Transmitter circuitry for a cellular phone

Telecommunications – Transmitter – Angle modulation

Reexamination Certificate

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Details

C455S550100, C455S091000

Reexamination Certificate

active

06304748

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a transmitter used in a communications systems. More particularly, the invention relates to a transmitter for a wireless phone, such as a cellular phone used in mobile communications systems.
An example for wireless phones are cellular phones which are designed to operate within the environment of one of several mobile communications networks. An exemplary environment is a mobile communications network according to a standard known as GSM (Global System for Mobile communications) created by the European Telecommunications Standards Institute (ETSI). In GSM, there is an assigned frequency band around 900 MHz for Standard GSM, and an assigned frequency band around 1800 MEz for DCS1800 (Digital Communications System, DCS). Other environments include systems known as Advanced Mobile Phone System (AMPS) operating in a frequency band around 800 MHz, and as Personal Communications System (PCS) operating in a frequency band around 1900 MHz.
As the number of users of cellular phones increases, some operators have added capacity to their networks by including more than only one frequency band in their networks. In the case of the GSM system, for example, the frequency bands around 900 MHz and 1800 MHz are now used to expand the capacities of certain networks.
Manufacturer of cellular phones, therefore, are developing a new generation of cellular phones which are operable at, for example, two frequency bands. A cellular phone operable at two frequency bands is referred to as a dual band cellular phone. As the dual band cellular phone has to transmit signals at both frequency bands, duplication of functions is required. Duplication of functions, however, leads to higher manufacturing costs and ultimately to higher prices for the dual band cellular phones.
SUMMARY OF THE INVENTION
There is therefore a need to keep the manufacturing costs caused by the duplication as low as possible. Further, there is a need to minimize size of dual band cellular phones because users have come to expect single band cellular phones to be small and to have an attractive design.
An aspect of the invention involves a transmitter comprising first and second amplifiers and a filter module. The first amplifier has a first input for a first signal at a first radio frequency band, and a first output for an amplified first signal. The first output is connectable to an antenna via a first signal path. The second amplifier has a second input for a second signal at a second radio frequency band and a second output for an amplified second signal. The second output is connectable to the antenna via a second signal path. The filter module is associated with the first and second signal paths and configured to receive a control signal which selectively operates the filter module at one of at least a first and second filter characteristics to selectively block undesired frequencies.
In one embodiment, the filter module filter module comprises a filter circuit and a switch controllable by the control signal. The filter circuit is configured to implement a first low pass filter when the switch is in a first switch state, and a second low pass filter when the switch is in a second switch state. Advantageously, the first and second low pass filters share filter components. The shared filter components include a combination of at least a capacitor and an inductor, and the switch selectively connects one of a first and second capacitors to this combination to form one of the first and second low pass filters.
Another aspect of the invention involves a wireless phone for a communications system. The phone is operable at a first radio frequency band and a second radio frequency band and includes such a transmitter.
A further aspect of the invention involves a cellular phone for a mobile communications system. The cellular phone is operable at a first radio frequency band and a second radio frequency band and includes a dual band transmitter. The dual band transmitter has first and second amplifiers and a filter module. The first amplifier has a first input for a first signal at a first radio frequency band, and a first output for an amplified first signal. The first output is connectable to an antenna via a first signal path. The second amplifier has a second input for a second signal at a second radio frequency band and a second output for an amplified second signal. The second output is connectable to the antenna via a second signal path. The filter module is associated with the first and second signal paths and configured to receive a control signal which selectively operates the filter module at one of a first and second filter characteristics to selectively block undesired frequencies.
Another aspect of the invention involves an amplifier module having first and second amplifiers and a filter module. The filter module is associated with first and second signal paths and configured to receive a control signal which selectively operates the filter module at one of at least a first and second filter characteristics to selectively block undesired frequencies.
A further aspect of the invention involves a method for filtering radio frequency signals in a wireless phone. The wireless phone includes a transmitter having a first amplifier configured to amplify signals at a first frequency band, and a second amplifier configured to amplify signals at a second frequency band. One of the first and second amplifiers is activated and a signal is fed to the activated amplifier. The activated amplifier amplifies the signal and feed the amplified signal to a filter module. The filter module has at least two filter characteristics defined for the first and second frequency bands. The filter module selects one of the at least two filter characteristics implemented in the filter module. The selected filter characteristic blocks undesired frequencies outside a frequency band of the signal fed to the activated amplifier. The filter module outputs the filtered signal to the antenna.
In one embodiment, the filter module includes a switch which operates between at least a first and second state to selectively add at least one filter element to a combination of shared filter elements in order to selectively implement the at least two filter characteristics.


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patent: 6091966 (2000-07-01), Meadows

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