Amplifiers – With semiconductor amplifying device – Including push-pull amplifier
Reexamination Certificate
2001-12-03
2003-03-18
Shingleton, Michael B (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including push-pull amplifier
C330S267000, C330S268000
Reexamination Certificate
active
06535063
ABSTRACT:
FIELD OF THE INVENTION
Generally, this invention relates to amplifiers, and in particular to class AB operational amplifier driver stages.
BACKGROUND OF THE INVENTION
Many electronic circuits use amplifiers to manipulate various signals within the circuit. The output of the amplifier may be connected to provide an output voltage to a load circuit. The design of the output stage may affect various operating aspects of the amplifier. For example, some amplifiers can deliver a high output current to the load. Other amplifiers can produce an output voltage swing that is approximately equal to the magnitude of the power supply for the amplifier circuit. Some amplifiers must provide an output that has a low crossover distortion. Yet other amplifiers are required to maintain gain and stability at relatively high frequencies. Each of these requirements places constraints upon the design of the output stage.
During operation, an amplifier circuit consumes current from a power supply. A portion of this current, known as the quiescent current, is used to bias the internal circuitry of the amplifier. A low quiescent current is desirable because it reduces the power consumption when the amplifier is operable at a light load, or with no load at all.
Previously developed amplifier output circuits have addressed some of these problems. For example, output circuits commonly referred to as class A circuits provide low output distortion. Unfortunately, class A circuits inherently consume large amounts of quiescent current. A second class of output circuits is referred to as class B circuits. These circuits consume very little quiescent current. However, class B circuits exhibit substantial crossover distortion. A hybrid of the class A and Class B output circuits is commonly referred to as class AB output circuits. Class AB circuits consume more quiescent current than equivalent class B circuits, but less quiescent current than equivalent class A circuits. As a result, they exhibit less crossover distortion than class B circuits but more crossover distortion than class A circuits.
Most amplifiers use class AB output circuits so as to achieve reasonable crossover distortion levels with a quiescent current of perhaps five to ten percent of the maximum allowable output current. These circuits typically have difficulty in achieving significantly lower levels of quiescent current. In addition, many prior amplifier circuits rely upon circuits which reduce the availability frequency response to reduce the quiescent current.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a six (6) transistor class AB output driver with minimal cross-over distortion. The output stage comprises a core of 4 transistors arranged such that the current gain from input to output is the average of &bgr;
n
and &bgr;
p
, irrespective of where the stage is biased. Two cascode transistors serve to bootstrap the collector-base capacitances for speed enhancement.
REFERENCES:
patent: 6278326 (2001-08-01), Murray et al.
patent: 36051012 (1985-03-01), None
Trask “High Efficiency Broadband Linear Push-Pull Power Amplifiers Using Linearity Augmentation” IEEE Symposium on Circuits and Systems vol. 2, 2002 pp 432-435.
Corsi Marco
Gibson Neil
Hagan Tobin
Brady W. James
Shingleton Michael B
Swayze, Jr. W. Daniel
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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