Colpitts Oscillator : Simscape Tutorial

Simscape Electrical is a software tool within the MATLAB/Simulink environment that allows engineers and scientists to model, simulate, and analyze electrical systems. It provides a library of pre-built electrical components, such as resistors, capacitors, and transformers, as well as tools for creating custom components.

With Simscape Electrical, users can create models of power electronics, electric drives, renewable energy systems, and more. They can also simulate the behavior of these systems under a wide range of conditions, such as varying loads and different operating conditions.

Simscape Electrical is designed to be user-friendly and allows for easy visualization of results. It also integrates with other Simulink tools, such as Simulink Design Optimization and Simulink Verification and Validation, to provide a complete system design and analysis environment. Overall, Simscape Electrical is a powerful tool for engineers and scientists working on electrical systems design and analysis.

A Colpitts oscillator is a type of electronic oscillator circuit that is used to generate a high frequency sinusoidal signal. It is named after its inventor, American engineer Edwin Colpitts.

The Colpitts oscillator uses a combination of capacitors and inductors to create a resonant circuit that produces a high-frequency signal. The resonant circuit is formed by a combination of two capacitors and an inductor, with a transistor amplifier that provides feedback to sustain the oscillation. The feedback network consists of a voltage divider, with the capacitors and inductor forming a tank circuit that is tuned to the desired frequency of oscillation.

The Colpitts oscillator is known for its ability to produce a high-quality, stable output signal over a wide range of frequencies. It is commonly used in radio and communication systems as a local oscillator, frequency synthesizer, or signal generator. It is also used in scientific and industrial applications that require precise and stable oscillations.

In this blog post, it is demonstrated how to design and simulate a Colpitts oscillator using Simscape Electrical, a software tool within the MATLAB/Simulink environment. The colpitts oscillator is designed with NPN bipolar junction transistor based amplifier using voltage divider BJT transistor biasing method in common emitter configuration. The frequency of the Colpitts oscillator is 100kHz.

Designing the Circuit

The Colpitts oscillator consists of a tank circuit, which is a combination of two capacitors and an inductor, with a BJT amplifier that provides feedback to sustain the oscillation. To design the circuit, we will start by selecting the values for the components. The component for the amplifier can be determined using the BJT amplifier calculator and the Colpitts oscillator tank component can be determined using the online oscillator calculator.

We will start by creating a new Simscape Electrical model and adding the components to the schematic.We will use the Electrical Sources library to add a voltage source and a ground node. We will also use the Electrical Elements library to add the capacitors and inductor, and the Semiconductors library to add the transistor. This is explained step by step with video demonstration in the  BJT amplifier with Simscape electrical tutorial.

We will use two 0.1µF capacitors and a 50µH inductor for the tank circuit. These values will create an oscillating sine wave with frequency of 100kHz. For the transistor amplifier, we will use an NPN transistor with a gain of 100. We will bias the transistor using voltage divider bias at the base with 10 kΩ resistor and 4.7kΩ resistor. We will also use the 250Ω resistor at the collector and 100Ω resistor at the emitter to bias the collector and emitter respectively. The circuit diagram build simscape electrical library components as shown below.

colpitts oscillator circuit diagram with simscape

Simulating the Circuit

Once we have designed the circuit, we can simulate it in Simscape Electrical to test its behavior. We will plot the voltage across the tank circuit to observe the oscillation. The model diagram below shows a voltage sensor block which connects the output of the oscillator to a time scope.

voltage sensor
The voltage sensor block is just a sub-system block whose content is shown below.

We will use the Simscape Electrical Solver Configuration tool to configure the simulation settings which is shown below.

solver configuration
 We will set the simulation time to inf and the simulation solver to be the variable-step solver.

model settings

After configuring the simulation settings, we can run the simulation to see the output of the circuit. The following shows the oscillator output signal waveform on the time scope.

colpitts oscillator signal in simscape simulation
Video demonstration
 The following video demonstrates working of Colpitts oscillator designed and simulated with Simscape electrical in Simulink.

Interpreting the Results

In the simulation, we observe a sinusoidal output voltage across the tank circuit, with a frequency of approximately 100kHz. The waveform is stable and exhibits a high-quality factor (Q-factor), indicating that the Colpitts oscillator is operating correctly.


In this blog post, we have demonstrated how to design and simulate a Colpitts oscillator using Simscape Electrical. By selecting appropriate values for the components and simulating the circuit in the software, we were able to observe the oscillation of the circuit and verify its behavior. This approach can be used to design and simulate a wide range of electronic circuits, making Simscape Electrical a powerful tool for engineers and scientists. After verifying the circuit one can build the colpitts oscillator on breadboard.

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