Method and apparatus for reducing transmitter AC-coupling droop

• US 20100073038A1
• Filed: 08/12/2009
• Published: 03/25/2010
• Est. Priority Date: 08/12/2008
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Pagnanelli, Chris
• Granted Patent: US 8,049,537 B2
• Time in Patent Office: Days
• 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 comprising:

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

a driver configured to amplify the signal;

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

one or more impedance mismatching devices configured to offset low frequency impedance mismatches of the driver and the line isolation device, with respect to the channel characteristic impedance.

2. The system of claim 1, wherein the one or more impedance mismatching devices consist of one or more of the following:

capacitor and inductor.

3. The system of claim 1, wherein the driver is selected from the group consisting of a voltage driver and a current driver and 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 a device selected from the group consisting of a transformer and a capacitor.

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

6. The system of claim 1, wherein the driver further comprises a resistor or resistance, which is selected to match the driver and resistor combination to the impedance of the channel.

7. A driver and line isolation system having droop compensation comprising:

a driver having an output impedance configured to amplify a signal to a level suitable for transmission over a channel;

a matching resistor configured to impedance match the matching resistor and the driver output impedance in relation to the channel;

a droop compensator configured create a mismatch between the matching resistor, the driver output impedance, and the droop compensator in relation to the channel; and

a line coupler configured to isolate high voltage transients on the channel from the driver.

8. The system of claim 7, wherein the driver comprises a voltage amplifier or a current amplifier.

9. The system of claim 8, wherein the driver is configured in differential mode as a voltage amplifier and a matching resistor is in series with the driver output and the droop compensator.

10. The system of claim 9, wherein the droop compensator comprises a capacitor and the line coupler comprises a transformer.

11. The system of claim 9, wherein the line coupler comprises a transformer and the droop compensator is configured to increase impedance looking into the transmitter from the channel in response to lower transition densities.

12. The system of claim 7, wherein the driver has two outputs and each output has a series connected resistor and capacitor, such that the two capacitors causes an impedance mismatch in relation to the channel.

13. A method for reducing voltage droop in response to low transition density comprising:

presenting an amplified signal from a driver to a matching resistor for impedance matching, the matching resistor configured to impedance match the driver and matching resistor to a channel;

droop compensating the amplified signal before or after the impedance matching, wherein droop compensating mismatches the impedance as compared to the channel;

presenting the amplified signal, after impedance matching and droop compensation, to a line coupler; and

presenting the output of the line coupler to the channel.

14. The method of claim 13, wherein the line coupler isolates the driver from high energy transients on the line.

15. The method of claim 13, wherein droop compensating comprises creating an impedance mismatch in relation to the channel.

16. The method of claim 15, wherein the impedance mismatch offsets mid-frequency impedance mismatches of the amplifier and the line coupler, with respect to the channel characteristic impedance.

17. The method of claim 16, wherein mid-frequency comprises frequencies greater than 1 megahertz.

18. The method of claim 13, wherein the line coupler comprises a transformer.

19. The method of claim 13, wherein when the amplified signal exhibits high transition density the droop compensation does not alter the amplified signal and when the amplified signal exhibits a reduction in transition density, the droop compensation matches the combined impedance of the driver, matching resistor and droop compensator to the combined impedance of the line coupler and the channel.