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Mixed Signal Design and Verification for IoT Designs

Mitch Heins, EDS Marketing Director, DSM division of Mentor Graphics

A typical Internet-of-Things (IoT) design consists of several different blocks including one or more sensors, analog signal processing for the sensors, an analog-to-digital converter and a digital interface such as I2C.  System integration and verification is challenging for these types of IoT designs as they typically are a combination of two to three different ICs.  The challenge is exacerbated by the fact that the system covers multiple domains including analog, digital, RF, and mechanical for packaging and different forms of multi-physics type simulations needed to verify the sensors and actuators of an IoT design.  The sensors and actuators are typically created as microelectromechanical systems (MEMS) which have a mechanical aspect and there is a tight interaction between them and the package in which they are encapsulated.

The verification challenge is to have the right form of models available for each stage of the design and verification process that work with your EDA vendor tool suite.  Many of the high volume IoT designs are now looking to integrate the microcontroller and radio as one die and the analog circuitry and sensors on second die to reduce cost and footprint.

In many cases the latest IoT designs are now using onboard analog and digital circuitry with multiple sensors to do data fusion at the sensor, making for “smart sensors”.  These ICs are made from scratch meaning that the designers must create their own models for both system-level and device-level verification.

Tanner EDA by Mentor Graphics has partnered with SoftMEMS to offer a complete mixed signal design and verification tool suite for these types of MEMS centric IC designs. The Tanner Analog and MEMS tool suites offers a complete design-capture, simulation, implementation and verification flow for MEMS-based IoT designs.  The Tanner AMS verification flow supports top-down hierarchical design with the ability to do co-simulation of multiple levels of design abstraction for analog, digital and mechanical environments.  All design-abstractions, simulations and resulting waveforms are controlled and viewed from a centrally integrated schematic cockpit enabling easy design trade-offs and verification.   Design abstractions can be used to swap in different models for system level vs device level verification tasks as different parts of the design are implemented.  The system includes support for popular modeling languages such as Verilog-AMS and Verilog-A.

The logic abstraction of the design is tightly tied to the physical implementation of the design through a correct-by-construction design methodology using schematic-driven-layout with interactive DRC checking.  The Tanner/SoftMEMS solution uses the 2D mask layout to automatically create a correct-by-construction 3D model of the MEMS devices using a process technology description file.

Figure 1: Tanner Analog Mixed Signal Verification Cockpit

The 3D model is combined with similar 3D package models and is then used in Finite Element or Boundary Element Analysis engines to debug the functionality and manufacturability of the MEMS devices including mechanical, thermal, acoustic, electrical, electrostatic, magnetic and fluid analysis.

Figure 2: 3D-layout & cross section created by Tanner SOFTMEMS 3D Modeler

A key feature of the design flow is that the solution allows for the automatic creation of a compact Verilog-A model for the MEMS-Package combination from the FEA/BEA analysis that can be used to close the loop in final system-level verification using the same co-simulation cockpit and test benches that were used to start the design.

An additional level of productivity can be gained by using a parameterized library of MEMS building blocks from which the designer can more quickly build complex MEMS devices.

Figure 3: Tanner S-Edit Schematic Capture Mixed Mode Schematic of the IoT System

Each building block has an associated parameterized compact simulation model.  By structurally building the MEMS device from these building blocks, the designer is automatically creating a structural simulation model for the entire device that can be used within the verification cockpit.

Figure 4:Tanner SoftMEMS BasicPro Suite with MEMS Symbol and Simulation Library

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