Xilinx, Inc.

Manoj Chirania

Venu M Kondapalli

Philip D Costello

Steven P Young

Martin L Voogel

Trevor J Bauer

Jason Helge Anderson

Tien Duc Pham

Ramakrishna K Tanikella

Subodh Gupta

Robert I-Che Fu

A programmable logic block provides an improved output delay by bypassing the memory array and multiplexer structure when programmed to function as a random access memory (RAM) and a new value is written to the RAM. A programmable logic block includes memory cells, a multiplexer structure, a memory element, a bypass select multiplexer, and a control circuit. The memory cells implement a RAM driven by a write data input signal and a write enable signal. Each memory cell drives an input terminal of the multiplexer structure. Under the control of the write enable signal, a bypass select multiplexer selects either the write data input signal (in RAM mode) or the output terminal of the multiplexer structure (in another mode), and passes the selected signal to a memory element. Thus, when in RAM mode, write data is simultaneously written to a specified location in the RAM and to the memory element.

Programmable logic block having reduced output delay during RAM write processes when programmed to function in RAM mode

A method of reducing power of a circuit is described. The method includes determining at least one unused selection input associated with stages of a multiplexer tree; pulling the at least one unused selection input to a constant value; and assigning predetermined values to unused data inputs of the multiplexer tree associated with the at least one unused selection input.

Method of reducing power of a circuit

An apparatus and method to accurately simulate negative bias and temperature instability (NBTI) and its effect. According to a first simulation method, a simulation netlist is automatically scanned for any P-type devices that are in a conductive state after application of an initial condition. Each conductive P-type device is automatically replaced with an NBTI device model and a first simulation cycle is executed. After the first cycle, each conductive P-type device is again replaced with an NBTI model and a second simulation cycle is executed. In a second simulation method, only those P-type devices transitioning from a non-conductive state to a conductive state are automatically replaced with an NBTI model prior to each half cycle of the second simulation method. The first simulation method provides robustness, while the second simulation method provides worst case verification in less time as compared to the first simulation method.

Method for simulation of negative bias and temperature instability

A method of calculating power usage of a lookup table (LUT) implemented on a programmable logic device can include determining input power usage of the LUT and determining output power usage of the LUT. The method further can include determining internal power usage of the LUT. Data rates, LUT configuration, and node capacitance information can be used in determining input, output, and internal power. A measure of power usage for the entire LUT can be provided by summing the input power usage, the output power usage, and the internal power usage.

Estimating LUT power usage

A method and apparatus is provided for the implementation of a process monitor vehicle (PMV) for memory cells. The memory cell PMV is useful in characterizing drive strength of the N-type and P-type field effect transistors (FETs) that are used to implement the memory cell. The memory cell PMV may be used, for example, to measure the amount of margin available for memory cell flips and how process variation affects the memory cell write margin. The memory cell PMV is implemented as a plurality of shift register bits interconnected as a ring oscillator, where each shift register bit is comprised of a memory cell. By adjusting the drive current for each memory cell and measuring the resultant change in oscillation frequency of the ring oscillator, information may be obtained concerning process variation and its effect on memory cell performance.

Process monitor vehicle

Lookup table circuits (LUTS) having multiple stages differently optimized to balance delays through the lookup table. A first multiplexing stage is optimized for a fast path from the control input to the data outputs, while a second and subsequent stage multiplexers are optimized for a fast path from data inputs to data outputs. In some embodiments, additional delay is introduced into the control inputs of the later stages, e.g., the LUT input paths with the smallest through-delays, in order to further balance the through-delays for the lookup table.

Lookup table with relatively balanced delays

An integrated circuit including a multiplexer circuit and numerous memory cells are coupled to one another for improved performance. The multiplexer circuit includes a first input terminal and a second input terminal respectively coupled to an output of a first memory and an output of a second memory cell of the numerous memory cells. The multiplexer may also include select terminals coupled to a control signal and a complement of the control signal. An output of the multiplexer circuit is selectively coupled to one of four possible signals, where two of the four signals are the control signal and the complement of the control signal.

Integrated circuit including a multiplexer circuit

Circuits and methods of implementing flip-flops in dual-output lookup tables (LUTs). A flip-flop is implemented by programming a dual-output LUT to include a first function implementing a master latch and a second function implementing a slave latch. An output of the master latch is provided at a first output terminal of the LUT, and an output of the slave latch is provided at a second output terminal of the LUT. The output of the master latch (the first output of the LUT) is coupled to a first input terminal of the LUT, where it drives both the first and second functions. The output of the slave latch (the second output of the LUT) is coupled to a second input terminal of the LUT, where it drives the second function. A clock signal is provided to both first and second functions via a third input terminal of the LUT.

Circuits and methods of implementing flip-flops in dual-output lookup tables

Interconnect driver circuits that can be used in the interconnect structures of dynamic integrated circuits (ICs) such as dynamic programmable logic devices (PLDs). An exemplary IC includes two or more logic circuits, and two or more self-resetting interconnect driver circuits coupled between the logic circuits. Each self-resetting interconnect driver circuit includes a multiplexer circuit driving a buffer circuit. In a first state, the buffer circuit drives a first value onto the output terminal of the buffer circuit. In a second state, the buffer circuit first drives a second value onto the output terminal of the buffer circuit and then returns to the first state. Several different circuits are described in detail.

