Abstract: A CAM circuit utilizes a relatively high operating voltage to control the memory portion of each CAM cell, and a relatively low operating voltage to control the logic portion of each CAM cell. The CAM cell memory portion includes a memory (e.g., SRAM) cell controlled by a word line to store data values transmitted on complementary bit lines. The CAM cell logic portion includes a comparator that compares the stored data values with an applied data value transmitted on complementary data lines, and discharges a match line when the stored data value differs from the applied data value. The memory cell is driven using the relatively high memory operating voltage (e.g., 2.5 Volts) such that the stored charge resists soft errors. The complementary data lines and match line used to operate the comparator are driven using the relatively low logic operating voltage (e.g., 1.2 Volts) to conserve power.

Abstract: A method of generating a priority address using a priority encoder that includes the steps of: (1) providing a plurality of match signals from a CAM cell memory array to the priority encoder, (2) generating a most significant address bit of the priority address in response to a first set of the match signals, and (3) generating a least significant address bit of the priority address in response to the most significant address bit and a second set of the match signals. In one embodiment, step (3) is implemented by splitting the determination of the least significant address bit into two separate determinations, and the using the most significant address bit to select the result of one of these two separate determinations. Using the most significant address bit to help determine the least significant address bit significantly increases the speed of determining the least significant address bit, thereby increasing the overall speed of the priority encoder.

Abstract: A content addressable memory (CAM) system that includes first and second CAM arrays, which generate first and second sets of match control signals, respectively, having higher and lower priorities, respectively. The first CAM array is enabled during a first memory cycle, and the first set of match control signals are analyzed. If a match exists in the first CAM array, a first priority encoder is enabled to process the first set of match control signals. If no match exists, the first priority encoder is not enabled, and a second memory cycle is initiated. The second CAM array is enabled during the second memory cycle, and the second set of signals is analyzed. If a match exists in the second CAM array, a second priority encoder is enabled to process the second set of match control signals. If no match exists, the second priority encoder is not enabled.

Abstract: An integrated circuit having an electrostatic discharge (ESD) protection circuit, a core protection circuit, a sensitive core circuit and peripheral circuitry is provided. The ESD protection circuit is coupled between the VDD voltage supply terminal and the VSS voltage supply terminal, and is capable of providing protection to the peripheral circuitry. The ESD protection circuitry requires help from core protection circuit to protect the sensitive core circuit. The core protection circuit and the sensitive core circuit are coupled in series between the VDD and VSS voltage supply terminals, with the core protection circuit coupled to the VDD voltage supply terminal. The sensitive core circuit has a VCC voltage supply terminal coupled to receive a VCC supply voltage from the core protection circuit. The core protection circuit is configured to cause the VCC supply voltage to rise slowly with respect to a rising voltage on the VDD voltage supply terminal during power-on of the integrated circuit.

Abstract: A CAM cell including three-transistor (3T) or four-transistor (4T) DRAM cells. Data is stored using intrinsic capacitance of each 3T or 4T DRAM cell, and is applied to the gate terminal of a pull-down transistor. Read operations are performed in the 3T and 4T DRAM cells without disturbing the stored data value by applying the stored data value to the gate terminal of a pull-down transistor and detecting the operating state (i.e., turned on or turned off) of a pull-down transistor, thereby avoiding the charge sharing problems associated with 1T DRAM cells.

Abstract: A ternary CAM cell including a binary SRAM CAM cell connected in series with a mask transistor between a match line and a discharge line, and a DRAM mask circuit for applying a mask (care/don't care) value to the gate terminal of the mask transistor. The binary CAM cell stores a data value that is compared with an applied data value, and opens the first portion of a discharge path between the match line and the discharge line when the applied data value fails to match the stored data value. The mask transistor is controlled by the DRAM mask circuit, which includes two associated DRAM memory cells that are connected by a bit line to a sense amplifier. The DRAM mask circuit is refreshed such that, during a read phase of the refresh operation, a data value is read only from the first DRAM memory cell and registered (refreshed) by the sense amplifier circuit. In the subsequent write phase of the refresh operation, the data value is written to the second DRAM memory cell.

