Coaxial data communication with reduced EMI
Data communication having improved electromagnetic interference (EMI) rejection when communicating through a coaxial cable is provided by using differential transmission and/or reception through a common-mode choke and a dissipative element resulting in extremely low radiated emissions and high immunity to external radiation interference in a low-cost way.
1. A transmission circuit using two coaxial cables each having a center conductor and a shield, comprising:
an integrated circuit comprising a differential driver having first and second outputs, and a differential receiver having first and second inputs;
a first common mode choke coupled between the first output of the differential driver and a center conductor of the coaxial cable, and between the second output of the differential driver and the shield of one of the coaxial cables, wherein the shield is directly connected with a first ground node;
a first terminating impedance coupled between the second output of the first differential driver and a second ground node;
a second common mode choke coupled between the first input of the differential receiver and the center conductor of the other coaxial cable, and between the second input of the differential receiver and the shield of the other coaxial cable;
second terminating impedances coupled between the first and second inputs of the differential receiver and the second ground node; and
a dissipative element coupled between the shield of the other coaxial cable and the first ground node.
2. The transmission circuit according to claim 1 , wherein the first terminating impedance comprises a first resistor and a first capacitance coupled in series, wherein a node between the first and second resistor is coupled with the first common mode choke.
3. The transmission circuit according to claim 2 , further comprising a second resistor coupled in parallel with the first capacitance.
4. The transmission circuit according to claim 2 , further comprising first and second DC-blocking capacitors coupled between the first and second outputs of the differential driver and the first common mode choke, and
third and fourth DC-blocking capacitors coupled between the first and second inputs of the differential receiver and the second common mode choke.
5. The transmission circuit according to claim 4 , further comprising a second capacitance coupled between the second ground and a node between the fourth DC-blocking capacitor and the second common mode choke.
6. The transmission circuit according to claim 5 , further comprising a third resistor coupled in parallel with the second capacitance.
7. The transmission circuit according to claim 1 , wherein the second ground node is connected to a digital ground plane.
8. The transmission circuit according to claim 1 , wherein the first ground node is connected to a chassis ground.
9. The transmission circuit according to claim 1 , wherein the first and the second ground nodes are coupled together.
10. A transmission circuit using two coaxial cables each having a center conductor and a shield, comprising:
an integrated circuit comprising a differential driver having first and second outputs, and a differential receiver having first and second inputs;
a first common mode choke coupled between the first output of the differential driver and a center conductor of the coaxial cable, and between the second output of the differential driver and the shield of one of the coaxial cables;
a first terminating impedance coupled between the second output of the first differential driver and a first ground node;
a dissipative element coupled between the shield of the coaxial cable and a second ground node;
a second common mode choke coupled between the first input of the differential receiver and the center conductor of the other coaxial cable, and between the second input of the differential receiver and the shield of the other coaxial cable, wherein the shield of the other coaxial cable is directly connected with the second ground node;
second terminating impedances coupled between the first and second inputs of the differential receiver and the first ground node.
11. A system for transferring information over a coaxial cable having a center conductor and a shield, said system comprising:
a data transmission device comprising:
a first integrated circuit comprising a differential driver having first and second outputs,
a first common mode choke coupled between the first output of the differential driver and the center conductor, and between a first ground node and the shield of one end of the coaxial cable, respectively;
a first terminating impedance coupled between the second output of the differential driver and the first ground node;
wherein the shield of the one end of the coaxial cable is directly connected with a second ground node; and
a data reception device comprising:
a second integrated circuit comprising a differential receiver having first and second inputs,
a second common mode choke coupled between the first and second inputs of the differential receiver and the center conductor and the shield of another end of the coaxial cable, respectively;
second terminating impedances coupled between each differential input of the differential receiver and a third ground node, and
a second dissipative element coupled between the shield of the another end of the coaxial cable and a fourth ground node.
12. The system according to claim 11 , further comprising a radio frequency bypass capacitor coupled between the third ground node and the differential input of the differential receiver not coupled to the center conductor of the coaxial cable through the second common mode choke.
13. The system according to claim 11 , further comprising:
a first printed circuit board having a first ground plane thereon, wherein the first integrated circuit is mounted on the first printed circuit board; and
a second printed circuit board having a second ground plane thereon, wherein the second integrated circuit is mounted on the second printed circuit board.
14. The system according to claim 13 , further comprising:
first and second transmission lines on the first printed circuit board and coupled between the first and second outputs, respectively, of the differential driver and the first common mode choke; and
third and fourth transmission lines on the second printed circuit board and coupled between the first and second inputs, respectively, of the differential receiver and the second common mode choke.
15. The system according to claim 11 , wherein the dissipative element comprises a dissipative resistor.
16. The system according to claim 14 , further comprising a DC-blocking capacitors coupled in series with the dissipative resistor and the fourth ground node.
17. The system according to claim 11 , further comprising:
third and fourth DC-blocking capacitors coupled between the first and second outputs of the differential driver and the first common mode choke; and
fifth and sixth DC-blocking capacitors coupled between the first and second inputs of the differential receiver and the second common mode choke.
18. A system for transferring information over a coaxial cable having a center conductor and a shield, said system comprising:
a data transmission device comprising:
a first integrated circuit comprising a differential driver having first and second outputs,
a first common mode choke coupled between the first output of the differential driver and the center conductor, and between a first ground node and the shield of one end of the coaxial cable, respectively;
a first terminating impedance coupled between the second output of the differential driver and the first ground node;
a dissipative element coupled between the shield of the one end of the coaxial cable and a second ground node; and
a data reception device comprising:
a second integrated circuit comprising a differential receiver having first and second inputs,
a second common mode choke coupled between the first and second inputs of the differential receiver and the center conductor and the shield of another end of the coaxial cable, respectively;
second terminating impedances coupled between each differential input of the differential receiver and a third ground node, and
wherein the shield of the another end of the coaxial cable is directly coupled with a fourth ground node.
19. The system according to claim 18 , further comprising a radio frequency bypass capacitor coupled between the third ground node and the differential input of the differential receiver not coupled to the center conductor of the coaxial cable through the second common mode choke.
20. The system according to claim 18 , further comprising:
a first printed circuit board having a first ground plane thereon, wherein the first integrated circuit is mounted on the first printed circuit board; and
a second printed circuit board having a second ground plane thereon, wherein the second integrated circuit is mounted on the second printed circuit board.
21. The system according to claim 20 , further comprising:
first and second transmission lines on the first printed circuit board and coupled between the first and second outputs, respectively, of the differential driver and the first common mode choke; and
third and fourth transmission lines on the second printed circuit board and coupled between the first and second inputs, respectively, of the differential receiver and the second common mode choke.
22. The system according to claim 18 , wherein the dissipative element comprises a dissipative resistor.
23. The system according to claim 21 , further comprising a DC-blocking capacitor coupled in series with the dissipative resistor and the second ground node.
24. The system according to claim 18 , further comprising:
third and fourth DC-blocking capacitors coupled between the first and second outputs of the differential driver and the first common mode choke; and
fifth and sixth DC-blocking capacitors coupled between the first and second inputs of the differential receiver and the second common mode choke.