Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2002-03-22
2003-09-16
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S261000
Reexamination Certificate
active
06621344
ABSTRACT:
FIELD OF THE INVENTION
This invention relates, in general, to a variable gain amplifier stage and more particularly to a variable gain amplifier stage that has a constant bandwidth.
BACKGROUND OF THE INVENTION
In general, the product of the gain of an amplifier stage and the bandwidth of the gain stage is fixed. Thus, if the gain stage has a variable gain, the bandwidth will vary inversely proportionately to the gain, so that, if the gain is increased, the bandwidth decreases and if the gain is decreased, the bandwidth increases. However, this increase in bandwidth is usually the result of a resonant peak in the frequency response of the amplifier stage.
Therefore, it is desirable to provide an amplifier stage that maintains a constant bandwidth over a wide range of gain settings, so that high signal quality can be maintained over a wide dynamic range.
BRIEF SUMMARY OF THE INVENTION
Accordingly, in a first aspect, the present invention provides a variable gain amplifier stage comprising first and second input terminals for receiving a differential input signal, first and second input transistors, the first input transistor having a base electrode coupled to the first input terminal, a first current electrode coupled to a first supply rail and a second current electrode coupled to a first voltage controlled current source, and the second input transistor having a base electrode coupled to the second input terminal, a first current electrode coupled to the first supply rail and a second current electrode coupled to a second voltage controlled current source, a differential pair of transistors having respective base electrodes coupled to the second current electrodes of the first and second transistors, respectively, first current electrodes coupled to the first supply rail via load components and second current electrodes coupled together and to a third voltage controlled current source, wherein the gains of the first and second voltage controlled current sources are matched, and first and second output terminals coupled respectively to the respective first current electrodes of the differential pair of transistors.
REFERENCES:
patent: 3491306 (1970-01-01), Nielsen
patent: 5399990 (1995-03-01), Miyake
patent: 5550513 (1996-08-01), Wong
Japanese Patent Abstract No. 2000307364, filed Nov. 2, 2000.
Japanese Patent Abstract No. 10198910, filed Jul. 31, 1998.
Agilent Technologie,s Inc.
Mottola Steven J.
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