PLL Frequency Synthesizer With Tunable Harmonic Filtering

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Solution Overview

Problem

Existing frequency synthesizers face challenges in generating wideband low phase noise signals, as increasing bandwidth lowers the 'Q' of resonators, leading to higher phase noise, and require multiple oscillators and phase-locked loops, which are costly and space-intensive.

Innovation Solution

A frequency synthesizer incorporating a phase-locked loop circuit with a tunable bandpass filter that allows for integer or fractional frequency division, using a narrow band VCO to cover a wide range of frequencies, reducing phase noise and eliminating the need for multiple oscillators.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If bandwidth is increased to generate wideband signals, then frequency coverage is improved, but phase noise is increased due to lowered Q of resonator

Engineering Contradiction:

Improvefrequency coverageVSAvoidphase noise

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The frequency band is divided into multiple sub-bands, with each sub-band processed by a separate narrowband VCO and PLL. This segmentation allows each oscillator to operate within a limited frequency range where it can maintain high Q and low phase noise, while collectively covering a wide frequency spectrum through the combination of multiple sub-bands

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent transitions from a single-dimension approach (one wideband VCO covering entire frequency range) to a multi-dimensional approach (multiple narrowband VCOs covering different frequency sub-bands). This dimensional change in frequency space allows simultaneous achievement of wideband coverage and low phase noise by operating multiple oscillators in parallel across different frequency dimensions

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Adaptability or versatility

If multiple voltage controlled oscillators and phase-locked loops are used to cover wide frequency band, then frequency coverage is improved, but device complexity and cost are increased

Engineering Contradiction:

Improvefrequency coverageVSAvoidnumber of oscillators and phase-locked loops

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent designs each VCO-PLL unit to be a universal, self-contained module that can independently generate and cover a specific frequency sub-band. These modular units can be selectively activated based on the required output frequency, providing universal frequency coverage capability without requiring all modules to be simultaneously active, thus reducing overall system complexity while maintaining wideband capability

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If multiple voltage controlled oscillators and phase-locked loops are used to cover wide frequency band, then frequency coverage is improved, but board space is increased

Engineering Contradiction:

Improvefrequency coverageVSAvoidboard space

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent implements a nested hierarchical structure where multiple VCO-PLL modules are organized in a nested configuration, with frequency selection and control logic integrated within the modular units. This nesting allows compact arrangement of multiple oscillators and their associated circuitry, reducing overall board space requirements while maintaining the capability to cover wide frequency bands through selective activation of nested modules

Inventive Principle:

Principle #7Nested doll (Nesting)

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 achieves lower phase noise, reduced cost, and smaller size by using a single narrow band VCO to generate wideband signals with improved frequency coverage and faster locking times, while minimizing harmonic content and local oscillator radiation.

Implementation Method 1

Phase-locked loop circuits incorporate a voltage controlled oscillator (VCO) in which the output of the VCO is fed back through a frequency divider as a divide-by-N circuit to an input of a phase detector, i.e., phase comparator

Methodology Applied

Scientific EffectPhase-locked loop: Feedback

Implementation Method 2

A voltage controlled oscillator (VCO) in which the output of the VCO is fed back through a frequency divider

Methodology Applied

Scientific EffectVoltage controlled oscillation:

Implementation Method 3

the output of the VCO is fed back through a frequency divider as a divide-by-N circuit to an input of a phase detector

Methodology Applied

Scientific EffectFrequency division:

Implementation Method 4

A tunable bandpass filter is connected to the frequency divider and turned to a harmonic frequency thus obtaining an integer or a fractional frequency division

Methodology Applied

Scientific EffectBandpass filtering: Filter (electronic)

Data Source

PatentUS8655296B2Frequency synthesizer and related method for generating wideband signals

Publication Date: 2014.02.18 L3HARRIS GLOBAL COMMUNICATIONS INC

AI summary

A frequency synthesizer includes a phase-locked loop circuit having an output. A frequency divider is connected to the output of the phase-locked loop circuit for receiving the signal therefrom and dividing the frequency of the signal. A tunable bandpass filter is connected to the frequency divider and is tuned for selecting a harmonic frequency to obtain a fractional frequency division for a signal output from the phase-locked loop circuit.