| 摘要 |
The automatic selecting circuit is suitable for use in a multi-system television receiver, enabling it to adapt automatically to any one of a number of different audio frequency broadcasting systems. The circuit basically comprises: a set of three ceramic filters CF1-3 for waveform shaping input signals of B/G, I or D/K systems respectively; a frequency converter 2 for converting the output from the set of filters to a predetermined frequency; an additional filter CFA for the M system; frequency detection circuitry 4, 7 which produces a logic signal indicating whether the input signal is B/G or I or D/K, or M system; an audio detector 3 which receives either the output of the frequency converter 2 or the output of the additional filter CF4; and selection circuitry 6 which determines which output is to be received by the audio detector 3, based on the logic signal. Circuit 8 is a resonance circuit for detector 3. <IMAGE> |
