THP Transmitter DC Nulling via Recursive Filter Merging
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Solution Overview
Problem
THP-based systems face challenges in imposing a narrow DC null on the output spectrum without resorting to high-order filters or recursive taps, which increases power consumption and complexity, especially in AC-coupled communication channels.
Innovation Solution
The implementation of a modulo-limited recursive filter and a DC nulling circuit that uses conditional add and subtract operations to create a narrow and stable notch at or near DC, utilizing a small portion of the PAM decision space as redundancy, thereby shaping the output spectrum without significantly increasing peak values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional FIR filtering is used to create a DC null after THP processing, then a DC null can be achieved, but the number of filters and power consumption increase significantly
Solution Approach 1:
The patent merges the DC nulling function with the existing THP recursive feedback filter by introducing a DC nulling coefficient that modifies the feedback path. This integration eliminates the need for separate FIR filters, achieving DC nulling through the existing filter structure while reducing overall system complexity and power consumption.
Solution Approach 2:
The patent changes the parameter of the recursive feedback filter by introducing a DC nulling coefficient (e.g., 0.5) that modifies the feedback path. This parameter modification enables the filter to create a DC null without requiring additional filter stages, thereby reducing complexity while maintaining the DC nulling function.
2Manufacturing precision
If high-order filters are used to create a narrow DC null, then spectral shaping is achieved, but power consumption and complexity increase
Solution Approach 1:
The patent combines the spectral shaping function with the existing THP recursive feedback filter structure. By integrating the DC nulling coefficient into the feedback path, the system achieves narrow spectral nulling without adding high-order filter stages, thereby reducing power consumption while maintaining precision.
Solution Approach 2:
The patent modifies the feedback path parameters by introducing a DC nulling coefficient that enables precise spectral shaping. This parameter change allows the system to achieve narrow DC nulls with minimal additional complexity and power consumption compared to traditional high-order filter approaches.
3Reliability
If recursive taps are added to compensate for FIR filters, then DC null cancellation is achieved, but device complexity increases
Solution Approach 1:
The patent merges the DC nulling function into the existing THP recursive feedback filter structure. By introducing a DC nulling coefficient that modifies the feedback path, the system achieves DC null cancellation without adding separate compensating recursive taps, thereby reducing overall device complexity.
Solution Approach 2:
The patent makes the existing recursive feedback filter multi-functional by enabling it to perform both THP equalization and DC nulling simultaneously. The DC nulling coefficient allows the same filter structure to serve dual purposes, eliminating the need for additional compensating recursive taps and reducing complexity.
Data Source
AI summary
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.