# US 2018/0026525 A1 · Communications system using hybrid common mode choke and kelvin sensing of voltage

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 2018/0026525 A1
- Document ID: US20180026525A1
- Status: Published application
- Kind: A1
- Application number: 15/653,170
- Filed: 2017-07-18
- Published: 2018-01-25
- Earliest claimed: 2016-07-25
- Assignees: Linear Technology Corporation
- Applicants: Linear Technology Corporation
- Inventors: Andrew J. Gardner
- Web page: https://patentgrep.com/patent/US20180026525A1

## CPC

- H03H 7/427: {Common-mode filters (H02J3/01 and H02M1/126 takes precedence)}
- H02M 1/44: Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
- H03H 1/0007: {of radio frequency interference filters}
- H03H 7/0138: {Electrical filters or coupling circuits}
- H04L 12/10: Current supply arrangements
- H04L 12/40045: {Details regarding the feeding of energy to the node from the bus}
- H04L 25/0272: {Arrangements for coupling to multiple lines, e.g. for differential transmission}
- H04L 25/0298: {Arrangement for terminating transmission lines}
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

In a communications system that conducts differential data via a pair of wires, AC common mode noise is undesirably coupled to the wires in a noisy environment. A hybrid common mode choke (HCMC) attenuates the AC common mode noise while passing the differential data to a PHY. The HCMC includes a CMC (windings with the same polarity) and a differential mode choke (windings with opposite polarities). The CMC attenuates the AC common mode noise, and the DMC passes the attenuated AC common mode noise to termination circuitry to eliminate it. Also disclosed is a technique for Kelvin sensing the DC voltage at the pair of wires, in a PoDL system, by detecting the voltage on wires that do not carry DC current, so as to provide a more accurate measurement.

## Claims

### Claim 1

A system for filtering AC common mode signals from a pair of wires carrying differential data comprising:
a first port having two first terminals coupled to a transceiver that receives the differential data;
a second port having two second terminals coupled to the pair of wires;
a third port having two third terminals connected to AC termination circuitry;
a common mode choke (CMC) coupled between the second port and the first port, the CMC comprising a first transformer with two windings having the same polarity; and
a differential mode choke (DMC) coupled between the first port and the third port, the DMC comprising a second transformer with two windings having opposite polarities,
wherein the CMC attenuates AC common mode signals on the pair of wires and substantially passes the differential data, and
wherein the DMC substantially passes the AC common mode signals that pass through the CMC from the pair of wires and applies the AC common mode signals to the termination circuitry to further attenuate the AC common mode signals prior to being received by the transceiver.

### Claim 2 (depends on 1)

The system of claim 1 wherein the AC termination circuitry comprises a first capacitor coupled between one of the third terminals and a reference voltage, and a second capacitor coupled between another of the third terminals and the reference voltage.

### Claim 3 (depends on 1)

The system of claim 1 wherein the AC termination circuitry comprises a first capacitor coupled between the two third terminals and a reference voltage.

### Claim 4 (depends on 1)

The system of claim 1 wherein the AC termination circuitry comprises the two third terminals connected to a reference voltage.

### Claim 5 (depends on 1)

The system of claim 1 further comprising a DC voltage source coupled to the pair of wires via a DC-coupling circuit, wherein the DC voltage source also acts as the AC termination circuitry.

### Claim 6 (depends on 5)

The system of claim 5 where the DC-coupling circuit comprises one or more inductors.

### Claim 7 (depends on 5)

The system of claim 5 wherein the DC coupling circuit comprises the DMC, and the DC voltage is coupled to the third port.

### Claim 8 (depends on 1)

The system of claim 1 wherein the transceiver comprises a PHY coupled to the first port via AC-coupling circuitry.

### Claim 9 (depends on 8)

The system of claim 8 wherein the AC-coupling circuitry comprises capacitors in series with the two first terminals and the PHY.