Abstract: Driver circuits are provided which also serve as termination and clamp in an IC tester. When it is to drive a port of a device under test (DUT) between two predetermined voltage levels, the driver's I/O terminal is switched between two predetermined voltage levels with an output impedance that matches the transmission line between the driver circuit and the DUT. When the DUT's port is supplying an output signal, the driver circuit can be programmed to provide one of two types of termination. If the DUT's port is specified as capable of driving the load, the transmission line between the driver circuit and the DUT is terminated by switching the driver circuit's I/O terminal to a predetermined voltage level with an impedance of Z.sub.0. If the DUT's port is not specified as being capable of driving such a termination load, the driver circuit functions like a Z-clamp circuit.

Abstract: A timing subsystem 10 including several test period generators for supplying a variety of timing signals to a device under test. Major, minor, and free-run period generators each supply various timing signals to a multiplexer 18, which selectively connects the timing signals to timing generators 20. A central processing unit 28 supplies data to the period generators and timing generators to define their respective timing signals. Timing signals generated by the major period generator 12 define the overall testing rate. The minor period generator 14 generates multiple timing signals within the periods of the major clock signals to permit higher clock rates. Timing signals that are independent of the major clock periods are generated by the free-run period generator 16. An external synchronizer circuit 26 provides a feedback loop from the device under test 22 to the major period generator. A reference driver trigger delay circuit 27 provides means for calibrating the timing generators.

Abstract: A system is disclosed which enables signals to be supplied at precisely desired times in an automatic test system. The apparatus includes a base delay memory which stores information representing the higher order bits of a time delay, while vernier memories store information relating to the lower order bits of the time delay. Offset memories enable storing calibration data. The base delay memory controls at least two counters in independent signal paths, while the vernier and offset memories control appropriate deskew units for further delaying the counter output signal as desired. The system enables sharing of resources, yet eliminates the need for repetitively loading correction data for deskew operations.

Abstract: Apparatus for delaying an electrical signal includes a sequence of stages, each for delaying the signal. A coarser stage delays the signal by multiples of a predetermined fundamental delay interval and a finer stage provides for fine adjustment of the delay. The fine stage includes an integral number N of delay elements, the total providing a delay interval greater than the fundamental delay interval, whereby the fine delay intervals compensate for fabrication tolerances to enable accurate calibration of the combined system by post-fabrication measurement. In one implementation each delay stage includes a tapped transmission line to provide delay intervals, in another a ramp generator is used.

Abstract: A system which enables signals to be supplied at precisely desired times in an automatic test system. The apparatus includes a base delay memory which stores information related to a base time delay, while a vernier memory stores information relating to timing corrections to be made to the base time delay. The base delay memory controls a counter while the correction memory controls a vernier deskew apparatus for further delaying the output signal from the counter. To prevent carries from the vernier memory from influencing the base delay memory, the most significant bit of the vernier memory is of the same significance as the least significant bit of the base delay memory. The most significant bit of the vernier memory is also connected to drive the counter, in effect providing the counter with two least significant bits, and enabling a single base delay memory to control more than one signal timing paths.

Abstract: Apparatus for delaying an electrical signal includes a sequence of stages, each for delaying the signal. A coarser stage delays the signal by multiples of a predetermined fundamental delay interval and a finer stage provides for fine adjustment of the delay. The fine stage includes an integral number N of delay elements, the total providing a delay interval greater than the fundamental delay interval, whereby the fine delay intervals compensate for fabrication tolerances to enable accurate calibration of the combined system by post-fabrication measurement. In one implementation each delay stage includes a tapped transmission line to provide delay intervals, in another a ramp generator is used.

Abstract: A formatting circuit for a high speed integrated circuit test system controls the application of timed data pulses to the input terminals of the device being tested, generates strobe signals to control comparators connected to the output terminals of the device being tested, and provides circuitry to decode error signals received from the device being tested. The formatting circuit routes all critical signal paths to the device under test over separate signal lines, thereby allowing compensation for the different propagation delay of each signal path. The input transitions and output strobe signals for the device being tested are not fixed in time with respect to the system clock, but are referenced to it. This enables drive data cycles and compare data cycles to be less dependent on the system clock, and permits them to overlap and cross test period boundaries.