Polyphase Multirate Filter Feedback for Deterministic Clock Crossing
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Solution Overview
Problem
Current multirate filters in cellular radio devices face challenges in providing deterministic delays across clock domains with unknown clock phase relationships, especially when handling diverse signal frequencies and clock jitters, which is critical for accurate timing in multi-mode cellular devices.
Innovation Solution
A real-time configurable, self-correcting multirate filter system that measures the phase relationship between input and output clock signals using a faster measurement clock, updates polyphase filter coefficients, and adjusts indices to ensure accurate sampling and timing synchronization across different communication standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If multirate filter is used for sample rate conversion in multi-mode cellular devices, then power and area requirements are reduced, but deterministic delay becomes difficult to achieve due to crossing clock domains and unknown clock phase relationships
Solution Approach 1:
The patent implements a feedback mechanism where the actual phase relationship between input and output clocks is measured and used to adjust the filter coefficients in real-time. This closed-loop approach compensates for clock phase variations and jitter, ensuring deterministic delay is achieved despite crossing clock domains.
Solution Approach 2:
The patent dynamically changes the filter coefficients based on the measured phase relationship between clocks. By adjusting the polyphase filter coefficients in real-time according to actual clock phase conditions, the system maintains accurate timing and deterministic delay while operating across different clock domains.
2Measurement precision
If lowest common sampling frequency is used to achieve exact timing corrections, then timing accuracy is improved, but device complexity and computational requirements increase significantly
Solution Approach 1:
The patent uses a dynamic polyphase filter structure where the effective filter coefficients are selected and adjusted in real-time based on the measured phase relationship. This dynamic approach allows the filter to adapt to different timing requirements without requiring a fixed high-complexity structure designed for the lowest common sampling frequency.
Solution Approach 2:
The patent segments the filter into multiple polyphase components, each handling different phases of the sampling process. By dividing the filter into manageable polyphase sections and selectively activating appropriate components based on measured phase relationships, the system achieves precise timing correction without the complexity of a single high-order filter operating at the lowest common sampling frequency.
3Adaptability or versatility
If multirate filter operates with diverse signal frequencies and clock jitters, then adaptability to multiple standards is improved, but timing synchronization becomes more difficult
Solution Approach 1:
The patent continuously measures the phase relationship between input and output clocks and feeds this information back to adjust the filter operation. This real-time feedback mechanism compensates for clock jitter and phase variations, maintaining synchronization accuracy despite operating with diverse signal frequencies and multiple standards.
Solution Approach 2:
The patent implements a universal polyphase filter structure that can handle multiple signal frequencies and clock rates by dynamically selecting and adjusting coefficients based on measured phase relationships. This multi-functional approach allows the same hardware to support multiple communication standards while maintaining timing synchronization through adaptive coefficient selection.
Data Source
AI summary
A system includes a polyphase multirate filter and a controller which, responsive to detecting a data stream: measures a current phase relationship between a current resampling filter input clock signal and a current multirate output clock signal; identifies, based on a mapping of the measured phase relationship within a pre-generated quantized mapping table, an initial polyphase filter coefficient index corresponding to the measured phase relationship; selects, based on the initial polyphase filter coefficient index identified, a corresponding polyphase filter component from within the multirate filter; configures the multirate filter to pass data from the data stream through the corresponding polyphase filter component to generate an initial output data sample; updates the initial polyphase filter coefficient index to a calculated next polyphase filter coefficient index value, in response to a request for generation of a next output data sample; and self-corrects the multirate filter responsive to a pre-identified error condition.