Controllable filter and high frequency apparatus using the same

摘要

A filter comprises an inductor, a first variable capacitance diode, a second variable capacitance diode having nearly identical characteristic as the first variable capacitance diode, a control terminal for applying voltage to the first and the second variable capacitance diodes, an input terminal, an output terminal and a signal line between the input terminal and the output terminal. A cutoff frequency is controllable with the voltage applied to the control terminal. The variable frequency filter which can receive a large signal has reduced size due to a structure in which the first and the second variable capacitance diodes having nearly identical characteristics are connected either in series or in parallel with their polarities reversed against each other.