Sampling Oscilloscope Jitter Measurement for 10 GHz Signals
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Solution Overview
Problem
Current methods for measuring jitter, particularly at high frequencies like 10 GHz, are inaccurate due to limited bandwidth and frequency responses of existing devices, making it challenging to determine the jitter immunity of semiconductor devices and ensuring compliance with communication protocols.
Innovation Solution
A method involving obtaining samples of a jitter-modulated signal, forming a histogram, fitting a probability distribution function that combines sinusoidal and random components, and characterizing jitter from these parameters to accurately determine jitter characteristics, using a test system with a programmable jitter injection module and a sampling device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If phase noise analyzers or real time oscilloscopes are used to measure jitter, then the measurement process is simple, but the bandwidth and frequency response are limited making them unsuitable for high frequency measurements
Solution Approach 1:
The patent uses a sampling oscilloscope as an intermediary device to measure jitter at high frequencies. The sampling oscilloscope captures samples of the signal at different time points, which are then processed to extract jitter characteristics. This intermediary approach enables high-frequency jitter measurement without requiring the entire measurement system to operate at the full signal frequency, thus achieving both high frequency capability and practical operability.
Solution Approach 2:
The patent replaces direct time-domain jitter measurement with a sampling-based approach combined with histogram analysis. Instead of directly measuring the continuous signal waveform with traditional oscilloscopes, the system takes discrete samples and uses statistical methods (histogram formation and probability distribution fitting) to characterize jitter. This substitution enables accurate high-frequency jitter measurement by converting a time-domain problem into a statistical analysis problem.
2Extent of automation
If automated test equipment with jitter injectors is used to characterize jitter immunity, then the measurement can be automated, but verification of the jitter injector's accuracy becomes complex
Solution Approach 1:
The patent implements a feedback mechanism where the sampling oscilloscope measures the actual jitter produced by the jitter injector and compares it to the programmed jitter amount. The system forms histograms of the measured signal, fits probability distribution functions, and extracts jitter characteristics to verify whether the jitter injector is producing the correct amount of jitter. This closed-loop feedback enables automated verification of jitter injector accuracy.
Solution Approach 2:
The measurement system uses itself to verify its own components. The sampling oscilloscope and histogram analysis apparatus that are part of the automated test equipment are used to verify the accuracy of the jitter injector within the same system. This self-service approach simplifies the overall verification process by using existing system resources rather than requiring separate external verification equipment.
3Ease of manufacture
If traditional jitter measurement methods are used, then the equipment is readily available, but the measurements are inaccurate for high frequency signals above 10 GHz
Solution Approach 1:
The patent employs dynamic sampling where the sampling rate and timing are adjusted based on the signal frequency being measured. The sampling oscilloscope can adapt its sampling parameters to accommodate different signal frequencies, making the same equipment suitable for a wide range of frequencies including high frequencies above 10 GHz. This dynamic adaptation allows readily available equipment to achieve high-frequency measurement capability.
Solution Approach 2:
The patent changes the measurement parameters by using statistical moment analysis of the signal samples rather than direct time-domain measurement. By forming histograms and fitting probability distribution functions, the system extracts jitter characteristics through parameter analysis rather than direct observation. This parameter change enables accurate high-frequency jitter measurement using equipment that would otherwise be inadequate for direct high-frequency observation.
Data Source
AI summary
A system and method for characterizing the jitter of a periodic signal. Samples of the signal are taken with a sampling device. A set of samples representing a particular value of the signal in multiple cycles of the periodic signal is collected. Those values are formed into a histogram. The histogram is matched to a probability distribution function. By identifying parameters that shape the probability distribution function to match the histogram of actual samples, characteristics of the jitter are determined. This technique may be employed as part of the calibration or verification of the jitter injection instrument such as might be used for testing semiconductor devices. Measurements may be made with a sampling device that is calibrated to NIST standards. In this way, the jitter measurements become NIST traceable.