Abstract: A level-shifting signal buffer contains a totem pole arrangement of MOS transistors connected to an output thereof and a control circuit that drives the totem pole arrangement of MOS transistors in a preferred manner so that none of the signals across the MOS transistors exceed predetermined limits that may damage the MOS transistors. A preferred signal buffer may include a PMOS pull-up transistor and an NMOS pull-down transistor arranged within a transistor totem pole. This transistor totem pole extends between a first power supply signal line that receives a first power supply signal (e.g., Vddext) and a reference signal line that receives a reference signal (e.g., GND). The PMOS pull-up transistor may be configured to support a maximum gate-to-drain voltage which is less than a difference in voltage between the first power supply signal and the reference signal.

Abstract: A four-state (quad) CAM cell that stores one of four logic values: a logic high value, a logic low value, a logic high don't care value, and a logic low don't care value. Each quad CAM cell includes a first memory cell, a second memory cell, a comparator circuit, and a control switch. The first memory cell stores a data value (i.e., logic high value or logic low value), and transmits this stored data value to the comparator circuit. The second memory cell stores a care/don't care data value that is transmitted to the control switch. Portions of the comparator circuit and the control switch form a discharge path between a match line and a discharge line connected to the quad CAM cell. The control switch is controlled by the care/don't care value to open/close a first part of the discharge path. The comparator circuit is controlled to open a second part of the discharge path when, for example, the stored data value is equal to an applied data value.

Abstract: A CAM cell array is disclosed in which a comparator function is performed by incorporating a selected transistor of each CAM cell latch into a signal path extending between a match line and a second (e.g., charge or discharge) line. A first terminal of the selected transistor is connected to the match line (or the second line), a second terminal is connected to an internal node of the latch, and a gate terminal of the selected transistor is controlled by the data value stored in the latch. The internal node of the latch is connected through a control transistor having a gate terminal connected to receive an applied data value. When the applied data value is equal to the stored data value, the match line is coupled to the second line along a signal path passing through the selected transistor and the pass transistor. During programming (i.e., when data values are written to the latch), the match line (or second line) carries a low/high voltage signal needed to set (flip) the latch into a desired state.

Abstract: A CAM array including volatile or non-volatile ternary CAM cells that discharge their associated match line through a special discharge line (e.g., a low match line), instead of through the bit line, is disclosed. Each ternary CAM cell includes a pair of storage elements that are used to store a data bit value, a comparison element that is used to compare the stored value with an applied data value, and a discharge element that is coupled between the discharge line and the match line. During operation, when the applied data value matches the stored value, the discharge element de-couples the discharge line from the match line (i.e., a high voltage on the match line remains high). Conversely, when the applied data value does not match the stored value, the discharge elements couple the discharge line to the match line, thereby discharging the match line to the discharge line.

Abstract: A CAM array includes non-volatile ternary CAM cells that use access transistors to easily read from and write to the non-volatile transistors. Each ternary CAM cell includes a pair of storage elements that are used to store a data bit value, and an access element that is used during CAM array operation. During a comparison operation, when the applied data value matches the stored value, the storage elements de-couple the match line from a discharging bit line (i.e., a high voltage on the match line remains high). Conversely, when the applied data value does not match the stored value, the storage elements couple the match line to a discharging bit line, thereby discharging the match line.

Abstract: A memory circuit that operates in response to a VCC supply voltage and a ground voltage is provided. The memory circuit includes a word line voltage generation circuit that generates a fixed word line voltage. The fixed word line voltage is selectively applied to word lines of the memory circuit. The word line voltage generation circuit generates the fixed word line voltage for all values of the VCC supply voltage between the minimum VCC supply voltage and the maximum VCC supply voltage. The fixed word line voltage is referenced to the ground voltage, rather than the VCC supply voltage. Because the ground voltage does not vary, the boosted word line voltage of the present invention can be controlled more precisely than prior art boosted word line voltages, which are referenced to the VCC supply voltage. This improved control enables the boosted word line voltage to be fixed for the entire range of the VCC supply voltage.

Abstract: A static random access memory (SRAM) system that includes a five-transistor SRAM cell and a cell voltage control circuit coupled to provide power to the SRAM cell. The cell voltage control circuit supplies the SRAM cell with the VCC supply voltage if the SRAM cell is not being written (i.e., during a read mode or a standby mode). If the SRAM cell is being written, the cell voltage control circuit supplies the SRAM cell with a cell voltage that is less than the VCC supply voltage. The lower cell voltage weakens pull-down transistors in the SRAM cell, thereby enabling logic high values to be written to the SRAM cell. In one embodiment, the cell voltage is less than the VCC supply voltage minus the threshold voltage of an access transistor of the SRAM cell. The cell voltage is high enough to enable the SRAM cell to reliably store data during a write disturb condition.

