Digital transmitter with equalization
AssigneeMassachusetts Institute of Technology
InventorWilliam J. Dally
Life of this patent
Estimating the term…
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.
Claims41
A communication system comprising:
- a digital transmitter;
- 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 as a logical function of bit history to emphasize transition signal levels relative to repeated signal levels, the equalizer generating the signal levels by applying different bits of a multiple bit input to parallel digital filter circuits and multiplexing outputs of the parallel digital filter circuits to provide a combined equalized output at a rate greater than the rate from each digital filter circuit.
A digital transmitter comprising an equalizer which emphasizes transition signal levels relative to repeated signal levels, the equalizer comprising:
- parallel digital filter circuits operating on different multiple bit portions of a multiple bit input;
- and
- a multiplexing circuit which multiplexes outputs of the parallel circuits to provide a combined equalized output at a rate greater than the rate from each digital filter circuit, the equalizer generating signal levels as a logical function of bit history.
A digital transmitter comprising an equalizer which emphasizes transition signal levels relative to repeated signal levels, the equalizer comprising:
- parallel digital filter circuits operating on different multiple bit portions of a multiple bit input;
- and
- a multiplexing circuit which multiplexes outputs of the parallel circuits to provide a combined equalized output at a rate greater than the rate from each digital filter circuit, the equalizer generating signal levels as a logical function of a current bit and an immediately previous bit.
A communication method comprising:
- transmitting a digital signal on a communication channel;
- and
- equalizing the digital signal as a logical function of bit history to emphasize transition signal levels relative to respected signal levels by multiplexing outputs of parallel digital filter circuits operating on different multiple bit portions of a multiple bit input to provide a combined equalized output at a rate greater than the rate from each digital filter circuit.
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 comprising:
- operating on different multiple bit inputs in parallel digital filter circuits;
- multiplexing outputs of the parallel filter circuits to provide a combined equalized output at a rate greater than the rate from each digital filter circuit, the digital signal being equalized as a logical function of bit history.
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 comprising:
- operating on different multiple bit inputs in parallel digital filter circuits;
- multiplexing outputs of the parallel filter circuits to provide a combined equalized output at a rate greater than the rate from each digital filter circuit, the digital signal being equalized as a logical function of a current bit and an immediately previous bit.
A communication system comprising:
- a digital transmitter which transmits baseband signals with a bandwidth of at least 100 MHz;
- a signal channel which receives signals from the transmitter;
- a digital receiver which detects signals from the signal channel;
- and
- an equalizer in the transmitter which generates signal levels as a logical function of bit history based on time since last signal transition to emphasize transition signal levels relative to repeated signal levels, the equalizer converting 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, the equalizer generating the signal levels by multiplexing outputs of parallel digital filter circuits operating on different multiple bit portions of the input signal to provide a combined equalized output at a rate greater than the rate from each digital filter circuit.
A method of digital communications comprising transmitting digital signals from a transmitter to a receiver on a signal channel, the method further comprising equalizing input baseband signals with a bandwidth of at least 100 MHz, the input signals having discrete signal levels at an input data rate and being transmitted as output signals having a greater number of discrete signal levels at the input data rate, the equalizer generating signal levels as a logical function of bit history to emphasize transition signal levels relative to repeated signal levels based on time since last signal transition, the equalizer generating the signal levels by multiplexing outputs of parallel logic circuits operating on different multiple bit inputs.
A digital transmitter comprising an equalizer which emphasizes transition signal levels relative to repeated signal levels, the equalizer comprising:
- parallel digital filter circuits operating on different multiple bit portions of a multiple bit input;
- and
- a multiplexing circuit which multiplexes outputs of the parallel circuits to provide a combined equalized output at a rate greater than the rate from each digital filter circuit, the equalizer driving full current in opposite directions on both sides of a transition and driving an attenuated current when a signal value remains unchanged.
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 comprising:
- operating on different multiple bit inputs in parallel digital filter circuits;
- multiplexing outputs of the parallel filter circuits to provide a combined equalized output at a rate greater than the rate from each digital filter circuit, the transition signal levels being emphasized by driving the full current in opposite directions on both sides of the transition and driving an attenuated current when a signal value remains unchanged.
A digital transmitter comprising an equalizer which generates output signal levels, the equalizer comprising:
- parallel digital filter circuits operating on different multiple bit portions of a multiple bit input;
- and
- a multiplexing circuit which multiplexes outputs of the parallel digital filter circuits to provide a combined equalized output at a rate greater than the rate from each digital filter circuit, the equalizer driving full current in opposite directions on both sides of a transition and driving an attenuated current when a signal value remains unchanged.
A digital transmitter comprising an equalizer which emphasizes transition signal levels relative to repeated signal levels, the equalizer converting an input baseband signal with a bandwidth of at least 100 MHz at an input data rate to an output signal having a greater number of discrete signal levels at the input data rate, equalization being based on time since last signal transition, the equalizer generating signal levels by multiplexing outputs of parallel logic circuits operating on different multiple bit inputs, the equalizer driving full current in opposite directions on both sides of a transition and driving an attenuated current when a signal value remains unchanged.
Dependencies are inferred from the claim text.