What is a differential attenuator?
Three resistors in series across the input, with the output taken across the middle one: Vout = Vin · Rm / (Ra + Rm + Rb). It scales a differential voltage down for a differential amplifier or ADC.
Vout = Vin · Rm / (Ra + Rm + Rb)
Differential attenuator calculator
Vin is applied across three resistors and Vout is taken across the middle one. Ra = Rb keeps both legs symmetric.
Attenuator specification
Vin is applied across Ra + Rm + Rb, Vout is taken across the middle resistor Rm. Ra = Rb keeps both legs symmetric.
Ratio examples (fractions accepted)
Comparison by series
Best attenuator found in each series, within the allowed current deviation.
| Series | Ra = Rb (outer) | Rm (output) | Ratio | Error | Current | Parts |
|---|
Highlighted row: overall best. Ratio = Rm / (Ra + Rm + Rb); “Parts” counts both Ra and Rb.
Frequently asked questions
Why keep Ra equal to Rb?
Equal outer resistors keep both legs symmetric, so a common-mode voltage is attenuated equally on both sides. Mismatch between Ra and Rb converts common-mode voltage into a differential error.
How much power do the resistors dissipate?
The branch current I = Vin / (Ra + Rm + Rb) flows through all three resistors; each one dissipates I²·R. With high input voltages, Ra and Rb carry most of the voltage and the power.