International Business Machines Corporation

John P Connor

Luigi Ternullo, Jr

Robert Dean Adams

Garrett Stephen Koch

Patrick R Hansen

Wagdi William Abadeer

George Maria Braceras

Donald Albert Evans

Alan L Roberts

Roy Childs Flaker

James J Covino

Jose Roriz Sousa

Robert J Gauthier, Jr

Christopher Stephen Putnam

Jason Edward Rotella

Stuart D Rapoport

Stuart J Hall

Marcel J Robillard

Steven Leschuk

An ESD protection circuit including the following: one or more inverters (I, I, I), each of the one or more inverters having an input and an output; an RC network () having an output node (RCT), output node (RCT) connected with the input of at least one of said one or more inverters; a clamping device (N) joined with the output of at least one of one or more inverters (I, I, I); and a feedback device (NKP) in communication with clamping device (N) and output node (RCT) of RC network (). An RC network may include one or more resistors, and one or more decoupling capacitors. In one embodiment, feedback device (NKP) is an NFET and each of one or more inverters (I, I, I) includes a PFET and NFET pair (P/N, P/N, P/N).

Electro-static discharge protection circuit

A Sequential Gray Code to Thermometer Code decoder circuit adapted for area efficient use at each pad of an integrated circuit chip for incrementally adjusting a digitally adjustable resistance for continuous or periodic adjustment of on-chip terminations. The sequential decoder for decoding a Gray code count to a T-bit Thermometer code count is constructed of a plurality (T) of cascaded decoder cells, each cell sensing the state of only one bit of the Gray code count. The decoder cells are cascaded to from decoding-latching stages each stage responsive to an individual one of single-bit changes between consecutive counts in the Gray code. Each stage contains a decoding-latching circuit adapted to detecting and latching the occurrence of one single-bit change in the Gray code.

Area efficient, sequential gray code to thermometer code decoder

A method and apparatus for providing programmable active termination of transmission lines with substantially reduced DC power consumption.

Method and apparatus for programmable active termination of input/output devices

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

An impedance matching system and a network for impedance matching at a driver circuit output for high frequency input-output devices. The impedance matching network comprises an adjustable-length transmission line having a length adjusted in proportion to the magnitude of transients on the driver circuit output and an input impedance, which is purely reactive, and is a function of its length. The purpose of the adjustable-length transmission line is to reduce transient voltages by providing a matching impedance for the reactive component of the impedance of the receiver circuit to the driver circuit. In the preferred embodiment, the impedance matching network comprises two parallel conductive lines formed on the system card, shorted by a movable stub, and connected in parallel to the driver circuit. Optionally, the impedance matching network further comprises a control circuit which detects overshoots and undershoots on the driver circuit output and provides a control current proportional to the magnitude of overshoots and undershoots to an electromagnetic adjustment mechanism which provides a linear adjustment to the moveable stub proportional to the control current.

Termination resistance independent system for impedance matching in high speed input-output chip interfacing

Termination impedance independent system for impedance matching in high speed input-output chip interfacing

An impedance matching system and a network for automatic impedance matching at a driver circuit output for high frequency input-output devices. The impedance matching network comprises a control circuit which varies a control voltage proportionally to the frequency of voltage transients that occur on the driver circuit output, an adjustment mechanism which provides a linear motion proportional to the control voltage, and an adjustable length transmission line whose length is adjusted in proportion to the frequency of voltage transients on the driver circuit output and whose impedance, which is purely reactive, is proportional to its length. The purpose of the adjustable length transmission line is to reduce transient voltages by providing a matching impedance for the reactive component of the impedance of the receiver network to the driver circuit. In the preferred embodiment, the impedance matching network is manufactured on the same chip as the driver circuit.

On-chip automatic system for impedance matching in very high speed

A CMOS off-chip driver circuit and a method of operating the circuit are provided. The circuit has two pull-down transistors and two pull-up transistors, each pull-up transistor has a gate. A voltage source provides voltage at a logic-high output voltage of approximately 3.3 volts. An output terminal is provided. Initially, a logic-low output voltage is applied to the gate of each of the two pull-up transistors. A condition is detected in which the voltage of the output terminal is greater than a predetermined threshold voltage. The predetermined threshold voltage is between approximately 2.5 volts and approximately 3.3 volts. The voltage applied to the gate of each of the pull-up transistors is raised to an intermediate level that is greater than the logic-low output voltage and less than the logic-high output voltage while the condition is detected. The intermediate level may be approximately 1.5 volts. A clamping mechanism is provided for sinking current from the output terminal to the voltage source, when the voltage of the output terminal is greater than the logic-high output voltage. The clamping mechanism sources current to the output terminal from a ground conductor that provides the logic-low output voltage to the pull-down transistor, when the voltage of the output terminal is less than the logic-low output voltage.

Method and apparatus for protecting circuits subjected to high voltage

An off-chip receiver circuit for interfacing an integrated circuit of a 2.5 Volt CMOS technology to a 3.3 Volt LVTTL bus. The off-chip receiver includes protection circuitry for preventing overstressing of the gate oxide caused by undershoot/overshoot peaks of -1 volt to 6 volts on the input.

Receiver input voltage protection circuit

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.

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Burlington, VT, United States of America

John P Connor