Switchable varicap-tuned RF amplifier circuit, e.g. for TV tuner, has tuned circuit with two series inductors and supply connection via both coils or to center tap

摘要

The amplifier has a switchable resonant circuit connected to the drain of a FET (A1) with a first capacitor (C1) and varactor diode (8) in parallel with two series-connected inductors (L2, L3). The supply voltage is connected to the junction of the inductors via a diode (11) and RF grounding capacitor (12), or to the two inductors together in series, an additional capacitor (3) being connected between the latter supply point and ground. The voltage applied when connection is made to the junction of the two inductors may be greater or less than that applied when the two coils are used in series. Independent claims are also included for the following: (a) a receiver for modulated high-frequency signals with a tuned amplifier circuit; and (b) an oscillator with a tuned amplifier circuit.