Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1997-11-07
2001-04-10
Vo, Nguyen (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S552100, C455S426100
Reexamination Certificate
active
06216012
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to power amplifier control of a transmitter, and specifically to power amplifier control of the transmitters of a dualband phone using a single power amplifier controller.
2. Description of Related Art
Mobile phones have recently gained widespread use throughout the world. Mobile phones communicate with a base station serving a predetermined area or cell. Each base station has a limited bandwidth within which to operate, depending upon the particular transmission technique utilized by the base station. This limited bandwidth is separated into a plurality of channels frequency-spaced evenly from one another, where these channels are used by the mobile phones within that base station's transmission area. Each base station may only handle a limited number of phones equal to the number of channels and time-slots on those channels provided by that base station. Therefore, the frequency spacing between channels is minimized in order to maximize the number of channels supported by the operating bandwidth of the base stations.
In order to prevent interference between signals on two adjacent channels, the power levels of the signals transmitted by the phones must be precisely controlled. As the mobile phones move around within a base station's cell, the power levels received at the base station will change. For instance, the power level received at the base station will increase as the phone moves closer to the base station if the signal continues to be transmitted at the same power level. Interference between adjacent channels will occur if the power level of a signal received at the base station from one of the phones is too large. Therefore, the system must constantly monitor and adjust the transmission power levels as the phones move within a base station's cell to avoid interference between channels. Most mobile phones typically have power levels between the range of 5 dBm to 33 dBm. Each phone includes a power amplifier controller (PAC) which controls a power amplifier for the transmitted signal. The PAC in each phone adjusts the transmitted power level to maintain a minimum interference between the signals received at the base station on all channels at a constant level. A certain amount of error correction is transmitted with each signal by the system, wherein the amount of error correction is predetermined based upon the constant interference level.
The capacity of base stations in highly populated areas can become saturated during time periods of high use. Mobile phones currently operate as single band phones, where the transmitted signal frequency is within the bandwidth of a base station operating on the same transmission method as the mobile phone. There is a need for mobile phones to operate with dual band transmissions to increase system capacity, so that the systems could choose between two transmission frequencies depending upon which bandwidth is less saturated and could achieve a better signal quality. A dualband phone requires two transmitters, one for each frequency band. Since the power levels of the signals transmitted by a mobile phone must be constantly adjusted, dualband mobile phones must also include a PAC for each transmitter. However, requiring two PACs in a dualband phone adds to the cost, complexity, and size of the dualband phone.
There is a need for a dualband system which selects between one of the two frequency bands to transmit a signal based upon the strength and quality of the transmitted signal received at a base station. Moreover, there is a need for a dualband phone having dualband power amplifier control using a single PAC.
OBJECTS AND SUMMARY OF THE INVENTION
It is a primary object of the present invention to overcome the aforementioned shortcomings associated with the prior art.
Another object of the present invention is to provide a dualband phone which selects between one of a plurality of frequency bands to transmit a signal based upon the strength and quality of the transmitted signal received at a base station.
Yet another object of the present invention is to provide a dualband phone having dualband power amplifier control using a single power amplifier controller to minimize the size, cost, and complexity of the dualband telephone.
These as well as additional objects and advantages of the present invention are achieved by providing a dualband phone having dualband power amplifier control using a single power amplifier controller. The dualband phone includes two power amplifiers, where each power amplifier amplifies the power of a signal transmitted at a different frequency band. A power amplifier controller is provided for controlling the amount of amplification performed by both of the power amplifiers. A power amplifier switching device is connected to the power amplifier controller for switching the connection of the power amplifier controller between the two power amplifiers, so that only one of the two power amplifiers is connected to the power amplifier controller at one time. The dualband phone further includes a processing device which monitors the quality and strength of the received signal transmitted by various base stations in the transmission region of the dualband phone. The processing device instructs the power amplifier switching device to switch its connection between the two power amplifiers based upon a determination of which frequency band provides the optimal balance between signal quality and signal strength, and the dualband phone then transmits within the selected frequency band.
The processing device includes a stored predetermined relationship between signal strength and a voltage driving the power amplifiers, where the processing device instructs the power amplifier controller to adjust the voltage driving the connected power amplifier according to the desired signal strength. The dualband phone monitors the quality and strength of the received signal during each duty cycle and the system selects which one of the two power amplifiers should be connected to the power amplifier controller for each duty cycle.
The dualband phone also includes a pair of power detectors attached to the output of the power amplifiers, respectively, where the power detectors measure the power of the signal transmitted from the connected power amplifier. The measured power of the transmitted signal is fed back to the power amplifier controller, wherein a feedback switching device selectively connects one of the two power detectors to the power amplifier controller. The feedback switching device operates in conjunction with the power amplifier switching device so that the power detector associated with the power amplifier connected to the power amplifier controller is also connected to the power amplifier controller. The power amplifier controller adjusts the voltage driving the power amplifier connected thereto based upon a difference between the desired power output by the connected power amplifier and the measured power of the signal output by the connected power.
The dualband phone further includes a transmitting antenna connected to the outputs of the power amplifiers. Directional couplers are positioned between the transmitting antenna and respective power detectors in order to prevent any signals incidentally reflected back from the transmitting antenna from entering either power detector. Thus, the measured output power signal fed back to the power amplifier controller will not include any extraneous values reflected from the transmitting antenna. In an alternative embodiment where the power amplifiers are current driven, the dualband phone may further include a voltage-to-current amplifier positioned between the power amplifier controller and the power amplifier switching device in order to convert the voltage control signal from the power amplifier controller to a current control signal.
REFERENCES:
patent: 5126686 (1992-06-01), Tam
patent: 5261121 (1993-11-01), Hashimoto
patent: 5355525 (1994-10-01), Lindmayer et
Conexant Systems Inc.
Ramos-Feliciano Eliseo
Thomas Kayden Horstemeyer & Risley, L.L.P.
Vo Nguyen
LandOfFree
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