The Evolution of SPICE Continues With PSPICE for TISeptember 17, 2020 by Jake Hertz
The new PSPICE for TI enables engineers to simulate complex analog circuits with unlimited analysis of TI power and signal-chain products.
A basic circuit with only a few components can be understood and evaluated by hand using fundamental theorems of electronics. However, once we start expanding our circuits—adding more nodes, more components, and more complexity—it becomes virtually impossible (or at least unbearably tedious) to do analysis by hand.
For this reason, simulators are essential in circuit design.
The internals of an op-amp show just how daunting hand analysis of circuits can be. Image used courtesy of Learning About Electronics
One of the earliest, and most powerful, circuit simulators was originally developed for integrated circuit analysis. Simulation Program with Integrated Circuit Emphasis, better known in the industry as SPICE, came to be in the late 1960s.
SPICE continues to be a mainstay in the industry, having improved and evolved significantly since its inception—from SPICE to PSPICE and LTSPICE to a new development from Texas Instruments: PSPICE for TI.
The Basics of SPICE
The original version of SPICE was a completely text-based simulator, requiring circuit designers to describe their circuit in what is known as a netlist.
A netlist is a text-based representation of a circuit, defining all components, their parameters, and their connections relative to other circuit components. With a well-defined netlist, SPICE then creates a matrix using classic theorems such as Kirchoff’s Voltage and Current Laws, which can then be used to solve for the node voltages and currents.
Example SPICE netlist. Image used courtesy of Visionics
Still, some components can’t be solved using a strictly nodal circuit solver. For example, components like transistors are not linear devices and as such, cannot be accurately represented with Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL). Instead, they are solved with more intricate methods that depend on things like model parameters and operating conditions. SPICE can also provide things like transient analysis using differential equations.
Obviously, SPICE has its limitations. The computational complexity of a SPICE netlist increases as the number of nodes increase. For this reason, large circuits may need to trade off accuracy in results for time complexity. Furthermore, SPICE can’t do things like EM analysis, which requires other specialized software.
The Next Upgrade: PSPICE and LTSPICE
Along with its computational issues, one of the biggest drawbacks of the original, text-based, SPICE was the tedium of creating a netlist. To manually type out and define the entire circuit in a text-based format was very time consuming and painstaking.
Example of an LTSPICE schematic and its corresponding netlist. Screenshot used courtesy of Tim Dean
Then came along SPICE variations, such as PSPICE and LTSPICE. These versions of SPICE provide a graphical user interface, helping designers create a circuit schematic using component symbols. These schematics then get converted into a netlist behind the scenes, allowing it to be run like a traditional SPICE netlist.
This was a game-changer, allowing for more intuitive and quicker circuit design.
PSPICE for TI
Aiming to further improve the capabilities of PSPICE, Texas Instruments has recently announced its newest product: PSPICE for TI.
One of the real improvements in PSPICE for TI is that the software offers full-featured circuit simulation with a library of more than 5,700 of TI's analog integrated circuit models, making it easier for engineers to evaluate components for new designs. This design and simulation environment allows users to simulate complex mixed-signal designs using the built-in library.
PSPICE for TI example use. Image used courtesy of Texas Instruments
This new software also includes automatic measurements and post-processing, Monte Carlo analysis, worst-case analysis, and thermal analysis.
SPICE’s Ongoing Legacy
Nearly 60 years after its inception, SPICE is still being used and upgraded—a testament to its value and ubiquity in circuit design.
With the improvements offered in PSPICE for TI, designers may more easily create and prototype designs before committing them to layout and fabrication, reducing time to market and development costs.