Co-Simulation Framework to Verify Large-Scale Mixed-Signal Designs.

Analog floating-gate transistors enable complex analog processing to be implemented in VLSI circuits, but simulating these elements in a SPICE simulator is challenging. The difficulty is setting the initial voltage on the floating-gate to start the simulation, a lack of simple methodology to change the inputs to the transistor in response to the changing charge on the floating-gate, and transistor models that do not include the injection and tunneling phenomenon that change the stored parameter on a floating-gate transistor. Another challenge is embedding complex, sequentially-triggered events required to simulate programming of a floating-gate transistor. A co-simulation framework is used to combine a circuit simulator with a system simulator which can model serially executing instructions to verify the functionality of a large-scale mixed-signal design with floating-gate elements. The framework offers a simple methodology to simulate the programming of a single floating-gate transistor using available models for injection and tunneling. An array of floating-gate elements that is a part of analog memory is verified using the co-simulation framework. A simple methodology is presented to create unique test benches for verifying designs that have a large number of inputs and outputs. The test bench is used in an interactive method, where the the inputs to the design can be changed during the simulation. The large-scale design is verified quickly by logging the simulation state of design elements, monitoring the results in the test bench and selectively plotting the results