Multi-layer RF filter and balun

1. A filter-balun combination for filtering an input signal provided to the filter-balun combination and providing a balanced output signal from the filter-balun combination, comprising:

a multi-layer planar substrate including multiple planar dielectric layers, multiple planar device layers comprising conducting material, and multiple conducting structures electrically coupling conducting material in different device layers through at least one dielectric layer;

a filter comprising a first inductor and a second inductor, the first inductor comprising electrically conducting traces formed in at least one of said multiple planar device layers, said first inductor having an input, an output, and at least one turn, the second inductor comprising electrically conducting traces formed in at least one of said multiple planar device layers, said second inductor being symmetrical to said first inductor about a plane that is equidistant from said first and second inductors and perpendicular to the surface of said multi-layer planar substrate, said second inductor having an input coupled to the output of said first inductor, said second inductor further having an output; and

a balun comprising a first electrically conducting central transmission line coupled to the output of said second inductor and forming in one of said multiple device layers a first path that includes first and second coil areas, said balun further comprising first and second output structures, each of which includes upper and lower electrically conducting transmission lines having first and second ends, the transmission lines forming substantially overlapping paths in planar device layers located above and below the device layer of said first electrically conducting central transmission line, wherein the substantially overlapping paths of said upper and lower electrically conducting transmission lines of the first output structure substantially overlap the first path of said first electrically conducting transmission line in the first coil area, and wherein the substantially overlapping paths of said upper and lower electrically conducting transmission lines of the second output structure substantially overlap the first path of said first electrically conducting central transmission line in the second coil area, and wherein the upper electrically conducting transmission line and lower electrically conducting transmission line of each of the first and second output structures are electrically coupled near where the electrically conducting transmission lines terminate and provide a signal output at the first ends of the transmission lines.

2. The filter-balun combination of claim 1 , further comprising:

a first ground plane located in a device layer different from the device layer of the first electrically conducting central transmission line; and

a second ground plane located in a different device layer from said first ground plane and said first electrically conducting central transmission line, wherein the upper electrically conducting transmission line of each of the first and second output structures is electrically connected to said first ground plane at the second end of the upper electrically conducting transmission lines, and wherein the lower electrically conducting transmission lines are electrically connected to said second ground plane at the second end of the lower electrically conducting transmission lines.

3. The filter-balun combination of claim 1 , wherein the multiple planar dielectric layers comprise low-temperature co-fired ceramic.

4. The filter-balun combination of claim 1 , further comprising a single electrically conductive via connecting the output of said first inductor, the input of said second inductor, and a ground plane formed in a device layer of the substrate.

5. The filter-balun combination of claim 1 , wherein the uppermost device layer of the filter is at least partially exposed to air.

6. The filter-balun combination of claim 1 , further comprising satellite radio receiver circuitry formed in said multi-layer planar substrate, wherein a signal provided to said input of said filter is filtered by said filter and balanced by said balun before being provided to said satellite radio receiver circuitry for further processing.

7. The filter-balun combination of claim 1 , wherein said filter and balun have a combined insertion loss of less than 1.5 dB at a center frequency of the filter.

8. The filter-balun combination of claim 1 , wherein said filter is a bandpass filter.

9. The filter-balun combination of claim 1 , wherein said second inductor is formed only in the same at least one of said multiple planar device layers as said first inductor.

10. A filter for filtering a signal carried by a signal transmission line, comprising:

a multi-layer planar substrate including multiple planar dielectric layers, multiple planar device layers comprising conducting material, and multiple conducting structures electrically coupling conducting material in different device layers through at least one dielectric layer;

a first inductor comprising electrically conducting traces formed in at least one of said multiple planar device layers, said first inductor having an input, and output, and at least one turn; and

a second inductor comprising electrically conducting traces formed in at least one of said multiple planar device layers, said second inductor being symmetrical to said first inductor about a plane that is equidistant from said first and second inductors and perpendicular to the surface of said multi-layer planar substrate, said second inductor having an input coupled to the output of said first inductor, said second inductor further having an output configured to provide a filtered signal to additional processing circuitry.

11. The filter of claim 10 , wherein said second inductor is formed only in the same at least one of said multiple planar device layers as said first inductor.

12. The filter of claim 10 , wherein the multiple planar dielectric layers comprise low-temperature co-fired ceramic.

13. The filter of claim 10 , further comprising a single electrically conductive via connecting the output of said first inductor, the input of said second inductor, and a ground plane formed in a device layer of the substrate.

