Abstract: A power-on reset circuit (30) for a memory (20) includes a DC model circuit (39), an N.sub.BIAS check circuit (64), and a NAND logic gate (71). A logic low power-on reset signal is provided at power-up of the memory (20) to establish initial conditions in a clock circuit (29) and in row and column predecoders/latches (24, 27). When the power supply voltage, a bandgap reference voltage, and a bias voltage all reach their predetermined voltages, the power-on reset circuit (30) provides a logic high power-on reset signal. In this manner, the power-on reset circuit (30) is assured of providing a logic low power-on reset signal until all of the proper voltage levels are reached. In addition, the power-on reset circuit models a DC circuit equivalent of an address buffer circuit (79) for compensating for process and temperature variations.

Abstract: A cache TAG RAM (25) includes a reduction circuit (39) for comparing match signals from a plurality of exclusive OR logic circuits (33, 34) and provides a hit signal when all of the TAG address bits of a stored TAG address is the same as input address bits. The reduction circuit (39) provides a miss signal when any one or more of the bits of the stored TAG address is not the same as the corresponding bits of the input address bits. In one embodiment, the reduction circuit (39) uses a plurality of transistors (77, 78) coupled to a conductor (75) for discharging the conductor (75) if one of the exclusive OR logic circuits (33, 34) indicates a miss. In another embodiment, the reduction circuit (39") charges the conductor. The comparison can be made using signals having small signal swing at high speed, and a reference voltage is not needed for the comparison.

Abstract: A CMOS driver circuit (20) has a high impedance driver (30) and a low impedance driver (36) connected to the near end of a transmission line (43). The output impedance of the high impedance driver (30) matches the characteristic impedance of the transmission line (43). As a digital signal from the CMOS driver circuit (20) transitions from one logic state to another, the low impedance driver (30) drives the transmission line (43) until a predetermined voltage before the signal reaches its steady state voltage. A sensing circuit (24) senses when the predetermined voltage is reached, and in response, provides a control signal to deactivate the low impedance driver (36). The high impedance driver (30) completes the signal transition. The high impedance driver (30) absorbs the reflected waves from the far end of the transmission line (43), reducing the effects of ringing, and increasing noise immunity.

Abstract: A cache TAG RAM (25) includes a TAG array (26), a small signal exclusive OR logic circuit (33, 34), a sense amplifier (36, 37), and another exclusive OR logic circuit (30, 31). A comparison of a stored TAG address to the input address signal is made by the small signal exclusive OR logic circuit (33, 34) to provide a hit signal very quickly. The stored TAG address that is lost during the exclusive OR operation is recovered by performing another exclusive OR on the match information and the input address signal. By using a small signal exclusive OR circuit to perform a comparison early, the hit signal can be generated very quickly.

Abstract: A BICMOS input stage includes a level shifting stage (35) and a level converter/buffer circuit (60). The input stage receives a single-ended GTL level input signal and a reference voltage, and in response, provides differential BICMOS level output signals. The input stage operates over a wide range of values for the reference voltage, does not require the generation of complex bias voltages, and provides well controlled output signals.

Abstract: A current-mode DAC (20) includes two sub-DACs (22, 36), and a calibrated attenuator (48). One sub-DAC (22) receives least-significant-bits (LSB) of a K-bit digital input signal, and the second sub-DAC (36) receives most-significant-bits (MSB) of the K-bit digital input signal. An output of the sub-DAC (22) is attenuated by an attenuator (50), and the attenuated signal is summed with an output of the second sub-DAC (36) to form an analog output signal. A 4-phase gain adjust sample and hold circuit (49) is used to calibrate the attenuator (50). The 4-phase gain adjust sample and hold circuit (49) samples the current from the attenuator (50), and removes device mismatch effects in the attenuator (50) which cause linearity errors in the current-mode DAC (20).

