Motorola Corporation

Ernest A Carter

Clinton C Kuo

Mark W McDermott

Joseph Jelemensky

Anthony E Kouvoussis

John K Eitrheim

Dorothy M Wood

A static RAM includes test features which provide for the detection of soft defects which may cause a defective SRAM cell to behave as a functional DRAM cell. Provision is made for writing either a high or a low logic state to each bit line of the SRAM while not writing any value to its complementary bit line and for sensing the state of each bit line independently of the state of its complementary bit line. In addition, a current test is provided which detects soft defects by means of the increased inverter leakage current caused thereby. It is possible, by properly combining these tests, to reliably detect all soft defects, thereby assuring the data retention capability of the SRAM. This technique avoids the long hold time and/or high temperature test techniques used in the prior art.

Static RAM with test features

Static RAM with soft defect detection

A memory has a programmable circuit which allows a user to select an amount of redundancy the memory has varying from zero percent to one-hundred percent. A received address is compared by the circuit with a redundancy percentage control signal to determine if the address falls within a redundant portion of the memory. If so, a redundancy enable signal is asserted to allow the memory to utilize the redundant circuitry.

User programmable redundant memory

An output buffer with reduced supply line disturbance is provided for use in high performance microprocessor circuits. The output buffer uses a resistor and transistor as a sensing circuit, in parallel with an output driver transistor, thereby providing a negative feedback path into the control circuitry for the output driver. The sensing circuit detects the strength of the output driver transistor, by monitoring the amount of capacitance on the output node when the output buffer is driving the output signal to a logic high or logic low state, and rapidly produces a control voltage. The current flowing through the driver transistor and the sensor transistor causes a voltage drop across the resistor, which is fedback into the control circuitry. The control voltage is fed back into the output buffer control circuitry, thereby facilitating the reduction of the current drive capabilities of the driver and sensor transistors. Thus, the control circuitry reduces the change in current flow (di/dt) attributable to the operation of the driver and sensor transistors during the output buffer logic state transition.

MOS output buffer with reduced supply line disturbance

A read-only-memory (ROM) having a plurality of enhancement and depletion transistors selectively arranged in an array with the gates of the transistors in each row connected in common to form word lines, and the current paths of the transistors in each column connected in series to form bit lines. The word lines are precharged and then allowed to float. The bit lines are then precharged, bootstrapping the word lines above the precharge level. A selected one of the word lines is thereafter discharged before one end of each of the bit lines is connected to ground. A selected bit line will either remain precharged or be discharged depending upon the type of transistor at the intersection of the selected word and bit lines.

Series read-only-memory having capacitive bootstrap precharging circuitry

A successive-approximation charge-redistribution analog-to-digital converter includes a binary weighted capacitive ladder for converting the least significant bits of the binary output representation and a resistive ladder for converting the higher order bits of the output representation. To achieve a half least significant bit shift, the capacitor of lowest capacitance in the ladder having a capacitance C is replaced by first and second capacitors each having a capacitance C/2. Each of these capacitors has a first terminal connected to the input of a comparator. Another input of the first capacitor is coupled to the low reference voltage. The second input of the second capacitor is coupled to one-eighth the high reference voltage during the sample phase and to the low reference voltage when the sample phase is completed. The resulting redistribution of charge which occurs at the input to the comparator is equivalent to minus one-half times the charge corresponding to one least significant bit. Thus, the stored sample to be converted is reduced in voltage by one-half least significant bit.

Analog to digital converter

In a successive-approximation charge-redistribution analog-to-digital converter which includes a binary weighted capacitive ladder network, an unknown analog input voltage is sampled only on the largest capacitor representing half the capacitance. The conversion phase proceeds utilizing all the capacitance and only half the reference voltage. This not only reduces circuit complexity, but also reduces problems associated with disruption of the charge stored on the capacitor.

Analog-to-digital converter using half range technique

An MOS voltage boost circuit includes a first field-effect-transistor coupled between ground and an output node and a second, depletion type, field effect transistor coupled between the output node and a source of supply voltage (V.sub.DD). The first transistor is turned off by a disabling signal, and the second transistor is turned on by an enabling signal derived, in part, from the disabling signal. This produces a first voltage at the output node. A third field-effect-transistor is capacitively coupled between the output node and the enabling signal to boost the output voltage when the enabling signal terminates.

Voltage booster circuit

A MOSFET incrementer circuit is disclosed which is adapted for use in conjunction with a clocked register for incrementing the binary value stored within the register. Each stage of the register has an input terminal which is used to determine whether or not the binary value stored in the particular stage is to be toggled. Each of the input terminals is precharged to a high level which corresponds to the no-increment mode of operation. After the input terminals are initially precharged, the input terminal of the least significant stage is driven to a low level to perform an increment. A plurality of series-coupled MOSFET devices are controlled according to output signals provided by each of the register stages for selectively coupling the low level present at the input terminal of the least significant stage to the input terminals of subsequent stages. When a low level is presented to the input terminal of a stage of the register, the binary value stored within the particular stage is toggled when the register is clocked, thereby causing the value stored within the register to be incremented. A common signal is used to initially precharge the voltage at each of the input terminals as well as to select an increment operation.

Incrementer with common precharge enable and carry-in signal

A latching circuit is disclosed having series connected first and second stage MOSFET devices within a first inverter circuit. An output signal provided at the upper node of the series connected devices is coupled by a feedback MOSFET to the input of a second MOSFET inverter. The output of the second MOSFET inverter is coupled to the gate of the first series connected MOSFET device while the input signal to be latched is coupled to the gate of the second of the series connected MOSFET devices. The lower output node of the series connected MOSFET devices is used to provide an output signal to a data bus so that the logic state stored by the latching circuit can be accessed. The latching circuit is controlled by timing signals such that the output signal provided by the lower node is in the proper logic state whenever the latching circuit is to be coupled to the data bus.

Bus driver/latch with second stage stack input

An MOS circuit possessing hysteresis and positive feedback for fast switching includes a first MOSFET having its gate connected to an input. A second depletion mode MOSFET has its drain connected to the source of the first MOSFET and its source connected to ground. A third depletion mode MOSFET has its drain connected to the source of the first MOSFET and its gate and source connected to the drain of a fourth MOSFET and to the gate of a fifth MOSFET. The gate of the fourth MOSFET is connected to the gate and source of a sixth depletion mode MOSFET and to the drain of the fifth MOSFET. The fifth MOSFET has its source connected to ground.

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Austin, TX, United States of America

Ernest A Carter