GopalKrishna Advanced Rural Research Foundation
GARRF Virtual Engineering & Electronics Laboratory
KALAM ZERO RESEARCH FUNDING LAB
EXPERIMENT 16
RC HIGH-PASS FILTER
FREQUENCY RESPONSE
SIGNAL PROCESSING
KALAM ZERO RESEARCH FUNDING LAB
In Experiment 15, we studied the RC low-pass filter. Now we investigate its complementary circuit: the RC high-pass filter.
A high-pass filter attenuates low-frequency components while allowing higher-frequency components to pass. This simple circuit introduces students to another fundamental idea in electronic signal conditioning.
| Experiment 15 | Experiment 16 |
|---|---|
| RC Low-Pass | RC High-Pass |
| Passes low frequencies | Passes high frequencies |
| Attenuates high frequencies | Attenuates low frequencies |
| Output across capacitor | Output across resistor |
Together, the two experiments demonstrate one of the most important ideas in signal processing: different circuit arrangements can select different portions of the frequency spectrum.
A high-pass filter allows higher-frequency components of a signal to pass while reducing lower-frequency components.
The basic high-pass circuit contains a capacitor in series with the input and a resistor connected from the output node to ground. The output is measured across the resistor.
At frequencies much lower than the cutoff frequency, the output is strongly attenuated. As frequency increases, the output approaches the input amplitude.
At the cutoff frequency, the output magnitude is approximately 70.7% of the input magnitude, corresponding to approximately −3 dB.
The output amplitude and phase change as the input frequency moves relative to the cutoff frequency.
At low frequencies the gain is small. Above the cutoff frequency the gain approaches unity.
| Trial | R | C | fc | Input f | Output | Gain | Phase |
|---|
Design a high-pass filter with a cutoff frequency close to 1 kHz.
Experiment with different combinations of R and C. Find at least three different R-C combinations that produce approximately the same cutoff frequency.
For:
The cutoff frequency is:
At a frequency much higher than 159 Hz, the output approaches the input amplitude. At frequencies much lower than 159 Hz, the output is strongly attenuated.
Many sensor systems contain unwanted low-frequency components, including slow drift, offsets and environmental variations. High-pass filtering provides a simple way of understanding how unwanted low-frequency components can be reduced.
In Structural Health Monitoring, engineers often analyse dynamic responses such as vibration, acoustic or electromechanical signals. Understanding high-pass filtering is an important foundation for designing signal-conditioning systems.
The same fundamental principle can later be implemented using active filters, digital filters and AI-based signal-processing systems.
Students can use CHITTI to explore high-pass filters, frequency response, signal conditioning, sensors and robotics.
“What is an RC high-pass filter?”
“Why does a capacitor pass high-frequency signals?”
“How do I calculate the cutoff frequency?”
“How can I design a 1 kHz high-pass filter?”
“How are high-pass filters useful in PZT SHM?”
This is a virtual experiment. If reproduced physically, use a current-limited laboratory supply and verify resistor, capacitor and instrument ratings before making connections.