Abstract: A content addressable memory (CAM) cell that includes a static random access memory (SRAM) cell that operates in response to a V.sub.CC supply voltage. A first set of bit lines coupled to the SRAM cell are used to transfer data values to and from the SRAM cell. The signals transmitted on the first set of bit lines have a signal swing equal to the V.sub.CC supply voltage. A second set of bit lines is coupled to receive a comparison data value. The signals transmitted on the second set of bit lines have a signal swing that is less than the V.sub.CC supply voltage. For example, the signal swing on the second set of bit lines can be as low as two transistor threshold voltages. The second set of bit lines is biased with a supply voltage that is less than the V.sub.CC supply voltage. A sensor circuit is provided for comparing the data value stored in the CAM cell with the comparison data value. The sensor circuit pre-charges a match sense line prior to a compare operation.

Abstract: A six transistor content addressable memory (CAM) cell that prevents disturb of non-written rows during a write operation. The CAM cell comprises an SRAM cell having a pair of cross-coupled inverters and a pair of access transistors. The SRAM cell stores a data value at the output node of one of the inverters and an inverse data value at the output node of the other one of the inverters. An access transistor is connected between each output node and a match line. The match line is connected across the access transistors such that the match line is coupled to the output nodes of the inverters when the access transistors are turned on. Data lines are connected to the gates of the access transistors, and are coupled to receive a data value and an inverse data value. The 6-T CAM cell of this embodiment can be coupled to a plurality of identical 6-T CAM cells to form an array. Each row of CAM cells is coupled to the same match line.

Abstract: A bias control circuit for controlling the bias current in a sense amplifier circuit. The bias control circuit maintains a substantially constant bias current when the V.sub.CC supply voltage decreases, thereby maintaining the operating speed of the sense amplifier circuit at a predetermined level. The bias control circuit also increases the bias current as the temperature of the sense amplifier circuit increases, thereby maintaining the operating speed of the sense amplifier circuit at the predetermined level. Furthermore, the bias circuit controls the logic low voltage provided by the sense amplifier circuit to be less than a predetermined threshold value, even as the V.sub.CC supply voltage increases.

Abstract: A compensation circuit which accounts for variations in both temperature and V.sub.CC supply voltage on an integrated circuit. The compensation circuit includes four quasi-independent compensation current sources, each of which generates a corresponding compensation current. The first compensation current source generates a first compensation current which has a positive slope with respect to temperature. The second compensation current source generates a second compensation current which has a negative slope with respect to temperature. The third compensation current source generates a third compensation current which has a negative slope with respect to the V.sub.CC supply voltage. The fourth compensation current source generates a fourth compensation current which has a positive slope with respect to the V.sub.CC supply voltage. The first, second, third and fourth compensation currents are summed to create a total compensation current.

Abstract: An input buffer insensitive to changes in supply voltage, temperature and other operational parameters comprises a decoupling capacitor and receives a reference voltage. In one embodiment, the input buffer comprises a CMOS invertor in which a PMOS transistor is provided to decouple the output signal from a fluctuation of the ground voltage ("ground bounce"). In one embodiment, a band gap type voltage regulator provides the reference voltage of the input buffer.

Abstract: In a sense amplifier, collectors of a first pair of transistors are connected to and drive the bases of a pair of output transistors, and the bases of the first pair of transistors and the emitters of the pair of output transistors are coupled to input nodes of the sense amplifier. The speed of the sense amplifier is enhanced over the prior art because changes in currents (or voltages) on the input nodes change both the emitter and base voltages of the pair of output transistors.

Abstract: An input buffer insensitive to changes in supply voltage, temperature and other operational parameters comprises a decoupling capacitor and receives a reference voltage. In one embodiment, the input buffer comprises a CMOS invertor in which a PMOS transistor is provided to decouple the output signal from a fluctuation of the ground voltage ("ground bounce"). In one embodiment, a band gap type voltage regulator provides the reference voltage of the input buffer.