Pulse or digital communications – Transmitters – Antinoise or distortion
Reexamination Certificate
2001-08-07
2004-05-04
Deppe, Betsy L. (Department: 2634)
Pulse or digital communications
Transmitters
Antinoise or distortion
C330S107000, C330S149000, C330S278000
Reexamination Certificate
active
06731694
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to linear transmitters and, more particularly, to a linear transmitter incorporating an isolator elimination element for maintaining stability of a feedback loop.
BACKGROUND OF THE INVENTION
Radio communication devices use antennas to provide for the efficient transmission of radio frequency (RF) communication signals. The transmitter portion of a radio communication device includes a power amplifier to amplify the RF signals before they are coupled to the antenna for transmission. For some modulation techniques, such as quadrature amplitude modulation (QAM), linear amplification is desired to prevent distortion of the modulated signal. However, when RF power amplifiers are operated in their most efficient manner at high drive levels, they usually provide a non-linear “compression” characteristic. This means that a change in the amplitude of a signal sent into the power amplifier results in a non-proportional change in the amplitude of the signal out of the amplifier, and therefore distortion. Non-linearities may also be caused by changes in load impedance, as may be caused by the operating environment of the power amplifier.
One manner of improving the linearity of an RF transmitter is to use a Cartesian feedback loop, whereby a feedback signal path is provided to create a negative feedback which compensates for compression in the power amplifier. In so doing, the level of energy transmitted on adjacent channel frequencies, known as splatter, is reduced. A component known as an isolator or circulator is sometimes inserted between the power amplifier and antenna in an effort to prevent changes in the power amplifier load from causing clipping and distortion, or from causing phase shifts that can make the Cartesian loop unstable. Although the isolator works well in some applications, it adds significant cost, size and weight to the design of a radio communication device.
Accordingly, it is desirable to provide Cartesian feedback linear transmitters that do not include isolators, yet are capable providing a stable and linear response without clipping and distortion. One such transmitter is described and claimed in the referenced U.S. Pat. No. 5,675,286 (“the '286 patent”). The transmitter of the '286 patent includes a circuit, termed an “isolator eliminator” circuit that provides for the elimination of the isolator by continuously tracking and correcting loop gain, phase and level set changes for the Cartesian feedback loop. The present invention discloses a transmitter incorporating an alternative form and manner of isolator elimination, but which otherwise has similar functionality as that of the '286 patent. Advantageously, the isolator eliminator of the present invention is implemented in software, executable by a processor such as a digital signal processor (DSP) to provide flexibility to accommodate multiple protocols including, but not limited to, integrated dispatch enhanced network (iDEN), Association of Public Safety Communication Officials Project 25 (APCO-25), terrestrial trunked radio (TETRA), global system for mobile communication (GSM), and Enhanced Data Rate for Global Evolution (EDGE).
REFERENCES:
patent: 5066923 (1991-11-01), Gailus et al.
patent: 5134718 (1992-07-01), Gailus
patent: 5559807 (1996-09-01), Van den Heuvel et al.
patent: 5574992 (1996-11-01), Cygan et al.
patent: 5675286 (1997-10-01), Baker et al.
patent: 5675287 (1997-10-01), Baker et al.
patent: 6211733 (2001-04-01), Gentzler
patent: 6275685 (2001-08-01), Wessel et al.
patent: 6388518 (2002-05-01), Miyatani
patent: 6512417 (2003-01-01), Booth et al.
Baker Michael Howard
Bozeki John Janos
Gailus Paul Howe
Minasi David H.
Deppe Betsy L.
Motorola Inc.
Pace Lalita W.
Santema Steven R.
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