LTspice vs. Ansys Nexxim Circuit: A Comparative Analysis for Circuit Simulation

ANsIntroduction

In modern electrical engineering, circuit simulation tools play a crucial role in designing and verifying circuits before physical implementation. LTspice and Ansys Nexxim Circuit are two widely used simulation tools, each offering unique advantages for engineers. This blog explores their features, compares their performance, and highlights the best use cases for each.

Background: The Importance of Circuit Simulation

SPICE (Simulation Program with Integrated Circuit Emphasis) has been a cornerstone in circuit analysis since its inception. Over the years, multiple variations of SPICE have emerged, including ISPICE, HSPICE, PSPICE, and LTspice, each catering to different needs. Almost all electrical engineers have used SPICE-based tools for verifying circuit designs, debugging performance issues, and optimizing circuit parameters.

Project Overview: Comparing LTspice and Ansys Nexxim Circuit

For this study, a two-stage operational amplifier (op-amp) was simulated using both LTspice and Ansys Nexxim Circuit. The key design specifications included:

• Gain @ 1kHz > 40dB
• Unity Gain Frequency > 50kHz
• Phase Margin > 45˚
• Gain Margin > 10dB
• Quiescent Current ≅ 100µA
• Compensation Capacitor < 30pF
• Compensation Resistor < 1000kΩ
• MOSFET Model: 0.18µm CMOS

The primary goal was to determine how each tool handled the circuit simulation process, from defining models and parameters to analyzing compensated and uncompensated results.

LTspice: Strengths and Workflow

LTspice is a widely used, free circuit simulation tool developed by Analog Devices. It allows engineers to:

• Define subcircuits using .model for MOSFETs
• Assign design parameters (W/L ratios, bias voltages) using .param definitions
• Use hierarchical subcircuits for modular design
• Perform transient and frequency-domain analysis
• Visualize circuit behavior with node plotting

LTspice is known for its simplicity and efficiency, making it an excellent choice for small-to-medium-sized analog circuit designs.

Ansys Nexxim Circuit: Advanced Features and Workflow

Nexxim Circuit, a part of Ansys’ circuit simulation suite, offers all the capabilities of LTspice with additional advanced analysis features. Key capabilities include:

• Defining model blocks for MOSFETs
• Using project variables for W/L ratios and bias voltages
• Performing transient, frequency-domain, and DC sweep analysis
• Conducting signal integrity, resonant, and time-varying noise analysis
• Using structure blocks for trace and via modeling
• Co-simulating with FEM (Finite Element Method) analysis
• Parameterizing and optimizing circuit designs

Results: LTspice vs. Nexxim Circuit Performance

The two tools were used to simulate both uncompensated and compensated versions of the op-amp. The results showed that both LTspice and Nexxim Circuit provided comparable basic simulation accuracy. However, Nexxim’s Optimetrics feature allowed advanced optimization of the circuit parameters, leading to an improved design with minimized component values while maintaining target performance.

Conclusion: Which Tool Should You Use?

• Use LTspice if you need a free, straightforward SPICE simulation tool for basic analog circuit design and debugging.
• Use Ansys Nexxim Circuit if you require advanced analysis, signal integrity testing, co-simulation with FEM, and automated circuit optimization for high-performance applications.

For engineers working on high-speed digital circuits, RF applications, or signal integrity-focused designs, Nexxim Circuit is the superior choice due to its extended analysis capabilities and optimization features. However, LTspice remains a go-to tool for quick, effective circuit verification in analog and power electronics design. Want to see LTspice and Nexxim Circuit in action? Watch our detailed breakdown and simulation walkthrough on YouTube! If you’re interested in learning more about circuit simulation techniques and best practices, don’t miss our upcoming webinar on LTspice vs. Ansys Nexxim Circuit: Advanced Simulation Techniques.