Differential Termination Calculator
Design differential-pair termination networks for USB, HDMI, LVDS, PCIe: series, parallel, Thevenin, and AC-coupled termination topologies.
How to Use
- Enter differential impedance Z_diff (90, 100, 120 Ω typical).
- Pick termination style: parallel, Thevenin, AC-coupled.
- Tool returns resistor values + power dissipation estimate.
Show Work
Topologies
History of Differential Termination
Differential signaling traces back to Alexander Graham Bell's 1881 twisted-pair telephone patent for common-mode noise cancellation. The modern 100-ohm-differential terminology emerged in the 1980s-90s with LVDS (National Semiconductor, 1994) and PCI / PCIe (2003). AC-coupled termination (series capacitors in each leg) was mandated by PCIe, SATA, and HDMI specs to preserve DC balance regardless of transmitter common-mode bias. Modern PHYs integrate source-matched termination on-chip.
About This Calculator
Enter differential impedance (match to PCB trace), pick topology (parallel for simple termination, Thevenin for common-mode bias, AC-coupled for PCIe/HDMI), common-mode voltage, and signal swing. The tool returns resistor and capacitor values.
For LVDS: simple 100 Ω parallel at receiver. For PCIe: 100 Ω differential + AC-coupling caps (receiver side). For HDMI sink: Thevenin to the chip\'s AVCC rail. Everything runs client-side.
About the Differential Termination Calculator
Meet the Differential Termination Calculator: a free, no-fuss tool for electronics and circuit design with nothing to install and no sign-up. Design differential-pair termination networks for USB, HDMI, LVDS, PCIe: series, parallel, Thevenin, and AC-coupled termination topologies.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Z_diff values?
USB 2.0: 90 Ω. HDMI/PCIe/LVDS/Ethernet: 100 Ω. Some older buses: 120 Ω. Always match PCB trace Z_diff to receiver termination for reflection-free reception.
Parallel vs Thevenin?
Parallel: single resistor across the pair at receiver. Simpler but no common-mode reference. Thevenin (split): two resistors to rails at midpoint; provides common-mode bias. Standard for LVDS without on-chip termination.
AC coupling?
Capacitors in series with the pair block DC while passing AC. Required by PCIe, HDMI (receiver side), and many modern high-speed interfaces. Cap typical 0.1 µF for 10+ Mbps signals.
How do I use the Differential Termination Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
USB 2.0 Termination
On-chip 45Ω to rail in the transmitter + 45Ω on the receive side = 90Ω end-to-end.
PCIe AC-Coupled
100 Ω diff + 0.1 µF series caps = lossless AC coupling required by spec.
LVDS to FPGA
100 Ω Thevenin bias network for FPGA without internal LVDS termination.
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