Single Cycle First Order Accumulator for Clock Data Recovery
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Solution Overview
Problem
Conventional digital accumulator circuits face latency issues in feedback loops, limiting their performance in clock and data recovery systems, as they require multiple clock cycles to generate an accumulated result, which increases latency and affects locking, tracking, and jitter performance.
Innovation Solution
A system and method for first-order accumulation of an error signal in a single clock cycle using combinational logic, where a limited gain value is summed with an accumulated value, and based on the resulting summed value, a correction signal is applied to adjust the value within specified limits, allowing for immediate storage and subsequent use in the next clock cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional digital accumulator circuits are used, then the accumulation operation can be performed, but the latency increases because multiple clock cycles are required to generate an accumulated result
Solution Approach 1:
The accumulation operation is segmented into distinct functional blocks: adder for summation, comparator for limit checking, and multiplexer for correction signal selection. This segmentation allows each block to operate independently and simultaneously, enabling single-clock-cycle completion of the entire accumulation process while maintaining manageable device complexity through modular design
Solution Approach 2:
The upper and lower limits are pre-established and stored in the device, and the correction signals are pre-calculated based on possible comparison outcomes. When the summed value is compared against these pre-set limits, the appropriate correction signal is immediately available, eliminating the need for iterative calculations and reducing latency to a single clock cycle
2Measurement precision
If multiple clock cycles are used for accumulation, then the accumulated result can be generated with higher precision, but the feedback loop latency increases, affecting locking, tracking, and jitter performance
Solution Approach 1:
The device implements immediate feedback by comparing the summed value against pre-established limits within the same clock cycle and applying the appropriate correction signal through a multiplexer. This same-cycle feedback mechanism ensures both high precision accumulation and minimal feedback loop latency, resolving the contradiction between precision and speed in feedback-controlled systems
3Device complexity
If a simple adder is used for accumulation, then the device complexity is reduced, but the latency cannot be reduced to a single clock cycle because conventional accumulators require multiple cycles
Solution Approach 1:
The adder, comparator, and multiplexer are merged into a single integrated accumulation device that operates as one unified circuit. This merging allows all operations (summation, comparison, and correction signal application) to occur simultaneously within a single clock cycle, achieving low latency without significantly increasing overall device complexity through efficient circuit integration
Data Source
AI summary
A method is provided for first order accumulation in a single clock cycle. The method accepts a limited gain value and an accumulated value stored in a previous clock cycle. Using combinational logic, the limited gain value is summed with the accumulated value. If the summed value is between upper and lower limits, a non-weighted correction signal is supplied, and the summed value is the storage value. If the summed value is greater than the upper limit, a positive weighting is supplied, the (upper limit+1) is subtracted from the summed value, and the result is the storage value. If the summed value is less than the lower limit, then a negative weighting is supplied, the lower limit is subtracted from the summed value, and the result is the storage value. The storage value is loaded in memory for use as the accumulated value in the subsequent clock cycle.