THS4211 Datasheet, PDF (19/41 Pages) Texas Instruments – LOW-DISTORTION HIGH-SPEED VOLTAGE FEEDBACK AMPLIFIER

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THS4211
THS4215
SLOS400D – SEPTEMBER 2002 – REVISED NOVEMBER 2004
APPLICATION INFORMATION
HIGH-SPEED OPERATIONAL AMPLIFIERS
The THS4211 and the THS4215 operational ampli-
fiers 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.
The THS4215 provides a power-down mode, provid-
ing 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 THS4211 as a DAC Output Buffer
• Driving an ADC With the THS4211
• Active Filtering With the THS4211
• Building a Low-Noise Receiver With the THS4211
• 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
WIDEBAND, NONINVERTING OPERATION
The THS4211 and the THS4215 are unity-gain,
stable 1-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 shows 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 impedances, 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 784-Ω total feedback-network
load, presents the THS4211 and THS4215 with an
effective output load of 305 Ω for the circuit shown in
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 de-
crease the loading effect of the feedback network on
the output of the amplifier, but this enhancement
comes at the expense of additional noise and poten-
tially lower bandwidth. Feedback-resistor values be-
tween 392 Ω and 1 kΩ are recommended for most
applications.
5 V _+VS
50 Ω Source
V_I
49.9 Ω
392 Ω
+
100 pF 0.1 µF 6.8 µF
+
THS4211
_
R_f
V_O
499 Ω
392 Ω
R_g
0.1 µF 6.8 µF
100 pF
+
-5 V ^-VS
Figure 75. Wideband, Noninverting Gain
Configuration
WIDEBAND, INVERTING GAIN OPERATION
Since the THS4211 and THS4215 are gen-
eral-purpose, wideband voltage-feedback amplifiers,
several familiar operational-amplifier applications cir-
cuits 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 a common requirement and offers sev-
eral 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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