Telecommunications – Transmitter – Power control – power supply – or bias voltage supply
Reexamination Certificate
1998-08-05
2001-05-15
Trost, William G. (Department: 2746)
Telecommunications
Transmitter
Power control, power supply, or bias voltage supply
C455S575100, C455S571000, C330S296000
Reexamination Certificate
active
06233440
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to RF signal processing, and in particular to an RF power amplifier with variable bias current.
BACKGROUND OF THE INVENTION
In cellular telephones and other communication devices, radio frequency (RF) power amplifiers are typically used to amplify RF signals prior to transmission. These RF power amplifiers typically generate an output power in the range of 50 mW to 3 watts. In such devices, linear amplification is desired to prevent signal distortion. Efficiency is also a consideration, especially for mobile devices such as cellular telephones, due to the limited quantity of energy stored in the accompanying battery.
Efficiency and linearity are often competing considerations. When high efficiency is important, a low amplifier transistor bias current is chosen, thereby increasing battery life and talk time. This generally results in acceptable distortion at low to moderate power levels, but creates unacceptable distortion at high power levels. When high linearity is important, a larger transistor bias current is chosen, reducing distortion to an acceptable level even at high power levels. The high bias current may also be required to obtain the maximum output power from the amplifier output transistor. However, the high bias current reduces battery life and talk time, particularly at low power levels.
SUMMARY OF THE INVENTION
Therefore, a need has arisen for an RF power amplifier that addresses the disadvantages and deficiencies of the prior art. In particular, a need has arisen for an RF power amplifier with high efficiency and high linearity at varying power levels without the need for external adjustment.
Accordingly, an RF power amplifier with variable bias current is disclosed. In one embodiment, the RF amplifier includes a peak detector that detects the peak level of the amplifier input signal. The peak detector generates an output signal in response to the peak level of the amplifier input signal. A bias voltage level setting circuit coupled to the peak detector receives the peak detector output signal and generates a bias voltage in response to the peak detector output signal. An amplifier circuit coupled to the bias voltage level setting circuit receives the bias voltage and the amplifier input signal, and generates an output signal in response to the bias voltage and the amplifier input signal.
A technical advantage of the present invention is that amplification of RF signals may be obtained with high linearity at varying power levels. Another technical advantage of the present invention is that high linearity may be attained while maintaining low bias current and high efficiency at varying power levels. Yet another technical advantage of the present invention is that high maximum output power may be obtained with high efficiency.
REFERENCES:
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patent: 4185242 (1980-01-01), Schaible
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patent: 4893347 (1990-01-01), Eastmond et al.
patent: 0 854 569 (1998-07-01), None
patent: WO 94/23491 (1994-10-01), None
patent: WO 98/00912 (1998-01-01), None
Ogonowsky Brian D.
Skjerven Morrill & MacPherson LLP
Smith Sheila
Stewart Daniel P.
Triquint Semiconductor, Inc.
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