Bias Tee Component Calculator
Calculate first-pass DC-block capacitor and DC-feed choke values for combining power and signal on one line.
Inputs and sizing rules
Size the DC-block capacitor and DC-feed choke for a first-pass bias tee estimate at one signal frequency.
First-pass component values
The series capacitor should look like a low impedance at the signal frequency so the AC signal can pass with limited loading. The feed inductor should look like a high impedance at the signal frequency so the RF or AC signal is isolated from the DC feed path. This is a single-frequency estimate only. Real designs depend on bandwidth, DC bias effects, ESR, ESL, self-resonant frequency, current rating, DCR, parasitic capacitance, connector transitions, return path, and layout.
First-pass bias tee component sizing
A bias tee uses a series capacitor to pass the signal while blocking DC, and a feed inductor to pass DC while presenting a high impedance to the signal path.
DC block capacitor
Choose a capacitor with low reactance at the selected signal frequency.
DC feed choke
Choose an inductor with high reactance at the selected signal frequency.
Single-frequency estimate
Use real impedance curves before committing to a broadband or RF design.
Related calculators
AC coupling capacitor calculator
Size a simpler DC-block capacitor from a high-pass cutoff target.
LC filter cutoff calculator
Check the related LC frequency created by the selected values.
Frequency period converter
Convert the sizing frequency into period or wavelength context.
Engineering notation converter
Convert capacitor and inductor values into readable engineering notation.
Engineering reference
Equations, assumptions, and design guidance
Sizes a DC-block capacitor and DC-feed choke from target reactance values at one selected frequency.
Equations and variables
Xc = 1 / (2*pi*f*C)Xl = 2*pi*f*L- f
- Sizing frequency (Hz)
- Xc
- Capacitor reactance target (ohm)
- Xl
- Inductor reactance target (ohm)
Assumptions and limitations
Assumptions
- The estimate is evaluated at a single frequency.
- Shortcut mode uses Xc <= Z0 / 10 and Xl >= 10 * Z0.
Limitations
- This is not a broadband RF model. Real parts depend on bandwidth, DC bias, ESR, ESL, self-resonant frequency, current rating, DCR, parasitic capacitance, connectors, return path, and layout.
Worked example and design use
10 MHz, 50 ohm line
Inputs: Z0 = 50 ohm, Xc target = 5 ohm, Xl target = 500 ohm
Outputs: C about 3.18 nF, L about 7.96 uH
Design guidance
- Use this as a first-pass starting point, then check real component impedance curves and layout parasitics.