Transformer with high common-mode rejection ratio (CMRR)

• US 10,511,278 B2
• Filed: 04/23/2018
• Issued: 12/17/2019
• Est. Priority Date: 04/23/2018
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Cheng, Haitao, Jin, Zhang
• Primary Examiner(s): Takaoka, Dean O
• Application Number:
  US15/959,824
• Publication Number:
  US 20190326872A1
• Time in Patent Office: 603 Days
• Field of Search: 333 25, 333 26
• CPC Class Codes: H01F 27/29 Terminals; Tapping arrangements for signal inductances
• CPC Class Codes: H01F 27/42 Circuits specially adapted for the purpose of modifying, or compensating for, electric characteristics of transformers, reactors, or choke coils circuits for controlling transformers, reactors or choke coils, for the purpose of obtaining a desired output H02P13/00; impedance networks H03H
• CPC Class Codes: H03H 7/09 Filters comprising mutual inductance
• CPC Class Codes: H03H 7/42 Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns
• CPC Class Codes: H03H 7/425 Balance-balance networks

Abstract

Certain aspects of the present disclosure are generally directed to a structure for a balanced-unbalanced (balun) transformer. For example, certain aspects of the present disclosure provide a transformer that generally includes a first winding having a first terminal coupled to an input node and a second terminal coupled to a reference potential node. The transformer may also include a first impedance coupled between a center tap of the first winding and the reference potential node, and a second winding magnetically coupled to the first winding and having a first terminal coupled to a first differential node of a differential output pair, a second terminal coupled to a second differential node of the differential output pair, and a center tap coupled to the reference potential node.

Claims

1. A transformer comprising:

a first winding having a first terminal coupled to an input node, and a second terminal coupled to a reference potential node;

a first impedance coupled between a tap of the first winding and the reference potential node, wherein the first impedance comprises a complex impedance; and

a second winding magnetically coupled to the first winding and having a first terminal coupled to a first differential node of a differential output pair, a second terminal coupled to a second differential node of the differential output pair, and a tap coupled to the reference potential node.

2. The transformer of claim 1, wherein the complex impedance comprises a capacitive element.

3. The transformer of claim 2, wherein the complex impedance further comprises an inductive element.

4. The transformer of claim 1, wherein the complex impedance comprises a resistive element coupled in series with a capacitive element.

5. The transformer of claim 1, wherein the complex impedance comprises a resistive element coupled in parallel with a capacitive element.

6. The transformer of claim 1, wherein the complex impedance comprises an inductive element and a resistive element.

7. The transformer of claim 6, wherein the complex impedance further comprises a capacitive element coupled in parallel with the resistive element and coupled in parallel with the inductive element.

8. The transformer of claim 1, further comprising:

a first switch configured to selectively couple the first impedance between the tap of the first winding and the reference potential node.

9. The transformer of claim 1, further comprising:

a second impedance; and

a second switch configured to selectively couple the second impedance between the tap of the first winding and the reference potential node.

10. The transformer of claim 1, wherein the tap of the second winding is coupled to the reference potential node through an alternating-current (AC) coupling capacitive element.

11. The transformer of claim 1, wherein the first winding and the second winding are configured with opposite polarities.

12. The transformer of claim 1, wherein the tap of the first winding comprises a center tap of the first winding, and wherein the tap of the second winding comprises a center tap of the second winding.

13. A method for signal conversion, comprising:

sinking a common-mode current from a tap of a first winding of a transformer to a reference potential node, wherein the common-mode current is sunk through a first impedance comprising a complex impedance, the first winding having a first terminal coupled to an input node, and a second terminal coupled to the reference potential node; and

generating a current across a second winding of the transformer corresponding to the common-mode current, the second winding being magnetically coupled to the first winding and having a first terminal coupled to a first differential node of a differential output pair, a second terminal coupled to a second differential node of the differential output pair, and a tap coupled to the reference potential node.

14. The method of claim 13, wherein sinking the common-mode current comprises:

selectively coupling the first impedance between the tap of the first winding and the reference potential node.

15. The method of claim 14, wherein sinking the common-mode current further comprises:

selectively coupling a second impedance between the tap of the first winding and the reference potential node.

16. The method of claim 13, wherein the tap of the first winding comprises a center tap of the first winding, and wherein the tap of the second winding comprises a center tap of the second winding.

17. The method of claim 13, wherein the complex impedance comprises a resistive element coupled in parallel with a capacitive element.

18. A method for signal conversion, comprising:

receiving a single-ended signal at a first terminal of a first winding of a transformer, a second terminal of the first winding being coupled to a reference potential node;

selectively coupling a complex impedance between a tap of the first winding and the reference potential node; and

generating a differential signal at a second winding of the transformer, a tap of the second winding being coupled to the reference potential node.

19. The method of claim 18, wherein the tap of the first winding comprises a center tap of the first winding, and wherein the tap of the second winding comprises a center tap of the second winding.

20. The method of claim 18, wherein the complex impedance comprises a resistive element coupled in series with a capacitive element.