-SPEED OPERATIONAL AMPLIFIERS
The THS4271 and the THS4275 operational
amplifiers set new performance levels, combining low
distortion, high slew rates, low noise, and a unity-gain
bandwidth in excess of 1 GHz. To achieve the full
performance of the amplifier, careful attention must
be paid to printed-circuit board (PCB) layout and
component selection.
The THS4275 provides a power-down mode,
providing the ability to save power when the amplifier
is inactive. A reference pin is provided to allow the
user the flexibility to control the threshold levels of the
power-down control pin.
Applications Section Contents
• Wideband, Noninverting Operation
• Wideband, Inverting Gain Operation
• Single-Supply Operation
• Saving Power with Power-Down Functionality and
Setting Threshold Levels with the Reference Pin
• Power Supply Decoupling Techniques and
Recommendations
• Using the THS4271 as a DAC Output Buffer
• Driving an ADC With the THS4271
• Active Filtering With the THS4271
• Building a Low-Noise Receiver with the THS4271
• Linearity: Definitions, Terminology, Circuit
Techniques and Design Tradeoffs
• An Abbreviated Analysis of Noise in Amplifiers
• Driving Capacitive Loads
• Printed Circuit Board Layout Techniques for
Optimal Performance
• Power Dissipation and Thermal Considerations
• Performance vs Package Options
• Evaluation Fixtures, Spice Models, and
Applications Support
• Additional Reference Material
• Mechanical Package Drawings
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WIDEBAND, NONINVERTING OPERATION
The THS4271 and the THS4275 are unity gain
stable, 1.4-GHz voltage-feedback operational
amplifiers, with and without power-down capability,
designed to operate from a single 5-V to 15-V power
supply.
Figure 75 is the noninverting gain configuration of 2
V/V used to demonstrate the typical performance
curves. Most of the curves were characterized using
signal sources with 50-Ω source impedance, and with
measurement equipment presenting a 50-Ω load
impedance. In Figure 75, the 49.9-Ω shunt resistor at
the V_IN terminal matches the source impedance of the
test generator. The total 499-Ω load at the output,
combined with the 498-Ω total feedback network load,
presents the THS4271 and THS4275 with an
effective output load of 249 Ω for the circuit of
Figure 75.
Voltage feedback amplifiers, unlike current feedback
designs, can use a wide range of resistors values to
set their gain with minimal impact on their stability
and frequency response. Larger-valued resistors
decrease the loading effect of the feedback network
on the output of the amplifier, but this enhancement
comes at the expense of additional noise and
potentially lower bandwidth. Feedback resistor values
between 249 Ω and 1 kΩ are recommended for most
situations.
5 V _+VS
50 Ω Source
V_I
49.9 Ω
249 Ω
+
100 pF 0.1 µF 6.8 µF
+
THS4271
_
R_f
V_O
499 Ω
249 Ω
R_g
0.1 µF 6.8 µF
100 pF
+
−5 V ^−VS
Figure 75. Wideband, Noninverting
Gain Configuration
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