International Business Machines Corporation

John Bula

Larry C Martin

Claude Louis Bertin

Alvar Antonio Dean

Thomas A Williams

Stephen B Barrett

Ashok C Patrawala

A mask generator for generating a mask having logical signals of a given level between positions indicated by beginning and ending addresses. Two decoders select respective binary signal lines indicating the starting and ending positions. The mask generator is composed of two mask generators operating on the higher and lower order binary signal lines respectively and which ripple from the ends of the mask towards the middle. Preferably, each of the dual mask generators has look-ahead carry capability.

Dual look ahead mask generator

Use of a residual charge bleed-off diode connected to the gate of an FET device in a Read Only Storage (ROS) is disclosed. The ROS is personalized by cutting selected gate leads in an array of FETs with a laser beam. Experience has shown that static electric charges on the lead due to handling prior to cutting become isolated at the gate after the gate lead is cut, producing an unpredictable conduction state for the FET instead of a solid off-state as desired. By providing a bleed-off diode which remains connected to the FET gate after the cut is made, the charges are allowed to leak away from those FETs whose gates have been cut while, at the same time, preventing the voltage of the FET gate from floating. The diode is oriented so as to offer a high impedance to current flowing from the gate node when the gate is biased for FET conduction. This minimizes the effect of the diode on circuit speed when the gate remains connected with the balance of the read only storage circuitry. If the gate and diode have been selectively severed from the balance of the read only storage circuitry, in the course of programming the storage, any residual charge on the gate is conducted through the diode by virtue of its reverse bias leakage or forward biased conduction state, depending upon the polarity of the residual charge on the gate.

Laser cut storage cell

The prior art, low power ratioless true/complement driver is improved upon by connecting a first isolation FET (T2) so that its gate is connected to drain potential (V.sub.DD) and by connecting to the second isolation FET (T4) so that its gate is connected to the phase-splitting node (1). This enables the number of clock pulse sources necessary to operate the generator circuit to be reduced by one so that the speed of the generator circuit is increased, by virtue of the second isolation FET (T4) having a gate size substantially smaller than the gate size of the inverting FET (T3) so that it will more rapidly switch from its on-state to its off-state than does the inverting FET.

Low power true/complement driver

A high speed true/complement driver circuit is disclosed wherein the time interval between the address and memory select pulses are minimized by utilizing a high speed enhancement/depletion mode inverter pair followed by a clocked signal isolation stage. A pair of enhancement mode/depletion mode inverters connected in cascade configuration serves to generate the true and complement output signals which are isolated from noise at the input line by a symmetric pair of clocked FETs.

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Rockville, MD, United States of America

John Bula