Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-03-15
2001-08-28
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S1540PB, C327S068000
Reexamination Certificate
active
06281699
ABSTRACT:
This invention relates generally to detector circuits for automatic test equipment, and more particularly to digital detector circuits for receiving differential signals from a device under test (DUT).
BACKGROUND OF THE INVENTION
Automatic test equipment (ATE) plays a significant role in the manufacture of semiconductor devices. Manufacturers generally use automatic test equipment—or “testers”—to verify the operation of semiconductor devices at the wafer and packaged device stages of semiconductor manufacturing processes. By testing semiconductor devices at these stages, manufacturers are able to reject defective devices early in the manufacturing process. Early detection of faults eliminates costs that would otherwise be incurred by processing defective parts, and thus reduces the overall costs of manufacturing. Manufacturers also use ATE to grade various specifications of devices. Devices can be tested and categorized within different bins that correspond to different levels of performance in significant areas, for example, speed. Parts can then be labeled and sold according to their levels of performance.
A tester generally includes a host computer that runs software for controlling various tests of the semiconductor devices. The software prescribes signal characteristics for applying stimuli to the DUT (device under test) and for sampling responses from the DUT. A pattern generator translates the signal characteristics into timing signals. Specialized circuitry called pin electronics then converts the timing signals into actual stimuli and timing windows.
Pin electronics are generally grouped among different circuits of the ATE called “channels.” The channels provide a signal interface between the tester and the DUT. Each channel typically includes a driver circuit and a detector circuit. The present invention pertains to a new type of detector circuit for use in pin electronics channels of ATE.
Detector circuits are used in automatic test equipment to sample digital signals generated by a device under test.
FIG. 1
illustrates a highly simplified ATE system. As shown in
FIG. 1
, a host computer
118
runs a test program for testing a DUT
122
via a plurality of digital channels, shown generally as channels
110
a
-
110
e.
Each of the plurality of channels
110
a
-
110
e
has an I/O terminal, respectively
120
a
-
120
e
, that can be coupled to the DUT
122
. Each channel typically includes a driver circuit
112
, a detector circuit
114
, and channel overhead circuitry
116
. The channel overhead circuitry
116
typically includes digital-to-analog converters (DACs) for establishing drive levels for the driver circuit
112
and for establishing detect levels for the detector circuit
114
. The channel overhead circuitry
116
typically also controls the driver circuit
112
to apply signal edges at precise instants in time, and controls the detector circuit
114
to sample input signals at precise instants in time. The channel overhead circuitry
116
may also include memory for storing digital patterns to be applied to the DUT by the driver circuit
112
and for storing digital states sampled by the detector circuit
114
.
Traditionally, the role of detector circuits in ATE has been for sampling single-ended signals, i.e., for determining whether a single-ended digital signal is in a high logic state, a low logic state, or a logic state between high and low (a “between” state). We have recognized, however, that there is also a need for sampling differential signals. In contrast with single-ended signals, which provide one signal for conveying a digital logic state with reference to a digital ground, differential signals convey digital logic states as differences between two signals, neither one of which is digital ground.
Rapidly developing technologies such as IEEE 1324 (Firewire) and LVDS (Low Voltage Differential Signaling) extensively use differential digital communication. These technologies impose strict specifications on differential signals. A need has arisen, therefore, for testing the specifications of differential digital signals using ATE.
SUMMARY OF THE INVENTION
With the foregoing background in mind, it is an object of the invention to test differential digital signals effectively and accurately.
To achieve the foregoing object and other objectives and advantages, a detector circuit for sampling digital signals from a device under test receives first and second differential input signals. The first and second differential input signals are coupled through respective impedances to an input of a measurement device. The measurement device generates an output indicative of whether the signal at the input of the measurement device is within a predetermined range.
According to one feature, the detector circuit also includes a differential detector having first and second inputs respectively receiving the first and second differential input signals. The differential detector generates an output indicative of whether a difference between the first and second differential input signals is within another predetermined range.
Additional objects, advantages, and novel features of the invention will become apparent from a consideration of the ensuing description and drawings.
REFERENCES:
patent: 4659997 (1987-04-01), Ferland et al.
patent: 4782290 (1988-11-01), Sakai et al.
patent: 4818934 (1989-04-01), Tamamura et al.
patent: 4885528 (1989-12-01), Tanaka et al.
patent: 5210527 (1993-05-01), Smith et al.
patent: 5579236 (1996-11-01), Tamamura et al.
patent: 5760599 (1998-06-01), Ehiro
patent: 5970074 (1999-10-01), Ehiro
patent: 6016566 (2000-01-01), Yoshida
patent: 6215324 (2000-01-01), Yoshida
Web document: “Fusion Focus”, downloaded Oct. 12, 1999 from http://www.ltx.com and http://www.ltx.com/products/hiperdif.html.
Brown Glenn W.
Hamdan Wasseem H.
Rubenstein Bruce D.
Teradyne, Inc.
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