Telecommunications – Transmitter – With feedback of modulated output signal
Reexamination Certificate
2000-04-12
2003-05-20
Chin, Vivian (Department: 2682)
Telecommunications
Transmitter
With feedback of modulated output signal
C455S436000, C455S553100, C455S127500, C455S093000, C370S335000, C370S902000, C330S295000
Reexamination Certificate
active
06567653
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to wireless communications systems and, in particular, to the use of a common transmit amplifier for both analog and digital transmissions.
When consumer-oriented wireless communications systems first appeared, underlying communications signaling was based on analog transmission schemes. North America, and the United States in particular, adopted an analog cellular wireless communications standard referred to as the Advanced Mobile Phone System (AMPS), embodied in the EIA/TIA-553 standard. While service area coverage was initially sparse in the early days of mobile terminal use, enthusiastic consumer adoption of mobile communications technology allowed service providers to build an extensive network of AMPS-based communication cells. Presently, most populous areas, and even many outlying areas, of the United States enjoy essentially continuous AMPS-based mobile communications service coverage.
As the underlying technologies evolved, however, communications service providers began offering enhanced communications services based on newer, digital communication standards. Examples of such standards include 800 MHz Code Division Multiple Access (CDMA) digital cellular as embodied in the EIA/TIA-95 standard, and 800 MHz Time Division Multiple Access (TDMA) digital cellular as embodied in the TIA/EIA-136 standard. Note that the 800 MHz versions of TIA/EIA-136 are sometimes referred to as digital AMPS, or D-AMPS. Digital-mode mobile terminals typically offer users enhanced features and convenience. For example, digital-mode mobile terminals typically consume less power than their analog counterparts, thereby providing extended battery life. Moreover, digitally based transmission standards can offer enhanced voice quality, greater call security, and better noise immunity. Other advantages potentially offered by the newer digital communication standards include various text-messaging services, and other data-oriented communications.
Understandably then, consumer preference has shifted away from analog-based systems in favor of the convenience and services associated with digital cellular services. One potential drawback for consumers not living in relatively dense population centers is that deployment of digital communications services has not yet reached the level of proliferation associated with the older analog (e.g., AMPS) systems. Thus, there are yet many geographic areas where only analog wireless communications service is available. Although digital coverage areas will eventually equal or exceed those of analog, mobile terminals capable of operating in either type of system offer consumers considerable advantage and convenience. For example, many people use mobile terminals as a matter of security when traveling. As many areas between cities are covered only by analog systems, having analog-compatibility represents a key capability for ensuring the ability to call for assistance if necessary.
Thus, designers typically include both analog and digital communications system compatibility in current mobile terminals, with such terminals commonly referred to as dual-mode mobile terminals. In North American markets, it is particularly common for mobile terminal to incorporate AMPS capability, along with digital cellular capability. However, the flexibility attendant with this design choice is not without penalty. For example, TIA/EIA-136 digital transmissions include both phase and amplitude modulations and thus require linear amplification. AMPS transmissions, on the other hand, are frequency modulation based and are essentially amplitude independent. Because AMPS transmit and receive operations are simultaneous (full-duplex), transmit amplifiers are on continuously. Thus, transmit amplifier operating efficiency is critical to achieving acceptable mobile terminal battery life for analog operation. Since the DC operating efficiency of an amplifier in non-linear saturated mode exceeds that of linear mode operation, AMPS-based mobile terminals typically do not use linear transmit signal amplification. Further, non-linear transmit signal amplification is permissible in AMPS because the transmission signaling scheme is amplitude independent.
Therefore, designers are left to choose between two unattractive propositions: include two separate transmit amplifiers in the mobile terminal, one biased for digital-mode operation and one biased for analog-mode operation; or include only one transmit amplifier biased for digital-mode operation and accept the attendant analog-mode operating inefficiency. Thus, there remains a need for a dual-mode mobile terminal that benefits from the economic advantages gained by using a single transmit amplifier for both analog and digital operations, but that does not suffer analog-mode operating inefficiencies.
SUMMARY OF THE INVENTION
The present invention includes methods and apparatus allowing a mobile communications terminal to advantageously use the same power amplifier for both digital and analog transmissions. Many mobile terminals are required to operate in newer, digital communications networks where such service is available, yet still maintain compatibility with older, analog communications networks. Operating efficiency concerns associated with using the same power amplifier for both analog and digital transmissions are addressed in the present invention by including provisions for linear (or quasi-linear) operation of the power amplifier when the mobile terminal is in digital mode, and for non-linear (saturated) operation of the power amplifier when the mobile terminal is in analog mode. In some embodiments, an advantageous operating-point control circuit allows the mobile terminal to set the transmit amplifier's operating point. Further, a switching arrangement may allow the mobile terminal to select full- or half-duplex operation, such that digital transmit signals bypass an included duplexer, while analog transmit signals are routed through the duplexer.
In exemplary embodiments, the present invention provides gain control for the transmit amplifier's input drive signal. Thus, the mobile terminal may adjust the drive level of the transmit power amplifier such that it operates in linear (or quasi-linear) mode when desired—such as in digital mode—and operates in a fully saturated mode when desired—such as in analog mode. Further, exemplary embodiments of present invention include a controllable switching arrangement permitting the mobile terminal to select various transmit and receive paths, based on current digital- or analog-mode operation. Output signals associated with a control unit within the mobile terminal provide for this operating-point control and transmit/receive path selection.
By including an exemplary embodiment of the present invention, a mobile terminal may use the same power amplifier for both digital and analog transmissions without sacrificing efficiency or signal fidelity in either mode. Further, some optional embodiments of the present invention incorporate provisions for combining basic analog and digital mode operation with alternate-band digital operation. With such embodiments, the mobile terminal may operate on different frequency bands while in digital mode, or change modes to operate within an analog communications system.
REFERENCES:
patent: 5175872 (1992-12-01), Borras
patent: 5251331 (1993-10-01), Schwent et al.
patent: 5432473 (1995-07-01), Mattila et al.
patent: 5530923 (1996-06-01), Heinonen et al.
patent: 5673287 (1997-09-01), Colvis et al.
patent: 5689817 (1997-11-01), Fok
patent: 5722063 (1998-02-01), Peterzell et al.
patent: 6061338 (2000-05-01), O
patent: 6091966 (2000-07-01), Meadows
patent: 6115585 (2000-09-01), Matero et al.
patent: 6298244 (2001-10-01), Boesch et al.
patent: 0675605 (1995-10-01), None
Afshar Kamran
Chin Vivian
Coats & Bennett P.L.L.C.
Ericsson Inc.
LandOfFree
Dual-mode communications transmitter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dual-mode communications transmitter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dual-mode communications transmitter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3019625