Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2000-02-09
2001-10-09
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S052000, C327S065000
Reexamination Certificate
active
06300804
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to automatic test equipment and more particularly a differential comparator having dispersion reduction circuitry for use in automatic test equipment.
BACKGROUND OF THE INVENTION
Differential comparators are often used to detect differential signals and to compare the detected quantity to some predefined threshold. Conventional differential comparators generally employ a multi-stage differential construction
20
, as shown in FIG.
1
. The stages correspond to a methodology of first detecting the differential voltage, then comparing the detected voltage to a reference voltage. The first stage, or input stage, comprises a differential amplifier
22
that includes respective differential inputs V
2
and V
1
and produces an output voltage (V
2
−V
1
) proportional to the detected difference signal. The output is fed for comparison as an input to a second stage, or threshold stage, that includes a differential amplifier
24
for comparison to a reference voltage Vref at a second input of the second stage. While the multi-stage configuration works well for its intended low performance applications, at high data rates the multi-stage structure generally becomes overly susceptible to a signal inaccuracy known as dispersion.
Dispersion is often recognized by those skilled in the art as the change in response time, or change in propagation delay, between the input and output of an electronic device. In contrast to a fixed propagation delay that can be measured, predicted and repeatedly calibrated out of a measurement with high accuracy, a changing propagation delay creates prediction inaccuracies with signal timings that may undesirably affect the overall measurement accuracy of the comparator. Typically, dispersion varies as a complex function of threshold signal level, frequency, and temperature.
What is needed and heretofore unavailable is a differential comparator that minimizes the effects of dispersion. The need also exists for the implementation of such a comparator in the pin electronics of a semiconductor tester to maximize accuracy and performance. The differential comparator of the present invention satisfies these needs.
SUMMARY OF THE INVENTION
The differential comparator of the present invention provides high accuracy semiconductor device testing for high bandwidth applications while minimizing dispersion effects on differential signals. This correspondingly results in higher tester accuracy and performance.
To realize the foregoing advantages, the invention in one form comprises a differential comparator including first and second input amplifier circuits. The input amplifier circuits have respective signal input terminals for receiving respective first and second complementary input signals and respective output terminals. The first and second input amplifier circuits cooperate to produce a difference signal. Reference signal circuitry is coupled to the input amplifier circuits and is operative to produce a predetermined reference signal for comparison to the difference signal. The input amplifier circuits and the reference signal circuitry cooperate to define a single stage.
In another form, the invention comprises a method of comparing a differential signal defined by complementary first and second signals to a reference signal. The method includes the steps of differentially amplifying the first and second signals with a differential amplifier having complementary first and second input amplifier circuits with respective complementary signal inputs for receiving the first and second signals; impressing a reference signal across the reference signal circuit; and comparing the detected difference signal to the reference signal.
Other features and advantages of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.
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Web Page Literature, LTX Corp., “HiPerPhase Differential I/O: How Fusion meets the challenges of testing digital signals”, date unknown.
Kreisman Lance M.
Lam Tuan T.
Nguyen Hiep
Teradyne, Inc.
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