Double-tuned circuit

Abstract

Between one end of a high-band tuning coil in a primary tuning circuit and one end of a high-band tuning coil in a secondary tuning circuit, a first switch diode and a second switch diode connected in series are provided. A second coupling coil is provided between the ground and the connection point of the first switch diode and the second switch diode. Both first switch diode and second switch diode are set to a continuity state or a non-continuity state to switch between a high-band state and a low-band state.

What is claimed is:  
     
         1 . A double-tuned circuit comprising: 
 a primary tuning circuit having a high-band tuning coil and a low-band tuning coil connected in series at one end of each coil;    a secondary tuning circuit having a high-band tuning coil and a low-band tuning coil connected in series at one end of each coil;    a first coupling coil disposed between the ground and the connection point where the other end of the low-band tuning coil in said primary tuning circuit is connected to the other end of the low-band tuning coil in said secondary tuning circuit;    a first switch diode and a second switch diode connected in series disposed between the one end of the high-band tuning coil in said primary tuning circuit and the one end of the high-band tuning coil in said secondary tuning circuit; and    a second coupling coil disposed between the ground and the connection point of said first switch diode and said second switch diode,    wherein, when a high-band television signal is received, said first switch diode and said second switch diode are set to a continuity state; and    when a low-band television signal is received, said first switch diode and said second switch diode are set to a non-continuity state.    
     
     
         2 . A double-tuned circuit according to    claim 1   , further comprising a first switching terminal and a second switching terminal, 
 wherein said first switch diode and said second switch diode are connected in series by their anodes or by their cathodes;    the anodes are connected to said first switching terminal in a DC-coupling manner;    the cathodes are connected to said second switching terminal in a DC-coupling manner; and    said first switch diode and said second switch diode are set to a continuity state or a non-continuity state by a band switching voltage applied to said first switching terminal and said second switching terminal.    
     
     
         3 . A double-tuned circuit according to    claim 2   , 
 wherein said first coupling coil is connected to the ground through a first DC-blocking capacitor;    said second coupling coil is connected to the ground through a second DC-blocking capacitor;    the connection point of said first coupling coil and the first DC-blocking capacitor is connected to said first switching terminal in a DC-coupling manner; and    the connection point of said second coupling coil and the second DC-blocking capacitor is connected to said second switching terminal in a DC-coupling manner.