Resistive Attenuator
Atten = 20 × log10(R2 / (R1 + R2))
Quick answer
This calculator solves Atten_dB = 20 × log10(R2 / (R1 + R2)) for Attenuation. With Series Resistor 0.47 kΩ, Shunt Resistor 1.03 kΩ, the result is -3.265 dB.
Calculator
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.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| Atten | Attenuation | dB | dB |
| R1 | Series Resistor | Ω | mΩ, Ω, kΩ, MΩ |
| R2 | Shunt Resistor | Ω | mΩ, Ω, kΩ, MΩ |
Step by step
- 1. What you know: Series Resistor 0.47 kΩ, Shunt Resistor 1.03 kΩ
- 2. The relation: Atten_dB = 20 × log10(R2 / (R1 + R2))
- 3. Substitute: R1 = 0.47 kΩ, R2 = 1.03 kΩ
- 4. Result: Attenuation = -3.265 dB
Worked examples
Minimum range
Given: Series Resistor 1 Ω, Shunt Resistor 2.2 Ω
Result: Attenuation = -3.255 dB
Low range
Given: Series Resistor 10 Ω, Shunt Resistor 22 Ω
Result: Attenuation = -3.255 dB
Typical
Given: Series Resistor 0.47 kΩ, Shunt Resistor 1.03 kΩ
Result: Attenuation = -3.265 dB
High range
Given: Series Resistor 4.7 kΩ, Shunt Resistor 10.3 kΩ
Result: Attenuation = -3.265 dB
Maximum range
Given: Series Resistor 47 kΩ, Shunt Resistor 103 kΩ
Result: Attenuation = -3.265 dB
How Attenuation changes with Series Resistor
| Series Resistor (input) | Attenuation (result) |
|---|---|
| 47 Ω | -0.3876 dB |
| 117.5 Ω | -0.9383 dB |
| 0.235 kΩ | -1.785 dB |
| 0.3525 kΩ | -2.557 dB |
| 0.47 kΩ | -3.265 dB |
| 0.705 kΩ | -4.529 dB |
| 0.94 kΩ | -5.633 dB |
| 1.88 kΩ | -9.021 dB |
| 3.29 kΩ | -12.45 dB |
| 4.7 kΩ | -14.91 dB |
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<p><a href="https://vbatpower.com/formulas/attenuation-resistor/">Resistive Attenuator</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Resistive Attenuator?
Use Atten_dB = 20 × log10(R2 / (R1 + R2)). With Series Resistor 0.47 kΩ, Shunt Resistor 1.03 kΩ, Attenuation works out to -3.265 dB.
What is the formula for Resistive Attenuator?
The formula is Atten_dB = 20 × log10(R2 / (R1 + R2)). A resistive attenuator (L-pad) reduces signal amplitude by a known amount using a voltage divider expressed in decibels.
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