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edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 3 8 EVALUATION OF A CO-SIMULATION APPROACH WITH MATLAB/SIMULINK AND CADENCE FOR FUNCTIONAL VERIFICATION OF ANALOG AND MIXED SIGNAL DEVICES Mathias Heitauer and Martin Versen Technical University of Applied Sciences Rosenheim, Germany martin.versen@th-rosenheim.de EDFAAO (2021) 3:8-12 1537-0755/$19.00 ©ASM International ® INTRODUCTION In modern integrated circuit (IC) design, the imple- mentation of purely digital ICs consists of a two-stage process in which a behavioral simulation is carried out based on a hardware description. After implementation in a specific technology, a post-fit simulation can be carried out to check the performance against the specification. Such a two-stage process is currently unknown for analog functions. With the introduction of the co-simulation interface “Cadence Virtuoso AMS Designer Simulator” from MathWorks in spring 2017, the possibility arose to inte- grateMATLAB/Simulink into the development process for a mixed-signal application-specific integrated circuit (ASIC). In particular, the verification, test, and failure analysis of a circuit against a technology-independent model in MATLAB/Simulink seems possible. In this workflow, a circuit diagram to be designed can be represented inMATLAB/Simulink (gray area in Fig. 1). In a second step, a sub-circuit designed in Cadence Virtuoso is verified against the technology-independent sub-circuit ina co-simulation (white area inFig. 1). The circuit diagram model shown inorange canalsobe ahardwaredescription language (HDL) representation of a digital circuit, so that extensive mixed-signal simulations are possible, which include digital and analog functions like analog-to-digital converters (ADC). If thismodel-based approach is applied and validated in the design phase, it can be used by alter- ing the original model for failure analysis (FA) of analog and mixed-signal devices. Here, this approach is applied to amodulator design with some intentional weaknesses to demonstrate the applicability. ADCs are essential blocks in sensor and automation systems and control loops. ADCs with delta-sigma (ΔΣ) modulation are used to achieve high resolution in con- versions. The ΔΣ modulator converts an input signal into a power density modulated output data stream. In this article, the development process is exercised with a very well-known analog example of a ΔΣ modulator. The systembehavior is simulatedwith theΔΣ and the Simsides toolbox. [1,2] The results are summarized in the second section of this article. After the system specification, the analog circuits are developedwithan ICdesignenvironment suchas Cadence Virtuoso. The modulator is manufactured in a CMOS process for example. For the development of transistor circuits, the manufacturer of the CMOS process provides libraries at the start of the actual design process, which leads to a loss of flexibility. The design of a ΔΣ modulator in the 180 nm technology of XFAB is shown in the third section. Theco-simulation interfacebetweenMATLAB/Simulink andCadence connects the system level design in Simulink and the model of the analog transistor circuit in Cadence Virtuoso with a so-called coupler block. This gives the designer the ability to simulate analog circuits built with Cadence Virtuoso and abstract systemswithinone simula- tion. The ΔΣmodulator could be simulated for example by using the analog transistor model of the modulator with Cadence Spectre and a digital filter for the conversion modeled in Simulink. Fig. 1 Workflow for a model-based development of subcircuit of a mixed-signal ASIC.