Resistive Attenuator

Formula

Description

A resistive attenuator (L-pad) reduces signal amplitude by a known amount using a voltage divider expressed in decibels. The attenuation is always negative since R2/(R1+R2) is always less than 1. Resistive attenuators are frequency-independent up to very high frequencies where parasitic capacitance becomes significant, making them useful for broadband signal reduction. They are commonly used to reduce signal levels to safe ranges for oscilloscope inputs, spectrum analyzers, and RF test equipment.

Variables

• Atten — Attenuation in decibels (dB, negative value)
• R1 — Series resistor (Ω)
• R2 — Shunt resistor to ground (Ω)

Practical Notes

For impedance-matched attenuators (T-pad or Pi-pad), additional resistors maintain the characteristic impedance. A 6 dB attenuator halves the voltage. A 20 dB attenuator reduces voltage by 10x. For precision attenuation, use 0.1% tolerance resistors. At RF frequencies, use purpose-built attenuator components with controlled impedance.