Xilinx, Inc.

Robert D Patrie

Robert W Wells

Robert O Conn

Christopher H Kingsley

Shahin Toutounchi

Daniel Y Chung

Zhi-min Ling

Jae Cho

Shekhar Bapat

Andrew W Lai

Eric Thorne

Vincent L Tong

David L Ferguson

Gil A Speyer

Steven P Young

Trevor J Bauer

Andrew J DeBaets

Anthony P Calderone

Michael M Matera

Rick W Dudley

Steven M Trimberger

Described are methods for implementing customer designs in programmable logic devices (PLDs). The defect tolerance of these methods makes them particularly useful with the adoption of 'nanotechnology' and molecular-scale technology, or 'molectronics.' Test methods identify alternative physical interconnect resources for each net required in the user design and, as need, reroute certain signal paths using the alternative resources. The test methods additionally limit testing to required resources so devices are not rejected as a result of testing performed on unused resources. The tests limit functional testing of used resources to those functions required in the user designs.

Application-specific methods for testing molectronic or nanoscale devices

Methods of utilizing partially defective PLDs, i.e., PLDs having localized defects. A partially defective PLD is tested for compatibility with a particular configuration bitstream. If the partially defective PLD is compatible with the bitstream (i.e., if the localized defect has no effect on the functionality of the design implemented by the bitstream), a product is made available that includes both the bitstream and the partially defective PLD. In some embodiments, the bitstream is stored in a memory device such as a programmable read-only memory (PROM). In some embodiments, the product is a chip set that includes the partially defective PLD and a separately-packaged PROM in which the bitstream has previously been stored. In some embodiments, the PROM is manufactured as part of the FPGA die.

Methods of utilizing programmable logic devices having localized defects in application-specific products

Disclosed methods for utilizing programmable logic devices that contain at least one localized defect. Such devices are tested to determine their suitability for implementing selected customer designs that may not require the resources impacted by the defect. If the FPGA is found to be unsuitable for one design, additional designs may be tested. The test methods in some embodiments employ test circuits derived from a user design to verify PLD resources required for the design. The test circuits allow PLD vendors to verify the suitability of a PLD for a given customer design without requiring the vendor to understand the design.

Application-specific methods useful for testing look up tables in programmable logic devices

Disclosed are methods for utilizing programmable logic devices that contain at least one localized defect. Such devices are tested to determine their suitability for implementing selected designs that may not require the resources impacted by the defect. If the FPGA is found to be unsuitable for one design, additional designs may be tested. The test methods in some embodiments employ test circuits derived from a user's design to verify PLD resources required for the design. The test circuits allow PLD vendors to verify the suitability of a PLD for a given user's design without requiring the PLD vendor to understand the user's design.

Application-specific testing methods for programmable logic devices

Fault coverage for the programmable interconnect of a programmable logic device (PLD) is provided. A user's design is modeled, thereby determining the programmable interconnect path in the device. The user's logic design is then modified, thereby facilitating the detection of faults. Specifically, any function generators in the PLD are implemented as predetermined logic gates, thereby forming a logic gate tree design. The synchronous elements in the user's design are preserved and transformed, if necessary, to provide controllability. Then, a vector can be exercised in the new design. A first readback of the PLD can be compared to a second readback of a fault-free model of the design.

Providing fault coverage of interconnect in an FPGA

A circuit measures the signal propagation delay through a selected test circuit. The test circuit is provided with a feedback path so that the test circuit and feedback path together form a free-running oscillator. The oscillator then automatically provides its own test signal that includes alternating rising and falling signal transitions on the test-circuit input node. A phase discriminator samples the output of the oscillator and accumulates data representing the signal propagation delay of either rising or falling signal transitions propagating through the test circuit. The worst-case delay associated with the test circuit can then be expressed as the longer of the two. Knowing the precise worst-case delay allows IC A designers to minimize the guard band and consequently guarantee higher speed performance.

Built-in self test using pulse generators

A new testing method uses a field programmable gate array to emulate faults, instead of using a separate computer to simulate faults. In one embodiment, a few (e.g., two or three) known good FPGAs are selected. A fault is introduced into the design of a FPGA configuration. The configuration is loaded into the FPGAs. A test vector is applied and the result is evaluated. If the result is different from that of a fault-free configuration, the fault is caught. One application of this method is to evaluate fault coverage. A fault model that can be used in the present invention is disclosed.

