Flux Simulator Tool

Flux includes a powerful simulator tool (currently in beta) that allows you to perform SPICE circuit simulations directly from the chat interface. This tool helps you quickly verify circuit behavior, troubleshoot design issues, and optimize component values without having to set up a separate simulation environment.

Overview

The simulator tool enables you to:

• Simulate electronic circuits using standard SPICE netlist syntax powered by Ngspice

• Simulate your existing schematic by pulling component values directly from your design

• Run transient, AC, DC, and operating point analyses

• Get automatic extraction of key metrics like -3 dB frequency, ripple, and gain

• Generate plots and visualizations (Bode plots, waveforms, etc.)

• Rerun or modify previous simulations without starting from scratch

• Access a built-in library of SPICE models for common components

How to Use the Simulator Tool

To simulate circuits using Flux, mention the SPICE simulator in your query.

When you use the simulator tool, Flux will:

1. Analyse your request to understand the circuit you want to simulate

2. Look for the built-in SPICE model library and reference templates for relevant examples

3. Generate a SPICE netlist based on your description (or your existing schematic)

4. Run the simulation using Ngspice

5. Automatically extract structured metrics (e.g., -3 dB frequency, ripple, gain)

6. Iterate if errors occur, fixing syntax, convergence, or time step issues and retrying automatically

7. Generate plots or visualizations if requested

8. Provide a detailed interpretation of results

Simulating Your Existing Schematic

One of the most powerful features of the simulator tool is the ability to simulate circuits you have already designed in Flux. When you ask the simulator to analyse your schematic, Flux reads the exact component values, net connections, and topology from your design so simulations use your actual R, C, L, and voltage source values rather than assumed defaults.

Supported Analysis Types

The simulator tool supports the following Ngspice analysis types:

AC Analysis

Frequency-domain analysis for filters, amplifiers, and frequency response characterization. The tool automatically extracts:

• -3 dB cutoff frequency

• DC gain and peak gain (in dB)

• Roll-off slope (dB/decade)

Transient Analysis

Time-domain analysis for step responses, switching circuits, and waveform characterization. The tool automatically extracts:

• Voltage ripple measurements (Vpp, ripple %)

• Min, max, and average values for each signal

• Steady-state behavior

DC Analysis

DC sweep analysis for transfer characteristics, bias point verification, and operating point analysis.

Operating Point Analysis

Static DC operating point analysis to check node voltages and branch currents throughout a circuit.

Plots and Visualizations

The simulator tool can generate plots and charts from simulation results. You can request visualizations like Bode plots, transient waveforms, or any other graphical representation of simulation data.

When you request a plot, the simulator generates it automatically and displays it inline in the chat.

Rerunning and Modifying Simulations

After running a simulation, you can ask the simulator to rerun it with modifications. The tool reuses the working netlist from the previous simulation and only changes what you request, making iterations fast and reliable.

SPICE Model Library

The simulator tool has access to a built-in library of SPICE models covering common components like op-amps, comparators, MOSFETs, and more. When your simulation requires a specific component model, the tool looks for the library and includes the appropriate model automatically.

You do not need to provide SPICE models yourself—just describe the component you want to use (e.g., "TL072 op-amp" or "LM393 comparator"), and the tool will find and include the correct model.

SPICE Netlist Format

If you prefer, you can provide your own SPICE netlist directly. The simulator tool works with standard SPICE netlist syntax. Here's a simple example:

Important notes:

1. Always include a .print directive to specify which node voltages or branch currents to output

2. End the netlist with .end

3. Include appropriate analysis commands (e.g., .tran, .ac, .dc, .op)

Example Use Cases

Here are some common use cases for the simulator tool:

Passive Filter Analysis

Active Filter Analysis

Current Analysis

Voltage and Current Ripple

RC Timing and Oscillators

Comparing Circuit Designs

Tips for Effective Simulations

To get the most out of the simulator tool:

1. Be specific about component values; specify resistance, capacitance, and other component values with appropriate units (e.g., 1k, 10uF, 100nH).

2. Describe the circuit topology, clearly explain how components are connected, or let the tool read from your schematic.

3. Specify the analysis type; clearly mention whether you want a transient, AC, DC, or operating point analysis.

4. Ask for specific metrics; tell the tool what you want to measure (e.g., "-3dB frequency", "output ripple", "gain at 1kHz").

5. Request visualizations: Ask for Bode plots, waveforms, or comparison charts to see your results graphically.

6. Iterate on results: Use the rerun capability to quickly explore different component values or circuit configurations.

7. Break down complex circuits: For very complex circuits, consider simulating smaller subsections first.

Automatic Error Handling

The simulator tool automatically handles common simulation issues by iterating on the netlist:

Syntax Errors

If the netlist has syntax errors, the tool will:

1. Identify the specific error in the Ngspice output

2. Generate a corrected version of the netlist

3. Retry the simulation with the corrected netlist

Convergence Issues

For convergence problems, the tool will:

1. Identify potential causes of convergence failure

2. Add appropriate .OPTIONS statements (e.g., RELTOL, ABSTOL, ITL1, ITL4)

3. Adjust initial conditions or component values if necessary

4. Retry with alternative simulation parameters

Time Step Issues

If time step errors occur, the tool will:

1. Adjust .TRAN parameters to use smaller time steps

2. Add .OPTIONS statements for tolerance control

3. Retry the simulation with adjusted parameters

Limitations

While the simulator tool is powerful, it has some limitations to be aware of:

• Simulations are powered by Ngspice and are limited to circuits that Ngspice can handle

• Certain specialized or proprietary SPICE models may not be available in the built-in model library

• Very large circuits with many components may take longer to simulate

• Simulations cover electrical behavior only. Thermal, mechanical, and electromagnetic effects are not included

• The tool works best with analog and mixed-signal circuits; purely digital simulations are not supported

Related Features

The simulator tool works well with other Flux chat capabilities:

• Flux Code Tool — Generate Python scripts for advanced data analysis or custom visualizations

• Flux File Tool — Extract information from component datasheets

• Flux Calculator Tool — Perform engineering calculations

• Flux Help Tool — Search Flux Editor documentation for guidance