Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2002-12-20
2004-08-31
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S136000
Reexamination Certificate
active
06784740
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to power amplifiers. More specifically, a radio frequency power amplifier is disclosed.
BACKGROUND OF THE INVENTION
Power amplifiers are used in a wide range of applications. Many communications systems, particularly wireless communication systems, use power amplifiers to amplify the signal before it is transmitted.
FIG. 1
is a block diagram illustrating a typical radio frequency (RF) power amplifier (PA) design. The voltage needed by the circuit is provided by voltage supply
125
. A load resistor
100
is coupled between the supply voltage and the output. Two transistors
105
and
1
10
are coupled in a cascode configuration, where transistor
110
receives an RF modulated input signal at its gate. The signal is amplified and output at terminal
120
of transistor
105
. A DC biasing voltage is applied to the gate of transistor
110
at junction
115
. The biasing voltage sets the linear range of the power amplifier.
To amplify an RF input signal with a non-constant envelope using a class A amplifier, the biasing voltage is typically fixed to a relatively high value so that there is a large current flowing through the circuit, enabling the power amplifier to linearly amplify an input signal of relatively high amplitude. Such a high biasing voltage leads to waste of power since a low amplitude input signal needs less DC current than a high amplitude input signal to achieve the desired gain. Moreover, as the amplitude of the input increases, the gain provided by the power amplifier decreases and the output of the higher amplitude input signal becomes compressed, causing non-linearity problems.
There have been attempts to predict the output envelope size and then set the biasing voltage accordingly. This approach can be quite complex, and sometimes introduces stability issues. It would be useful to have a stable power amplifier that has low power consumption and provides good linearity.
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Ghannouchi, F. M., et al, “An Adaptive Linearizer Using Feedback and Dynamic Biasing Techniques for SSPAs”, Mircrowave and Optoelectronics Conference, 1995, proceedings, 1995 SMBO/IEEE MTT-S International, vol. 1, Jul. 24-27, 1995, pp. 369-372.
Miers, T.H., et al., “A Thorough Investigation of Dynamic Bias on Linear GaAs FET Power Amplifier Performance”, Microwave Symposium Digest, 1992, IEEE MTT-S International, Jun. 1-5, 1992, pp. 537-540, vol. 2.
Smely, Dieter, et al, “Improvement of Efficiency and Linearity of a Harmonic Control Amplifier by Envelope Controlled Bias Voltage”, Microwave Symposium Digest, 1998 IEEE MTT-S International, vol. 3, Jun. 7-12, 1998, pp. 1667-1670.
IEEE Std 802.11a-1999.
IEEE Std 802.11b/D8.0, Sep. 2001.
Atheros Communications Inc.
Choe Henry
Van Pelt & Yi LLP
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