Amplifiers – With semiconductor amplifying device – Including push-pull amplifier
Reexamination Certificate
2001-02-07
2003-04-01
Nguyen, Patricia T. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including push-pull amplifier
C330S255000, C330S267000
Reexamination Certificate
active
06542034
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electronics and, more particularly, to an operational amplifier.
BACKGROUND OF THE INVENTION
Operational amplifiers are used in various applications in analog electronics. An operational amplifier is a circuit characterized by having two inputs, that is, an inverting or negative input and a non-inverting or positive input. The operational amplifier includes an output, that is, a single-ended amplifier, or two outputs, that is, a double-ended amplifier which is also known as a fully differential amplifier.
Theoretically, an operational amplifier has infinite differential input impedance. In practice, operational amplifiers have a very high differential input impedance. Theoretically, operational amplifiers have an infinite gain voltage-driven output voltage. In practice, however, operational amplifiers have a very high gain. Theoretically, operational amplifiers also have an infinite output-current capability which is also symmetrical in the two cases of a leading edge and of a trailing edge of the output signal, and an infinite rate of variation (slew rate) of the output current over time.
Operational amplifiers which are symmetrical from the point of view of their output-current capabilities but which have a single amplification stage and, hence low overall gain, are readily known by one skilled in the art. Other known operational amplifiers include two amplification stages in cascade, and thus have a sufficiently high overall gain. However, these operational amplifiers are not symmetrical with regard to their output-current capabilities.
Operational amplifiers with more than two stages are critical from a stability point of view. In fact, it is known that operational amplifiers are normally used with a feedback network between the input and the output. To ensure the stability of the feedback loop in which the operational amplifier is connected, it is necessary to provide compensation capacitors within the amplifier. This increases the area occupied by the amplifier and reduces the slew rate.
SUMMARY OF THE INVENTION
In view of the foregoing background, an object of the present invention is to provide an operational amplifier with sufficiently high gain which is not critical from the stability point of view, and which at the same time is symmetrical with respect to its output-current capability.
According to the present invention, this object is achieved by an operational amplifier comprising a first stage, and a second stage with an input connected to an output of the first stage and an output connected to a load. The second stage comprises, between its input and its output, a first signal path for driving the load in a first direction and a second signal path for driving the load in the opposite direction. The first and second signal paths have substantially equal gains for small signals, substantially equal output impedances for small and large signals, and substantially equal output-current capabilities.
REFERENCES:
patent: 5471170 (1995-11-01), Genest
patent: 5670910 (1997-09-01), Kato
patent: 5900783 (1999-05-01), Dasgupta
patent: 5955908 (1999-09-01), Tam
patent: 6057734 (2000-05-01), Xu
patent: 6300836 (2001-10-01), Belyi
Itakura Et Al. “10 &mgr;A Quiescent Current Opamp Design for LCD Driver ICs” IDICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, JP, Institute of Electronics Information and Comm. Tokyo, vol. E81, No. 2, Feb. 1, 1998, pp. 230-236, XP000773921.
Clerici Giancarlo
Tomasini Luciano
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Jorgenson Lisa K.
Nguyen Patricia T.
STMicroelectronics S.r.l.
LandOfFree
Operational amplifier with high gain and symmetrical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Operational amplifier with high gain and symmetrical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Operational amplifier with high gain and symmetrical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3115647