PLL Direct Feedforward Circuit for Phase Noise Reduction

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Solution Overview

Problem

Phase-locked loops (PLLs) suffer from phase noise due to imperfections in components like the voltage-controlled oscillator, charge pump, and loop filter, which is exacerbated by miniaturization efforts.

Innovation Solution

The integration of a direct feedforward circuit within the PLL, which receives the error signal from the phase detector and adjusts the voltage fed into the voltage-controlled oscillator (VCO) to correct phase errors, thereby reducing phase noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If miniaturization of PLL components is pursued, then device size is reduced, but phase noise increases

Engineering Contradiction:

ImprovePLL device sizeVSAvoidphase noise

Core Design Contradiction:

Volume of moving objectVSObject-generated harmful factors

Solution Approach 1:

The PLL system is segmented into two parallel correction paths: a traditional feedback path through the charge pump and loop filter, and a new direct feedforward path that processes error signals independently. This segmentation allows the direct correction of phase noise without being constrained by the miniaturized component dimensions, thus reducing phase noise while maintaining small device size.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An intermediary feedforward circuit is introduced that receives error signals directly from the phase detector and applies corrections to the VCO input. This intermediary path bypasses the miniaturized charge pump and loop filter components, providing a clean correction mechanism that is not degraded by the size reduction of other PLL components.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If traditional feedback-only PLL structure is used, then circuit simplicity is maintained, but phase noise correction is insufficient

Engineering Contradiction:

Improvecircuit structureVSAvoidphase noise

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The invention enhances the traditional feedback mechanism by adding a direct feedforward feedback path. The phase detector error signals are processed through both the conventional charge pump-loop filter feedback path and a new direct feedforward path that directly adjusts the VCO control voltage, providing dual-path phase noise correction.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The feedforward circuit merges with the existing feedback structure by combining error signal processing from the phase detector with the VCO control input. This merging creates a unified PLL architecture where both feedforward and feedback paths work together to suppress phase noise, achieving superior performance without requiring completely separate systems.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS12334939B2Phase-locked loop (PLL) with direct feedforward circuit

Publication Date: 2025.06.17 TEXAS INSTRUMENTS INC

AI summary

A phase-locked loop (PLL) device includes: 1) a detector configured to output an error signal to indicate a phase offset between a feedback clock signal and a reference clock signal; 2) a charge pump coupled to the detector and configured to output a charge pump signal based on the error signal; 3) an integrator with a feedback path, an input node, a reference node, and an output node, wherein the input node is coupled to the charge pump and receives the charge pump signal; 4) a voltage-controlled oscillator (VCO) coupled to the output node of the integrator via a resistor; and 5) a feedforward circuit coupled directly to the detector and configured to apply an averaged version of the error signal to correct a voltage level received by the VCO.