Amplifiers – Sum and difference amplifiers
Reexamination Certificate
2001-12-21
2003-12-02
Mottola, Steven J. (Department: 2817)
Amplifiers
Sum and difference amplifiers
C330S144000
Reexamination Certificate
active
06657489
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to operational amplifiers and, more specifically, to an operational amplifier circuit with improved feedback factor.
BACKGROUND OF THE INVENTION
Many analog circuit blocks, such as amplifiers, equalizers, control loops, and the like, extensively use operational amplifiers (op-amps) designed with large open-loop gains. The use of op-amps with negative feedback generally simplifies design due to many desirable traits exhibited by negative feedback systems, including insensitivity to variations in DC gain, increased linearity, improved power supply rejection ratio, and the like.
However, when such systems are used in configurations in which the op-amp has to gain up the input signal, only a fraction of the open-loop gain is available to provide the benefits of a negative feedback closed-loop system. The ratio of available gain to open-loop gain, which is called the feedback factor, is an important issue in the design of the op-amp, as well as the design of the overall circuit block.
To simplify the design of the op-amp and to reduce overall power consumption, the op-amp circuits are generally designed with a feedback factor as close to unity as possible. However, in conventional systems, the feedback factor is typically limited to less than unity because of the op-amp having to gain up the input signal. Thus, op-amp circuits having a low feedback factor result in higher power consumption, greater area requirements, higher capacitance on op-amp inputs, which causes attenuation in the feedback factor at relatively high frequencies, and other disadvantages as compared to op-amp circuits having a feedback factor closer to unity.
SUMMARY OF THE INVENTION
In accordance with the present invention, an operational amplifier circuit with improved feedback factor is provided that substantially eliminate or reduce disadvantages and problems associated with conventional systems. In particular, a current conveyor is included as part of the operational amplifier circuit, which allows a feedback factor that is close to unity while still providing large signal path gains.
According to one embodiment of the present invention, an operational amplifier circuit with improved feedback factor is provided that includes an input impedance, an operational amplifier, and a current conveyor. The input impedance is operable to receive an input signal. The operational amplifier comprises an inverting input node, a non-inverting input node, and an output node. The operational amplifier is operable to generate an output signal at the output node based on the input signal. The current conveyor is coupled between the input impedance and the inverting input node of the operational amplifier. The current conveyor is operable to provide a low impedance to the input impedance and a high impedance to the operational amplifier.
Technical advantages of one or more embodiments of the present invention include providing an improved operational amplifier circuit. In a particular embodiment, a current conveyor is used to isolate an operational amplifier from its input network. As a result, the gain factor for the operational amplifier circuit remains unaffected, while the feedback factor for the operational amplifier remains close to unity irrespective of the gain factor. Accordingly, an operational amplifier circuit is provided with a feedback factor close to unity, as well as with reduced power consumption, decreased area requirements, and lower capacitance on inputs to the operational amplifier.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, description, and claims.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.
REFERENCES:
patent: 3898580 (1975-08-01), Millsap
patent: 4070632 (1978-01-01), Tuttle
patent: 6340916 (2002-01-01), Chen et al.
Kamal Abu-Hena M.
Mohan Jitendra
Varadarajan Devnath
Ziazadeh Ramsin
Mottola Steven J.
National Semiconductor Corporation
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