International Business Machines Corporation

Robert Dean Adams

John P Connor

Luigi Ternullo, Jr

Garrett Stephen Koch

Roy Childs Flaker

George Maria Braceras

Donald Albert Evans

James J Covino

Alan L Roberts

Jose Roriz Sousa

Howard L Kalter

Erik L Hedberg

Kevin A Batson

Phillip J Nigh

James W Dawson

Patrick R Hansen

Fred John Towler

Henry A Bonges, Iii

Kenneth S Gray

Stuart D Rapoport

Edmond S Cooley

Frederick G Adams

True and complement data signals are provided to a multiplexer, which selects one of them based on a selection signal for capture by a single scannable latch in response to a clock signal. The scannable latch then provides the captured signal for testing by testing logic.

Method and apparatus for testing differential signals

A testing device for slowly bleeding charge away from a primary node in a dynamic logic circuit. A properly functioning keeper device in the dynamic logic circuit will maintain the primary node in a precharged state even in the face of this bleeding device. If the logic circuit output flips after the bleeder device begins bleeding charge, a defective keeper device is thereby identified.

Testing method for dynamic logic keeper device

A logic gate is provided that comprises a sensing circuit coupled to a test output and to an internal node of the logic gate. The sensing circuit is adapted to sense a voltage on the internal node and to output a signal indicating a level of the voltage. The sensing circuit is not used during normal operation of the logic gate and preferably comprises only a single FET that is directly coupled to both the internal node and to the test output. The logic gate also preferably comprises a pre-charge circuit for pre-charging the test output to a predetermined voltage level prior to testing. An IC chip may be formed from a plurality of the logic gates wherein each logic gate comprises a sensing circuit coupled to a test output and to an internal node of the logic gate. Each sensing circuit may be coupled to the same test output or to a unique test output for the sensing circuit's logic gate. The sensing circuits are not used during normal operation of the IC chip.

Fault identification by voltage potential signature

A method of testing a first memory such as a RAM having data storage at a plurality of individually addressable storage locations is provided. A portion of the address for the addressable locations of the first memory is supplied as an output from a second memory such as a CAM. The second memory includes a decoder to provide a decoded address as input signals to the second memory. During the testing, first memory specific addresses are provided to the decoder as input. These first memory specific addresses are decoded by the decoder and are gated as input signals to address the first memory. In this way, the decoder which in normal operation provides decoded input signals to the CAM is used to provide input signals to the RAM, thus obviating the need for any scan chain latches surrounding the RAM. This enables conventional testing apparatus to provide the necessary test protocol for the RAM through the decoder normally used by the CAM.

Testing associative memory

A memory Array Built-In Self-Test (ABIST) circuit is disclosed that will test a multi-port memory array. A programmable pattern generator for the ABIST circuit allows for different R/W data operations to be performed at the same or adjacent address locations within a multi-port memory array. The programmable pattern generator comprises a data generator, a read/write controller, and an address counter, each having the same number of outputs as ports of the multi-port memory array. The programmable pattern generator also comprises a frequency controller. The data generator is programmed with the appropriate data patterns for the memory array, and the read/write controller is programmed with the appropriate read/write patterns for the memory array. The address counter is to provide the same or different addresses on each port of the multi-port array, and the frequency controller is programmed with the appropriate frequency information to determine the number of read/write operations per cell in the memory array. The combination of programmable data, programmable read/write sequences, programmable address counter, and programmable frequency allows for determistic testing of a multi-port memory array, a plurality of single-port memory arrays, or a combination thereof by providing unique read/write sequences to the same or to adjacent memory locations.

Memory array built-in self test circuit for testing multi-port memory

A topology for arranging a plurality of transistors between a signal source and an off-chip receiver, using a single power supply voltage. A pass through NFET has a gate controlled by a network comprised of two transistors arrayed between the power supply voltage and the drain of the NFET, which limits overshoots to the power supply voltage and reduces undershoots. Further reduction of undershoots is accomplished by an additional network of transistors, optimally including a PFET in series with the pass through NFET.

Dynamic dielectric protection circuit for a receiver

An ABIST circuit for testing a memory array has a blanket write subcycle (WC), an RC3 subcycle, and an RC4 subcycle. The ABIST circuit includes a programmable pattern generator that provides eight programmable data bits, eight programmable read/write bits, and two programmable address frequency bits to determine the specific test patterns applied to the memory array. The address frequency bits determine how many memory cycles will be performed on each cell of the memory array. In X1 mode, only one memory cycle is performed on each cell during any given subcycle. In X2 mode, two memory cycles are performed on each cell, allowing a cell to be written, then subsequently read in the same subcycle. In X4 mode, four memory cycles are performed on each cell, and in X8 mode, all eight bits of read/write and data are used on each cell, resulting in eight memory cycles for each cell within the memory array.

