Techniques for alleviating the need for DC blocking capacitors in high-speed differential signal pairs

• US 20070097658A1
• Filed: 10/28/2005
• Published: 05/03/2007
• Est. Priority Date: 10/28/2005
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Yang, Zhiping, Arumugham, Vinayagam
• Granted Patent: US 7,262,974 B2
• Time in Patent Office: Days
• US Class Current: 361/780
• CPC Class Codes: H01L 2223/6638 Differential pair signal lines
• CPC Class Codes: H01L 2224/16227 the bump connector connecting to a bond pad of the item
• CPC Class Codes: H01L 2924/15192 Resurf arrangement of the internal vias
• CPC Class Codes: H01L 2924/19041 being a capacitor
• CPC Class Codes: H01L 2924/19105 in a side-by-side arrangement on a common die mounting substrate
• CPC Class Codes: H05K 1/0231 Capacitors or dielectric substances
• CPC Class Codes: H05K 1/0245 Lay-out of balanced signal pairs, e.g. differential lines or twisted lines
• CPC Class Codes: H05K 1/0298 Multilayer circuits
• CPC Class Codes: H05K 1/162 incorporating printed capacitors
• CPC Class Codes: H05K 2201/09236 Parallel layout layout of balanced signal pairs H05K1/0245; superposed layout H05K2201/09672
• CPC Class Codes: H05K 2201/09309 Core having two or more power planes; Capacitive laminate of two power planes
• CPC Class Codes: H05K 2201/10689 Leaded Integrated Circuit [IC] package, e.g. dual-in-line [DIL]

Abstract

A circuit board has a first component interface configured to connect to a first circuit board component, a second component interface configured to connect to a second circuit board component, a differential signal pair electrically connecting the first component interface to the second component interface, and a signal return path configured to operate as a signal return pathway for the differential signal pair. The signal return path includes first conductive material which is in electrical communication with the first component interface, second conductive material which is in electrical communication with the second component interface, and a dielectric which provides direct current separation between the first and second conductive material. Such a circuit board may alleviate the need for DC blocking capacitors along the differential pair, and along other differential pairs when the circuit board has multiple differential pairs connecting the first and second component interfaces.

Claims

1. A circuit board module, comprising:

a first component;

a second component; and

a circuit board having;

a first component interface on which the first component is mounted;

a second component interface on which the second component is mounted;

a differential signal pair electrically connecting the first component interface to the second component interface; and

a signal return path configured to operate as a signal return pathway for the differential signal pair, the signal return path including first conductive material which is in electrical communication with the first component interface, second conductive material which is in electrical communication with the second component interface, and a dielectric which provides direct current separation between the first and second conductive material.

2. A circuit board module as recited in claim 1 wherein the first conductive material includes a first ground plane;

wherein the second conductive material includes a second ground plane;

wherein the dielectric forms a non-conductive circuit board layer separating the first ground plane and the second ground plane to create an embedded capacitor within the circuit board.

3. A circuit board module as recited in claim 2, further comprising:

a set of discrete direct current blocking capacitors, each discrete direct current blocking capacitor having a first terminal which is in electrical communication with the first ground plane, and a second terminal which is in electrical communication with the second ground plane.

4. A circuit board module as recited in claim 3 wherein the differential signal pair includes two direct current contiguous metallic pathways connecting the first component interface and the second component interface, the circuit board being free of DC blocking capacitors electrically connected to the differential signal pair.

5. A circuit board module as recited in claim 3 wherein the first component is an area array package device;

wherein the first component interface is a surface mount technology mounting location for the area array package device;

wherein the second component is a circuit board connector; and

wherein the second component interface is a mounting location for the circuit board connector to enable the area array package device to communicate with an external device through the circuit board connector.

6. A circuit board module as recited in claim 3 wherein the first component is a first area array package device;

wherein the first component interface is a first surface mount technology mounting location for the first area array package device;

wherein the second component is a second area array package device; and

wherein the second component interface is a second surface mount technology mounting location for the second area array package device to enable differential-mode communication between the first and second area array package devices.

