| 摘要 |
PURPOSE:To improve remarkably the selectivity of a device by constituting the titled circuit of the 1st stage formed by an NAND circuit, and the NAND circuit added to the pre-stage of an NOR circuit of the final stage. CONSTITUTION:One more stage of the NAND circuit is added to the conventional circuit. When ''L'' is applied to all input terminals CP1, CP2 and CP3 of a control signal, a signal of frequency fref1 is outputted to an output of the NAND circuit 16, and ''H'' is outputted to other NAND circuits 17-21. Thus, the signal fref1 is outputted at an output of the NAND circuit 22 and ''L'' is outputted at other NAND circuits 17-23, 24. These outputs pass through NOR circuits 25 and D4, and the signal fref1 is selected and outputted at a terminal fref. Thus, since signals other than the selected signal are attenuated completely, the S/N of the circuit is improved remarkably. |