Memory array built-in self-test circuit having a programmable pattern

The present invention provides a device for testing memory having write cycles and read cycles. A BIST state machine changes the data applied to the memory's DI port during read cycles to a value different from that of the data stored in the currently addressed memory location. The BIST-generated expect data also is at a different value from that of data at the memory's DI port and at the same value as the data stored at the current memory address location during read operations. With this arrangement, flush through defects can be detected which would not have been detectable by prior BIST machines.

Test converage of embedded memories on semiconductor substrates

An ABIST circuit for testing a memory array has a blanket write subcycle (WC), an RC.sub.3 subcycle, and an RC.sub.4 subcycle. The ABIST circuit includes a programmable pattern generator that provides eight programmable data bits, eight programmable read/write bits, and two programmable address frequency bits to determine the specific test patterns applied to the memory array. The address frequency bits determine how many memory cycles will be performed on each cell of the memory array. In X1 mode, only one memory cycle is performed on each cell during any given subcycle. In X2 mode, two memory cycles are performed on each cell, allowing a cell to be written, then subsequently read in the same subcycle, In X4 mode, four memory cycles are performed on each cell, and in Xg mode, all eight bits of read/write and data are used on each cell, resulting in eight memory cycles for each cell within the memory array.

A method and circuit are provided to detect if any bit stored in a given location in a memory is different from the data expected. The circuit includes logic to read each of the bits stored in the cells at given locations from memory and to generate a fail signal based on the data expected to be stored if the stored data is different from the expected data. The circuit also preferably includes logic to compare the True data and expect data read from each cell and generating the fail signal if they are the same. Additional logic circuitry is also preferably provided which determines if a node of the circuit remains in a precharged condition.

Method and apparatus to determine erroneous value in memory cells using

A test method and structure is provided to determine the end count of a predetermined succession or series of binary numbers wherein one number and its relation in the succession to the end count number is known. The structure includes a circuit for generating a binary digit output and a device for storing at least a portion of the said one number which preferably is the penultimate number in a sequential series. A succession of binary numbers is generated as output of the circuit. the outputted numbers are compared to the portion of the stored number. A READY signal is outputted when the stored number compares with the outputted number. On a subsequent cycle, a control signal is generated when the generated number following the READY signal corresponds to the end count number. The inventor also contemplates programmable end count numbers.

Rapid compare of two binary numbers

An associated memory structure having a plurality of memories amenable for testing and a method of testing the memories is provided. First and second memories are formed, wherein data in the first memory provides a basis for at least a portion of the input to the second memory during functional operation of two memories. Preferably, an output latch for receiving the output test data from the first memory is provided. Means are provided for loading the first memory with data which is utilized as a basis for providing at least a portion of the input to the second memory. An access path from the output port of the first memory to the input port of the second memory allows use of the data in the first memory to generate at least a portion of the input to the second memory. The first memory is first tested independently of the second memory. Thereafter, the first memory is loaded with preconditioned data that is used as a basis for inputs to the second memory during testing of the second memory. The second memory is then tested by generating inputs to the first memory during testing of the second memory. Thus, outputs of the first memory constitute at least a portion of test data inputted to the second memory. A latch is provided to capture the output of the test data from the second memory.

Using one memory to supply addresses to an associated memory during

The present invention, provides a single BIST which can test various memories of different sizes, types and characteristics by using a state machine to select and generate all patterns required for testing all of the memories on the chip, and impressing all of the data, including expected data, and address information on all of the memories simultaneously. The BIST also generates unique (separate) control signals for the various memories and impresses these control signals on the various memories. The BIST selectively asserts the various control signals so as to apply (write) the data and to read and capture (load result) failure information only to/from those memories whose unique controls are asserted. Selective assertion of a memory's write enable signal prevents multiple writes to a location which can potentially mask cell write and leakage defects while selective assertion of a memory's load result signal is performed only when valid memory output data is expected so as not to capture false error information. The control signals instruct those memories that do not use a particular sequence of inputs or any portion of a given sequence of inputs to 'ignore' such signals, thereby generating the necessary signals to form the test patterns for each and every memory, the data and address information for those patterns, the control signals to write and read each memory, and capture error information for that particular memory. Hence, a single BIST can be used to test a multiplicity of memories of different sizes and different types.

BIST tester for multiple memories

A redundancy system formed on a semiconductor chip is provided which includes circuits for testing a memory array to locate a faulty element therein, a register for storing an address of the faulty element and electrical fuses blown in response to binary digits of the address stored in the register upon application of an enable signal from a single input to the semiconductor chip. The enable signal passes through logic circuits on the chip such that the fuses cannot be programmed or blown unless the enable signal is present. An address decoder coupled to outputs from the fuses substitutes a redundant element for the faulty element.

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Essex Junction, VT, United States of America

Robert Dean Adams