Transformer of the balanced-unbalanced type
A transformer of the balanced-unbalanced type includes a primary inductive circuit and a secondary inductive circuit housed inside an additional inductive winding connected in parallel to the terminals of the secondary circuit and inductively coupled with the primary circuit and the secondary circuit.
1. A transformer comprising:
a primary winding;
a secondary winding; and
an additional winding surrounding the primary winding and the secondary winding, the additional winding being inductively coupled to the primary winding and the secondary winding, wherein the additional winding is coplanar with the primary and secondary winding, and wherein the additional winding is electrically directly connected in parallel with the secondary winding, wherein at least two turns of the additional winding surround a portion of an outermost turn of each of the primary and secondary windings.
2. The transformer of claim 1 , wherein the additional winding has an octagonal shape.
3. The transformer of claim 1 , wherein the primary winding, secondary winding, and additional winding are disposed over a semiconductor substrate.
4. The transformer of claim 1 , wherein the transformer is of the balanced-unbalanced type.
5. The transformer of claim 1 , wherein an innermost turn of the additional winding surrounds a portion of an outermost turn of the primary winding or the secondary winding.
6. The transformer of claim 1 , wherein at least two turns of the additional winding surround a portion of an outermost turn of each of the primary and secondary windings.
7. A device comprising:
an antenna;
a first circuit; and
a transformer coupled between the antenna and the first circuit, the transformer comprising:
a primary winding;
a secondary winding inductively coupled to the primary winding, the secondary winding having a first terminal and a second terminal;
an additional winding inductively coupled to the primary and secondary windings, the additional winding having a first terminal and a second terminal;
a first capacitor electrically directly connected between the first terminal of the secondary winding and the first terminal of the additional winding; and
a second capacitor electrically directly connected between the second terminal of the secondary winding and the second terminal of the additional winding, wherein at least two turns of the additional winding surround a portion of an outermost turn of each of the primary and secondary windings, and wherein the primary, secondary, and additional windings are formed in a plurality of metal levels.
8. The device of claim 7 , wherein the first circuit comprises a low noise amplifier (LNA).
9. The device of claim 7 , wherein a portion of the additional winding is symmetric and coplanar with a portion of the primary winding and a portion of the secondary winding.
10. The device of claim 7 , wherein:
the antenna is coupled to a first terminal of the primary winding of the transformer; and
a second terminal of the primary winding of the transformer is coupled to ground.
11. The device of claim 7 , wherein the first circuit is differentially coupled to the additional winding of the transformer.
12. The device of claim 7 , wherein the transformer has a transformation ratio greater than 2.
13. The device of claim 7 , wherein the additional winding comprises a tap point configured to receive a polarizing voltage, the polarizing voltage configured to polarize the first circuit without polarizing the secondary winding.
14. The device of claim 13 , wherein the tap point is a center-tap point.
15. The device of claim 13 , further comprising a direct current voltage source coupled to the tap point and configured to provide the polarizing voltage.
16. The device of claim 15 , wherein a portion of a radiofrequency signal that passes through the first and second capacitor and through the additional winding is based on a ratio between a capacitance value of the first capacitor or the second capacitor and an inductance of the additional winding, and wherein the ratio is between 5 and 10.
17. The device of claim 7 , wherein the first circuit comprises a power amplifier (PA).
18. A method comprising:
coupling an antenna to a reference terminal via a primary winding of a transformer;
coupling a secondary winding of the transformer to an additional winding of the transformer, the additional winding of the transformer being coplanar with the primary and secondary winding of the transformer and surrounding the primary and secondary winding of the transformer wherein at least two turns of the additional winding surround a portion of an outermost turn of each of the primary and secondary windings;
differentially coupling the additional winding of the transformer to a first circuit; and
polarizing the first circuit without polarizing the secondary winding by:
electrically directly connecting in parallel a first capacitor between a first terminal of the secondary winding and a first terminal of the additional winding;
electrically directly connecting in parallel a second capacitor between a second terminal of the secondary winding and a second terminal of the additional winding; and
providing a voltage to a tap of the additional winding.
19. The method of claim 18 , further comprising coupling the reference terminal to ground.
20. The method of claim 18 , further comprising receiving a radiofrequency signal with the antenna.
21. The method of claim 18 , wherein polarizing the first circuit comprises generating a polarization current higher than 50 mA and providing the polarization current to the first circuit.