Echo cancellation circuit for a Bi-directional current mode link

• US 6,344,756 B1
• Filed: 11/14/2000
• Issued: 02/05/2002
• Est. Priority Date: 11/14/2000
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Preuss, Curtis Walter, Hanson, Charles C., Cecchi, Delbert Raymond
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): LE, DON P
• Application Number:
  US09/712,594
• Time in Patent Office: 448 Days
• Field of Search: 326/21, 326/26, 326/30, 326/82, 326/83, 326/86
• US Class Current: 326/26
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04L 25/0272 Arrangements for coupling to multiple lines, e.g. for differential transmission
• CPC Class Codes: H04L 25/0282 Provision for current-mode coupling
• CPC Class Codes: H04L 25/0294 Provision for current-mode coupling

Abstract

An echo cancellation circuit for neutralizing signal reflections in a differential link interface, and a method for achieving the same. The differential link interface includes a line driver that generates a line drive signal and a replica driver for generating a replica signal that mirrors the line drive signal within the differential link. The echo cancellation circuit includes a slope adjustment device within the replica driver for temporarily altering the slope of the replica line drive signal during a signal reflection at the output of the line driver, such that the amplitude of the replica signal corresponds to the amplitude of the line drive signal during the signal reflection.

Claims

1. A circuit for neutralizing signal reflections in a differential link interface, wherein said differential link interface includes a line driver that generates a line drive signal, said circuit comprising:

a replica driver for generating a replica signal that mirrors said line drive signal within said differential link; and

a slope adjustment device for temporarily altering the slope of said replica line drive signal during a signal reflection at the output of said line driver, such that the amplitude of said replica signal corresponds to the amplitude of said line drive signal during said signal reflection.

2. The circuit of claim 1, wherein said line driver includes n drive current sources that each generate 1/n of the total drive current, and wherein said slope adjustment device comprises m current sources, wherein at least one of said m current sources generates 1/z of the total replica current, wherein m>

n and z>

n.

3. The circuit of claim 1, wherein said line driver includes n drive current sources that each generate 1/n of the total drive current, and wherein said slope adjustment device comprises m current sources, wherein at least one of said m current sources generates 1/z of the total replica current, wherein m<

n and z<

n.

4. The circuit of claim 1, wherein said line driver is a current driver having a plurality of parallel drive current sources that generate said line drive current in response to receiving a line drive control signal.

5. The circuit of claim 4, wherein said replica driver is a current driver having a plurality of current sources that generate said replica signal in response to said line drive control signal.

6. The circuit of claim 4, wherein said line drive control signal is a logic input signal for initiating communication from a data processing device within said differential link interface.

7. The circuit of claim 5, further comprising:

an n^th drive current source having an output drive current amplitude of x; and

an n^th replica current source having an output replica current amplitude of y, wherein y≢

x.

8. The circuit of claim 5, wherein each of said plurality of drive current sources includes a drive control input for receiving said line drive control signal, and wherein said slope adjustment circuit further comprises at least one delay element between each of said control inputs such that said control inputs are temporally cascaded with respect to said line drive control signal and said plurality of drive current sources are sequentially activated in accordance with the delay of said line drive control signal across said delay elements.

9. The circuit of claim 8, wherein each of said plurality of current sources within said replica driver includes a drive control input for receiving said line drive control signal, and wherein said slope adjustment device further comprises at least one delay element between each of said control inputs such that said control inputs for said replica driver are temporally cascaded with respect to said line drive control signal and said plurality of current sources within said replica current driver are sequentially activated in accordance with the delay of said line drive control signal across said delay elements.

10. The circuit of claim 9, wherein the delay induced by said delay elements of said slope adjustment device is a function of both the delay induced by said line drive delay elements and an anticipated arrival time of a signal reflection such that the slope of said replica signal corresponds to the slope of said drive current during said signal reflection.

11. A method for neutralizing signal reflections in a differential link interface, wherein said differential link interface includes a line driver that generates a line drive signal, said method comprising:

generating a replica signal that mirrors said line drive signal within said differential link; and

temporarily altering the slope of said replica line drive signal during a signal reflection at the output of said line driver, such that the amplitude of said replica signal corresponds to the amplitude of said line drive signal during said signal reflection.

12. The method of claim 11, wherein said differential link includes a receiver that receives data at a common medium shared by said line drive signal, said method further comprising subtracting said replica signal from said line drive signal at the input of said receiver such that said receiver extracts an incoming signal superimposed on said line drive signal.

13. The method of claim 11, further comprising generating said line drive current in response to receiving a line drive control signal.

14. The method of claim 13, wherein said line driver comprises a plurality of current sources, and wherein said replica signal is generated within a replica driver comprising a plurality of current sources, said method further comprising setting the amplitude of each of said current sources within said replica driver relative to the output amplitudes of said current sources within said line driver such that the output signal of said replica driver approximates said line drive signal during a signal reflection.

15. The method of claim 14, wherein each of said plurality of current sources within said line driver includes a drive control input for receiving said line drive control signal, said method further comprising delaying said line drive control signal between each of said control inputs such that said control inputs are temporally cascaded with respect to said line drive control signal and said plurality of drive current sources are sequentially activated in accordance with the delay of said line drive control signal across said delay elements.

16. The method of claim 15, wherein each of said plurality of current sources within said replica driver includes a drive control input for receiving said line drive control signal, said method further comprising delaying said line drive control signal between each of said control inputs such that said control inputs for said replica driver are temporally cascaded with respect to said line drive control signal and said plurality of current sources within said replica driver are sequentially activated in accordance with the delay of said line drive control signal across said delay elements.

17. The method of claim 16, wherein the delay induced by said delay elements of said slope adjustment device is a function of both the delay induced by said line drive delay elements and an anticipated arrival time of a signal reflection such that the slope of said replica signal corresponds to the slope of said drive current during said signal reflection.