PLL Local Oscillator Phase Rotation for Interference Cancellation
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Solution Overview
Problem
In single-chip cellular transceivers supporting carrier aggregation, interference between Phase Locked Loops (PLLs) degrades noise performance due to phase noise sidebands in the Local Oscillator (LO) signal, particularly when PLLs operate at similar or harmonic frequencies, affecting throughput in both downconversion and upconversion processes.
Innovation Solution
A system with a Phase Locked Loop (PLL) and an error compensation subsystem that applies phase rotation to the LO signal based on the phase detector output, using a phase rotator and multiplier to mitigate phase errors caused by interference, effectively compensating for phase errors in both downconverted and upconverted signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple PLLs are enabled simultaneously to support carrier aggregation, then the transceiver can operate in multiple frequency bands, but interference between PLLs degrades noise performance
Solution Approach 1:
The patent measures the phase error caused by interference using a phase detector, then applies compensating phase rotation to convert the harmful interference effect into a correctable parameter, thereby maintaining signal quality despite multiple PLLs operating simultaneously
Solution Approach 2:
The system uses a phase detector to continuously monitor phase error in the LO signal and feeds this information back to an error compensation subsystem that applies real-time phase rotation correction, creating a closed-loop system that actively counteracts interference effects
2Ease of operation
If PLLs operate at the same or harmonic frequencies to simplify frequency planning, then frequency allocation is easier, but phase noise sidebands degrade throughput
Solution Approach 1:
The patent transforms the harmful phase noise sidebands caused by harmonic frequency operation into a measurable and correctable parameter by using phase detection and applying compensating phase rotation, allowing the system to maintain both simple frequency planning and high throughput
3Reliability
If phase error compensation is applied to mitigate interference, then noise performance improves, but system complexity increases
Solution Approach 1:
The patent introduces a phase detector as an intermediary component that measures phase error, and an error compensation subsystem that applies phase rotation as a mediator to correct the interference effect, balancing improved noise performance with acceptable system complexity
Data Source
AI summary
Systems and methods for mitigating interference in a Local Oscillator (LO) signal generated by a Phase-Locked Loop (PLL) are disclosed. In one embodiment, a system includes a PLL and an error compensation subsystem. The PLL includes a Controlled Oscillator (CO) that provides a LO output signal based on a control signal, a phase detector that generates a phase detector output signal that is indicative of a phase error between a feedback signal that is a function of the LO output signal and a reference signal, and a loop filter that filters the phase detector output signal to provide the control signal for the CO. The error compensation subsystem applies, based on the phase detector output signal, a phase rotation to a signal derived from the LO output signal to thereby compensate for a phase error in the signal resulting from a phase error in the local oscillator output signal.