Tunable filter having a capacitive circuit connected to ground

Claim 2

A tunable filter, comprising: first and second resonant structures coupled by a capacitive coupler, the capacitive coupler comprising: first and second variable capacitive tuning elements, each having a positive terminal; and a capacitive circuit coupling the variable capacitive tuning elements, the capacitive circuit comprising a capacitive pi-network coupled at the positive terminals of the variable capacitive tuning elements, the capacitive pi-network having at least one element directly electrically connected to ground.

Claim 3

The tunable filter of claim 1, wherein the capacitive pi-network comprises linear elements.

Claim 4

The tunable filter of claim 1, wherein the capacitive circuit includes impedance transformation circuitry.

Claim 5

The tunable filter of claim 1, wherein the capacitive pi-network comprises fixed-value capacitors, wherein at least one of the fixed-value capacitors is connected to electrical ground.

Claim 6

The tunable filter of claim 4, wherein the capacitive pi-network comprises: first and second shunted capacitors coupled in series from electrical ground to the positive terminals of the first and second variable capacitive tuning elements, respectively; and a third capacitor coupled in series between the positive terminals of the first and second variable capacitive tuning elements.

Claim 7

A linearized tunable filter, comprising: first and second resonators coupled by a capacitive circuit, the capacitive circuit comprising: first and second variable capacitive tuning elements each having a non-linear response, each variable capacitive tuning element having a positive terminal; first and second shunted capacitors being directly connected between electrical ground and the positive terminal of the first and second variable capacitive tuning elements, respectively; and a third capacitor coupled in series between the first and second variable capacitive tuning elements.

Claim 8

A linearized tunable filter, comprising: first and second resonators coupled by a capacitive circuit, the capacitive circuit comprising: first and second variable capacitive tuning elements each having a non-linear response, each variable capacitive tuning element having a positive terminal; first and second shunted capacitors being directly connected between electrical ground and the positive terminal of the first and second variable capacitive tuning elements, respectively; and a third capacitor coupled in series between the first and second variable capacitive tuning elements.

Claim 9

The linearized tunable filter of claim 6, wherein the variable capacitance element comprises a varactor.

Claim 10

The linearized tunable filter of claim 6, wherein the first and second shunted capacitors comprise fixed-value capacitors.

Claim 11

The linearized tunable filter of claim 6, wherein the third capacitor comprise a fixed-value capacitor.

Claim 12

A tunable filter, comprising: a first resonator circuit; a second resonator circuit, comprising: first and second inductive resonators coupled by a capacitive circuit, the capacitive circuit comprising: first and second varactors, each having a cathode; first and second capacitors being shunted directly to ground, and being coupled in series to the cathode of the first and second varactors, respectively; a third capacitor coupled in series with the cathodes of the first and second varactors; and coupling means for coupling the first and second resonator circuits.

Claim 13

A tunable filter, comprising: a first resonator circuit; a second resonator circuit, comprising: first and second inductive resonators coupled by a capacitive circuit, the capacitive circuit comprising: first and second varactors, each having a cathode; first and second capacitors being shunted directly to ground, and being coupled in series to the cathode of the first and second varactors, respectively; a third capacitor coupled in series with the cathodes of the first and second varactors; and coupling means for coupling the first and second resonator circuits.

Claim 14

A radio comprising: a radio receiver, the radio receiver including a tunable circuit, the tunable circuit comprising first and second resonant structures interconnected by a capacitive coupler, the capacitive coupler comprising: first and second variable capacitive tuning elements, each having a positive terminal; and a capacitive circuit coupling the first and second variable capacitive tuning elements, the capacitive circuit having a capacitive pi-network coupled at the positive terminals of the variable capacitive tuning elements, and having at least one element of the capacitive pi-network directly connected to ground.

Claim 15

A radio comprising: a radio receiver, the radio receiver including a tunable circuit, the tunable circuit comprising first and second resonant structures interconnected by a capacitive coupler, the capacitive coupler comprising: first and second variable capacitive tuning elements, each having a positive terminal; and a capacitive circuit coupling the first and second variable capacitive tuning elements, the capacitive circuit having a capacitive pi-network coupled at the positive terminals of the variable capacitive tuning elements, and having at least one element of the capacitive pi-network directly connected to ground.

Claim 16

The radio of claim 11, wherein the capacitive pi-network comprises linear elements.

Claim 17

The radio of claim 11, wherein the capacitive pi-network comprises fixed-value capacitors.

Claim 18

The radio of claim 13, wherein the capacitive pi-network of fixed-value capacitors comprises: first and second shunted capacitors coupled in series from electrical ground to the positive terminals of the first and second variable capacitive tuning elements, respectively; and a third capacitor coupled in series with the positive terminals of the first and second variable capacitive tuning elements.