Abstract: A static random access memory (20) with programmable preset data includes two bit line pairs for each column of memory cells (31-36). In response to a control signal during a programming cycle, preset programming logic (28) charges one of the bit line pairs of each column of memory cells to a predetermined logic state and the other bit line pair to a logical complement of the predetermined logic state. Memory cells (31-36) of each column of memory cells are coupled to either one of the two bit line pairs by mask programming. During the programming cycle, each of the memory cells (31-36) store programmed data depending upon which bit line pair each memory cell is coupled to. The memory (20) provides the advantages of a static random access memory and the nonvolatility of a read only memory.

Abstract: A delay locked loop (44) includes an arbiter circuit (86), a VCD circuit (85), and a collapse detector (88). The arbiter circuit (86) receives an input signal and provides a retard signal to adjust the amount of propagation delay of VCD circuit (85), in order to synchronize the phases of the input signal to an output signal of the VCD circuit (85). The collapse detector (88) detects if the output signal of the VCD circuit (85) has failed to change logic states within a predetermined length of time. The delay locked loop (44) can lock the phases of two signals having different frequencies.

Abstract: A memory (20) includes a write control delay locked loop (52) for controlling a write cycle of the memory (20). The delay locked loop (52) includes an arbiter circuit (264), a voltage controlled delay (VCD) circuit (260), and a VCD control circuit (265). The arbiter circuit (264) compares a clock signal to a delayed clock signal from the VCD circuit (260). In response, the arbiter circuit (264) provides a retard signal to the VCD control circuit (265). The VCD control circuit (265) receives the retard signal and adjusts a propagation delay of the delayed clock signal to compensate for changes in the clock frequency, as well as to compensate for process, temperature, and power supply variations.

Abstract: A latching ECL to CMOS input buffer (20) has an input buffer (21) for receiving an ECL input signal, a CMOS latch (35), and driver circuits (55, 65). Transmission gates (31, 32) are used to couple the input buffer (21) to the latch (35) in response to a CMOS clock signal being a logic low. The driver circuits (55, 65) are coupled to transmission gates (31, 32). While the clock signal is a logic low, input nodes of the first and second driver circuits (55, 65) are precharged to a relatively high voltage in order to isolate the input signal from the first and second driver circuits (55, 65). The latch (35) both latches the logic state of the ECL input signal and converts the ECL input signal to CMOS logic levels. This allows an input signal to be latched and level converted within a relatively short period of time.

Abstract: A nonvolatile memory (20) includes an array of floating gate transistors (22) organized as rows and columns. Word lines of adjacent rows are coupled together to form shared word lines. In one embodiment, a coupling transistor (56-61) is used to couple the sources of the floating gate transistors (36, 39-55) of a row to a predetermined potential in response to the shared word line being selected. The sources of the unselected floating gate transistors of the array (22) are isolated. In another embodiment, an inverter (113, 114, and 115) couples the sources to zero volts in response to the shared word line being selected. The conductivity of the floating gate transistors (36, 39-55) is controlled in response to the logic state of the shared word lines to ensure that unselected cells do not adversely affect the operation of the nonvolatile memory.

Abstract: An ECL-to-CMOS buffer having a single-sided delay comprises an ECL logic gate, a level converter, a plurality of series connected inverters, and a NOR gate. The ECL logic gate receives an ECL level input signal, and provides complementary intermediate level logic signals. The level converter receives the intermediate level logic signals and provides a CMOS level output signal. The NOR gate receives the CMOS level output signal, via the series connected inverters, at an input terminal after a predetermined delay. One of the intermediate level logic signals is also received by the NOR gate at a second input terminal. The CMOS level output signal is delayed for a predetermined time in a low-to-high transition, with no unwanted delay in a high-to-low transition.

Abstract: A bit line load (380) is coupled to a bit line pair and includes bipolar pull up transistors (389, 403), P-channel load transistors (390, 404), a NAND logic gate (395), and a P-channel equalization transistor. The NAND logic gate (395) senses a differential voltage on the bit line pair, and provides an equalization signal. When a write control signal indicates the end of a write cycle, the equalization signal initiates precharge and equalization of the bit line pair.

Abstract: Compensation for a second pole located at an internal node (107 and 108) of a two pole cascode differential amplifier (30) is accomplished by introducing a left half plane zero in the transfer function of the cascode differential amplifier (30). This is done by coupling a compensation capacitor (46, 47) between an output node (105, 106) and the internal node (107, 108) of the cascode differential amplifier (30). The compensation capacitors (46, 47) improve high frequency performance of the amplifier (30) by improving phase margin and increasing stability.

