| 摘要 |
PURPOSE:To avoid the deterioration of input/output unmatched characteristics, by providing a transformer coupling circuit for the input and output of a high- pass filter and designing the circuit so as to provide low-pass filter characteristics. CONSTITUTION:Earth parallel branches of the input and output of the high-pass filter consisting of LC resonance circuits between input and output terminals are provided with the transformer coupling circuit comprising transformers T1 and T2. A tap P of the transformer T1 is connected to the input terminal, and a total leakage inductance Lsigma' of the transformer T1 is Lsigma'=Lsigma1+Lsigma2/n<2>, where (n) is the winding ratio of a winding L10 toward the ground side from the tap P and a winding L11 toward the capacitor C1, and Lsigma1, Lsigma2 are the primary and secondary leakage inductances respectively. Through this leakage inductance and a stray capacitance of the parallel branches synthesized and multiplied by n<2>, a low-pass filter taking higher than the pass band as a cut-off frequency is formed. |
