Digital transmitter with equalization

• US 20030235253A1
• Filed: 02/24/2003
• Published: 12/25/2003
• Est. Priority Date: 06/20/1997
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Dally, William J.
• Granted Patent: US 7,099,404 B2
• Time in Patent Office: Days
• US Class Current: 375/259
• CPC Class Codes: H04B 1/0483 Transmitters with multiple parallel paths
• CPC Class Codes: H04B 1/1081 Reduction of multipath noise by equalising H04B7/005
• CPC Class Codes: H04B 1/16 Circuits
• CPC Class Codes: H04B 3/04 Control of transmission; Equalising
• CPC Class Codes: H04L 1/0042 Encoding specially adapted to other signal generation operation, e.g. in order to reduce transmit distortions, jitter, or to improve signal shape H04L1/0067 takes precedence
• 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 25/03019 adaptive, i.e. capable of adjustment during data reception
• CPC Class Codes: H04L 25/03025 using a two-tap delay line
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 25/03878 Line equalisers; line build-out devices
• CPC Class Codes: H04L 25/03885 adaptive
• CPC Class Codes: H04L 27/01 Equalisers baseband equalizers at the transmitter end H04L25/03343; in analogue transmission systems H04B3/04, H04B7/005

Abstract

An equalizer provided in a digital transmitter compensates for attenuation in a signal channel to a digital receiver. The equalizer generates signal levels as a logical function of bit history to emphasize transition signal levels relative to repeated signal levels. The preferred equalizer includes an FIR transition filter using a look-up table. Parallel circuits including FIR filters and digital-to-analog converters provide a high speed equalizer with lower speed circuitry. The equalizer is particularly suited to in-cabinet and local area network transmissions where feedback circuitry facilitates adaptive training of the equalizer.

Claims

1. A communication system comprising:

a digital transmitter which outputs a number of signal levels at a data rate;

a signal channel which receives signals from the transmitter;

a digital receiver which detects signals from the signal channel; and

an equalizer which generates signal levels at the data rate as a logical function of bit history to emphasize transition signal levels relative to repeated signal levels.

2. A communication system as claimed in claim 1 wherein the equalizer is in the transmitter.

3. A communication system as claimed in claim 1 wherein the equalizer converts an input signal having discrete signal levels at an input data rate to an output signal having a greater number of discrete signal levels at the input data rate.

4. A communication system as claimed in claim 1 wherein the signals are baseband signals with a bandwidth of at least 100 MHz.

5. A communication system as claimed in claim 1 wherein the transmitter and receiver are within a common cabinet.

6. A communication system as claimed in claim 1 wherein the transmitter and receiver are on a common local area network.

7. A communication system as claimed in claim 1 wherein the equalizer is in the transmitter and is adapted to modify level of equalization as a function of signals detected at the receiver.

8. A digital transmitter comprising an equalizer which comprises:

a delay circuit which receives an input signal at a data rate; and

circuitry which receives a signal from the delay circuit to generate signal levels at the data rate which emphasize transition signal levels relative to repeated signal levels.

9. A digital transmitter as claimed in claim 8 wherein the equalizer converts an input signal having discrete signal levels at an input data rate to an output signal having a greater number of discrete signal levels at the input data rate.

10. A digital transmitter as claimed in claim 8 wherein the signals are baseband signals with a bandwidth of at least 100 MHz.

11. A digital transmitter as claimed in claim 8 wherein the equalizer is adapted to modify level of equalization as a function of signals detected at a receiver.

12. A communication method comprising:

transmitting a digital signal with signal levels at a data rate on a communication channel; and

equalizing the digital signal as a logical function of bit history to emphasize transition signal levels relative to repeated signal levels.

13. A method as claimed in claim 12 wherein an input digital signal has discrete signal levels at an input data rate and the equalized signal has a greater number of discrete signal levels at the input data rate.

14. A method as claimed in claim 12 wherein the signals are baseband signals with a bandwidth of at least 100 MHz.

15. A method as claimed in claim 12 wherein the digital signal is transmitted to a receiver within a common cabinet.

16. A method as claimed in claim 12 wherein the digital signal is transmitted to a receiver on a local area network.

17. A method as claimed in claim 12 wherein equalization of the digital signal is performed in a transmitter and is adapted as a function of signals detected at a receiver.

18. A method of communications comprising generating a digital signal and equalizing the digital signal in a transmitter by emphasizing transition signal levels relative to repeated signal levels at a data rate.

19. A method as claimed in claim 18 wherein the digital signal has discrete signal levels at an input data rate and the equalized digital signal has a greater number of discrete signal levels at the input data rate.

20. A method as claimed in claim 18 wherein the digital signal is a baseband signal with a bandwidth of at least 100 MHz.

21. A method as claimed in claim 18 wherein the digital signal is transmitted to a receiver within a common cabinet.

22. A method as claimed in claim 18 wherein the digital signal is transmitted to a receiver on a local area network.

23. A method as claimed in claim 18 wherein equalization of the output signal is adapted as a function of signals detected at a receiver.

24. A method as claimed in claim 18 wherein the digital signal is equalized as a logical function of a current bit and an immediately previous bit.

25. A digital transmitter comprising an equalizer which comprises:

a delay circuit which receives an input signal at a data rate; and

circuitry which receives a signal from the delay circuit to generate transmitted signal levels based on time since last signal transition.

26. A digital transmitter which receives an input signal at a data rate and comprising an equalizer which generates output signal levels, the equalizer comprising;

parallel logic circuits operating on different multiple bit inputs to provide parallel equalized signals; and

a multiplexer multiplexing outputs of the parallel logic circuits to generate a transmitted signal at the data rate.

27. A digital transmitter comprising an equalizer which comprises:

a delay circuit which receives an input signal at a data rate; and

circuitry which receives a signal from the delay circuit to generate output signal levels based on a current bit and an immediately previous bit.