7. A circuit board module as recited in claim 6, further comprising:

a first power supply configured to provide power to the first area array package device; and

a second power supply configured to provide power to the second area array package device, the second power supply being different than the first power supply;

wherein the first conductive material is configured to connect to an input ground terminal of the second power supply; and

wherein the second conductive material is configured to connect to an output ground terminal of the second power supply.

8. A circuit board module as recited in claim 7 wherein the second conductive material is configured to connect to all ground terminals of the second area array package device.

9. A circuit board module as recited in claim 7 wherein the first conductive material is configured to connect to all core ground terminals of the second area array package device;

and wherein the second conductive material is configured to connect to all I/O ground terminals of the second area array package device.

10. A circuit board module as recited in claim 2 wherein the first conductive material includes multiple first ground planes;

wherein the second conductive material includes multiple second ground planes, the multiple first ground planes and the multiple second ground planes combining to form ground plane pairs, each ground plane pair including a first ground plane and a second ground plane;

and wherein the dielectric forms multiple non-conductive circuit board layers, each non-conductive circuit board layer separating the first ground plane and the second ground plane of a respective ground plane pair.

18. A circuit board as recited in claim 2 wherein the first conductive material includes multiple first ground planes;

wherein the second conductive material includes multiple second ground planes, the multiple first ground planes and the multiple second ground planes combining to form ground plane pairs, each ground plane pair including a first ground plane and a second ground plane; and

wherein the dielectric forms multiple non-conductive circuit board layers, each non-conductive circuit board layer separating the first ground plane and the second ground plane of a respective ground plane pair.

11. A circuit board, comprising:

a first component interface configured to connect to a first circuit board component;

a second component interface configured to connect to a second circuit board component;

a differential signal pair electrically connecting the first component interface to the second component interface; and

a signal return path configured to operate as a signal return pathway for the differential signal pair, the signal return path including first conductive material which is in electrical communication with the first component interface, second conductive material which is in electrical communication with the second component interface, and a dielectric which provides direct current separation between the first and second conductive material.

12. A circuit board as recited in claim 11 wherein the first conductive material includes a first ground plane;

wherein the second conductive material includes a second ground plane;

wherein the dielectric forms a non-conductive circuit board layer separating the first ground plane and the second ground plane to create an embedded capacitor within the circuit board.

13. A circuit board as recited in claim 12, further comprising:

a set of discrete direct current blocking capacitors, each discrete direct current blocking capacitor having a first terminal which is in electrical communication with the first ground plane, and a second terminal which is in electrical communication with the second ground plane.

14. A circuit board as recited in claim 13 wherein the differential signal pair includes two direct current contiguous metallic pathways connecting the first component interface and the second component interface, the circuit board being free of DC blocking capacitors electrically connected to the differential signal pair.

15. A circuit board as recited in claim 13 wherein the first component interface is a surface mount technology mounting location for an area array package device;

and wherein the second component interface is a mounting location for a circuit board connector to enable the area array package device to communicate with an external device through the circuit board connector.

16. A circuit board as recited in claim 13 wherein the first component interface is a first surface mount technology mounting location for a first area array package device;

and wherein the second component interface is a second surface mount technology mounting location for a second area array package device to enable differential-mode communication between the first and second area array package devices.

17. A circuit board as recited in claim 16 wherein a first power supply is configured to provide power to the first area array package device;

wherein a second power supply is configured to provide power to the second area array package device, the second power supply being different than the first power supply;

wherein the first conductive material is configured to connect to an input ground terminal of the second power supply; and

wherein the second conductive material is configured to connect to an output ground terminal of the second power supply.

19. A circuit board, comprising:

first component connecting means for connecting to a first circuit board component;

second component connecting means for connecting to a second circuit board component;

a differential signal pair electrically connecting the first component connecting means to the second component connecting means; and

a signal return path configured to operate as a signal return pathway for the differential signal pair, the signal return path including first conductive material which is in electrical communication with the first component connecting means, second conductive material which is in electrical communication with the second component connecting means, and a dielectric which provides direct current separation between the first and second conductive material.

20. A circuit board as recited in claim 19 wherein the first conductive material includes a first ground plane;

wherein the second conductive material includes a second ground plane;

wherein the dielectric forms a non-conductive circuit board layer separating the first ground plane and the second ground plane to create an embedded capacitor within the circuit board.