Low Pass Filter Calculator
Calculate cutoff frequency, component values, and gain for RC, RL, and op-amp low pass filters
Calculate Low Pass Filter Parameters
Resistor value in Ohms
Capacitor value
Target frequency for -3dB point
Filter Analysis Results
Formula Used
fc = 1 / (2πRC)
Where R = 1000Ω, C = 100.000 nF
Circuit Diagram
RC Low Pass Filter
|
C
|
GND
Output taken across capacitor
Example Calculation
1 kHz RC Low Pass Filter
Target cutoff: 1 kHz
Resistor: 3.3 kΩ
Required capacitor: 47 nF
Calculation
fc = 1 / (2πRC)
C = 1 / (2πRfc)
C = 1 / (2π × 3300 × 1000)
C = 48.2 nF ≈ 47 nF
Actual fc = 1.026 kHz
Filter Types
RC Filter
Simple passive filter using resistor and capacitor
fc = 1/(2πRC)
RL Filter
Passive filter using resistor and inductor
fc = R/(2πL)
Inverting Op-Amp
Active filter with gain and phase inversion
G = -Rf/Ri
Non-Inverting Op-Amp
Active filter with gain, no phase inversion
G = 1 + Rf/Rg
Design Tips
Choose cutoff frequency 10× higher than highest signal frequency
Use standard component values for practical circuits
RC filters are simple but RL filters avoid DC voltage drop
Op-amp filters provide gain and better input/output isolation
Consider component tolerances in final design
Understanding Low Pass Filters
What is a Low Pass Filter?
A low pass filter is an electronic circuit that allows low-frequency signals to pass through while attenuating (reducing) high-frequency signals. The cutoff frequency (fc) is the point where the output signal is reduced by 3dB (about 70.7% of the input amplitude).
How It Works
- •Frequency-dependent impedance of reactive components
- •Capacitive reactance decreases with frequency
- •Inductive reactance increases with frequency
- •Creates voltage divider with frequency response
Passive vs Active Filters
Passive Filters (RC, RL)
- • No external power required
- • Simple and inexpensive
- • Unity gain maximum
- • Loading effects possible
Active Filters (Op-Amp)
- • Can provide gain
- • Good input/output isolation
- • Requires power supply
- • More complex but versatile
⚠️ Design Considerations
- • Component tolerance affects accuracy
- • Temperature stability of components
- • Input/output impedance matching
- • Power supply requirements (active filters)
✓ Applications
- • Audio system bass enhancement
- • Anti-aliasing in data acquisition
- • EMI/RFI noise reduction
- • Signal conditioning circuits
📋 Key Parameters
- • Cutoff frequency (fc at -3dB)
- • Roll-off rate (20dB/decade for 1st order)
- • Pass-band gain
- • Input/output impedance