THS4271 Datasheet, PDF (18/38 Pages) Texas Instruments – LOW NOISE, HIGH SLEW RATE, UNITY GAIN STABLE VOLTAGE FREEBACK AMPLIFIER

THS4271
THS4275
SLOS397E − JULY 2002 − REVISED JANUARY 2004
www.ti.com
APPLICATION INFORMATION
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 layout and component selection.
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.
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
D Wideband, Noninverting Operation
D Wideband, Inverting Gain Operation
D Single Supply Operation
D Saving Power With Power-Down Functionality and
Setting Threshold Levels With the Reference Pin
D Power Supply Decoupling Techniques and
Recommendations
D Using the THS4271 as a DAC Output Buffer
D Driving an ADC With the THS4271
D Active Filtering With the THS4271
D Building a Low-Noise Receiver With the THS4271
D Linearity: Definitions, Terminology, Circuit
Techniques and Design Tradeoffs
D An Abbreviated Analysis of Noise in Amplifiers
D Driving Capacitive Loads
D Printed Circuit Board Layout Techniques for Optimal
Performance
D Power Dissipation and Thermal Considerations
D Performance vs Package Options
D Evaluation Fixtures, Spice Models, and Applications
Support
D Additional Reference Material
D Mechanical Package Drawings
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
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
VI
49.9 Ω
249 Ω
+
100 pF 0.1 µF 6.8 µF
+
THS4271
_
Rf
VO
499 Ω
249 Ω
Rg
0.1 µF 6.8 µF
100 pF
+
−5 V ^−VS
Figure 75. Wideband, Noninverting Gain
Configuration
WIDEBAND, INVERTING GAIN OPERATION
Since the THS4271 and THS4275 are general-purpose,
wideband voltage-feedback amplifiers, several familiar
operational amplifier applications circuits are available to
the designer. Figure 76 shows a typical inverting
configuration where the input and output impedances and
noise gain from Figure 75 are retained in an inverting
circuit configuration. Inverting operation is one of the more
common requirements and offers several performance
benefits. The inverting configuration shows improved slew
rates and distortion due to the pseudo-static voltage
maintained on the inverting input.
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