14. The filter of claim 10 , wherein the filter is a band-pass filter.

15. The filter of claim 10 , wherein the uppermost device layer is at least partially exposed to air.

16. The filter of claim 10 , further comprising satellite radio receiver circuitry formed in said multi-layer planar substrate, wherein a signal provided to said input of said filter is filtered by said filter before being provided to said satellite radio receiver circuitry for further processing.

17. A balun for joining a balanced signal-carrying transmission line to an unbalanced transmission line, comprising:

a multi-layer planar substrate including multiple planar dielectric layers, multiple planar device layers comprising conducting material, and multiple conducting structures electrically coupling conducting material in different device layers through at least one dielectric layer; and

a balun comprising a first electrically conducting central transmission line configured to receive and carry an electromagnetic signal, said electrically conducting central transmission line forming in one of said multiple device layers a first path that includes first and second coil areas, said balun further comprising first and second output structures, each of which includes upper and lower electrically conducting transmission lines having first and second ends, the transmission lines forming substantially overlapping paths in planar device layers located above and below the device layer of said first electrically conducting central transmission line, wherein the substantially overlapping paths of said upper and lower electrically conducting transmission lines of the first output structure substantially overlap the first path of said first electrically conducting central transmission line in the first coil area, and wherein the substantially overlapping paths of said upper and lower electrically conducting transmission lines of the second output structure substantially overlap the first path of said first electrically conducting central transmission line in the second coil area, and wherein the upper electrically conducting transmission line and lower electrically conducting transmission line of each of the first and second output structures are electrically coupled near where the electrically conducting transmission lines terminate and provide a signal output at the first ends of the transmission lines.

18. The balun of claim 17 , further comprising:

a first ground plane located in a device layer different from the device layer of the first electrically conducting central transmission line; and

a second ground plane located in a different device layer from said first ground plane and said first electrically conducting central transmission line, wherein the upper electrically conducting transmission line of each of the first and second output structures is electrically connected to said first ground plane at the second end of the upper electrically conducting transmission lines, and wherein the lower electrically conducting transmission lines are electrically connected to said second ground plane at the second end of the lower electrically conducting transmission lines.

19. The balun of claim 17 , wherein the multiple planar dielectric layers comprise low-temperature co-fired ceramic.

20. The balun of claim 17 , further comprising satellite radio receiver circuitry formed in said substrate, wherein a signal provided to said first electrically conducting central transmission line is balanced by said balun before being provided by said first and second output structures to said satellite radio receiver circuitry for further processing.

21. A filter-balun combination for filtering an input signal provided to the filter-balun combination and providing a balanced output signal from the filter-balun combination, comprising:

a multi-layer planar substrate including multiple planar dielectric layers, multiple planar device layers comprising conducting material, and multiple conducting structures electrically coupling conducting material in different device layers through at least one dielectric layer;

a filter comprising a first inductor and a second inductor, the first inductor comprising electrically conducting traces formed in at least one of said multiple planar device layers, said first inductor having an input, an output, and at least one turn, the second inductor comprising electrically conducting traces formed only in the same at least one of said multiple planar device layers as said first inductor, said second inductor being symmetrical to said first inductor about a plane that is equidistant from said first and second inductors and perpendicular to the surface of said multi-layer planar substrate, said second inductor having an input coupled to the output of said first inductor, said second inductor further having an output; and

a balun comprising a first electrically conducting central transmission line coupled to the output of said second inductor and forming in one of said multiple device layers a first path that includes first and second coil areas, said balun further comprising first and second output structures, each of which includes upper and lower electrically conducting transmission lines having first and second ends, the transmission lines forming substantially overlapping paths in planar device layers located above and below the device layer of said first electrically conducting central transmission line, wherein the substantially overlapping paths of said upper and lower electrically conducting transmission lines of the first output structure substantially overlap the first path of said first electrically conducting central transmission line in the first coil area, and wherein the substantially overlapping paths of said upper and lower electrically conducting transmission lines of the second output structure substantially overlap the first path of said first electrically conducting central transmission line in the second coil area, and wherein the upper electrically conducting transmission line and lower electrically conducting transmission line of each of the first and second output structures are electrically coupled near where the electrically conducting transmission lines terminate and provide a signal output at the first ends of the transmission lines.