Band-pass filters allow signals within a certain frequency range to pass through while attenuating signals outside this range. Active band-pass filters, which include amplification components like operational amplifiers (OpAmps), are particularly useful for enhancing signal quality and selecting specific frequency bands.
Objective
The goal of this experiment is to construct an active band-pass filter using a Red Pitaya, analyze its frequency response, and observe the effects of modifying component values on the filter's performance.
Materials and Setup
- Red Pitaya or equivalent signal generator and oscilloscope.
- Resistors: 2 x 100 ohm.
- Capacitors: 1 x 47 ÎĽF (C1) and 1 x 100 nF.
- Breadboard and connecting wires.
- Oscilloscope probes set to x1 mode.
Necessary Equations
The cutoff frequencies (fc) of a band-pass filter can be calculated using the formula:
The frequency response of an active band-pass filter is also influenced by the operational amplifier's characteristics and the specific configuration of resistors and capacitors around it.
Experiment
Let’s fire up a Red Pitaya and build the circuit.
You know the drill. Signal generator channel 1 and input channel 1 to filter input, channel 2 to output. Both probes in x1 mode and run the bode analyzer! Both resistors are 100 ohm, the big capacitor (C1) is 47 uF, the small one is 100 nF, and here is what I got:
Nothing too special, sure, but we can move cutoff frequencies to alter the filter’s characteristics. This can be done either by changing resistors or changing capacitors. The following bode plot shows filter’s characteristics where C1 or R1 got changed by a factor of 10. I will let the reader try to determine which component got changed. Hint: take a look at the Y axis.
Conclusion
This experiment offers a practical introduction to active band-pass filters, from construction through to analysis. By engaging with the process of building the filter, conducting frequency response analysis, and observing the impact of component modifications, learners gain a comprehensive understanding of how band-pass filters function and how their characteristics can be adjusted to meet specific needs. This hands-on approach not only solidifies theoretical concepts but also enhances skills in practical circuit analysis and design.