PLL Oscillator Compensation for Frequency Pushing and Pulling
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Solution Overview
Problem
Existing frequency compensation techniques for phase-locked loops (PLL) are inefficient in mitigating frequency pushing/pulling effects caused by aggressors such as power supply and ground bounce, RF leakage, and electromagnetic coupling, leading to degraded transmitter performance characterized by error vector magnitude, RMS, and phase errors.
Innovation Solution
A method and circuit for frequency pushing/pulling compensation in PLLs, which computes an error signal, estimates aggressor transfer characteristics, filters the signal to produce a correction term, and normalizes it to apply to the oscillator's frequency control word, effectively mitigating the impact of aggressors on the oscillator's frequency stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If traditional isolation techniques (physical separation, ferrite elements, shielding) are used to mitigate frequency pushing/pulling, then oscillator stability is improved, but device complexity and cost increase
Solution Approach 1:
The patent implements a feedback mechanism where the phase error signal from the PLL is fed back through a filter and summer to generate a compensation signal that is added to the frequency control word. This closed-loop feedback system automatically counteracts frequency pushing/pulling effects without requiring complex physical isolation components, thereby improving oscillator stability while reducing device complexity
Solution Approach 2:
The patent replaces mechanical/physical isolation techniques (ferrite elements, shielding, physical separation) with a digital signal processing approach. By using digital filtering and mathematical operations on the phase error signal to generate frequency compensation, the system eliminates the need for expensive and complex electromagnetic isolation components
2Reliability
If wide tuning range is used in ADPLL to maintain lock during frequency jumps, then reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by proactively compensating for frequency pushing/pulling effects before they cause the PLL to lose lock. The compensation signal is generated in advance based on the phase error and aggressor signal characteristics, adjusting the frequency control word to prevent frequency jumps that would require wide tuning range to accommodate
3Measurement precision
If aggressive filtering of error signal is used to remove aggressor effects, then measurement precision is improved, but loss of information increases
Solution Approach 1:
The patent applies local quality by selectively filtering only the specific frequency components corresponding to the aggressor signal, rather than applying broad-spectrum filtering. The filter is designed with specific characteristics matched to the aggressor frequency, allowing precise removal of harmful components while preserving other important signal information in the phase error
Data Source
AI summary
A system and method for frequency pushing/pulling compensation in phase-locked loops including a method for cancelling frequency push/pull in an oscillator of a transmitter. The method includes computing an error signal from a signal of a phase locked loop, wherein the error signal includes an aggressor signal. Transfer characteristics are computed for the aggressor signal. A transmitted signal is filtered using the transfer characteristics to produce a correction term. The correction term is applied to a frequency control word being provided to the oscillator.