| 摘要 |
PURPOSE: An apparatus for generating an intermediate frequency(IF) in a transmission circuit of a mobile terminal for triple mode use is provided to vary a turning circuit capacitance value of a voltage controlled oscillator(VOC) by a mode control signal of a controller, so as to simultaneously generate 255.38MHz and 130.38MHz IFs needed in a transmission circuit. CONSTITUTION: A controller(100) outputs a frequency control signal to a phase locked loop IC(PLL IC)(210) which is one of components of an intermediate frequency(IF) transmission chip(IFT chip)(200), and outputs a mode control signal to a tuning circuit(300). The IFT chip(200) comprises as follows. A voltage controlled oscillator(VCO)(220) generates an 130.38MHz or an 255.38MHz IF signal by a resonant frequency determined by the tuning circuit(300). The PLL IC(210) inputs a frequency control signal output from the controller(100), and simultaneously inputs a frequency signal fed back from the VCO(220), then outputs a phase-fixed frequency tuning voltage. An automatic gain controlling circuit is built in the IFT chip(200). The tuning circuit(300) inputs the frequency tuning voltage output from the PLL IC(210), and simultaneously inputs the mode control signal output from the controller(100), then varies a capacitance value according to the inputted frequency tuning voltage and the mode control signal. The tuning circuit(300) decides the resonant frequency of the VCO(220).
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