Method and apparatus for measuring jitter
First Claim
1. A method of characterizing jitter in a signal, comprising:
- obtaining a plurality of samples of the signal;
forming a histogram of the sample values;
fitting a probability distribution function to the histogram, wherein fitting comprises providing a plurality of probability distribution functions, each characterized by a set of parameters, and identifying one of the plurality of probability distribution functions that differs from the histogram by the smallest amount, wherein identifying comprises computing for each of the plurality of probability distribution functions an error value representative of the differences between said probability distribution function and the histogram, and identifying the probability distribution function having the smallest error value; and
determining characteristics of the jitter from parameters of the probability distribution function identified as fitting the histogram.
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Abstract
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.
22 Citations
20 Claims
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1. A method of characterizing jitter in a signal, comprising:
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obtaining a plurality of samples of the signal; forming a histogram of the sample values; fitting a probability distribution function to the histogram, wherein fitting comprises providing a plurality of probability distribution functions, each characterized by a set of parameters, and identifying one of the plurality of probability distribution functions that differs from the histogram by the smallest amount, wherein identifying comprises computing for each of the plurality of probability distribution functions an error value representative of the differences between said probability distribution function and the histogram, and identifying the probability distribution function having the smallest error value; and determining characteristics of the jitter from parameters of the probability distribution function identified as fitting the histogram. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of verifying the performance of a programmable jitter injection device, comprising:
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a) programming the jitter injection device to generate a jitter modulated signal having a programmed amount of jitter, the jitter modulated signal being modulated according to a modulating function; b) forming a histogram of times of occurrence of a value of the jitter modulated signal; c) fitting a probability distribution function to the histogram, the probability distribution function having a component proportional to a probability distribution function of the modulating function and a component proportional to a probability distribution function of a random function, wherein fining comprises providing a plurality of probability distribution functions, each characterized by a set of parameters, and identifying one of the plurality of probability distribution functions that differs from the histogram by the smallest amount, wherein identifying comprises computing for each of the plurality of probability distribution functions an error value representative of the differences between said probability distribution function and the histogram, and identifying the probability distribution function having the smallest error value; and d) characterizing jitter from the component proportional to a probability distribution function of the modulating function of the probability distribution function identified as fining the histogram. - View Dependent Claims (15, 16, 17)
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18. A test system configured for providing a signal with a programmed amount of jitter in a signal, the test system comprising:
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a reference clock; a programmable jitter injection module comprising; a phase modulator having a modulation input a signal input, and a modulated output, the modulated output being the signal input phase modulated by an amount proportional to the modulation input; a synthesizer circuit having an output generated from the reference clock, the output of the synthesizer circuit utilized as the signal input; a sampling device receiving the modulated output and providing as an output a plurality of samples of the modulated output; a computer processor receiving the plurality of samples of the modulated output, the computer processor having a program associated therewith, the program controlling the computer to analyze the samples by forming a histogram of sample values and fitting to the histogram a probability distribution function having at least one component representative of the probability distribution function of the modulation input, wherein fitting comprises providing a plurality of probability distribution functions, each characterized by a set of parameters, and identifying one of the plurality of probability distribution functions that differs from the histogram by the smallest amount, wherein identifying comprises computing for each of the plurality of probability distribution functions an error value representative of the differences between said probability distribution function and the histogram, and identifying the probability distribution function having the smallest error value. - View Dependent Claims (19, 20)
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Specification