Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-02-24
2001-12-11
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S763010, C324S1540PB, C714S724000, C714S727000, C714S025000, C365S200000
Reexamination Certificate
active
06329833
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to integrated circuits (ICs), and more particularly to systems and methods for testing digital integrated circuits.
BACKGROUND OF THE INVENTION
Most electronic systems include multiple digital integrated circuits (ICs), such as PLDS, ASICs, memory devices, and processors, that are mounted on printed circuit boards (PCBs). Each PCB includes a pattern of printed metal lines (e.g., copper tracks) formed on a board of insulating material. The ICs are typically soldered to the copper tracks at specific locations on the PCB, and the copper tracks provide signal paths for transmitting binary signals between the ICs of the electronic system.
Before ICs are soldered to a PCB to form an electronic system, the ICs are typically tested to verify that all of the ICs properly communicate with each other. In particular, the ICs are tested to verify that the binary output signals (logic high and logic low) from a first IC are properly interpreted at the input terminals of a second IC. This testing involves measuring the low-level input voltage (Vil) and high-level input voltage (Vih) of each IC of the system. Vil and Vih are direct current (DC) characteristics of all digital ICs. The Vil of an IC represents the maximum allowable input voltage that will be interpreted as a logic low (e.g. 0) by the IC. The Vih of an IC represents the minimum allowable input voltage that will be interpreted as a logic high (e.g., 1) by the IC. For example, a particular IC may interpret all input signals below 0.8 Volts as having logic low values, and all input signals above 2.0 Volts as having logic high values. Accurate measurement of Vil and Vih are important for predicting whether various ICs in the same electronic system can understand each other correctly.
FIG. 1
is a diagram showing a conventional system for measuring the Vil and Vih of an IC. The system requires a human operator
110
to manually control a power supply
120
using manual controls
122
and a display
125
such that power supply
120
transmits a desired test voltage from output terminal
127
to the input terminal
133
of an IC device-under-test (DUT)
130
. Input terminal
133
of DUT
130
is connected to an output terminal
138
(i.e., such that the logic input signal at input terminal
133
produces a corresponding logic output signal at output terminal
138
). Output terminal
138
of DUT
130
is probed by an oscilloscope
140
such that the output signal from DUT
130
, which is generated in response to the applied voltage from power supply
120
, is transmitted to an input terminal
142
of oscilloscope
140
. Oscilloscope
140
includes a screen
145
from which human operator
110
visually observes a graphical representation of the output signal from DUT
130
. Test data related to the Vil and Vih testing of DUT
130
is then manually entered by human operator
110
into a computer
150
using an input device (e.g., keyboard)
152
and a display
155
.
FIG. 2
is a flow diagram showing the conventional method of measuring the Vil of DUT
130
(Vih is measured in a similar manner). For Vil measurements, an initial test voltage is set to VCC (e.g., 3.3 Volts) (Step
210
). After connecting DUT
130
between power supply
120
and oscilloscope
140
, as shown in
FIG. 1
, human operator
110
manually adjusts power supply
120
to apply the initial test voltage to DUT
130
(Step
220
). The initial test voltage is significantly higher than the expected Vil for DUT
130
to assure that DUT
130
generates a logic high output signal (e.g., VCC). Human operator
110
then verifies that the output signal from DUT
130
is high by observing the graphical representation on screen
145
of oscilloscope
140
(Step
230
). When the output signal from DUT
130
is high (“N” in Step
240
), human operator
110
mentally calculates an incrementally decreased applied voltage (Step
250
). This incremental voltage is calculated by subtracting a resolution value from the previously used applied test voltage. Human operator
110
selects the resolution value (i.e., degree of accuracy). After mentally calculating the adjusted applied voltage, human operator
110
manually adjusts power supply
120
to generate the adjusted applied voltage (Step
220
) and observes the output signal from DUT
130
on screen
145
of oscilloscope
140
(Step
230
). The process of incrementally decreasing the applied voltage and observing the output signal is repeated until a logic low output signal (e.g., ground or 0 Volts) is observed on screen
145
(“Y” in Step
240
). This change in the output signal indicates that the actual Vil for DUT
130
is within the resolution range of the most recent applied voltage. This final applied voltage is then assigned as Vil for DUT
130
(Step
260
), and human operator
110
manually enters this value into computer
150
(Step
270
).
In practice, several problems are created by the conventional method of measuring vil and Vih. As indicated in
FIG. 1
, human operator
110
is used as a feedback control and must divide his attention between power supply
120
, oscilloscope
140
, and computer
150
. If the applied voltage is changed too fast, operator
110
may miss the actual Vil/Vih voltage level. Further, because human operator
110
must manually enter the Vil/Vih values into computer
150
, a rapid measurement pace may result in translation errors. Conversely, if the voltage is changed too slowly, the repetitious and meticulous measurement process becomes tedious for human operator
110
, who may then make mental errors. This problem becomes even more significant when the measurement process is used to measure Vil/Vih for multiple terminals on multiple DUTs under varying conditions of VCC and temperature. Further, the significant amount of operator time to perform these measurements can significantly increase the overall cost of an electronic system incorporating DUT
130
.
Other problems arise that are attributed to the use of oscilloscope
140
(see FIG.
1
). If the ground level of power supply
120
is not exactly the same as the ground level of oscilloscope
140
, then measurements read from screen
145
of oscilloscope
140
can be inaccurate by the difference between the two ground levels. For this reason, it is difficult to maintain a consistent and high resolution for all Vil and Vih measurements over all combinations of DUTs and terminals of an electronic system using the conventional method. This problem arises even when very expensive state-of-the-art instruments are used.
What is needed is a system and a method for measuring Vil and Vih that overcome the problems described above that are associated with the conventional system and method.
SUMMARY OF THE INVENTION
The present invention is directed to a measurement system for automatically measuring the Vil and Vih of integrated circuits (ICs). The measurement system includes a computer and a power supply that are connected to respective output and input terminals of a IC device-under-test (DUT), thereby forming a closed loop. The computer transmits a control signal to a power supply, which in turn applies a corresponding test voltage to the input terminal of an IC device-under-test (DUT). An output terminal of the DUT is connected to the parallel port of the computer. Automatic measurement of the Vil and Vih of the DUT is performed by operating the computer to systematically alter the control signal applied to the power supply, and detecting the logic state at the output terminal of the DUT. Because control signals are transmitted from, and DUT output signals read by, the computer, the need for the human operator feedback used in the conventional method is eliminated, thereby reducing the risk of error. Further, because the output signal from the DUT is transmitted to the computer, the need for the oscilloscope used in the conventional measurement system is also eliminated, thereby further reducing the possibility of measurement error.
The present invention is also directed to a method for measuring
Bever Patrick T.
Brown Glenn W.
Hamdan Wasseem H.
Xilinx , Inc.
LandOfFree
System and method for automatically measuring input voltage... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for automatically measuring input voltage..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for automatically measuring input voltage... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2586936