Directional couplers for RF power detection
View Patent ↗Very small size true directional couplers have a coupling coefficient that is independent on load VSWR. The coupler uses coupled inductors with a compensation circuit including a resistor and a capacitor, or just a capacitor. Wideband operation is suitable for many portable applications such as power detection and control for GSM, DCS-PCS, CDMA/WCDMA, Bluetooth, and WLAN systems.
1. A radio frequency (RF) directional coupler, comprising:
a substrate;
an input port on the substrate;
a coupling port on the substrate;
a load port on the substrate;
a ballast resistor port on the substrate; and
a coupled inductor on the substrate comprising a first inductor having a first terminal coupled to the input port, a second terminal coupled to the load port, a second inductor having a first terminal coupled to the coupling port and a second terminal coupled to the ballast resistor port, wherein the coupled inductor has a footprint less than about 165 microns by about 155 microns.
2. The RF directional coupler of claim 1 , wherein the first inductor comprises about 3.25 turns of rectangular shaped material.
3. The RF directional coupler of claim 2 , wherein the rectangular shaped material is about 5 microns wide and about 2 microns thick.
4. The RF directional coupler of claim 1 , wherein the substrate comprises at least one of an integrated circuit, a printed circuit board, and a low temperature co-fired ceramic implementation.
5. The RF directional coupler of claim 1 , wherein the substrate is about 100 microns thick.
6. The RF directional coupler of claim 1 , wherein the first inductor comprises a material selected from the group consisting of gold, copper, and aluminum.
7. The RF directional coupler of claim 1 , wherein the first inductor has a dielectric constant of about 12.9.
8. The RF directional coupler of claim 1 , wherein the coupled inductor has an internal opening of about 25 microns by about 25 microns.
9. The RF directional coupler of claim 1 , wherein a spacing between the first inductor and second inductor is about 5 microns.
10. The RF directional coupler of claim 1 , wherein the first inductor is in a substantially stacked relationship over the second inductor forming a dual layer coupled inductor with about a 4 micron air gap between the first inductor and the second inductor.
11. The RF directional coupler of claim 10 , wherein the first inductor is about 2 microns thick and the second inductor is about 1 micron thick.
12. The RF directional coupler of claim 10 , wherein the coupled inductor has a footprint of about 85 microns by 85 microns.
13. A radio frequency (RF) directional coupler, comprising:
a substrate;
a GSM input port on the substrate;
a power detector port on the substrate;
a DOS-PCS input port on the substrate;
a GSM output port on the substrate;
a ballast resistance port;
a DCS-PCS output port on the substrate;
a coupled inductor on the substrate comprising a first inductor having a first terminal coupled to the GSM input port and a second terminal coupled to the GSM output; a second inductor having a first terminal coupled to the power detector port and a second terminal coupled to the ballast resistance port, wherein the second inductor is in a substantially stacked relationship over the first inductor; and a third inductor having a first terminal coupled to the DCS-PCS input port and a second terminal coupled to the DCS-PCS output port, wherein the third inductor is in a substantially stacked relationship over the second inductor.
14. The RF directional coupler of claim 13 , wherein the coupled inductor has an internal opening of about 25 microns by about 15 microns.
15. The RF directional coupler of claim 13 , wherein the first inductor is about 2 microns thick, the second inductor is about 1 micron thick and the third inductor is about 0.5 microns thick.
16. The RF directional coupler of claim 13 , wherein the footprint of the coupled inductor is less than about 95 microns by about 95 microns.
17. A radio frequency (RF) directional coupler, comprising:
a substrate;
an input port on the substrate;
a coupling port on the substrate;
a load port on the substrate;
a ballast resistor port on the substrate; and
a coupled inductor on the substrate comprising a first inductor having a first terminal coupled to the input port and a second terminal coupled to the load port; and a second inductor having a first terminal coupled to the coupling port and a second terminal coupled to the ballast resistor port, wherein at least a portion of the first inductor is arranged over the second inductor.
18. The RF directional coupler of claim 17 , wherein the first inductor comprises about 3.25 turns of rectangular shaped material.
19. The RF directional coupler of claim 18 , wherein a spacing between the first inductor and second inductor is about 5 microns.
20. The RF directional coupler of claim 17 , wherein the first inductor and the second inductor comprises a material selected from the group consisting of gold, copper, and aluminum.