| 摘要 |
PURPOSE: An apparatus for compensating weak electric field of AM/FM tuners in a phase locked loop is provide to independently control the tuned outputs from a tuning circuit and a mixer and prevent deterioration of sound quality by automatically increasing sensitivity in case that a tuner enters a weak electric region. CONSTITUTION: An antenna(10) is connected sequentially to a first tuning circuit(30), a radio signal amplifying circuit(32), a second tuning circuit(34), a mixer(36), an intermediate frequency amplification circuit(38) and a quad detector(40). The first tuning circuit(30), the second tuning circuit(34) and the mixer(36) are connected respectively to a first digital/analog converter(42), a second digital/analog converter(44) and a third digital/analog converter(46). A controller(50) is connected to the first digital/analog converter(42), the second digital/analog converter(44) and the third digital/analog converter(46). The controller(50) is further connected to a signal meter terminal of the quad detector(40). The mixer(36) is connected to a local oscillator(48), which is coupled to the controller(50) to form a phase locked loop.
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