| 摘要 |
PURPOSE: A direct conversion type tuner fabricated by a CMOS process is provided to simplify a fabrication process and reduce a cost by constituting a circuit unit for converting a radio frequency broadcast signal into baseband I/Q signals as one chip. CONSTITUTION: A low-pass filter(301) passes a radio frequency broadcast signal and cancels its noise. An automatic gain controller(302) controls a gain of the radio frequency broadcast signal. A radio frequency amplifier(303) amplifies the radio frequency broadcast signal to a certain level. A frequency converter(310) mixes the radio broadcast signal with a local oscillation frequency to convert it into a baseband I/Q signal, filters and outputs the I/Q signal. The first and second intermediate frequency gain controllers(304,305) control a gain of the I/Q signal. A crystal device(306) provides a reference signal. The frequency converter(310) includes a low-noise amplifier(311) for receiving and amplifying the radio frequency broadcast signal, the first mixing circuit(312) for mixing the radio frequency broadcast signal with an intermediate frequency signal and extracting a baseband I signal, the second mixing circuit(313) for mixing the radio frequency broadcast signal with an intermediate frequency signal and extracting a baseband Q signal, the first and second variable pass filters(314,315) for filtering signals outputted from the first and second mixing circuits(312,313), a voltage control oscillator(316) for generating two same intermediate frequency signals with a phase difference of 90 degree and applying them to the first and second mixing circuits(312,313), and a PLL(Phase Locked Loop) circuit(317) for adjusting the oscillation frequency of the voltage control oscillator(316).
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