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Abstract

A dual mode, portable cellular telephone utilizes an rf switch to control the rf signal path through its rf output stage. A voltage controlled oscillator (VCO) generates an rf signal that is selectively modulated with an fm modulation signal. In an FM modulation mode, the rf signal generated by the VCO is amplified by a first rf amplifier and a second rf amplifier, and then applied to a power amplifier. The power amplifier couples the amplified rf signal to an antenna for broadcasting. A first rf signal path through the rf output stage thus includes the VCO, first rf amplifier, second rf amplifier, and power amplifier, and the resulting rf output signal is FM modulated. In a digital modulation mode, the rf signal generated by the VCO is unmodulated, having a fixed frequency. This is achieved by making the fm modulation signal be a constant signal. The fixed frequency signal is amplified by the first rf amplifier and then applied to a digital modulator as a local oscillator signal. The digital modulator then modulates the local oscillator signal using appropriate modulation signals, and applies the resulting digitally modulated rf signal to the power amplifier. A second rf signal path through the rf output stage thus includes the VCO, first rf amplifier, digital modulator and power amplifier. Control of the rf signal path is achieved by switchably connecting and disconnecting power to the digital modulator and the second rf amplifier.

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First Claim