Oscilloscope Timebase Locking for Low-Noise Phase Jitter Measurement

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Solution Overview

Problem

Existing phase noise measurement instruments, such as SSAs and spectrum analyzers, are limited by offset frequency range and cannot accurately measure data-type or spread-spectrum clock-type signals, while oscilloscopes suffer from correlated phase noise measurement floors due to shared timebase systems.

Innovation Solution

Phase-locking the timebase reference oscillators of multiple oscilloscope chassis together at a low adjustment update rate, typically 1 Hz or less, to uncorrelate phase noise between channels and improve measurement accuracy using cross-correlation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If multiple oscilloscopes share a common timebase system to ensure coherency, then measurement coherency is improved, but phase noise correlation between channels increases

Engineering Contradiction:

Improvemeasurement coherencyVSAvoidphase noise measurement accuracy

Core Design Contradiction:

Stability of the object's compositionVSMeasurement precision

Solution Approach 1:

The patent divides the timebase system into separate independent timebase units for each oscilloscope channel, rather than sharing a common timebase. This segmentation allows each channel to have its own independent timebase reference, eliminating the correlation of phase noise between channels while still enabling cross-correlation measurements to remove uncorrelated noise components.

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If dedicated phase noise measurement systems (SSAs) are used, then measurement accuracy is improved, but offset frequency range is limited

Engineering Contradiction:

Improvephase noise measurement accuracyVSAvoidoffset frequency range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent makes the oscilloscope serve multiple functions by enabling it to perform both general waveform analysis and phase noise measurements. By implementing cross-correlation algorithms and providing options for independent or common timebase operation, the oscilloscope becomes a universal instrument that can handle various measurement types including phase noise, jitter, and spectral analysis across wide frequency ranges.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If cross-correlation is used to average out internal phase noise, then measurement noise floor is reduced, but correlated phase noise from shared timebase cannot be removed

Engineering Contradiction:

Improvemeasurement noise floorVSAvoidcorrelated phase noise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent introduces dynamic configurability to the timebase system, allowing users to switch between common timebase mode (for coherency-critical applications) and independent timebase mode (for phase noise measurements). This dynamic adaptation enables the system to optimize its behavior based on the measurement requirements, providing both coherency when needed and independence when phase noise measurement is the goal.

Inventive Principle:

Principle #15Dynamics

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

Enhances phase noise measurement accuracy to match or exceed that of dedicated phase noise measurement systems, overcoming limitations in offset frequency range and correlated noise floors.

Implementation Method 1

a phase detector circuit to detect a frequency and phase difference between the two clock signals

Methodology Applied

Scientific EffectPhase detection:

Implementation Method 2

a voltage controlled oscillator to tune an output frequency of the timebase reference oscillator of at least one of the first and second oscilloscopes based on the determined frequency and phase difference

Methodology Applied

Scientific EffectVoltage controlled oscillation:

Implementation Method 3

phase-locking the timebase reference oscillators of the first and second oscilloscopes together

Methodology Applied

Scientific EffectPhase-locking:

Data Source

PatentUS20250362323A1Method and system for phase jitter and phase noise measurements using oscilloscopes

Publication Date: 2025.11.27 KEYSIGHT TECHNOLOGIES INC

AI summary

A method for measuring the phase jitter and phase noise of a signal-under-test (SUT) includes providing first and second oscilloscopes each having a timebase reference oscillator, the timebase reference oscillator of each of the first and second oscilloscopes configured to generate a timebase reference signal of a given output frequency. The method further comprises phase-locking the timebase reference oscillators of the first and second oscilloscopes together, applying the SUT to an input channel of the first oscilloscope and to an input channel of the second oscilloscope, and generating a first phase jitter measurement of the SUT using the first oscilloscope and generating a second phase jitter measurement of the SUT using the second oscilloscope. The method still further includes obtaining the phase noise of the SUT from the first and second phase jitter measurements to obtain the phase noise of the SUT.