Miniature radio frequency directional coupler for cellular applications
A directional coupler with increased directivity and reduced overall footprint area is disclosed. There is an input port, an output port, a coupled port, and a ballasting port. A primary chain of serially connected inductors is connected to the input port and the output port, while a secondary chain of serially connected inductors is connected to the coupled port and the ballasting port. A first compensation capacitor is connected to the input port and the coupled port, and a second compensation capacitor is connected to the input port and the ballasting port.
1. A directional coupler comprising:
an input port;
an output port;
a coupled port;
a ballasting port;
a primary chain of inductors comprising a plurality of inductors connected serially, wherein a first inductor of the primary chain of inductors is connected to the input port and a last inductor of the primary chain of inductors is connected to the output port;
a secondary chain of inductors comprising a plurality of inductors connected serially, wherein a first inductor of the secondary chain of inductors is connected to the coupled port and a last inductor of the secondary chain of inductors is connected to the ballasting port;
a first compensation capacitor connected to the input port and the coupled port; and
a second compensation capacitor connected to the input port and the ballasting port;
wherein the primary chain of inductors is inductively coupled to the secondary chain of inductors.
2. The directional coupler of claim 1 wherein the primary chain of inductors comprises two inductors and the secondary chain of inductors comprises two inductors.
3. The directional coupler of claim 2 wherein the physical arrangement of the inductors consists of an alternating pattern of the first primary chain inductor, the first secondary chain inductor, the second primary chain inductor, and the second secondary chain inductor.
4. The directional coupler of claim 2 wherein the physical arrangement of the inductors consists of the two primary chain inductors being located outside of the two secondary chain inductors, such that the arrangement follows the pattern of the first primary chain inductor, the first secondary chain inductor, the second secondary chain inductor, and the second primary chain inductor.
5. The directional coupler of claim 2 wherein the physical arrangement of the inductors consists of the two primary chain inductors being located next to the two secondary chain inductors, such that the arrangement follows the pattern of the first primary chain inductor, the second primary chain inductor, the first secondary chain inductor, and the second secondary chain inductor.
6. The directional coupler of claim 1 further comprising a third compensation capacitor connected to the input port and the first secondary chain inductor.
7. The directional coupler of claim 6 further comprising a fourth compensation capacitor connected to the input port and the output port.
8. The directional coupler of claim 1 further comprising a dielectric layer, wherein the inductors are spiral conductive traces.
9. The directional coupler of claim 8 , wherein the primary chain of inductors and secondary chain of inductors are situated on different metal layers.
10. The directional coupler of claim 8 further comprising:
a first primary underpath formed on the dielectric layer connecting the input port to a first primary chain spiral conductive trace;
a second primary underpath formed on the dielectric layer connecting the first primary chain spiral conductive trace to a second primary chain spiral conductive trace;
a first secondary underpath formed on the dielectric layer connecting the coupled port to a first secondary chain spiral conductive trace;
a second secondary underpath formed on the dielectric layer connecting the first secondary chain spiral conductive trace to a second secondary chain spiral conductive trace.
11. The directional coupler of claim 10 further comprising at least one capacitive stub connecting the primary chain to the secondary chain.
12. The directional coupler of claim 10 , wherein the primary chain has a first predefined width, the secondary chain has a second predefined width, the primary underpath has a third predefined width, the secondary underpath has a fourth predefined width, and the primary chain is separated from the secondary chain by a fifth predefined distance.
13. The directional coupler of claim 12 , wherein the first predefined width is greater than the second predefined width.
14. The directional coupler of claim 13 , wherein the third predefined width is greater than the first predefined width and the fourth predefined width is substantially equal to the second predefined width and the fifth predefined distance.
15. The directional coupler of claim 14 , wherein the first predefined width is approximately 5 μm, the second predefined width is approximately 2.5 μm, the third predefined width is approximately 20 μm, the fourth predefined width is approximately 2.5 μm, and the fifth predefined distance is approximately 2.5 μm.
16. The directional coupler of claim 15 , having a footprint area of approximately 105 μm by 85 μm.
17. The directional coupler of claim 15 , having a footprint area of approximately 130 μm by 110 μm.
18. The directional coupler of claim 8 , wherein the dielectric layer is on a semiconductor substrate.
19. The directional coupler of claim 8 , wherein the dielectric layer is on a low temperature co-fired ceramic (LTCC) substrate.
20. The directional coupler of claim 8 , wherein the dielectric layer is on a thin-film printed substrate.
21. The directional coupler of claim 8 , wherein the dielectric layer is on a laminate substrate.
22. The directional coupler of claim 10 , wherein the primary chain of inductors is disposed in a spaced, parallel and partially coextensive relationship with the secondary chain of inductors.