RF Electronics Chapter 10: Operational Amplifiers Page 340
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Chapter 10
Operational Amplifiers
Introduction
Operational amplifiers (OpAmps) with 3 dB bandwidths larger than 1.5 GHz are now
available. Such operational amplifiers are used in consumer applications like hard disk
drives, computer monitors, industrial and medical applications, such as CAT scanners. In
addition, one can use these operational amplifiers for IF amplifiers in many
communication receiver applications.
These high-speed amplifiers fall into two categories [1, 2, 4]:
Voltage Feedback Amplifiers
Current Feedback Amplifiers
The Voltage Feedback amplifiers have the same properties as common operational
amplifiers, such as the LF356 or LM741, used at low frequencies. The Voltage feedback
amplifiers have lower noise, better dc performance and more freedom in feedback
impedance selection.
The Current Feedback [3, 4] amplifiers on the other hand have faster slew rates and lower
distortion, but have restrictions on feedback configurations.
Voltage Feedback Amplifier Theory
If an operational amplifier has input voltages V1 and V2 at the input terminals, then for a
voltage feedback amplifier the output voltage is:
V
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where A(s) is the open loop gain, which is frequency dependent. Consider the
non-inverting amplifier configuration:
Figure 10.1. Non-inverting Amplifier [1]
If �
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Eqn. 10.2
Then
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When A(s) is very large, then the gain is approximately;
RF Electronics: Design and Simulation
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