Multi-rate FIR Filter Using Rate-Dependent Bit Stuffing
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Solution Overview
Problem
Conventional FIR filters face challenges in supporting high data rates while maintaining complexity and power efficiency, particularly when operating in multiple sub-rate modes, as they require complex logic and increased latency, making it difficult to close timing at high data rates.
Innovation Solution
Implementing a multi-rate FIR filter using rate-dependent bit stuffing on the cursor while maintaining full-rate spacing for pre- and post-cursors, reducing logic complexity and avoiding additional pipeline flops and interface changes, thereby supporting multiple data rate modes efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional FIR filters are designed to support different data rates, then multi-rate operation is achieved, but circuit complexity increases and timing closure becomes impractical at high data rates
Solution Approach 1:
The patent implements a universal FIR filter architecture that operates at multiple data rates (full-rate, half-rate, quarter-rate, eighth-rate) using the same filter coefficients and logic structure. The filter can be configured to support different signal rates without requiring separate filter designs, achieving multi-functionality through a single unified circuit that adapts to various operating conditions.
Solution Approach 2:
The patent changes operational parameters (data rate selection) rather than structural parameters to achieve multi-rate operation. By using rate-select logic that controls the timing and spacing of pre-cursor, cursor, and post-cursor bits based on the selected data rate, the filter maintains the same physical structure while adapting to different operating speeds, thereby avoiding complexity increases.
2Adaptability or versatility
If conventional FIR filters are designed to support different data rates, then multi-rate operation is achieved, but timing closure becomes difficult at high data rates
Solution Approach 1:
The patent implements dynamic timing adjustment where the spacing between pre-cursor, cursor, and post-cursor bits changes based on the selected data rate. The logic dynamically adapts the timing relationships between filter taps to match the operating rate, allowing the same circuit to meet timing requirements across full-rate, half-rate, quarter-rate, and eighth-rate operations without compromising timing closure.
3Reliability
If full-rate pre-cursors and post-cursors are generated separately for each sub-rate mode, then rate-specific optimization is achieved, but logic complexity and latency increase
Solution Approach 1:
The patent merges the generation of pre-cursors and post-cursors into a single unified logic structure that operates at full-rate. Instead of implementing separate generation circuits for each sub-rate mode, the design combines all cursor generation logic into one unit that produces the appropriate timing relationships for any selected data rate, thereby reducing overall logic complexity and latency while maintaining rate-specific performance characteristics.
Data Source
AI summary
Embodiments include systems and methods for implementing a multi-rate FIR by using rate-dependent bit stuffing on the cursor, while using rate-independent (e.g., full-rate) spacing on the pre- and post-cursor. For example, in the FIR data path, the cursor bit output is generated using bit stuffing, depending on a selected rate mode (e.g., full-rate, half-rate, quarter-rate, eighth-rate, etc.), but the spacing of the pre-cursor, cursor, and post-cursor are maintained at 1 UI apart (i.e., the full-rate spacing) for all rate modes. Such an approach can appreciably reduce complexity of the logic and can appreciably relieve the critical timing path.