RECEIVING TUNER FOR COMMON-USE OF DIGITAL AND ANALOG BROADCASTING

摘要

PURPOSE: A receiving tuner for common-use of digital and analog broadcasting is provided to simply receive both analog broadcasting using an FM modulation mode and digital broadcasting using a QPSK(Quadrature Phase Shift Keying) modulation mode by commonly using the PLL of FM and I/Q demodulators. CONSTITUTION: A first RF amp(101) amplifies RF signals input from an LNB(Low Noise Block down Converter). An RF automatic gain controller(102) controls the gain of the amplified RF signals. An RF band pass filter(104) passes the RF signals amplified by a second RF amp(103). A PLL(105) provide the tuning voltage corresponding the phase difference between the oscillation frequency of a first oscillator(106) and reference frequency to the first oscillator(106), and provide band variable voltage to the RF band pass filter(104). A second mixer(203) mixes the output signals of a second oscillator(202) to the IF output signals of an IF amp(112). A first base band signal amp(205) amplifies the output signals of a first low pass filter(204). A phase shifter(206) shifts the output signals of the second oscillator(202) by 90 deg. A third mixer(207) mixes the output signals of the phase shifter(206) to the IF output signals of the IF amp(112). A second base band amp(209) amplifies the output signals of a second low pass filter(208). An AGC detector(126) supplies AGC detection voltage to two automatic gain controllers(102,109).