Interconnect driver circuits for dynamic logic

A lookup table (LUT) is programmable to function as a flip-flop. The LUT includes a plurality of memory cells, a plurality of transmission gates, and first and second logic gates. The transmission gates are coupled between the memory cells and an output terminal of the LUT to form a multiplexer circuit selecting one of a plurality of values stored in the memory cells and providing the selected value to the output terminal. First and second logic gates are included in two of the paths through the multiplexer, also providing first and second feedback paths within the LUT. These feedback paths enable the programmable implementation of first and second latches that form the flip-flop. Another subset of the memory cells can be optionally used to implement a function that drives the data input of the flip-flop.

Lookup table circuits programmable to implement flip-flops

A programmable logic block provides two lookup table (LUT) output signals to a general interconnect structure in an integrated circuit (IC), one output terminal of the logic block being dedicated to a first LUT output signal, and the other output terminal having a selectable input that can provide either of the two LUT output signals to the general interconnect structure. An IC includes an interconnect structure (e.g., a programmable interconnect structure) and a programmable logic block coupled to the interconnect structure. The programmable logic block includes a LUT having two output terminals. A first LUT output terminal is non-programmably coupled to the interconnect structure via a first output terminal of the logic block. Both the first and the second LUT output terminals are programmably coupled to the interconnect structure via a second output terminal of the logic block, e.g., via a programmable multiplexer selecting between the two LUT output terminals.

Programmable logic block with dedicated and selectable lookup table outputs coupled to general interconnect structure

A programmable logic block provides N-bit and M-bit (e.g., (N/2)-bit) lookahead functionality for carry chains traversing the logic block, N and M being integers greater than one. An exemplary programmable logic block includes four carry multiplexers that together form a 4-bit lookahead carry chain. The 4-bit lookahead carry chain also provides a 2-bit lookahead output after the second carry multiplexer. Alternatively, the last two bits of the 4-bit lookahead carry chain can be used as a 2-bit lookahead carry chain. In one embodiment, the programmable logic block also includes four function generators associated with the four carry multiplexers. Each function generator drives a select terminal of the associated carry multiplexer. The 4-bit and 2-bit carry chains can be programmably coupled to an interconnect structure of the PLD at the carry out output terminals. In some embodiments, an initialization value can also be provided to the 4-bit and 2-bit carry chains.

Programmable logic block with carry chains providing lookahead functions of different lengths

A programmable lookup table optionally provides two input signals and two output signals to an interconnect structure of a programmable integrated circuit when programmed to function as a random access memory (RAM). An integrated circuit includes an interconnect structure and a N-input lookup table (LUT) having input and output terminals coupled to the interconnect structure. The LUT can be configured to function as a single-bit wide RAM (e.g., a (2**N)&#xd7;1 RAM) having N input address signals coupled to the interconnect structure and one output signal coupled to the interconnect structure, or as a multi-bit wide RAM (e.g., a (2**(N&#x2212;1))&#xd7;2 RAM) having fewer than N (e.g., N&#x2212;1) input address signals coupled to the interconnect structure and at least two output signals coupled to the interconnect structure. Optionally, the LUT can also be configured as shift register logic, e.g., a 2**(N&#x2212;1)-bit shift register or two 2**(N&#x2212;2)-bit shift registers.

Programmable lookup table with dual input and output terminals in RAM mode

A programmable lookup table for an integrated circuit (IC) optionally provides two input signals and two output signals to an interconnect structure of the programmable IC when programmed to function as shift register logic. According to one embodiment, an integrated circuit includes an interconnect structure and a N-input lookup table (LUT) having input and output terminals coupled to the interconnect structure, where N is a integer. The LUT can be configured to function as a (2**(N&#x2212;1))-bit shift register having a shift in input signal and one output signal coupled to the interconnect structure, or as a two (2**(N&#x2212;2))-bit shift registers having two shift in input signals and two output signals coupled to the interconnect structure. In some embodiments, each bit of the shift register includes two memory cells of the LUT, a first memory cell functioning as a master latch and a second memory cell functioning as a slave latch.

Programmable lookup table with dual input and output terminals in shift register mode

A programmable logic block reduces output delay by bypassing a final slave latch when programmed to function as a shift register. The logic block includes memory cells, a multiplexer structure, and a bypass select multiplexer (BSM). The memory cells are coupled in series to form a shift register controlled by a shift clock, each bit including two paired memory cells implementing master and slave latches. Each memory cell drives an input terminal of the multiplexer structure. The BSM drives a select terminal of the multiplexer structure and selects one signal from each pair of the memory cells. The shift clock drives one data input terminal of the BSM. When in shift register mode, the shift clock simultaneously shifts a value in each master latch to the corresponding slave latch and selects a value from one of the master latches. The output path bypasses the slave latch of the selected bit.

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Palo Alto, CA, United States of America

Manoj Chirania