Dual Reference Oscillator Switching for PLL Phase Noise Control
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Solution Overview
Problem
The transition to 5G wireless devices requires higher frequency reference crystal oscillators to manage phase noise, but these high-frequency oscillators have increased power consumption and larger frequency tolerance variations, posing challenges for phase noise management and efficiency.
Innovation Solution
Implementing a wireless device with two reference crystal oscillators, one operating at a lower frequency (20-40 MHz) for initial synchronization and power efficiency, and a higher frequency (100 MHz or more) for stringent phase noise requirements, allowing the device to switch between them based on carrier frequency and synchronization state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high frequency reference crystal oscillator (100 MHz or more) is used to reduce phase noise amplification and maintain low phase noise levels at 10 GHz and above, then phase noise performance is improved, but power consumption increases significantly (5 to 10 times greater than 20-40 MHz XO) and frequency tolerance deteriorates (40-50 ppm versus 10 ppm)
Solution Approach 1:
The patent implements dynamic switching between two reference crystal oscillators based on operational conditions. The system transitions from a low-frequency XO (20-40 MHz) during initial synchronization to a high-frequency XO (100 MHz or more) when stringent phase noise requirements are needed, and back again when returning to idle state. This dynamic adaptation resolves the contradiction by using the high-power oscillator only when necessary for phase noise performance.
Solution Approach 2:
The patent changes the operating parameters of the reference oscillator system by switching between two different frequency values (20-40 MHz and 100 MHz or more). This parameter change allows the system to optimize between power consumption and phase noise performance based on the current operational state, using the appropriate frequency range for each phase of operation.
2Measurement precision
If a high frequency reference crystal oscillator (100 MHz or more) is used to reduce phase noise amplification, then phase noise performance is improved, but frequency tolerance variations increase (40-50 ppm versus 10 ppm)
Solution Approach 1:
The system dynamically selects the reference oscillator frequency based on operational requirements. During initial synchronization where frequency tolerance is less critical, the low-frequency XO with better stability (10 ppm) is used. When high carrier frequencies require stringent phase noise control, the system switches to the high-frequency XO despite its larger tolerance variations, thus resolving the contradiction by matching oscillator characteristics to operational needs.
3Measurement precision
If the PLL bandwidth is increased to suppress phase noise from the controlled oscillator, then phase noise performance is improved, but the phase noise from the reference crystal oscillator is amplified more (by frequency ratio 20 log10(ƒo/ƒXO)), requiring even higher XO frequency
Solution Approach 1:
The patent segments the reference oscillator operation into distinct phases: initial synchronization using low-frequency XO and active operation using high-frequency XO. This segmentation allows the system to manage PLL bandwidth requirements separately for each phase, using the appropriate reference frequency to control phase noise amplification without requiring excessive PLL bandwidth adjustment.
Data Source
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AI summary
Systems and methods are disclosed herein that relate to a wireless device that intelligently uses different reference crystal oscillators (XOs) for a PhaseLocked Loop(s) (PLL(s)) in a transceiver of the wireless device. Embodiments of a method of operation of a wireless device comprising a first XO that operates at a first reference frequency and a second XO that operates at a second reference frequency that is greater than the first reference frequency are disclosed. In some embodiments, the method of operation of the wireless devices comprises making a decision as to whether to configure a receiver of the wireless device to use the first XO or the second XO and configuring the receiver of the wireless device to use the first XO or the second XO in accordance with the decision.