公开(公告)号：US3636455A

公开(公告)日：1972-01-18

申请号：US3636455D

申请日：1969-09-29

Applicant: TELEFUNKEN PATENT

Inventor： MINNER WILLY ,  LINDNER GERHARD

IPC: H03H7/01 ,  H03H7/10 ,  H04B1/18

CPC classification number: H03H7/0161

Abstract: A tunable input circuit with high selectivity for feeding a signal to a variable-frequency band-pass filter with tuning elements identical to those of the input circuit. The high selectivity produced by the input circuit is a minimum in the range of the received frequency and a maximum in the range of the image frequency. The input circuit is a bridge having four arms with impedances in them and four points connecting the arms. The impedances are diagonally matched, and one set is variable. One set of diagonally opposite points connecting the arms is connected between an antenna lead and ground. A voltage-variable capacitance (such as a voltage-variable diode) is connected between the other pair of connecting points. A tuning voltage is fed back to the voltage-variable capacitance means. This voltage is preferably the same voltage used to tune the band-pass filter.