Trimmer circuit for oscillating circuit, e.g. for HF receiver - has trimmer capacitor in parallel with varactor diode facing opposed varactor diode in series

摘要

A trimming circuit for a resonating circuit has two varactor diodes connected in series in opposed directions. They are both in parallel to the inductance of the oscillating circuit, while one (C1) is in parallel to the trimmer capacitor (C2). A control d.c. voltage (U) is supplied to the diodes via a high resistance or choke (D). The capacitance of the diodes is adjustable. The capacitor (C2) is switched in parallel to the diode whose switching capacitance has the smaller effect. The control voltage-resonance frequency characteristic in the upper frequency range does not so sharply fall off in dependence on the trimmer capacitance.