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Simulation of a Mixture of Analog and Digital Circuits

IP.com Disclosure Number: IPCOM000050331D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 51K

Publishing Venue

IBM

Related People

Bach, WS: AUTHOR [+2]

Abstract

This article describes a technique for simulating a mixture of analog and digital circuits. When employing custom integrated circuit chips, it often is desirable to mix analog and digital circuits on a single chip. Mixed analog and digital circuits implemented on a single VLSI (very large-scale integration) chip may, for example, be less expensive and more reliable than the same circuits implemented on multiple chips. When simulating circuit operation as a part of chip development, a single simulator and single data base are both required to provide the data integrity necessary to functionally verify a design which contains a mix of analog and digital hardware macros. A single data base will insure that the hardware will perform as simulated.

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Simulation of a Mixture of Analog and Digital Circuits

This article describes a technique for simulating a mixture of analog and digital circuits. When employing custom integrated circuit chips, it often is desirable to mix analog and digital circuits on a single chip. Mixed analog and digital circuits implemented on a single VLSI (very large-scale integration) chip may, for example, be less expensive and more reliable than the same circuits implemented on multiple chips. When simulating circuit operation as a part of chip development, a single simulator and single data base are both required to provide the data integrity necessary to functionally verify a design which contains a mix of analog and digital hardware macros. A single data base will insure that the hardware will perform as simulated. A single simulator is easier to use and is able to verify the interfaces between the analog and digital hardware macros.

Presently, several significant event simulators are available for evaluation of digital hardware macros. Several other simulators are also available which support analog hardware macros. However, few simulators support both analog and digital circuits simultaneously. For those designs where the number of digital hardware macros greatly outnumber the analog hardware macros, it is desirable to use a significant event simulator for the overall simulation. Analog hardware macros bear some appearance similarities to digital hardware macros. They both may be represented (Fig. 1) physically by input pins I, output pins 0 and a boundary or area 14 within which the hardware macro circuits are contained. The significant difference between analog and digital hardware macros is found in the interpretation of the voltage values on the input pins I and output pins O. Hardware macro input and output pins I and 0 are digital if they can be modeled as having three distinct voltage ranges. (This definition is extendable to ranges of other physical parameters, i.e., charge, current, flux, etc.) A first voltage range is interpreted as Logic 0; a second voltage range is not defined; while the third voltage range is interpreted as a logic 1.

Hardware macro input and output pins I and 0 are analog if they must be modeled by more than three voltage ranges or states. Although most analog signals on a chip are continuous (infinite number of ranges), for simulation purposes, an analog signal may often be satisfactorily approximated by the digitized value of the analog signal. To achieve satisfactory simulation accuracy, the voltage difference between successive points of the digitized signal should be less than the discernable voltage difference of the analog hardware macro. The mixed analog digital simulation technique of this article supports analog hardware macros with the following characteristics: 1) Analog hardware macros must have digital controlling inputs

which synchronize the macro with the surrounding digital

hardware macros.

2) The ou...