Power over data lines system using split or coupled CMCs and DMCs for coupling DC voltage and attenuating common mode noise
A PoDL system conducts differential data and DC power over the same wire pair, and various DC coupling techniques are described that improve DC voltage coupling while attenuating AC common mode noise. Pairs of differential mode chokes (DMCs) are used to share current supplied by a power supply. In one embodiment, one DMC is coupled to the line side of a common mode choke (CMC), and one DMC is coupled to the PHY side of the CMC. The line-side DMC has windings that are loosely magnetically coupled so that DMC does not present a very low impedance to AC common mode noise on the wires. Therefore, the performance of the wires' RC termination circuitry is not adversely affected by the line-side DMC when minimizing reflections of common mode signals. The DMCs may use the same magnetic core, and the CMC may be series CMCs that used the same magnetic core.
1. A Power over Data Lines (PoDL) circuit for connection to a first wire and a second wire of a wire pair comprising:
a transceiver having a first terminal and a second terminal, the transceiver for transmitting differential data over the first wire and the second wire and receiving differential data from the first wire and the second wire;
a first AC-coupling device coupled to the first terminal;
a second AC-coupling device coupled to the second terminal;
a first common mode choke (CMC) having a first winding coupled to the first AC-coupling device and having a second winding coupled to the second AC-coupling device;
a second CMC having a first winding coupled in series between the first winding of the first CMC and a third terminal of the PoDL circuit for coupling to the first wire, the second CMC having a second winding coupled in series between the second winding of the first CMC and a fourth terminal of the PoDL circuit for coupling to the second wire,
wherein the first CMC and the second CMC share a common magnetic core;
termination circuitry coupled to the third terminal and the fourth terminal for terminating the first wire and the second wire to reduce reflections;
a first differential mode choke (DMC) having a first pair of terminals coupled to nodes between the first CMC and the second CMC, and having a second pair of terminals configured to be coupled to a power supply; and
a pair of inductors having a third pair of terminals coupled to nodes between the second CMC and the third terminal and the fourth terminal, and having a fourth pair of terminals configured to be coupled to the power supply.
2. The circuit of claim 1 further comprising the power supply coupled to nodes between the first DMC and the pair of inductors for supplying a DC voltage across the first DMC and across the pair of inductors, such that DC power and the differential data are transmitted over the first wire and the second wire.
3. The circuit of claim 2 wherein the power supply is a multiphase power supply that supplies power to the first DMC and the pair of inductors.
4. The circuit of claim 2 wherein the power supply is a single-phase power supply that simultaneously supplies power to the first DMC and the pair of inductors.
5. The circuit of claim 2 further comprising a powered device coupled to the wire pair for being powered by the power supply.
6. The circuit of claim 1 wherein the pair of inductors comprises a second DMC.
7. The circuit of claim 6 wherein the first DMC has windings with a magnetic coupling coefficient greater than 0.85, and wherein the second DMC has windings with a magnetic coupling coefficient less than 0.75.
8. The circuit of claim 6 wherein the first DMC and the second DMC share the same magnetic core.
9. The circuit of claim 1 wherein the first DMC has a magnetic coupling coefficient greater than 0.95.
10. The circuit of claim 1 wherein the first AC-coupling device comprises a first capacitor, and wherein the second AC-coupling device comprises a second capacitor.
11. The circuit of claim 1 wherein the pair of inductors comprises a matched pair of inductors.
12. The circuit of claim 1 wherein the termination circuitry comprises a resistor-capacitor circuit coupled to the third terminal and the fourth terminal.
13. The circuit of claim 12 wherein the resistor-capacitor circuit comprises:
a first resistor and a first capacitor connected between the third terminal and ground; and
a second resistor and a second capacitor connected between the fourth terminal and ground.
14. The circuit of claim 1 wherein the third terminal and the fourth terminal are connected to the wire pair.
15. The circuit of claim 1 wherein the first CMC and the second CMC have split windings.
16. The circuit of claim 1 wherein the first CMC and the second CMC are cascaded.
17. A Power over Data Lines (PoDL) circuit for connection to a first wire and a second wire of a wire pair comprising:
a transceiver having a first terminal and a second terminal, the transceiver for transmitting differential data over the first wire and the second wire and receiving differential data from the first wire and the second wire;
a first AC-coupling device coupled to the first terminal;
a second AC-coupling device coupled to the second terminal;
a first common mode choke (CMC) having a first winding coupled in series between the first AC-coupling device and a third terminal of the PoDL circuit for connection to the first wire, and a second winding coupled in series between the second AC-coupling device and a fourth terminal of the PoDL circuit for connection to the second wire;
termination circuitry coupled to the third terminal and the fourth terminal for terminating the first wire and the second wire to reduce reflections;
a first differential mode choke (DMC) having a first pair of terminals coupled to nodes between the first CMC and the transceiver, and having a second pair of terminals configured to be coupled to a power supply; and
a second DMC having a third pair of terminals coupled to nodes between the first CMC and the third terminal and the fourth terminal, and having a fourth pair of terminals configured to be coupled to the power supply,
wherein the first DMC and the second DMC share a same magnetic core.
18. The circuit of claim 17 further comprising the power supply coupled to nodes between the first DMC and the second DMC for supplying a DC voltage across the first DMC and across the second DMC, such that DC power and the differential data are transmitted over the first wire and the second wire.
19. The circuit of claim 18 wherein the power supply is a multiphase power supply that supplies power to the first DMC and the second DMC.
20. The circuit of claim 18 wherein the power supply is a single phase power supply that simultaneously supplies power to the first DMC and the second DMC.
21. The circuit of claim 17 further comprising a second CMC having a first winding coupled in series between the first winding of the first CMC and the first AC-coupling device, the second CMC having a second winding coupled in series between the second winding of the first CMC and the second AC-coupling device, wherein the first DMC is coupled to nodes between the first CMC and the second CMC.
22. The circuit of claim 17 wherein the first DMC has windings with a magnetic coupling coefficient greater than 0.85, and wherein the second DMC has windings with a magnetic coupling coefficient less than 0.75.
23. A method performed by a Power over Data Lines (PoDL) circuit connected to a first wire and a second wire of a wire pair comprising:
transmitting differential data over the first wire and the second wire and receiving the differential data from the first wire and the second wire by a transceiver having a first terminal and a second terminal;
blocking DC voltages from being applied to the first terminal and the second terminal;
conducting the differential data through a first common mode choke (CMC) having a first winding coupled to a first AC-coupling device and having a second winding coupled to a second AC-coupling device;
conducting the differential data through a second CMC having a first winding coupled in series between the first winding of the first CMC and a third terminal of the PoDL circuit for coupling to the first wire, the second CMC having a second winding coupled in series between the second winding of the first CMC and a fourth terminal of the PoDL circuit for coupling to the second wire,
wherein the first CMC and the second CMC share a common magnetic core;
terminating the first wire and the second wire with termination circuitry to reduce reflections; and
supplying DC power to the wire pair by a power supply coupled to a first differential mode choke (DMC) and a second DMC, such that DC power and the differential data are transmitted over the first wire and the second wire,
wherein the first DMC has a first pair of terminals coupled to nodes between the first CMC and the second CMC, and has a second pair of terminals coupled to the power supply, and
wherein the second DMC has a third pair of terminals coupled to nodes between the second CMC and the wire pair, and has a fourth pair of terminals coupled to the power supply.
24. The method of claim 23 wherein the first DMC has windings with a magnetic coupling coefficient greater than 0.85, and wherein the second DMC has windings with a magnetic coupling coefficient less than 0.75.