Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-07-15
2002-12-03
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S1540PB
Reexamination Certificate
active
06489797
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
REFERENCE TO MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
The present invention relates to devices for generating and measuring electrical outputs, and more particularly, to voltage and current sources for generating and measuring electrical outputs having variable current and/or voltage characteristics, wherein the outputs are provided to electrical devices being evaluated by a testing system.
A testing system for testing electrical devices such as integrated circuits typically includes a test head connected to a mainframe system by a section of cable. The test head may also be mounted to a manipulator arm to provide a mechanical advantage to assist the user in moving the test head. The device under test (hereinafter referred to as “DUT”) mounts on test head such that electrical leads of the DUT are electrically coupled to corresponding test leads of the test head. In general, the mainframe system evaluates the DUT by providing a variety of signals to the DUT and evaluating how the DUT responds to those signals. It is also useful to ascertain how the DUT alters the signals provided by the mainframe system, especially for test signals whose voltage and/or current characteristics exhibit a wide dynamic range. For example, the mainframe system may arrange to provide a 5 volt test signal to an input of the DUT, then evaluate the state of the DUT output signals, along with the current draw of the DUT on that 5 volt test signal. How the DUT alters the test signal can provide significant information regarding the functionality of the DUT. In some test situations, a DUT may require a particular voltage or current input in addition to the control signals. For example, a semiconductor switch may be used to control the flow of a relatively large amount of current for a motor or other high current sink. Such a semiconductor switch may not only include control inputs and diagnostic outputs, but also an input that receives the relatively large electrical flow from a high power source, and an output that directs the electrical flow to the current sink. When the DUT includes this sort of device, the test system must not only supply low level control signals, but also higher power inputs.
In many prior art test systems, all such test signals between the mainframe system and the test head must travel via the section of cable connecting them. The testing system also generally supplies operating power to the DUT. Many such systems include DUT power supplies in the mainframe so that power delivered to the DUT travels through the cable. During the testing procedure, advanced, state-of-the-art DUTs often transition from a standby mode to an active mode, such that the DUT current draw can vary by a factor of 500 or more (e.g., 0.02 A to 10 A). These DUT power transitions can occur in just a few clocks cycles, which translates to a large current slew rate. Hereinafter, the term “voltage and current source” is used to generally describe a power supply (i.e., a continuous power source), a relatively high capacity voltage and current source (i.e., a pulsed power source, such as that described above for driving a semiconductor switch). In prior art systems, these two functions are typically implemented by two individual components because of the unique nature of each of the functions, thus affecting the size, power requirements, cost and reliability of the overall test system.
To provide convenient access to the DUT, as well as relatively free manipulation of the entire test head, the section of cable between the test head and the electrical instruments residing within the mainframe may be in excess of ten feet. A long cable corresponds to large series inductance, which introduces a low pass filter (hereinafter referred to as “LPF”) between the power supply and the DUT. The LPF created by the cable removes high frequency components, so that the transition edges of signals transmitted via the cable are effectively slowed. Thus, the practical consequence of the cable being between the test head and the mainframe is that the DUT does not receive a true representation of the signal that the mainframe generates. In prior art systems, the location of the voltage and current source, especially one having a wide dynamic range (with respect to voltage and/or current; e.g., current transitions from microamps to amps), is generally irrelevant, because the bandwidth (hereinafter referred to as “BW”) of most such devices isn't high enough to be limited by the LPF. In other words, typical prior art voltage and current sources simply can't keep up with the current transition requirements of modem DUTs, so no motivation exists for placing such a device closer to the DUT.
Some prior art systems include a voltage and current source at an intermediate location between the mainframe and the test head, often somewhere nearer to the test head than the mainframe. A cable connecting the voltage and current source to the test head is present, but it is typically significantly shorter than the ten feet as described above. Although such sources are specifically designed for higher bandwidth, the cable still imposes limitations on the test signal transitions.
There are a number of factors that have traditionally discouraged mounting voltage and current sources within a test head, nearer to the DUT, thus reducing the intervening cable length. One of these factors includes cooling considerations. A voltage and current source capable of providing the amount of power that the DUT requires typically dissipates a significant amount of heat. This dissipated heat adversely affects the DUT, along with the associated electronics, if the heat is not efficiently removed from the test head. Traditional, air based cooling systems are generally not efficient enough to remove this heat, so designers often locate these power supplies outside of the test head.
Another factor discouraging voltage and current source in the test head is that a power supply capable of providing the amount of power that the DUT requires typically occupies a significant amount of physical space. This is especially true for linear mode power supplies, which are often used for DUT supplies because of the high quality regulation they provide. Thus, designers typically conserve test head space by locating the DUT power supply outside of the test head. Until very recently, the current input requirements of integrated electrical devices have been relatively modest, typically within a few amps. As more functionality is added and clock rates increase, the current input requirements of integrated electrical devices are increasing dramatically. Such high capacity continuous current and voltage sources are typically physically large, and so can not be included in the limited space of a test head. In some applications, large, continuous output voltage and current sources are used for their high output capability, even though the nature of the application does not require a continuous output. Further, a relatively recent practice is to design integrated electrical devices with integrated semiconductor power switches. Thus, such a device requires the same high current output source that a stand-alone semiconductor switch (described herein) requires.
Another factor weighing in favor of locating the voltage and current source outside of the test head is essentially organizational in nature. The group that tests highly integrated very large scale integration (hereinafter referred to as VLSI) digital devices is usually physically separate from the mixed signal test group. Although the VLSI group often encounters the aforementioned fast transition problem, they do not have the analog expertise to solve the problem. Conversely, although the mixed signal group possesses the expertise to solve such a problem, they are typically not aware of the problem.
A category of prior art voltage and current sources can provide a predetermined output profile i
MacDonald Bruce
Perkins Philip
Kerveros J
LTX Corporation
McDermott & Will & Emery
Metjahic Safet
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