Phase Locked Loop High Frequency Filter Harmonic Attenuation

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Solution Overview

Problem

Phase locked loops (PLLs) face challenges in attenuating harmonics, leading to unwanted spurs in output signals due to continuous updating of phase difference signals at reference frequencies, which affect signal quality and circuit efficiency.

Innovation Solution

Incorporating a high frequency filter with a pole greater than the reference frequency and less than the oscillation frequency, coupled with a low pass filter, to attenuate harmonics and reduce spurious coupling, thereby improving signal quality and reducing circuit area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a conventional low pass filter is used to filter the phase difference signal, then the signal bandwidth is reduced, but harmonics at reference frequency multiples are not effectively attenuated causing unwanted spurs in the output signal

Engineering Contradiction:

Improveharmonic attenuationVSAvoidsignal quality

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The filtering function is segmented into two distinct stages: a low pass filter for bandwidth control and a high frequency filter specifically targeting harmonic attenuation. This segmentation allows each filter to perform its specialized function optimally, with the high frequency filter specifically designed to attenuate reference frequency multiples that cause spurs while the low pass filter manages the overall signal bandwidth.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The high frequency filter acts as an intermediary component between the phase difference signal generation and the controlled oscillator. It specifically targets and attenuates the harmful harmonic frequencies (multiples of reference frequency) that would otherwise appear as unwanted spurs in the output signal, thereby improving signal quality without compromising the essential bandwidth control function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If the phase difference signal is continuously updated at reference frequency, then the phase locking accuracy is maintained, but harmonics are generated causing spurious coupling and reduced circuit efficiency

Engineering Contradiction:

Improvephase locking accuracyVSAvoidspurious coupling

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The continuous updating of the phase difference signal at reference frequency, which generates harmful harmonics, is converted into a benefit by using these same harmonic frequencies as the target for the high frequency filter. The filter is specifically designed with poles at reference frequency multiples to exploit and attenuate these harmonics, transforming the harmful spurious coupling into a controlled filtering opportunity that improves overall signal quality.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Ease of manufacture

If traditional filtering methods are used, then circuit implementation is simple, but circuit area is increased and harmonic attenuation is insufficient

Engineering Contradiction:

Improvefiltering implementationVSAvoidcircuit area

Core Design Contradiction:

Ease of manufactureVSArea of stationary object

Solution Approach 1:

The high frequency filter is designed to perform multiple functions simultaneously: it attenuates harmonics at reference frequency multiples, reduces spurious coupling, and works in conjunction with the low pass filter to achieve overall signal conditioning. This multi-functionality allows a single circuit implementation to address multiple filtering requirements without proportionally increasing circuit area, as the filter structure is optimized to handle various frequency components efficiently.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively attenuates harmonics and spurious coupling, enhancing the signal quality of PLLs by reducing unwanted spurs and minimizing circuit area, particularly in semiconductor implementations.

Implementation Method 1

a high frequency filter of which a pole is greater than the reference frequency and less than a frequency of the oscillation signal

Methodology Applied

Scientific EffectFrequency filtering: Filter (electronic)

Data Source

PatentUS8791732B2Phase locked loop

Publication Date: 2014.07.29 MEDIATEK INC

AI summary

A phase locked loop is provided. The phase locked loop includes a detector, a controlled oscillator and a filtering unit coupled between the detector and the controlled oscillator. The detector generates a phase difference signal according to a reference frequency and an oscillation signal. The controlled oscillator generates the oscillation signal according to a filtered signal. The filtering unit filters the phase difference signal to generate the filtered signal, and the filtering unit has a high frequency filter of which a pole is greater than the reference frequency and less than a frequency of the oscillation signal.