Texas Instruments Corporation

John N Sackett

Denis F Spicer

Simon C Garth

Michael M Rumsey

The operation of analog circuit blocks is simulated on a digital computer by a computer program in which each analog circuit block is represented by a procedure call including details of input signal name(s) and value(s), output signal name(s) and value(s), the operating parameters for the block and the sampling instant for the evaluation of the or each output signal value. The interconnections between blocks are represented by the use of the same signal names. Each sampling instant indicates when the value of an output signal will have changed by a predetermined amount since the previous sampling instant. A common sampling time is used for the circuit and is selected as the earliest of the sampling instants of the circuit blocks. The simulation can include digital circuit blocks represented by an event-driven or a levelised compiled code model, with analog/digital conversion to handle the interconnections between analog and digital circuit blocks. A feedback connection around part of the analogue circuit is handled by progressive adjustment of the feedback input signal value while other input signal values are held constant.

Method of simulating the operation of a circuit having analog and

Electron beam apparatus for use in testing integrated circuits uses a magnetic electron objective lens having a first end adjacent the circuit under test and a second end remote from the circuit. The magnetic field of the lens increases steeply to a maximum near the first end and falls gradually towards the second end. Secondary electrons emitted from the circuit are accelerated strongly by an electrostatic field into the first end of the lens and are retarded abruptly to speeds of the same order as their emission speeds in the region of maximum magnetic field. Further gradual retardation of the electrons takes place so that the electrons approach the second end of the lens parallel to the axis of the lens at substantially their emission speeds. A filter grid located at the second end of the lens and a collector of electrons passing through the filter grid enable the emission speeds of the secondary electrons to be measured.

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Bedford, United Kingdom

John N Sackett