National Semiconductor Corporation

Roy K Yamanouchi

D Kevin Covey

Sandra G Schneider

Robert Walter Williams

The present invention provides a structured integrated circuit design methodology. The methodology is based on describing a two-phase logic function using a high level behavioral description flow chart, properly sizing devices to be used in the circuit for speed and reducing trial and error in circuit layout implementation using novel chip planning techniques. The methodology begins with the definition of signal types based on the circuit function that creates a particular signal and the type of input signal that feeds the circuit function. A rigid set of rules is then established for use of the signal types. Next the technical specification of the two-phase logic function is defined and utilized to create a behavioral flow chart using defined symbols. An associated database of corresponding Boolean equations is then created that defines the parameters of the various elements of the flow chart. The Boolean equations are then converted to a logic diagram either by coded state assignment or by direct implementation. The resulting logic diagram is then analyzed for speed utilizing a Figures of Merit technique for establishing device sizes. The resulting circuit design may then be carried through to layout utilizing conventional computer aided design (CAD) tools.

Structured logic design method using figures of merit and a flowchart

Each cell of a static latch implemented in MOS transistor circuitry includes an MOS transistor configured to operate a depletion mode and operably coupled to communicate an output node of the cell to an input node of the cell in absence of a control signal, to effect the latching operation. Presence of the control signal allows data to be efficiently written to the cell by enabling a transfer gate to establish a communication path for the data to the input node of the cell, while at the same time disabling the MOS transistor to terminate communication of the output node of the cell to its input node during the write operation.

Single device transfer static latch

An improved strobe line driver circuit is disclosed that generates a plurality of strobe signals in response to a corresponding plurality of enable signals and a first clock signal. The circuit includes a clock enable transistor that generates a second clock signal. The circuit also includes a plurality of transistor pairs coupled to the first and second clock signals. Each transistor pair receives one enable signal and generates a corresponding strobe signal.

Strobe line driver circuit

An error correcting network adapted for encoding and decoding data transferred to and from a bubble memory has parallel linear encoder/decoder circuits. An error syndrome generated in response to a parity error in an initial read operation is used by one encoder/decoder circuit for correcting the parity error during a subsequent reread of the data. The error syndrome is also stored in a latch for comparison with a second error syndrome generated in response to the data during the reread operation. A true comparison between the two error syndromes verifies that that data has not changed between the two read operations due to a soft error and that the error correction of the first encoder/decoder circuit is valid.

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San Jose, CA, United States of America

Roy K Yamanouchi