Operational Amplifier Filter Design Experiment

Introduction

Filters are essential components in electronics for isolating specific frequency ranges in signals. This experiment involves designing and testing a low-pass filter using an operational amplifier (op-amp). Low-pass filters allow low frequencies to pass while attenuating higher frequencies, making them ideal for audio processing and communication systems.

Objective

The objective of this tutorial is to design an op-amp low-pass filter, observe its frequency response, and identify its cutoff frequency, where attenuation begins.

Components Required

• Operational Amplifier (e.g., LM741 or TL081)
• Resistors (e.g., 10kΩ, 100kΩ)
• Capacitor (e.g., 0.1 µF or 1 µF)
• DC Power Supply (e.g., ±12V for the op-amp)
• Signal Generator (for input frequency sweep)
• Oscilloscope (to observe the output waveform)
• Breadboard and Connecting Wires

Circuit Diagram

Note: The low-pass filter is configured with a resistor in series with the input and a capacitor between the inverting input and the output of the op-amp.

Procedure

1. Set Up the Circuit: Assemble the low-pass filter circuit by connecting the resistor (10kΩ) in series with the input signal and the capacitor (0.1 µF) between the inverting input and the op-amp's output.
2. Power the Op-Amp: Connect a dual DC power supply (e.g., ±12V) to the op-amp to ensure proper operation.
3. Apply Input Signal: Connect a signal generator to the input, starting with a low-frequency sine wave (e.g., 100 Hz).
4. Observe the Output: Attach the op-amp filter's output to an oscilloscope and measure the signal's amplitude at 100 Hz.
5. Perform a Frequency Sweep: Gradually increase the input frequency using the signal generator and observe how the output amplitude changes.
6. Determine the Cutoff Frequency: Record the frequency at which the output amplitude drops to approximately 70.7% (3 dB point) of its low-frequency value.

Observations and Analysis

• At low frequencies (below the cutoff frequency), the output signal matches the input signal in amplitude.
• Near the cutoff frequency, the output amplitude starts to decrease.
• Above the cutoff frequency, the filter effectively attenuates the high-frequency signals.

Conclusion

In this experiment, we designed and analyzed a low-pass filter using an op-amp. This filter effectively blocks high-frequency signals while allowing low-frequency signals to pass. The cutoff frequency is determined by the resistor and capacitor values, making the design adaptable for various applications in signal conditioning and audio systems.