DPLL Cycle Slip Correction Using TDC Phase Value Adjustment
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Solution Overview
Problem
Digital phase-locked loops (DPLLs) face challenges in quickly relocking the phase of the output clock to the reference clock after a cycle slip event, which can take a long period of time, leading to phase difference wrapping around from 2π to 0, affecting synchronization and stability.
Innovation Solution
Incorporation of a cycle slip detector circuit that immediately detects cycle slips and adjusts the digital output value by an integer multiple of the reference clock period, enabling rapid correction and maintaining phase lock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a conventional DPLL is used without a cycle slip detector circuit, then the device complexity is reduced, but the relocking time after a cycle slip event increases significantly
Solution Approach 1:
The cycle slip detector circuit continuously monitors the digital output value from the TDC and compares it against threshold values before a cycle slip completes. By detecting potential cycle slips early and preparing correction actions in advance, the system can rapidly correct phase errors once they occur, significantly reducing relocking time without requiring complete system redesign
Solution Approach 2:
The cycle slip detector circuit acts as an intermediary component between the TDC and the filter/VCO system. It intercepts the digital output value, detects cycle slip conditions by comparing against thresholds, and applies corrections before the error propagates through the system. This mediator approach enables rapid cycle slip detection and correction while maintaining the overall DPLL architecture
2Reliability
If the phase difference wrapping around from 2π to 0 is allowed to occur without immediate correction, then the device operation is simpler, but the synchronization stability deteriorates
Solution Approach 1:
The cycle slip detector circuit implements a feedback mechanism where the digital output value from the TDC is continuously monitored and compared against threshold values. When a cycle slip is detected (phase difference wrapping from 2π to 0 or vice versa), the circuit generates a correction signal that feeds back to adjust the digital output value, ensuring continuous phase synchronization and maintaining reliability
Solution Approach 2:
The system changes the parameter being monitored from raw phase difference to a corrected phase difference that accounts for cycle slips. By detecting when the phase difference exceeds threshold values (indicating wrapping), the system applies parameter corrections to the digital output value, transforming the phase representation to maintain continuity and stability without requiring complete system redesign
Data Source
AI summary
A digital phase-locked loop (DPLL) includes a voltage-controlled oscillator to generate an output clock, a filter coupled to the voltage-controlled oscillator, and a time-to-digital converter (TDC) that receives a reference clock and a feedback clock. The feedback clock is derived from the output clock. The TDC generates a digital output value. The DPLL also includes a cycle slip detector circuit coupled to the TDC. The cycle slip detector circuit detects a cycle slip based on the digital output value and adjusts the digital output value by a second digital value that corresponds to an integer multiple of a period of the reference clock.