Continuously Tunable Impedance Matching Network Using BST Capacitor
An impedance matching circuit employs a variable capacitor, such as a BST capacitor. The bias voltage to the variable capacitor may be adjusted in order to match several different frequencies used with the antenna to the signal source.
1 . A tunable impedance matching circuit coupled between a signal source and an antenna, the tunable impedance matching circuit comprising:
a variable capacitor coupled in series to the signal source, a capacitance of the variable capacitor being adjustable according to a bias voltage applied to the variable capacitor;
a first inductor coupled in series to the variable capacitor and the antenna; and
a second inductor coupled to a node between the variable capacitor and the first inductor,
wherein a combined impedance of the tunable impedance matching network and the antenna is tunable to match an impedance of the signal source by adjusting the bias voltage applied to the variable capacitor.
2 . The tunable impedance matching circuit of claim 1 , wherein the variable capacitor is a BST (Barium Strontium Titanate) capacitor including BST as dielectric.
3 . The tunable impedance matching circuit of claim 1 , wherein the variable capacitor is a dominant tuning component in the tunable impedance matching circuit.
4 . The tunable impedance matching circuit of claim 1 , wherein the first inductor is a dominant tuning component in the tunable impedance matching circuit.
5 . The tunable impedance matching circuit of claim 1 , wherein:
a first terminal of the variable capacitor is coupled to the signal source and the bias voltage, and a second terminal of the variable capacitor is connected to both the first inductor and the second inductor;
a first terminal of the first inductor is coupled to the second terminal of the variable capacitor and to the second inductor, and a second terminal of the first inductor is connected to the antenna; and
a first terminal of the second inductor is connected to the second terminal of the variable capacitor and the first terminal of the first inductor, and a second terminal of the second inductor is connected to ground.
6 . The tunable impedance matching circuit of claim 1 , wherein the bias voltage is a DC voltage coupled to the variable capacitor via a DC bias resistor.
7 . The tunable impedance matching circuit of claim 6 , further comprising a DC blocking capacitor coupled in series to the signal source to block the DC voltage from reaching the signal source.
8 . A tunable impedance matching circuit coupled between a signal source and an antenna, the tunable impedance matching circuit comprising:
a first, variable capacitor coupled in parallel to the signal source, a capacitance of the first, variable capacitor being adjustable according to a bias voltage applied to the first, variable capacitor;
an inductor coupled in parallel to the variable capacitor; and
a second capacitor coupled between the first, variable capacitor and the inductor,
wherein a combined impedance of the tunable impedance matching network and the antenna is tunable to match an impedance of the signal source by adjusting the bias voltage applied to the first, variable capacitor.
9 . The tunable impedance matching circuit of claim 8 , wherein the first, variable capacitor is a BST (Barium Strontium Titanate) capacitor including BST as dielectric.
10 . The tunable impedance matching circuit of claim 8 , wherein the first, variable capacitor is a dominant tuning component in the tunable impedance matching circuit.
11 . The tunable impedance matching circuit of claim 8 , wherein the inductor is a dominant tuning component in the tunable impedance matching circuit.
12 . The tunable impedance matching circuit of claim 8 , wherein:
a first terminal of the first, variable capacitor is coupled to the signal source and to the bias voltage, and a second terminal of the variable capacitor is connected to ground;
a first terminal of the second capacitor is connected to the first terminal of the variable capacitor, and the second terminal of the second capacitor is connected to both the inductor and the antenna; and
a first terminal of the inductor is connected to the second terminal of the second capacitor and to the antenna, and a second terminal of the inductor is connected to ground.
13 . The tunable impedance matching circuit of claim 8 , wherein the bias voltage is a DC voltage coupled to the first, variable capacitor via a DC bias resistor.
14 . The tunable impedance matching circuit of claim 13 , further comprising a DC blocking capacitor coupled in series to the signal source to block the DC voltage from reaching the signal source.