Low Pass / High Pass / Band Pass Filter Calculator
🔍 Overview of Filter Types
| Filter Type | Function |
|---|---|
| Low Pass Filter (LPF) | Allows low frequencies to pass, blocks high frequencies |
| High Pass Filter (HPF) | Allows high frequencies to pass, blocks low frequencies |
| Band Pass Filter (BPF) | Allows a specific band of frequencies |
📘 1. Low Pass Filter (LPF)
✅ Function:
Passes frequencies below a cutoff frequency fc attenuates higher frequencies.
🔧 Common Circuits:
- RC (Resistor-Capacitor)
- RL (Resistor-Inductor)
- RLC (Series or Parallel) — for sharper roll-off
📐 Cutoff Frequency:
- RC: fc=1/(2πRC)
- RL: fc=R/2πL
⚙️ Applications:
- Anti-aliasing before ADC
- Audio tone shaping (bass filters)
- Sensor signal filtering (temperature, pressure)
- Removing switching noise from power rails
📘 2. High Pass Filter (HPF)
✅ Function:
Passes frequencies above a cutoff frequency, blocks lower frequencies.
🔧 Common Circuits:
- RC High Pass
- RL High Pass
- RLC
📐 Cutoff Frequency:
- RC: fc=1/2πRC (same as LPF)
⚙️ Applications:
- AC coupling (removes DC offset)
- Audio treble filters
- Removing low-frequency drift or slow-varying noise
- Power-on glitch suppression
📘 3. Band Pass Filter (BPF)
✅ Function:
Passes a specific range of frequencies centered around f0f_0f0
🔧 Common Circuits:
- Series RLC Band Pass
- Parallel RLC Band Pass
📐 Formulas:
- Center frequency: f0=1/(2πsqrt(LC))
- Bandwidth:
- Series RLC: BW=R/2πL
- Parallel RLC: BW=1/RC
⚙️ Applications:
- Communication systems (tuned RF circuits)
- Audio equalizers (mid-band shaping)
- ECG/EEG medical filtering
- Vibration sensing in specific frequency bands
📦 Filter Type vs. Use Case Matrix
| Application | Filter Type | Notes |
|---|---|---|
| Audio low-end filtering | RC/RLC Low Pass | Cuts high-frequency hiss |
| Removing DC offset from signal | RC High Pass | Often used before op-amps |
| Extracting specific RF signal | RLC Band Pass | Sharp tuning with narrow BW |
| Cleaning PWM for analog use | RC Low Pass | Converts PWM to smooth DC |
| Vibration analysis (FFT prep) | LPF & BPF combo | Isolates structural modes |