System and method for transmitter electromagnetic interference (EMI) reduction

• US 8,462,880 B2
• Filed: 08/26/2009
• Issued: 06/11/2013
• Est. Priority Date: 08/26/2009
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Micrel Incorporated (Microchip Technology Incorporated)
• Inventors: Lin, Sheng, Chang, Menping
• Primary Examiner(s): Fan, Chieh M
• Assistant Examiner(s): Perez, James M
• Application Number:
  US12/548,229
• Publication Number:
  US 20110051819A1
• Time in Patent Office: 1,385 Days
• Field of Search: 375295-296, 375/242, 375/244, 375257-258, 375/309
• US Class Current: 375/296
• CPC Class Codes: H04B 15/02 Reducing interference from electric apparatus by means located at or near the interfering apparatus
• CPC Class Codes: H04B 3/30 Reducing interference caused by unbalanced currents in a normally balanced line

Abstract

A device for Electro-Magnetic Interference (EMI) reduction in an Ethernet system has an Ethernet compatible device. The Ethernet compatible device has a filter for adjusting a signal outputted by the Ethernet compatible device for EMI reduction.

Claims

1. A device for Electro-Magnetic Interference (EMI) reduction in an Ethernet system comprising:

an Ethernet compatible device;

a cable of length L coupled to the Ethernet compatible device, wherein the cable length L is greater than 0 meters but less than 100 meters in length; and

a programmable filter coupled between the Ethernet compatible device and the cable for adjusting transmit signal amplitude and phase by the Ethernet compatible device for EMI reduction, wherein the programmable filter is selected to have an amplitude and frequency response having characteristics of a Cat 5 cable of length equal to 100-L meters for said EMI reduction.

2. A device for Electro-Magnetic Interference (EMI) reduction in accordance with claim 1 wherein the programmable filter comprises:

a storage registry; and

an adder which combines an output signal from the storage registry with a signal from the Ethernet compatible device.

3. A device for Electro-Magnetic Interference (EMI) reduction in accordance with claim 1 wherein the transmitter device comprises:

a device to transmit data coupled to the programmable filter;

a DAC coupled to an output of the device to transmit data to convert a digital signal into analog form; and

a driver coupled to an output of the DAC.

4. A device for Electro-Magnetic Interference (EMI) reduction in an Ethernet system comprising:

an Ethernet compatible device coupled to a cable of length L, wherein the cable length L is greater than 0 meters but less than 100 meters in length; and

a filter coupled to the Ethernet compatible device for adjusting the amplitude and phase of an output signal of the Ethernet compatible device for EMI reduction in the Ethernet system, wherein the filter is a programmable filter selected to have an amplitude and frequency response having characteristics of a Cat 5 cable of length 100-L meters for said EMI reduction.

5. A device for Electro-Magnetic Interference (EMI) reduction in accordance with claim 4 wherein the programmable filter comprises:

a shift registry for storing data of the Ethernet compatible device;

a plurality of multipliers coupled to the shift registry and to a storage registry for combining data from the shift registry and the storage registry; and

an adder which combines the output data of the plurality of multipliers.

6. A device for Electro-Magnetic Interference (EMI) reduction in accordance with claim 5 wherein the storage registry contains data of Cat 5 cable attenuation.

7. A device for Electro-Magnetic Interference (EMI) reduction in accordance with claim 4 wherein the Ethernet compatible device is a transmitter device.

8. A device for Electro-Magnetic Interference (EMI) reduction in accordance with claim 7 wherein the transmitter device comprises:

a device to transmit data coupled to the programmable filter;

a DAC coupled to an output of the device to transmit data to convert a digital signal into analog form; and

a driver coupled to an output of the DAC.

9. A data transmission system comprising:

a first Ethernet compatible device;

a second Ethernet compatible device;

a cable coupled to the first Ethernet device and the second Ethernet device, the cable having a length L, wherein the cable length L is greater than 0 meters but less than 100 meters in length; and

a filter coupled to the first Ethernet compatible device for adjusting amplitude and phase of a signal outputted by the first Ethernet compatible device for EMI reduction in the data transmission system, wherein the filter is a programmable filter selected to have an amplitude and frequency response having characteristics of a Cat 5 cable of length 100-L meters for said EMI reduction.

10. A device for Electro-Magnetic Interference (EMI) reduction in accordance with claim 9 wherein the programmable filter comprises:

a shift registry for storing data of the Ethernet compatible device;

a plurality of multipliers coupled to the shift registry and to a storage registry for combining data from the shift registry and the storage registry; and

an adder which combines the output data of the plurality of multipliers.

11. A device for Electro-Magnetic Interference (EMI) reduction in accordance with claim 10 wherein the storage registry contains data of Cat 5 cable attenuation.

12. A device for Electro-Magnetic Interference (EMI) reduction in accordance with claim 9 wherein the first Ethernet compatible device is a transmitter device comprising:

a device to transmit data coupled to the programmable filter;

a DAC coupled to an output of the device to transmit data to convert a digital signal into analog form; and

a driver coupled to an output of the DAC.