Fault emulation testing of programmable logic devices

Described are methods and circuits for accurately placing signal transitions, or &ldquo;edges,&rdquo; simultaneously on two or more pins of an integrated circuit (IC). A conventional tester is connected to an integrated circuit, such as a programmable logic device. The integrated circuit is adapted to include a coincidence detector that compares the timing of edges on two input pins of the integrated circuit. The coincidence detector indicates when the two edges are coincident, allowing an operator of the tester to adjust the tester to establish coincidence. The amount of offset necessary to provide coincident edges is stored in a database for later use in deskewing edges used in subsequent tests. The integrated circuit can be a programmable logic device configured to include one or more coincidence detectors with which to place edges relative to one another on different pins.

Methods and circuits for precise edge placement of test signals

Described is a test circuit that can be instantiated on a programmable logic device to perform at-speed functional tests of programmable resources, including internal memory and routing resources. The resources to be tested are configured to instantiate a counter circuit connected to the address terminals of a linear-feedback shift register (LFSR). LFSRs are cyclic, in the sense that when clocked repeatedly they go through a fixed sequence of states. Consequently, an LFSR that starts with a known set of data has a predictable set of data after a given number of clock periods. The LFSR is preset to a known count and clocked a known number of times. The resulting count is then compared with a reference. If the resulting count matches the reference, then all of the resources used to implement the test circuit, including the memory and routing resources used to implement the LFSR, are deemed fully functional at the selected clock speed. A test circuit employing an LFSR can be duplicated many times on a given device under test to consume (and therefore test) as many resources as possible.

Methods and circuits for testing programmable logic

A circuit measures the signal propagation delay through a selected test circuit. The test circuit is provided with a feedback path so that the test circuit and feedback path together form a free-running oscillator. The oscillator then automatically provides its own test signal that includes alternating rising and falling signal transitions on the test-circuit input node. A phase discriminator samples the output of the oscillator and accumulates data representing the signal propagation delay of either rising or falling signal transitions propagating through the test circuit. The worst-case delay associated with the test circuit can then be expressed as the longer of the two. Knowing the precise worst-case delay allows IC designers to minimize the guard band and consequently guarantee higher speed performance.

Built-in AC self test using pulse generators

A circuit measures the signal propagation delay through a selected test circuit. The test circuit is provided with a feedback path so that the test circuit and feedback path together form a free-running oscillator. The oscillator then automatically provides its own test signal that includes alternating rising and falling signal transitions on the test-circuit input node. These signal transitions are counted over a predetermined time period to establish the period of the oscillator. The period of the oscillator is then related to the average signal propagation delay through the test circuit. The invention can be applied to synchronous components that might fail to oscillate by connecting the asynchronous set or clear terminal to the output terminal so that the oscillator oscillates at a frequency determined by the clock-to-out delay of those components. The configuration can thus be used to characterize synchronous and asynchronous components to provide data for predicting the timing behavior of circuits that include those or similar components.

Built-in self test method for measuring clock to out delays

A circuit measures a signal propagation delay through a series of memory elements. In one embodiment the memory elements are configured in series so that together they form a delay circuit. In another embodiment the memory elements are configured in a loop to form a ring oscillator. Each memory element propagates a signal to a subsequent memory element so that the time the signal takes to traverse all of the memory elements is proportional to the average delay induced by the individual elements. This proportionality provides an effective means for measuring the delays of those components. Various embodiments of the invention measure the speeds at which memory elements can be preset, cleared, written to, read from, or clock enabled.

Circuit for measuring signal delays in synchronous memory elements

A circuit measures the signal propagation delay through a selected test circuit. The test circuit is provided with an inverting feedback path so that the test circuit and feedback path together form a free-running oscillator. The oscillator then automatically provides its own test signal that includes alternating rising and falling signal transitions on the test-circuit input node. These signal transitions are counted over a predetermined time period to establish the average period of the oscillator. Finally, the average period of the oscillator is related to the average signal propagation delay through the test circuit. One embodiment of the invention includes a phase discriminator that samples the output of the oscillator and accumulates data representing the duty cycle of that signal. The duty cycle can then be combined with the average period of the test signal to determine, separately, the delays associated with falling and rising edges propagating through the test circuit.

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Scotts Valley, CA, United States of America

Robert D Patrie