Hewlett Packard Enterprise Development LP

Can Li

Catherine Graves

John Paul Strachan

Thomas Van Vaerenbergh

Dejan S Milojicic

Kimberly Keeton

Kivanc Ozonat

Systems are methods are provided for implementing an analog content addressable memory (analog CAM), which is particularly structured to allow for an amount of variance (fuzziness) in its search operations. The analog CAM may search for approximate matches with the data stored therein, or matches within a defined variance. Circuitry of the analog CAM may include transistor-source lines that receive search-variance parameters, and/or data lines that receive search-variance parameters explicitly within the search input data. The search-variance parameters may include an upper bound and a lower bound that define a range of values within the allotted amount of fuzziness (e.g., deviation from the stored value). The search-variance parameters may program (using analog approaches) the analog CAM to perform searches having a modifiable restrictiveness that is tuned dynamically, as defined by the input search-variance. Thus, highly efficient hardware for complex applications involving fuzziness are enabled.

Methods and systems for an analog cam with fuzzy search

An analog error correction circuit is disclosed that implements an analog error correction code. The analog circuit includes a crossbar array of memristors or other non-volatile tunable resistive memory devices. The crossbar array includes a first crossbar array portion programmed with values of a target computation matrix and a second crossbar array portion programmed with values of an encoder matrix for correcting computation errors in the matrix multiplication of an input vector with the computation matrix. The first and second crossbar array portions share the same row lines and are connected to a third crossbar array portion that is programmed with values of a decoder matrix, thereby enabling single-cycle error detection. A computation error is detected based on output of the decoder matrix circuitry and a location of the error is determined via an inverse matrix multiplication operation whereby the decoder matrix output is fed back to the decoder matrix.

Analog error detection and correction in analog in-memory crossbars

Systems and methods for an optical ternary content addressable memory (TCAM) are provided. The optical TCAM implements a time-division multiplexing (TDM) based encoding scheme to encode each bit position of a search word in the time domain. Each bit position is associated with at least two time slots. The encoded optical signal comprising the search word is routed through one or more modulators configured to represent a respective TCAM stored word. If a mismatch between at least one bit position of the search word and at least one TCAM stored word occurs, a photodetector or photodetector array will detect light.

Time division multiplexing (TDM) based optical ternary content addressable memory (TCAM)

An analog content addressable memory (aCAM) that enables parallel searching of analog ranges of values and generates analog outputs that quantify matches between input data and stored data is disclosed. The input data can be compared with the stored data, and the input data can be determined to match the stored data based on a value associated with the input data being within a range associated with the stored data. The aCAM can generate an analog output that represents a number of matches and a number of mismatches between the input data and the stored data. Based on the analog output, whether the input data matches the stored data and a degree to which the input data matches the stored data can be determined.

Analog content addressable memory with analog input and analog output

Methods and systems for an analog CAM with fuzzy search

Examples described herein relate to a decision tree computation system in which a hardware accelerator for a decision tree is implemented in the form of an analog Content Addressable Memory (a-CAM) array. The hardware accelerator accesses a decision tree. The decision tree comprises of multiple paths and each path of the multiple paths includes a set of nodes. Each node of the decision tree is associated with a feature variable of multiple feature variables of the decision tree. The hardware accelerator combines multiple nodes among the set of nodes with a same feature variable into a combined single node. Wildcard values are replaced for feature variables not being evaluated in each path. Each combined single node associated with each feature variable is mapped to a corresponding column in the a-CAM array and the multiple paths of the decision tree to rows of the a-CAM array.

Hardware accelerator with analog-content addressable memory (a-CAM) for decision tree computation

Encoding of domain logic rules in an analog content addressable memory (aCAM) is disclosed. By encoding domain logic in an aCAM, rapid and flexible search capabilities are enabled, including the capability to search ranges of analog values, fuzzy match capabilities, and optimized parameter search capabilities. This is achieved with low latency by using only a small number of clock cycles at low power. A domain logic ruleset may be represented using various data structures such as decision trees, directed graphs, or the like. These representations can be converted to a table of values, where each table column can be directly mapped to a corresponding row of the aCAM.

Accelerating constrained, flexible, and optimizable rule look-ups in hardware

Systems, devices, circuits, methods, and non-transitory computer readable media that enable storing and searching arbitrary segments of ranges of analog values are disclosed. Various analog content addressable memory (aCAM) circuit implementations having the capability to store and search outside of a range of values, within any of multiple disjoint ranges, or outside of multiple ranges are disclosed. The disclosed aCAM circuit implementations make searching for complex input features more flexible and efficient, thereby yielding a technological improvement over conventional solutions. In some implementations, an aCAM may include multiple pull-down transistors connected in series to a match line that is pre-charged, in which case, the aCAM detects a match if the match line is not discharged by the pull-down transistors, which occurs if at least one pull-down transistor is in an OFF state. In other implementations, an aCAM includes pass gates connected to a match line to detect a match.

Analog content addressable memory for storing and searching arbitrary segments of ranges

Examples disclosed herein relate to digital hash code generation. A digital hash code generating device comprising a plurality of variable conductance elements. Each variable conductance element is coupled to a selected row line and to a selected column line of a crossbar array. Each variable conductance element comprises a conductance from a stochastic distribution of conductance. A plurality of comparator elements and each comparator element is connected to a set of at least two column lines. The plurality of comparator elements generates a hash code in response to a vector input applied to the plurality of row lines of the crossbar array.

Generating hash codes for locality sensitive hashing

An analog content addressable memory cell includes a match line, a high side, and a low side. The high side encodes a high bound on a range of values and includes a first three terminal memory device. The first three terminal memory device includes a first gate that sets a high voltage bound of the first three terminal memory device. Specifically, an input voltage applied at the first gate of the first memory device, if higher than the high voltage bound, turns the first memory device ON which discharges the match line. Similarly, the low side encodes a lower bound on a range of values and includes a second three terminal memory device. The second three terminal memory device includes a second gate that sets a low voltage bound of the second three terminal memory device. Specifically, an input voltage applied at the second gate of the second memory device, if lower than the low voltage bound, turns the first memory device ON which discharges the match line.

Analog content addressable memory utilizing three terminal memory devices

Systems and methods for an optical ternary content addressable memory (TCAM) is provided. In various embodiments, one or more search words can be encoded in a multi-wavelength input signal. Each bit position associated with a set of wavelengths of the input signal, each wavelength corresponding to a logic value. A plurality of copies of the input signal can be coupled to an optical search engine comprising a plurality of rows of stored words. In various embodiments, the search word may be encoded in the amplitude of a single wavelength. Each bit position can be associated with a set input waveguides, and a logic value can be encoded based on whether amplitude of the associated wavelength is detected on a respective input waveguide of the set of waveguides. A mismatch of at least one bit is indicated if light is detected on an output of the optical TCAM.

Wavelength division multiplexing (WDM)-based and multipath interferometry based optical ternary content addressable memory (TCAM)

A reprogrammable dot product engine ternary content addressable memory (DPE-TCAM) is provided. The DPE-TCAM comprises a TCAM crossbar array comprising a plurality of match lines and a plurality of search lines. Each search line and match line are coupled together by a memory cell. A plurality of search line drivers are configured to apply a voltage signal to the search lines representing bits of a search word. Current sensing circuitry is coupled to the output of the plurality of match lines and configured to sense a current on the match lines, the sensed current indicating whether the search word and a stored word matched and, if not, the degree of mismatch between the two words.

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Palo Alto, CA, United States of America

Can Li