Space-optimized printed balun

• US 6,359,528 B1
• Filed: 03/09/2000
• Issued: 03/19/2002
• Est. Priority Date: 03/09/2000
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Inventors: Dao, Andy
• Primary Examiner(s): Bettendorf, Justin P.
• Assistant Examiner(s): TAKAOKA, DEAN O
• Application Number:
  US09/522,116
• Time in Patent Office: 740 Days
• Field of Search: 333/25, 333/26
• US Class Current: 333/26
• CPC Class Codes: H01P 5/10 for coupling balanced lines or devices with unbalanced lines or devices

Abstract

A printed balun satisfies performance requirements for operation at a desired operational frequency (e.g., ƒ=5.3 GHz) while minimizing space requirements on a circuit board. Segments of microstrip are connected at right angles that define fingers whose dimensions can be tailored for operation at a desired operational frequency while minimizing the corresponding space required on a circuit board. Minimal separation between the fingers avoids undesirable internal interference. Mounted at the edges of distinct fingers are the necessary ports for operation of the balun including a single-ended port, an isolation port, and two differential ports.

Claims

1. A balun, comprising:

a single-ended port;

an isolation port;

a first differential port;

a second differential port;

a microstrip, wherein

the microstrip defines a plurality of fingers including a first finger that connects to the single ended port, a second finger that connects to the isolation port, a third finger that connects to the first differential port, and a fourth finger that connects to the second differential port.

2. A balun, as claimed in claim 1, wherein angles formed by the microstrip are approximately ninety degrees.

3. A balun, as claimed in claim 2, wherein the microstrip defines a central segment that is transverse to the fingers.

4. A balun as claimed in claim 3, wherein the balun operates at a frequency of approximately 5.3 GHz.

5. A balun, as claimed in claim 1, wherein the microstrip includes copper.

6. A balun as claimed in claim 1, wherein the balun operates at a frequency of approximately 5.3 GHz.

7. A balun as claimed in claim 1, wherein the balun operates at a frequency of approximately 4.2 GHz.

8. A balun, comprising:

a single-ended port;

an isolation port;

a first differential port;

a second differential port;

a microstrip, wherein

the microstrip defines a plurality of fingers including a first finger that connects to the single ended port, a second finger that connects to the isolation port, a third finger that connects to the first differential port, and a fourth finger that connects to the second differential port, and the microstrip defines a central segment transverse to the plurality of fingers and which couples the plurality of fingers to each other;

a clockwise distance along the microstrip from the single-ended port to the first differential port is approximately equal to a clockwise distance along the microstrip from the first differential port to the isolation port

the clockwise distance along the microstrip from the single-ended port to the first differential port is approximately equal to a clockwise distance along the microstrip from the isolation port to the second differential port; and

the clockwise distance along the microstrip from the single-ended port to the first differential port is approximately equal to one-third of a clockwise distance along the microstrip from the second differential port to the single-ended port.

9. A balun, as claimed in claim 8, wherein angles formed by the microstrip are approximately ninety degrees.

10. A balun, as claimed in claim 9, wherein the microstrip defines a central segment that is transverse to the fingers.

11. A balun as claimed in claim 10, wherein the balun operates at a frequency of approximately 5.3 GHz.

12. A balun, as claimed in claim 8, wherein the microstrip includes copper.

13. A balun as claimed in claim 8, wherein the balun operates at a frequency of approximately 5.3 GHz.

14. A balun as claimed in claim 8, wherein the balun operates at a frequency of approximately 4.2 GHz.

15. A method for designing a printed balun, comprising:

determining a geometry of the balun, the geometry depending on a plurality of design parameters and including a microstrip defining a plurality of fingers;

wherein the plurality of fingers include a first finger that connects to a single ended port, a second finger that connects to a isolation port, a third finger that connects to a first differential port, and a fourth finger that connects to a second differential port;

determining materials of the balun, the materials being characterized by material parameters;

determining positions on the balun for the single-ended port, the isolation port, the first differential port, and the second differential port;

choosing an operating frequency for the balun;

determining values for the design parameters for acceptable performance of the balun at the operating frequency.

16. The method of claim 15, wherein determining design parameters comprises:

setting constraints on the design parameters, the constraints including constraints based on the operating frequency, the material parameters, and the positions for the single-ended port the isolation port the first differential port and the second differential port; and

finding values for the design parameters that satisfy the constraints on the design parameters.

17. The method of claim 16, wherein setting constraints on the design parameters further comprises:

simulating performance of the balun based on the values for the design parameters.

18. The method of claim 17, wherein simulating performance of the balun comprises evaluating amplitude differences and phase differences at the first differential output port and the second differential output port.

19. The method of claim 18, wherein simulating performance of the balun further comprises evaluating return losses at the single-ended port, the first differential port and the second differential port.