Test system with differential signal measurement
First Claim
1. A method of performing a measurement on a differential signal, comprising:
- a) providing each leg of the differential signal to an input of a comparator having at least a first and second input;
b) introducing a plurality of bias levels into the comparison, whereby the output of the comparator is a first logical value when the value at the first input exceeds the value at the second input by the bias level;
c) taking a plurality of sets of samples of the output of the comparator, with a set of samples for each of the bias levels, each of the samples in each of the sets correlated in time to a point on the waveform;
d) selecting a set of samples having values with a predetermined percentage of a predetermined logical value; and
e) associating the bias value used to take the samples in the selected set with the value of the differential signal at the point on the waveform.
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Accused Products
Abstract
A test system with easy to fabricate hardware to make measurements on differential signals. The two legs of a differential signal are applied to a comparator. A variable bias is introduced into the comparison operation. By taking multiple measurements with different bias levels, the level of the differential signal may be determined. The time of measurements relative to the start of the signal can be varied to allow plots of the signal to be made. Variability of the signal caused by noise can be measured by collecting sets of data points with the same bias level at the same relative time. Circuitry for introducing bias into the comparison is disclosed that allows measurements to be made with a pre-packaged, commercially available high speed comparator.
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Citations
24 Claims
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1. A method of performing a measurement on a differential signal, comprising:
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a) providing each leg of the differential signal to an input of a comparator having at least a first and second input;
b) introducing a plurality of bias levels into the comparison, whereby the output of the comparator is a first logical value when the value at the first input exceeds the value at the second input by the bias level;
c) taking a plurality of sets of samples of the output of the comparator, with a set of samples for each of the bias levels, each of the samples in each of the sets correlated in time to a point on the waveform;
d) selecting a set of samples having values with a predetermined percentage of a predetermined logical value; and
e) associating the bias value used to take the samples in the selected set with the value of the differential signal at the point on the waveform. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An automatic test system suitable for making measurements of a differential signal applied as an input to the test system, the test system having a measurement circuit comprising:
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a) a comparator having;
i) a first and second signal input terminals ii) an output providing a logical signal indicating the results of a comparison; and
iii) a timing input controlling the time at which a comparison is made;
b) means for biasing the comparison by a variable amount in response to a control signal;
c) control circuitry providing a timing signal connected to the timing input of the comparator and a control signal to the means for biasing; and
d) data analysis circuitry having an input coupled to the output of the comparator, the data analysis circuitry determining parameters of the differential signal from the output of the comparator. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification