Amplifiers – With semiconductor amplifying device – Including class d amplifier
Reexamination Certificate
2000-10-06
2001-11-27
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including class d amplifier
C330S296000, C330S297000
Reexamination Certificate
active
06323731
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to RF amplifiers, particularly switch mode RF amplifiers.
DESCRIPTION OF RELATED ART
Conventional RF amplifier architectures follow a linear approach in which amplifying elements—i.e., transistors—are operated in their linear region. Although such operation is relatively inefficient, it is well-understood. To improve efficiency, various switch-mode amplifier architectures have been proposed, beginning most notably with the Class E amplifier architecture described in U.S. Pat. No. 3,900,823 to Sokal et al. (1975), incorporated herein by reference. In Class E operation, amplifying elements are operated as switches, resulting in a non-linear system. The foregoing patent describes the use of negative feedback techniques to control the output signal of a non-linear, switch-mode amplifier.
Other patents describe architectures in which multiple non-linear amplifier stages are paired or ganged and the output signals thereof combined to form a resulting linear output signal. Examples of such patents include U.S. Pat. No. 5,990,738 and references cited therein. To the extent that switch-mode RF amplifiers have been put into practice, the use of feedback control or superposition has typically been followed.
One exception is French Patent 2,768,574, incorporated herein by reference. This patent describes a switch-mode RF amplifier architecture that does not rely on feedback to control the output amplifier output signal. Nevertheless, the proposed architecture is subject to various practical limitations not addressed in the patent. In particular, experience has shown that the proposed architecture is subject to distinct amplitude modulation frequency limitations and that the output signal exhibits limited dynamic range. High frequency operation and wide dynamic range are key to emerging high-speed wireless data communication initiatives.
Dynamic bias control has been proposed in conventional RF amplifier architectures for the purpose of improving efficiency. See for example U.S. Pat. No. 6,025,754. Bias control is also discussed in the aforementioned U.S. Pat. No. 3,900,823. However, none of the foregoing prior art describes the effective use of dynamic bias control in a switch-mode RF amplifier to achieve an output signal having wide dynamic range.
SUMMARY OF THE INVENTION
The present invention, generally speaking, provides for the effective use of dynamic bias control in a switch-mode RF amplifier to achieve an output signal having wide dynamic range. In one aspect, a method is provided of amplifying an RF signal to produce a variable output signal using an amplifier including a final amplification stage having a control terminal. The method includes: applying to the control terminal of the final amplification stage a drive signal and a bias signal; and varying the bias signal as a function of a desired output power of the variable output signal. The drive signal and the bias signal together cause the final amplification stage to be driven repeatedly between two states, a hard-on state and a hard-off state, without operating in a linear operating region for an appreciable percentage of time, and the final amplification stage is controlled without continuous or frequent measurement and feedback adjustment of the variable output signal.
In another aspect, an amplifier is provided having a variable output signal and including a final amplification stage having a control terminal; a driver stage preceding the final amplification stage, the driver stage producing a drive signal applied to the control terminal of the final amplification stage; and control circuitry producing a variable bias signal, also applied to the control terminal of the final amplification stage. The control circuitry varies the bias signal as a function of a desired output power of the variable output signal. Once again, the drive signal and the bias signal together cause the final amplification stage to be driven repeatedly between two states, a hard-on state and a hard-off state, without operating in a linear operating region for an appreciable percentage of time, and the final amplification stage being controlled without continuous or frequent measurement and feedback adjustment of the variable output signal.
REFERENCES:
patent: 5392004 (1995-02-01), Masliah
patent: 5789983 (1998-08-01), Fujita
patent: 5986503 (1999-11-01), Ichikawa
patent: 5994963 (1999-11-01), Kawai et al.
Choe Henry
Pascal Robert
Tropion, Inc. Corp.
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