Systems and methods for spectral shaping of pre-equalized transmitter signals
AssigneeAnalog Devices, Inc.
InventorCharles Razzell
Life of this patent
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Abstract
Simple, low-cost systems and methods allow to shape the output spectrum of pre-equalized Tomlinson Harashima Precoding (THP)-equalized transmitters in a manner such as to create a relatively narrow DC null to facilitate transmission over DC-null channels in AC-coupled communication channels. Advantageously, this may be accomplished without significantly adding to the peak value of the to-be-transmitted signal and without the need to resort to high-order filters in the signal path or the use of recursive taps to compensate such filters.
Claims20
A method for communication over alternate current-coupled (AC-coupled) channels using Thomlinson Harashima-equalized (TH P-equalized) transmitters, the method comprising:
- at a first modulo reduction circuit, receiving the sum of (i) a baseband signal having an amplitude range and (ii) a feedback signal from a recursive filter forming the poles of an equalizer transfer function;
- applying a modulo reduction to limit the amplitude range to generate a bounded signal;
- using a first logic circuit to determine whether the bounded signal satisfies a first condition that is associated with a parameter;
- using a second logic circuit to determine whether the bounded signal satisfies a second condition;
- and
- providing the first and second conditions to a correction circuit to determine whether to apply a modulo-equivalent offset to the bounded signal to generate an output signal having a frequency spectrum that comprises a notch at or near zero Hertz;
- and
- transmitting the output signal over an AC-coupled communication channel to a receiver.
A system for communicating over alternate current-coupled (AC-coupled) channels using Thomlinson Harashima-equalized (THP-equalized) transmitters:
- a first modulo reduction circuit that in response to receiving the sum of (i) a baseband signal having an amplitude range and (ii) a feedback signal from a recursive filter forming the poles of an equalizer transfer function, applies to the sum a modulo reduction to limit the amplitude range to generate a bounded signal;
- a summing circuit coupled to receive the bounded signal and output a DC null signal;
- an amplitude zone detector circuit coupled to the first modulo reduction circuit, the amplitude zone detector circuit determines whether the bounded signal falls in a range such that a transmission of a modulo-equivalent signal would increase a signal headroom of a signal amplitude less or equal to a limit;
- an aggregation circuit that in response to receiving the direct current (DC) null signal generates a DC average of the DC null signal, the DC average having a first sign;
- a logic circuit coupled to the amplitude zone detector circuit, the logic circuit, in response to determining to apply a modulo constant, generates a signal whose sign is opposite to the first sign;
- and
- a balance correction circuit coupled to the logic circuit, the balance correction circuit, in response to receiving the signal, applies a modulo-equivalent offset to the bounded signal to generate an output signal having a frequency spectrum that comprises a notch at or near zero Hertz.
Dependencies are inferred from the claim text.