Time-Interleaved Injection-Locked VCO Circuits for Jitter Reset
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Solution Overview
Problem
Jitter accumulation in Voltage Controlled Oscillators (VCOs) is a significant issue, particularly at low frequencies, due to positive feedback noise enhancement, which is exacerbated by traditional injection locking methods and proportional to the reference clock frequency.
Innovation Solution
Employing a pair of time-interleaved injection locked VCOs, where one VCO is turned off while the other is oscillating, and using a control circuit to select outputs via a multiplexer, thereby limiting jitter accumulation below an acceptable threshold by alternating between VCOs and optionally resetting deselected VCOs to reduce parasitic capacitance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional injection locking is employed to track reference clock phase, then phase noise filtering is improved, but jitter accumulation increases proportionally with reference clock frequency
Solution Approach 1:
The system divides the single VCO operation into multiple segments by employing a plurality of VCO branch circuits (first VCO, second VCO, etc.) that operate in alternating time intervals. Each VCO segment processes a portion of the reference clock cycles, preventing any single VCO from accumulating excessive jitter over extended periods while maintaining continuous phase-locked operation.
Solution Approach 2:
The control circuit implements periodic switching between multiple VCO branches, activating one VCO for a predetermined number of reference clock cycles then switching to the next VCO in the sequence. This periodic rotation ensures each VCO operates only during intervals when its accumulated jitter remains below the threshold, systematically preventing jitter accumulation while maintaining continuous output.
2Reliability
If multiple VCOs are employed in parallel to reduce jitter accumulation, then jitter performance improves, but device complexity increases
Solution Approach 1:
Multiple VCO branch circuits are merged into a unified time-interleaved architecture where they share common control circuitry, reference clock input, and output combining logic. The control circuit manages all VCO branches through a single systematic approach, and the multiplexer combines their outputs into one unified output signal, achieving jitter reduction without proportionally increasing overall system complexity.
Solution Approach 2:
Each VCO branch circuit is designed with identical structure and functionality, serving as a universal module that can be replicated. The control circuit universally manages all VCO branches using the same switching and selection logic, allowing the system to scale by simply adding more identical VCO modules rather than designing increasingly complex differentiated circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces jitter accumulation, maintaining it below a threshold, thereby improving phase noise performance and extending the time before jitter surpasses acceptable limits, as demonstrated by experimental improvements in in-band phase noise reduction.
Implementation Method 1
Injection locked VCOs exhibit jitter accumulation dependent on the effective bandwidth achieved by the injection locking process
Data Source
AI summary
Digital jitter accumulation reduction techniques and circuits are proposed to mitigate jitter accumulation in Voltage Controlled Oscillators (VCOs). In order to reduce jitter accumulation, employing a pair of identical injection locked VCOs is proposed in an interleaved fashion. Further jitter accumulation reductions can be provided by employing a plurality of identical injection locked VCOs selected in a cascading fashion. Yet further jitter accumulation reductions can be provided by resetting the deselected VCO(s).