| 摘要 |
PURPOSE: A frequency mixer of a mobile communication system is provided to increase a phase noise and sensibility of a local oscillating frequency generator by preventing a signal supplied to the local oscillating frequency generator from a receiving circuit. CONSTITUTION: A frequency mixer of a mobile communication system comprises a local oscillating frequency generator(111), an amplifier(109), an attenuator(125), and a high gain amplifier. The amplifier(109) outputs to a down converter(107) of a receiving circuit(110) by amplifying a local oscillating signal outputted from the local oscillating frequency generator(111). The attenuator(125) sets off a received signal supplied to the generator(111) from an up converter(115), by being connected between the generator(111) and the up converter(115) of the receiving circuit(110). The high gain amplifier amplifies and outputs the local oscillating frequency to a high gain. The local oscillating frequency outputted from the generator(111) becomes weak by being influenced by the attenuator(125), if the received signal is set off in the attenuator(125). The high gain amplifier(127) amplifies the local oscillating frequency to the high gain for compensating the weaken local oscillating frequency, to output into the up converter(115).
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