Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2001-11-15
2004-03-23
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S255000
Reexamination Certificate
active
06710654
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to amplifiers and in particular, operational amplifiers including class AB amplifiers.
BACKGROUND OF THE INVENTION
High-speed operational amplifiers (“op-amps”) that are capable of accepting, amplifying and outputting signals with minimal distortion or noise caused by the amplifier itself, are desirable in analog circuits. There are different op-amp architectures that are suitable for high-speed applications in analog circuits. The two main circuit topologies for voltage feedback op-amps are the folded cascode op-amp and the class AB op-amp. The folded cascode op-amp offers low noise, low distortion, high gain, wide bandwidth and good DC performance, but poor slew rate performance. The class AB op-amp offers improved slew rate performance but poor noise and DC performance.
There is desired an improved op-amp that retains the advantages of these configurations and overcomes the disadvantages.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a folded cascode op-amp using a hyperbolic cosine (“cosh”) comparator for the biasing of the transistors, thus transforming the relationship of output current with respect to differential voltage input from a hyperbolic tangent function (“tanh”) to a hyperbolic sine function (“sinh”). In this manner, the folded cascode op-amp has slew rate characteristics similar to a class AB op-amp but with low noise, low distortion and better DC performance. The transformation makes the conventional folded cascode op-amp very fast without affecting its desirable parameters of low noise, low distortion, high gain, wide bandwidth and good DC performance.
REFERENCES:
patent: 5815039 (1998-09-01), Kimura
patent: 5912834 (1999-06-01), Kimura
patent: 5933054 (1999-08-01), Kimura
patent: 6107858 (2000-08-01), Kimura
Acosta Julio E.
Parkhurst Charles
Brady W. James
Choe Henry
Swayze, Jr. W. Daniel
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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