Pi Attenuator Calculator
Calculate resistor values for Pi (π) attenuator circuits with equal or unequal impedances
Calculate Pi Attenuator Resistor Values
Choose equal for simple attenuation, unequal for impedance matching
Amount of signal reduction required
Unit for impedance values
Source and load impedance (both equal)
Resistor Values
K Factor: 0.00 (attenuation ratio)
Attenuation: 0.0 dB
Circuit: Equal impedances (50 Ω)
Design Recommendations
Example Calculation
40 dB Equal Impedance Attenuator
Requirements: 40 dB attenuation
Impedance: 50 Ω (source and load)
K Factor: 10^(40/20) = 100
Calculation Steps
R₁ = 50 × (100 + 1) / (100 - 1) = 51.0 Ω
R₂ = 50 × (100² - 1) / (2 × 100) = 2499.75 Ω
Result: R₁ = 51 Ω, R₂ = 2500 Ω
Power ratio: Input/Output = 10,000:1
Common Attenuation Values
Standard Impedances
50 Ω
Most RF/microwave systems
75 Ω
Video and cable TV systems
600 Ω
Audio and telephony
377 Ω
Free space impedance
Applications
Signal level control in RF systems
Impedance matching between stages
Isolation between circuit blocks
Protection of sensitive inputs
Test equipment calibration
Antenna matching networks
Understanding Pi Attenuators
What is a Pi Attenuator?
A Pi attenuator is an electronic circuit that reduces signal amplitude while maintaining impedance matching. It's called "Pi" because its topology resembles the Greek letter π, with two series resistors and one shunt resistor.
Why Use Pi Attenuators?
- •Precise signal level control
- •Impedance matching capability
- •Good isolation between stages
- •Wide frequency response
Equal Impedance Formulas
K = 10^(Attenuation_dB/20)
R₁ = Z₀ × (K + 1) / (K - 1)
R₂ = Z₀ × (K² - 1) / (2K)
Unequal Impedance Formulas
R₁ = Zₛ × (K² - 1) / (K² - 2K√(Zₛ/Z_L) + 1)
R₂ = 0.5√(Zₛ × Z_L) × (K² - 1) / K
R₃ = Z_L × (K² - 1) / (K² - 2K√(Z_L/Zₛ) + 1)
Circuit Topology
Equal Impedances
R₁ and R₃ are equal series resistors, R₂ is the shunt resistor. Used when source and load impedances are the same.
Unequal Impedances
All three resistors have different values. Used for impedance matching between different source and load impedances.
Design Considerations
Power Rating
Resistors must handle the power dissipated. Use P = I²R for each resistor.
Frequency Response
Parasitic capacitance and inductance affect high-frequency performance.
Standard Values
Use standard resistor values or precision resistors for exact attenuation.