Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2000-07-03
2001-09-04
Kim, Jung Ho (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C330S133000, C330S285000
Reexamination Certificate
active
06285239
ABSTRACT:
FIELD OF THE INVENTION
The invention relates in general to a bias circuit and, in particular, to a dynamically controllable bias circuit for radio frequency (RF) power amplifiers.
BACKGROUND OF THE INVENTION
Radio frequency power amplifiers are used in numerous wireless communication applications. Many of these applications are in the field of consumer electronics, which are portable and require batteries. Although battery technology has advanced significantly in recent years, battery powered communication devices require maximum power efficiency for transmission of RF signals while using as little energy as possible.
Current wireless systems have increasing power amplifier linearity requirements to minimize adjacent and alternate channel distortion. A commonly applied technique to improve the linearity of RF power amplifiers is to increase their quiescent current so that the transistors forming the amplifier operate in a more linear portion of the current-to-voltage (i/v) curve. Unfortunately, increasing the quiescent current of the amplifier requires the amplifier to constantly operate at a high idle current even when small input signals do not demand the same linearity as larger inputs. Thus, there is a need for a bias current control technique that automatically adjusts bias currents based on the effective magnitude of the input signal being amplified to meet linearity requirements as well as maximize operating efficiency.
SUMMARY OF THE INVENTION
The present invention fulfills this need by providing bias circuitry configured to adjust bias current to one or more power amplifier stages based upon the level of the input signal. A feed-forward circuit senses the input power level of the input signal and dynamically adjusts the bias current for one or more amplifiers in the amplification path to ensure each amplifier is operating in a linear region for the given signal level. For amplifier configurations having multiple amplification stages, the bias circuitry provides proportional bias currents to each stage as necessary for the progressively increasing signal levels. The bias circuitry automatically increases bias currents only as needed to eliminate excessive quiescent bias currents that prior biasing techniques required to ensure linear operation.
The bias circuitry may be constructed using traditional bipolar and BiCMOS technology while the power amplifier may incorporate gallium arsenide (GaAs) heterojunction bipolar transistor (HBT) or MESFET technology, as well as traditional silicon-based technology. The GaAs HBT and MESFET technology allows for the design of very efficient amplifier circuitry, but is very expensive and often sensitive to temperature and the manufacturing process. Preferably, the biasing circuitry incorporates the more traditional bipolar and BiCMOS technology, which is inexpensive, easy to manufacture, and stable over temperature variations, while the amplifier circuitry incorporates the more expensive and efficient semiconductor technologies. Although the amplification circuitry may include traditional silicon-based technologies, the present invention allows implementation of different technologies in a single chip set to provide improved performance at a relatively low cost.
These and other aspects of the present invention will become apparent to those skilled in the art after reading the following description of the preferred embodiments when considered with the drawings.
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Iyer Nathan R.
Kay Michael R
Kim Jung Ho
RF Micro Devices, Inc.
Withrow & Terranova, P.L.L.C.
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