Power-shifting rf amplifiers

Details Power-shifting rf amplifiers Power-shifting rf amplifiers

2002-06-21

2004-06-08

Choe, Henry (Department: 2817)

Amplifiers

With semiconductor amplifying device

Including plural amplifier channels

C330S084000, C330S286000, C330S12400D

Reexamination Certificate

active

06747517

ABSTRACT:

STATEMENT RE FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO SEQUENCE LISTING
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to radio frequency (rf) or microwave rf power amplifiers. More particularly, the present invention pertains to rf power amplifiers in which field-effect devices are connected in series to proportionally divide a dc supply voltage, and in which both apparatus and method are provided for proportionally shifting or selectively switching rf power between/among a plurality of rf outputs and/or a plurality of antennas.
2. Description of the Related Art
Binary-phase-shift-key (BPSK) modulation is a form of digital modulation in which the rf carrier is phase shifted 180 degrees (inverted) as a digital input changes from 0 to 1. A demodulator, that is a part of an rf receiver, demodulates these phase inversions to recover the original digital stream. Commonly, demodulation is accomplished by a Costas Loop.
A common encoder consists of the rf carrier being inserted into an rf input port of a mixer while a digital input is inserted into an input port of a local oscillator. As the digital input into the input port of the local oscillator changes from an above ground voltage (1) to below ground (0), the output of the mixer changes phase from 0 degrees to 180 degrees.
If the input to the local oscillator were to change polarity (0 to 1, or 0) instantaneously, the phase of the rf output would also change polarity instantaneously. This would cause the output rf spectrum to spread to an unacceptable width.
To prevent this spread in the rf output spectrum (spectrum splatter), commonly, the input to the local oscillator port is filtered (usually with a Bessel filter). As a result, the rf output decreases as the voltage to the input port of the local oscillator is decreased, and the rf output decreases to zero when the input to the local oscillator passes through 0.0 volts. Then the rf output increases in amplitude (with inverted phase) as the voltage to the local oscillator input increases to the opposite extreme.
Therefore, as the filtered input passes through 0.0 volts as the polarity changes, the rf output also passes through a zero rf output condition. This creates a problem in that the rf power amplifier section stages of conventional transmitters consists of several stages biased to Class C. In a Class C amplifier, a zero rf input signal causes the amplifier to shut off. If a Class C amplifier were to follow the above-described encoder, it would shut off every time the input data changes state. This turning off and on of the Class C stages would cause the rf output to occupy far more of the frequency spectrum than allowed by federal regulations.
Lautzenhiser et al., in U.S. patent application Ser. No. 10/028,844, filed Dec. 20, 2001, solves the above-mentioned problems with phase-shifting in general, and binary-phase-shift-key (BPSK) modulation in particular, in that the rf output stays relatively constant as the phase shifts. In one embodiment the phase shifts up to 180 degrees generally linear with a variable phase-control voltage, or shifts 180 degrees in response to a filtered BPSK input.
More particularly, the phase shifts from 0 to 90 degrees in response to a phase-control voltage increasing from 0.0 volts dc to 5.0 volts dc during which time the rf output remains substantially constant; and the rf output continues to be relatively constant as the phase shifts from 90 to 180 degrees as the filtered BPSK input increases from 5.0 volts dc to 10.0 volts dc.
To phase shift the rf output to some angles the entire source-voltage is utilized by a selected one of the solid-state amplifying devices, or FETs, and to phase shift the rf output to other phase angles the source-voltage is dividingly shared, in selected proportions, by two adjacent ones of the solid-state amplifying devices.
Since the rf output remains substantially constant during changes in the phase angle, turning off and on of Class C stages following the encoder is avoided, frequency splatter is avoided, and the occupied frequency spectrum of the rf output follows theoretical values more closely.
In the present invention, in Lautzenhiser et al., application Ser. No. 10/028,844 which was filed on Dec. 20, 2001 and which is incorporated herein by reference thereto, and in Lautzenhiser et al., U.S. patent application Ser. No. 10/091,056 which was filed on Mar. 4, 2002 and which is incorporated herein by reference thereto, two or more solid-state amplifying devices, or FETs, are connected in series in a totem-pole arrangement, and dividingly share a dc source-voltage.
While all three of the above-identified patent applications dividingly share a dc source-voltage, they dividingly share the dc source-voltage for different purposes.
U.S. patent application Ser. No. 10/028,844, two or more solid-state devices, or FETs, are series connected, in a totem-pole arrangement, for the purpose of equally sharing a dc source-voltage that is too high for a single solid-state amplifying device, or FET.
In application Ser. No. 10/091,056, rather than dividing the dc source-voltage equally between/among a plurality of FETs, the dc source-voltage is divided in selected proportions between/among the FETs. And the purpose is different. The dc source-voltage is divided in selected proportions for the purpose of selectively shifting the phase of the rf output.
In the present patent application, similarly to application Ser. No. 10/091,056, the dc source-voltage is also divided in selected proportions between/among a plurality of FETs. But the purpose is different. In the present invention, the dc source-voltage is divided in selected proportions for the purpose of shifting any selected percentage of the rf output, or selectively switching the entire rf output, between/among a plurality of rf outputs or antennas.
Finally, in application Ser. No. 10/091,056 gains of the FETs are selectively controlled in a manner that preferably results in progressive, and generally linear, phase shifting in response to a control input. In contrast, in the present invention, gains of the FETs are controlled in response to a control input to shift selected proportions of the total rf output, or switch the total rf output, between/among a plurality of rf outputs in accordance with any selected pattern and rate, and in accordance with any selected time frame.
However, all three inventions share a common problem. Unless proper rf decoupling is achieved, the maximum rf power output is extremely limited and/or reliability and component life are seriously endangered.
More particularly, totem-pole arrangement of solid-state amplifying devices was taught in a paper published in
IEEE Transactions on Microwave Theory and Techniques,
Volume 46, Number 12, of December 1998, in an article entitled,
“A
44-
Ghz High IP
3
InP
-
HBT Amplifier with Practical Current Reuse Biasing.”
As taught in the IEEE article, in totem pole circuits two, or more, solid-state amplifying devices are used in series for dc operation, but they are used in parallel for rf operation, thereby supposedly solving the disparity between source-voltages and working voltages.
However, totem pole, voltage-dividing, or current-sharing circuits, have been used only at low rf powers, as in the above-referenced article wherein the power was in the order of 10.0 milliwatts. At higher rf powers, inadequate rf decoupling has resulted in low power efficiency, oscillation, a decrease in reliability of the circuits, and destruction of the solid-state amplifying devices.
In contrast to the extremely low rf outputs in which the prior art has been able to utilize totem pole circuitry, Lautzenhiser et al., in the aforementioned patent applications, teach apparatus and method for rf decoupling in which the principles thereof may be used to make totem pole circuits that are limited only by power limitations of the solid-state amplifying devices that are used in the totem pole.
In totem pole circuits, problems with rf dec

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