Abstract: A synchronous memory (20) has parallel data output registers (34) and a dummy path (46). The output data from a memory array (22) is provided to the parallel output registers (34). The output registers (34) provide two parallel, interleaved, output data paths. The data in each path changes every other cycle of a clock signal. Dummy path (46) contains delay elements that model a propagation delay for a data path of the memory (20) during a read cycle. Using parallel data output registers (34) increases a time in which data is valid during the read cycle. The dummy path (46) tracks the output data signal in terms of process, power supply and temperature variations to ensure that the correct data is acquired during the read cycle.

Abstract: A synchronous memory (50) having a looped global data line (80) reduces a difference between minimum and maximum propagation delays between different locations in a memory array (51) during a read cycle of the memory (50). The looped global data line (80) has a first portion (80') and a second portion (80"). The first portion (80') extends along an edge of the memory array (51) in a direction substantially parallel to a direction of the word lines of the array (51). Sense amplifiers (73-78) are coupled to the first portion (80') of the looped global data line (80). At one end of the array (51), the second portion (80") of the looped global data line extends back in an opposite direction to the first portion (80') and is coupled to output data circuits (84). Reducing the difference in propagation delays improves noise margins and allows increased operating speed.

Abstract: A substrate bias generating circuit (20) provides a substrate bias voltage to a substrate (50) of an integrated circuit. A voltage-to-current converter circuit (22) provides a constant current proportional to a bandgap generated reference voltage. P-channel transistors (34 and 35) then provide constant current sources for a voltage level sensing circuit (36) based on the bandgap generated reference voltage. The voltage level sensing circuit (36) monitors the level of the substrate bias voltage, and when the substrate bias voltage reaches a predetermined voltage level, provides a first control signal for activating an oscillator (47). A level converter (43) is provided to amplify, or level convert the first control signal for more reliable control of the oscillator. A substrate bias generating circuit (20) provides a precisely controlled substrate bias voltage to the substrate (50) that is independent of process, temperature, and power supply variations.

Abstract: A fully differential switched-capacitor biquad low pass filter (40) includes a first stage (54), second stage (56), common-mode circuits (55, 72), and feedback transmission gates (73, 74). The first stage (54) includes a first operational amplifier (47), and the second stage (56) includes a second operational amplifier (69). Glitches, or transients, which are caused by the operational amplifiers (47, 69) operating in slew rate limit mode, are prevented from affecting the differential output signals of the filter (40) when the filter (40) is operating with a continuous time output. This is accomplished by preventing the operational amplifiers (47, 69) from operating in slew rate limit mode, or by adjusting the clock signals such that the output of the filter (40) is not coupled to an operational amplifier (47, 69) that is recovering from operation in slew rate limit mode.

Abstract: A pipelined memory (20) has a synchronous operating mode and an asynchronous operating mode. The memory (20) includes output registers (34) and output enable registers (48) which are used to electrically switch between the asynchronous operating mode and the synchronous operating mode. In addition, in the synchronous operating mode, the depth of pipelining can be changed between a three stage pipeline and a two stage pipeline. By changing the depth of pipelining, the memory (20) can operate using a greater range of clock frequencies. In addition, the operating frequency can be changed to facilitate testing and debugging of the memory (20).

Abstract: A fully differential line driver circuit (25) includes an input differential amplifier (26) and double-ended differential amplifiers (27, 28). A first output driver stage (29) includes a pair of series connected transistors (30, 31), and a second output driver stage includes a pair of series connected transistors (33, 34). The differential amplifiers (27, 28) provide bias and signals voltages to the gates of the series connected transistors (30, 31, 33, 34). The output stages (29, 32) provide differential output signals for driving a low impedance load. The clamping circuits (35-38) control overlap currents in the output stages (29, 32). Common-mode feedback is used to ensure a common-mode voltage of the differential output signals remains at a predetermined voltage to ensure maximum signal swing and thus, maximum efficiency.