Parametric Analysis of Electronic Circuits with uSimmics (formerly QucsStudio) [2026]

Simulation
2024.07.20

Parametric analysis in uSimmics (formerly QucsStudio) lets you systematically vary a specific circuit parameter and quantify its effect on performance — an indispensable technique in electronics design. This article walks through the complete procedure using a series LC circuit as the example: sweeping the capacitor value across four choices and plotting the resulting voltage frequency response step by step.

What You’ll Learn

  • The concept of parametric analysis (Parameter Sweep) and its practical applications in circuit design
  • How to configure the Parameter Sweep block in uSimmics (formerly QucsStudio)
  • How to assign variables to component values for dynamic control during a sweep
  • The workflow for combining AC analysis with Parameter Sweep to evaluate frequency response
  • How to read simulation results and apply them to design optimization

What Is Parametric Analysis?

Parametric analysis (also called a Parameter Sweep) involves systematically varying one or more circuit parameters — resistance, capacitance, supply voltage, etc. — and observing circuit behavior under each condition. In professional electronics design it serves several key purposes:

Key Applications

  1. Sensitivity evaluation
    Quantifies how much each individual parameter influences overall circuit behavior — gain, bandwidth, resonant frequency, and so on.

  2. Optimization
    Searches for the parameter values that maximize or minimize a performance metric such as output power, efficiency, or bandwidth.

  3. Robustness assessment (design for manufacturability)
    Evaluates how sensitive a design is to component tolerances and parameter variation, confirming that the circuit will perform adequately across its expected manufacturing spread.

Step-by-Step Procedure in uSimmics (formerly QucsStudio)

The example below uses a series LC circuit with a fixed 10 nH inductor. The capacitance is swept across four values — 10 pF, 33 pF, 56 pF, and 100 pF — and the voltage frequency response is simulated for each.

Step 1: Build the Circuit

  1. Launch uSimmics (formerly QucsStudio) and create a new project.
  2. From the Components tab, select an Inductor and a Capacitor and place them on the schematic canvas.
  3. Connect the inductor and capacitor in series. Set the inductor value to 10 nH (fixed for this example).
  4. Add a signal source (Power Source) and a ground symbol to complete the circuit.
  5. Place a testpoint at the input side of the inductor to serve as the voltage measurement node.

Step 2: Assign a Variable to the Capacitor

  1. Double-click the capacitor to open its properties dialog. In the capacitance (C) value field, enter the variable name Cvar.
  2. This makes the capacitor value a variable that the Parameter Sweep block can control.
  3. Variable names can be anything, but a short, descriptive alphanumeric name is recommended.

Step 3: Configure the AC Simulation

  1. From the Simulations tab, add an AC Simulation block to the schematic.
  2. Set the following parameters:
  3. Start frequency: 10 MHz
  4. Stop frequency: 1 GHz
  5. Frequency steps: choose a point count or logarithmic sweep as appropriate.

Step 4: Configure the Parameter Sweep

  1. From the Simulations tab, add a Parameter Sweep block to the schematic.
  2. Select Cvar as the parameter to sweep.
  3. Choose a sweep type:
Type Description
Linear Steps through values at equal intervals
Logarithmic Steps through values on a logarithmic scale
List Uses an explicit list of arbitrary values
  1. For this example, select List and configure as follows:
  2. Type: list
  3. Value: 10p; 33p; 56p; 100p

This runs the simulation four times — once for each capacitance value.

Step 5: Run the Simulation

  1. Click the Simulate button to start the simulation.
  2. A Cartesian Plot display will be added automatically (or add one manually).
  3. Plot testpoint.v (the voltage at the testpoint) on the graph.

Step 6: Evaluate the Results

  1. Analyze the resulting graph to assess how capacitance affects the voltage frequency response.
  2. The resonant frequency of a series LC circuit ($f_r = \frac{1}{2\pi\sqrt{LC}}$) depends on the capacitance C, so each capacitor value will produce a peak (voltage maximum) at a different frequency.

  3. The 10 pF case will show the highest resonant frequency; the 100 pF case will show the lowest.

  4. Use the analysis to select the optimal capacitance. If needed, adjust the sweep conditions and re-run the simulation.

Further Applications of Parametric Analysis

Parametric analysis extends well beyond LC resonance evaluation. Common use cases include:

  • Filter design — Finding the optimal C or L value that sets a target cutoff frequency
  • Amplifier design — Evaluating how bias resistor values affect gain and operating point
  • Power supply design — Assessing how output capacitance affects load transient response
  • RF circuit design — Optimizing impedance-matching network parameters

Summary

Parametric analysis is an essential method for optimization and performance evaluation during the design phase. The Parameter Sweep block in uSimmics (formerly QucsStudio) lets you efficiently evaluate multiple component-value conditions in a single simulation run. The key to accurate parametric analysis is properly linking three elements: variable assignment on the component, the AC Simulation block, and the Parameter Sweep block. Use the procedure in this article as a starting point and apply parametric analysis to a wide variety of circuits.

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