Method and apparatus for reducing transmitter AC-coupling droop

• US 8,049,537 B2
• Filed: 08/12/2009
• Issued: 11/01/2011
• Est. Priority Date: 08/12/2008
• Status: Expired due to Fees

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Pagnanelli, Chris
• Primary Examiner(s): LUU, AN T
• Application Number:
  US12/583,086
• Publication Number:
  US 20100073038A1
• Time in Patent Office: 811 Days
• Field of Search: None
• US Class Current: 327/108
• CPC Class Codes: H04L 25/0278 Arrangements for impedance matching
• CPC Class Codes: H04L 25/0284 Arrangements to ensure DC-balance
• CPC Class Codes: H04L 25/0298 Arrangement for terminating transmission lines

Abstract

As part of a transmitter and receiver system a droop compensator is provided between the channel isolation device and the driver system to compensate for reduced transition densities. The droop compensator is configured to improve power transfer to the channel in response to reductions in transition density without affecting power transfer during periods of high transition density. The droop compensator creates an impedance mismatch between the matching circuit and driver in relation to the line impedance. The droop compensator may comprise passive elements, such as capacitors, inductors, or resistor, or active elements including transistors or power control modules. The droop compensator may be configured to operate with transformer line couplers or capacitor line couplers, and either current drivers or voltage drivers.

Claims

1. A system for reducing voltage droop in a communication system, the system comprising:

a signal source configured to generate a signal, the signal to be transmitted over a communication channel having a characteristic impedance;

a voltage driver configured to i) amplify the signal and ii) output the signal on a first signal line and a second signal line;

a line isolation device configure to isolate the voltage driver from the channel;

a matching resistance configured to match the characteristic impedance, the matching resistance including

a first resistor connected in series with the first signal line between i) the voltage driver and ii) the line isolation device, and

a second resistor connected in parallel to the first resistor and in series with the second signal line between i) the voltage driver and ii) the line isolation device; and

a voltage droop compensator configured to offset low frequency impedance mismatches of the voltage driver and the line isolation device with respect to the characteristic impedance, wherein the voltage droop compensator includes at least one of

i) a first capacitor connected in series between the first resistor and the line isolation device and, and a second capacitor connected in series between the second resistor and the line isolation device, and

ii) a first inductor connected in parallel with the first resistor and a second inductor connected in parallel with the second resistor.

2. The system of claim 1, wherein the line isolation device comprises a transformer and the voltage droop compensator is configured to increase impedance looking into the signal source from the communication channel in response to lower transition densities.

3. The system of claim 1, wherein the signal source comprises a digital to analog converter associated with a transmitter.

4. The system of claim 1, wherein the line isolation device comprises i) a transformer when the voltage droop compensator includes the first capacitor and the second capacitor, and ii) a capacitive line coupling when the voltage droop compensator includes the first inductor and the second inductor.

5. The system of claim 1, wherein the offset comprises an offset as to the characteristic impedance.

6. A system for reducing voltage droop in a communication system, the system comprising:

a signal source configured to generate a signal, the signal to be transmitted over a communication channel having a characteristic impedance;

a current driver configured to i) amplify the signal and ii) output the signal on a first signal line and a second signal line;

a line isolation device configure to isolate the current driver from the channel;

a matching resistance configured to match the characteristic impedance, the matching resistance including a first resistor connected i) between the first signal line and the second signal line, and ii) between the current driver and the line isolation device; and

a voltage droop compensator configured to offset low frequency impedance mismatches of the current driver and the line isolation device with respect to the characteristic impedance, wherein the voltage droop compensator includes an inductor connected i) in parallel to the first resistor, ii) between the first signal line and the second signal line, and iii) between the first resistor and the line isolation device.

7. The system of claim 6, wherein the signal source comprises a digital to analog converter associated with a transmitter.

8. The system of claim 6, wherein the line isolation device comprises a capacitive line coupling.

9. The system of claim 6, wherein the offset comprises an offset as to the characteristic impedance.

10. A system for reducing voltage droop in a communication system, the system comprising:

a signal source configured to generate a signal, the signal to be transmitted over a communication channel having a characteristic impedance;

a current driver configured to i) amplify the signal and ii) output the signal on a first signal line and a second signal line;

a line isolation device configure to isolate the current driver from the channel;

a matching resistance configured to match the characteristic impedance, the matching resistance including

a first resistor connected i) between the first signal line and the second signal line, and ii) between the current driver and the line isolation device, and

a second resistor connected in series with the first resistor between the first signal line and the second signal line; and

a voltage droop compensator configured to offset low frequency impedance mismatches of the current driver and the line isolation device with respect to the characteristic impedance, wherein the voltage droop compensator includes i) a first capacitor connected in series with the first resistor and the second resistor and ii) a second capacitor connected in series with the first capacitor, the first resistor, and the second resistor.

11. The system of claim 10, wherein the signal source comprises a digital to analog converter associated with a transmitter.

12. The system of claim 10, wherein the line isolation device comprises a transformer.

13. The system of claim 10, wherein the offset comprises an offset as to the characteristic impedance.

14. The system of claim 10, wherein the line isolation device comprises a transformer and the voltage droop compensator is configured to increase impedance looking into the signal source from the communication channel in response to lower transition densities.