Abstract: A Radio Frequency (RF) circuit includes an active portion and a tuned portion. The active portion receives an RF signal and that operates upon the RF signal. The tuned portion couples to the active portion and includes a first inductor, a second inductor, and a switch. When the switch is closed, the second inductor couples to the first inductor and the tuned portion has first tuning characteristics. When the switch is open, the second inductor is decoupled from the first inductor and the tuned portion has second tuning characteristics. The tuned portion may include lumped or parasitic capacitance. The tuned portion alternately includes an inductor having a first terminal, a second terminal, an intermediate tap, and a switch that couples between the second terminal and the intermediate tap. When the switch is closed the tuned portion has first tuning characteristics and when the switch is open, the tuned portion has second tuning characteristics.

Abstract: A Radio Frequency (RF) circuit includes an active portion and a tuned portion. The active portion receives an RF signal and that operates upon the RF signal. The tuned portion couples to the active portion and includes a first inductor, a second inductor, and an NMOS transistor. The NMOS transistor has a gate, a drain, a source, and a body. The drain and source operably couple/decouple the second inductor to/from the first inductor. The drain and source are biased at respective operating voltages (greater than ground and less than a first voltage supply) by the active portion and the tuning portion. The body couples to a first voltage supply, via a control circuit or switch in some cases. Applying a second voltage supply (that is greater than the first voltage supply) to the gate turns ON the NMOS transistor.

Abstract: A double-tuned circuit of a tuner that can be switched for tuning to a plurality of frequency bands by turning a switching diode ON or OFF restrains degradation of a selectivity caused by an undesirable additional tuning circuit or parasitic tuning circuit formed by a capacitance generated when the switching diode is OFF and inter-terminal capacitance of a resistor. A double-tuned circuit of a tuner is also provided that exhibits good selectivity with reduced damping to a tuning circuit in a low-band receiving mode, and also exhibits a wider tuning range. A feed resistor for high-band receiving is directly connected to a switching diode in a primary tuning circuit, and the feed resistor for high-band receiving is connected to a switching diode via a coil in a secondary tuning circuit.

Abstract: A band switching circuit of a tuner comprises a tuning circuit, a switching diode connected to the tuning circuit, a pair of band switching terminals coupled across the switching diode. A novel transistor is inserted between one of the band switching terminals and one end of the switching diode with one PN junction of the novel transistor opposing in polarity to the PN junction of the switching diode.

Abstract: The invention relates to a two-circuit resonant bandpass filter for television tuners for switching a first frequency band to a second frequency band. The bandpass filter has a common primary circuit to which two secondary circuits are coupled, a first of the secondary circuits being connected via an electronic switch to the primary circuit which, together with the reactances of the first secondary circuit, short circuits, in the closed condition, the second secondary circuit.