SS-PLL Pre-Charge Circuit for Automatic Frequency Locking
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Solution Overview
Problem
Sub-sampling Phase-Locked Loops (SS-PLLs) face challenges in distinguishing between different harmonics of a reference frequency and have a limited frequency acquisition range, making it difficult to lock successfully, especially at high frequencies like those used in millimeter wave applications, due to the sinusoidal characteristic of the sub-sampling phase detector (SSPD) and the need for precise voltage-controlled oscillator (VCO) frequency tuning.
Innovation Solution
The implementation of a pre-charge circuit and coarse tuning mechanism within the SS-PLL system, which includes a frequency locking loop (FLL) and a switch to facilitate frequency locking, allows for automatic search and acquisition of the locking frequency, reducing the need for precise VCO frequency accuracy and enhancing resistance to frequency transient disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an additional frequency locking loop (FLL) or digital counter/calibrator is used to achieve precise VCO frequency, then frequency locking accuracy is improved, but device complexity and susceptibility to switching transients increase
Solution Approach 1:
The patent applies preliminary action by pre-charging the sampling device before the actual sampling operation. The pre-charge circuit sets the initial voltage level of the sampling device to match the expected signal level, ensuring that when sampling begins, the device is already in the correct operating state. This eliminates the need for additional FLL or digital counter components to correct frequency errors, as the frequency accuracy is achieved through the preliminary pre-charge action rather than complex post-processing or additional locking loops.
2Speed
If switching from FLL or digital counter to SS-PLL is performed, then frequency acquisition is achieved, but VCO frequency shifts occur due to disturbance or charge re-distribution
Solution Approach 1:
The patent implements beforehand cushioning by introducing a pre-charge circuit that prepares the sampling device in advance before the actual frequency locking operation. The pre-charge circuit charges the sampling device to the appropriate voltage level before switching from FLL to SS-PLL, cushioning against the charge re-distribution that would otherwise occur during switching. This preliminary preparation prevents frequency shifts and maintains VCO stability during the transition, eliminating the need for complex switching mechanisms or additional stabilization components.
3Reliability
If sub-sampling phase detector with sinusoidal characteristic is used, then phase noise performance is improved, but frequency acquisition range is limited
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the operating parameters of the sub-sampling phase detector through the pre-charge circuit. By changing the initial voltage state of the sampling device before operation, the effective detection characteristics are modified. This allows the sinusoidal characteristic detector to operate effectively across a wider frequency range while maintaining its excellent phase noise performance, as the pre-charge parameter adjustment optimizes the detector's response across different frequency conditions without requiring a fundamentally different detection mechanism.
Data Source
AI summary
An apparatus and method are provided. The apparatus includes a phase locked loop (PLL) configured to generate a reference signal; a sub-sampling PLL (SS-PLL) connected to the PLL and configured to sub-sample the reference signal; and a first pre-charge circuit connected to a sampling device of the SS-PLL and configured to facilitate frequency locking of the SS-PLL.