Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
1999-12-21
2001-10-09
Shingleton, Michael B (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S292000, C330S300000, C330S311000
Reexamination Certificate
active
06300831
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally related to operational amplifier circuits, and more particularly to a folded-cascode type amplifier.
BACKGROUND OF THE INVENTION
Operational amplifiers (Op Amps) are integrated circuits commonly used in a variety of electronic applications including the amplification of analog signals. Op Amps are also commonly used in a variety of other circuit designs including filters, integrators, comparators and the like. The Op Amp has two inputs, one being the positive input and generally referenced as the non-inverting input, and a negative input commonly referred to as the inverting input.
One type of operational amplifier is the folded-cascode amplifier. As with most operational amplifiers, it is desired that the power consumption of the overall circuitry comprising the amplifier be kept as low as possible, including the quiescent current. In the case of the folded-cascode amplifier, it is desired to boost the transconductance (Gm) of the amplifier without sacrificing the operating bandwidth of the amplifier. Power consumption is typically increased significantly when ting to increase transconductance.
There is desired an improved folded-cascode amplifier with expanded bandwidth and with reduced power consumption.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a folded-cascode amplifier having the small signal transconductance gm of an input stage transferred to the output stage, reducing overall current consumption, and providing expanded bandwidth. The present invention achieves these technical advantages with a main amplifier that may be a PMOS folded-cascode amplifier, and using a second amplifier. A boosting amplifier provides a pole at its output node, which is at a fairly low frequency. A novel compensation scheme is used to introduce a zero to cancel out this pole, and as a side benefit, there is introduced another zero that is used to cancel out a second pole of the original folded-cascode amplifier so that the bandwidth is actually expanded. Boosting amplifiers and two compensation capacitors are provided in the present invention to achieve these technical advantages.
By using a boosting amplifier, and an additional small signal current such as 20 uA, all of the small signal transconductance gm of the input stage is transferred to the output stage, thus eliminating the requirement for an additional 100 uA of current at the input stage for a given transconductance Gm of conventional folded-cascode amplifiers. Two compensation capacitors, serve two purposes. First, they generate a dominant pole to the main amplifier and a little Miller Effect, with the value of these two capacitors being much smaller than for conventional foldedcascode amplifiers. Second, the two compensation capacitors introduce two zeros which cancel out two high frequency poles so that the bandwidth of the amplifier is expanded.
REFERENCES:
patent: 5039954 (1991-08-01), Bult et al.
patent: 6177838 (2001-01-01), Chiu
patent: 2333197 (1999-07-01), None
Brady III W. James
Hernandez Pedro P.
Shingleton Michael B
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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