Opportunistic PLL Reference Synthesis for Low-Noise RF Signals
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current phase locked loops (PLLs) face limitations in achieving high spectral purity of RF signals due to fixed reference frequency, leading to performance degradation and significant periodic errors, especially in dense channelization standards like 5G, where the ratio between desired RF frequency and fixed reference frequency increases, resulting in elevated in-band noise and spurious signals.
Innovation Solution
The implementation of an opportunistic PLL that generates a reference signal of intermediate frequency synchronized with a low-frequency oscillator, utilizing a high-performance narrow bandwidth digitally controlled oscillator (DCO) to alleviate performance impairments and provide a wide choice of effective ratios, thereby creating a very low jitter PLL that filters fractional spurs and mitigates in-band noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed reference frequency is used in a PLL, then the system structure is simple, but the spectral purity of RF signals deteriorates due to periodic errors and elevated in-band noise
Solution Approach 1:
The patent implements a dynamic reference frequency selection mechanism that adapts the reference frequency based on the desired RF output frequency. Instead of using a fixed reference frequency, the system dynamically chooses from multiple reference frequencies to optimize the division ratio and minimize periodic errors, thereby improving spectral purity while maintaining manageable system complexity through structured control logic.
Solution Approach 2:
The system changes the reference frequency parameter dynamically based on the desired RF output frequency. By selecting different reference frequencies from a set of available frequencies, the system optimizes the division ratio N to reduce periodic errors and improve spectral purity. This parameter change approach resolves the contradiction by allowing flexible adaptation without fundamentally redesigning the entire PLL structure.
2Adaptability or versatility
If the ratio between RF frequency and reference frequency increases, then the frequency range coverage is improved, but phase noise and in-band noise are elevated
Solution Approach 1:
The system dynamically adjusts the reference frequency selection based on the desired RF output frequency to optimize the division ratio. By adaptively choosing reference frequencies that minimize the ratio N while still covering the required frequency range, the system reduces phase noise and in-band noise. This dynamic adaptation resolves the contradiction by allowing wide frequency coverage without sacrificing noise performance.
Solution Approach 2:
The system changes the reference frequency parameter to optimize the division ratio for different RF frequency ranges. By selecting appropriate reference frequencies from multiple available options, the system maintains a controlled division ratio that minimizes phase noise while achieving broad frequency coverage. This parameter optimization resolves the trade-off between versatility and noise performance.
3Adaptability or versatility
If a high division ratio is used to achieve desired RF frequency, then the frequency flexibility is improved, but periodic errors and spurious signals increase
Solution Approach 1:
The system dynamically selects the reference frequency to optimize the division ratio for each desired RF frequency. By adaptively choosing reference frequencies that result in lower division ratios, the system reduces periodic errors and spurious signals while maintaining frequency flexibility. This dynamic optimization resolves the contradiction by allowing frequency adaptation without incurring the penalties of high division ratios.
Solution Approach 2:
The system changes the reference frequency parameter to minimize the division ratio N for the desired RF frequency. By selecting from multiple reference frequency options, the system finds the optimal combination that reduces periodic errors and spurious signals while achieving the required frequency flexibility. This parameter optimization resolves the trade-off between versatility and error reduction.
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 significantly reduces phase noise, enhances spectral purity, and allows for the use of lower-cost components, improving the usability of RF signals in high-performance standards by reducing the noise contribution and allowing for flexible frequency adjustments.
Implementation Method 1
A PLL synchronizes the RF signal being generated by an oscillator circuit with a reference signal to ensure that that the RF signal is phase-aligned with respect to other signals in the device
Implementation Method 2
The implementation of an opportunistic PLL that generates a reference signal of intermediate frequency synchronized with a low-frequency oscillator
Implementation Method 3
utilizing a high-performance narrow bandwidth digitally controlled oscillator (DCO) to alleviate performance impairments and provide a wide choice of effective ratios, thereby creating a very low jitter PLL that filters fractional spurs and mitigates in-band noise
Data Source
AI summary
Systems, methods, and circuitries are provided to generate a radio frequency (RF) signal having a desired radio frequency fRF. In one example a frequency synthesizer system includes a clock, an opportunistic phase locked loop (PLL), and an RF PLL. The clock circuitry is configured to generate a clock signal having a frequency fXTL. The opportunistic phase locked loop (PLL) is configured to generate a reference signal having a reference frequency fREF that is close to a free-running frequency of an oscillator in the opportunistic PLL. The opportunistic PLL is configured to synchronize the reference signal to the clock signal. The RF PLL is configured to generate the RF signal having the desired radio frequency and to synchronize the RF signal with the reference signal.