DIFFERENTIAL DRIVER WITH COMMON-MODE VOLTAGE TRACKING AND METHOD

• US 20080037617A1
• Filed: 08/13/2007
• Published: 02/14/2008
• Est. Priority Date: 08/14/2006
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Tang, Bill, Ta, Paul
• Granted Patent: US 8,027,377 B2
• Time in Patent Office: Days
• US Class Current: 375/220
• CPC Class Codes: H03F 2203/45101 Control of the DC level being present
• CPC Class Codes: H03F 2203/45138 Two or more differential amplifiers in IC-block form are combined, e.g. measuring amplifiers
• CPC Class Codes: H03F 2203/45418 the CMCL comprising a resistor addition circuit
• CPC Class Codes: H03F 2203/45466 the CSC being controlled, e.g. by a signal derived from a non specified place in the dif amp circuit
• CPC Class Codes: H03F 2203/45681 the LC comprising offset compensating means
• CPC Class Codes: H03F 3/45183 Long tailed pairs H03F3/4521, H03F3/45237 take precedence
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/45632 in differential amplifiers with FET transistors as the active amplifying circuit H03F3/4578 takes precedence
• CPC Class Codes: H04L 25/0276 Arrangements for coupling common mode signals

Abstract

In a transceiver, a transmitter circuit is provided substantially the same common-mode voltage regardless of whether the transceiver is in a transmitting or receiving mode. In one embodiment, the transmitter circuit includes a driver circuit which, in the transmission mode of the transceiver, drives an output differential signal, and which, in the receiving mode of the transceiver, provides a termination circuit for an input differential signal. A variable resistor is provided to connect between a supply voltage and the driver circuit, the resistance of the variable resistor is selected such that the common-mode voltage of the output differential signal of the transmission mode substantially equals the common-mode voltage in the input differential signal of the receiving mode.

Claims

1. A transceiver circuit having a transmission mode and a receiving mode, comprising:

a receiver circuit for receiving an input differential signal during the receiving mode;

a transmitter driver circuit wherein, in the transmission mode, the transmitter driver circuit drives an output differential signal, and wherein, in the receiving mode, the transmitter driver circuit provides a termination circuit for the input differential signal; and

a variable resistive circuit connecting between a supply voltage and the transmitter driver circuit wherein, in the transmission mode, the variable resistive provides a first resistance and wherein, in the receiving mode, the variable resistor provides a second resistance, such that a common-mode voltage of the output differential signal substantially equals a common-mode voltage in the input differential signal at the termination circuit.

2. A transceiver as in claim 1, wherein the variable resistive circuit comprises a resistor network in which one or more switches are provided to connect resistors in the resistive network.

3. A transceiver as in claim 2, wherein the variable resistive circuit includes a first resistive current path and a second resistive current path, wherein the switches disconnects the second resistive current path during the receiving mode.

4. A transceiver as in claim 1, wherein the transmitter driver circuit is rendered non-conducting during the receiving mode, and wherein the variable resistive circuit further comprises one or more switches which operate in the receiving mode to conduct a current approximating a current drawn by the transmitter driver circuit in the transmission mode.

5. A transceiver as in claim 1, wherein the transmitter driver circuit provides in the transmitter a current comprising a tail current.

6. A transceiver as in claim 1, further comprises a transmitter driver a pre-emphasis current.

7. A transceiver as in claim 1, wherein the transmitter driver circuit further provides for tracking, in the receiving mode, a current that is provided in the transmission mode.

8. A transceiver as in claim 7, wherein the current that is provided in the transmission tracks a tail current.

9. A transceiver as in claim 7, wherein the current that is provided in the transmission tracks a pre-amphasis current.

10. A transceiver as in claim 1, wherein the variable resistive circuit comprises a resistor having a resistance substantially equal to one-half the resistance of the termination circuit.

11. A method for maintaining a common-mode voltage in a transceiver circuit which provides an output differential signal during a transmission mode and receives an input differential signal during a receiving mode, comprising:

providing a transmitter driver circuit which, in the transmission mode, drives the output differential signal, and wherein, in the receiving mode, provides a termination circuit for the input differential signal; and

providing a first resistance between a supply voltage and the transmitter driver circuit during the transmission mode and providing a second resistance in the receiving mode, such that a common-mode voltage of the output differential signal substantially equals a common-mode voltage in the input differential signal at the termination circuit.

12. A method as in claim 11, wherein the first resistance and the second resistance are provided by a variable resistive circuit which comprises a resistor network in which one or more switches are provided to connect resistors in the resistive network.

13. A method as in claim 12, wherein the variable resistive circuit includes a first resistive current path and a second resistive current path, further comprising using the switches to disconnect the second resistive current path during the receiving mode.

14. A method as in claim 13, wherein the transmitter driver circuit is rendered non-conducting during the receiving mode, further comprising providing one or more switches which operate in the receiving mode to conduct a current approximating a current drawn by the transmitter driver circuit in the transmission mode.

15. A method as in claim 11, further comprising providing in the transmitter a tail current.

16. A method as in claim 11, further comprising providing in a transmitter a pre-emphasis current.

17. A method as in claim 11, further comprising providing, in the receiving mode, a current that is provided in the transmission mode.

18. A method as in claim 17, wherein the current that is provided in the transmission tracks a tail current.

19. A method as in claim 17, wherein the current that is provided in the transmission tracks a pre-amphasis current.

20. A method as in claim 17, wherein providing the first resistance comprises providing a resistor having a resistance substantially equal to one-half the resistance of the termination circuit.

21. A transceiver that maintains a common-mode voltage between a transmission mode and a receiving mode, comprising:

means for driving an output differential signal in the transmission mode and for providing a termination circuit for the input differential signal in the receiving mode; and

means for providing a first resistance between a supply voltage and the transmitter driver circuit during the transmission mode and providing a second resistance in the receiving mode, such that a common-mode voltage of the output differential signal substantially equals a common-mode voltage in the input differential signal at the termination circuit.

22. A transceiver as in claim 21, wherein the means for proving a first resistance comprises a resistor network in which one or more switches are provided to connect resistors in the resistive network.

23. A transceiver as in claim 22, wherein the resistor network includes a first resistive current path and a second resistive current path, further comprising using the switches to disconnect the second resistive current path during the receiving mode.

24. A transceiver as in claim 21, further comprising means for providing a tail current.

25. A transceiver as in claim 21, further comprising means for providing a pre-emphasis current.

26. A transceiver as in claim 21, further comprising means for tracking in the receiving mode a current that is provided in the transmission mode.

27. A transceiver as in claim 21, wherein the means for providing a first resistance comprises a resistor having a resistance substantially equal to one-half the resistance of the termination circuit.