Random Edge Injection Locking for BLE Oscillator Spur Reduction
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Solution Overview
Problem
Injection-locked digital phase locked loops (IL-DPLLs) in Bluetooth Low Energy (BLE) technology face issues with periodic errors and spurs due to non-linearity in the delay of the digitally controlled oscillator, leading to reference and fractional spurs in the output spectrum.
Innovation Solution
A circuit and method implementing random edge injection locking, using a digitally controlled delay line and a pseudo-random binary sequence generator to inject pulses at different phases of the oscillator, breaking repeating patterns and compensating for phase errors, thereby reducing reference and fractional spurs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a digitally controlled delay line is used to generate injection pulses at fixed phases, then the injection locking function is achieved, but periodic errors and spurs are introduced due to non-linearity
Solution Approach 1:
The patent applies dynamics by making the injection phase variable rather than fixed. The system dynamically selects different phases of the oscillator for injection based on a pseudo-random sequence, which changes the injection timing and breaks the periodic repetition that causes spurs. This dynamic phase selection resolves the contradiction by maintaining injection locking while eliminating the harmful periodic errors.
Solution Approach 2:
The patent uses periodic action in a modified form by employing a pseudo-random sequence that periodically changes the injection phase. Instead of fixed periodic injection at the same phase, the system uses periodic switching between multiple phases according to a pseudo-random pattern, which maintains the periodic injection function while breaking the harmful periodicity that causes spurs.
2Adaptability or versatility
If the delay of the digitally controlled delay line changes periodically in fractional-N mode, then frequency tuning is achieved, but non-linearity introduces periodic error leading to fractional spurs
Solution Approach 1:
The patent applies dynamics by dynamically changing the injection phase according to a pseudo-random sequence that correlates with the fractional-N delay variations. This dynamic phase adjustment compensates for the non-linear delay changes, maintaining frequency tuning capability while canceling out the periodic errors that would otherwise create fractional spurs.
Solution Approach 2:
The patent employs feedback by using a pseudo-random sequence generator that provides a phase select signal correlated with the fractional-N operation. This feedback mechanism adjusts the injection phase in response to the delay line's periodic changes, thereby compensating for non-linearity and eliminating fractional spurs while preserving frequency tuning.
3Device complexity
If injection pulses are injected to a fixed phase of the oscillator, then the circuit structure is simple, but repeating patterns cause spurs in the output spectrum
Solution Approach 1:
The patent applies dynamics by implementing a phase selector that chooses from multiple oscillator phases based on a pseudo-random sequence. This adds dynamic phase selection capability with minimal additional circuit complexity, breaking the repeating injection patterns that cause spurs while maintaining overall system simplicity.
Solution Approach 2:
The patent applies segmentation by dividing the single fixed-phase injection into multiple phase options. Instead of injecting at one fixed phase, the system segments the injection across multiple oscillator phases and selectively activates them according to a pseudo-random sequence, thereby breaking harmful patterns with minimal complexity increase.
Data Source
AI summary
A circuit for facilitating random edge injection locking of an oscillator comprises a clock signal and a digitally controlled delay line, where the digitally controlled delay line is configured to delay the clock signal, thereby generating a delayed clock signal. The circuit further comprises an edge selector configured to generate a phase select signal with a random pulse sequence. Moreover, the circuit comprises a pulse generator downstream to the digitally controlled delay line configured to generate injection pulses from the delayed clock signal for at least two phases of the oscillator based on the phase select signal.