<differentialpair />

Why use a differential pair?

A differential signal, such as USB D+ and D-, travels over a positive and a negative trace. If one route is longer than the other, the two halves of the signal arrive at different times.

<differentialpair /> tells a supported autorouter which two existing traces form the pair and how much their routed lengths may differ. It does not create electrical connections; add those with <trace />.

This element currently constrains length matching only. It does not configure differential impedance, trace width, pair spacing, or parallel routing.

Quick start with trace names

Use trace names when the same circuit creates the traces and the constraint. Give each <trace /> a unique name, then reference those names from <differentialpair />.

export default () => (
  <board width="24mm" height="12mm">
    <chip
      name="U_HOST"
      footprint="soic8"
      pinLabels={{ pin1: "USB_DP", pin2: "USB_DM" }}
      pcbX={-7}
      pcbY={-2}
    />
    <chip
      name="U_DEVICE"
      footprint="soic8"
      pinLabels={{ pin1: "USB_DP", pin2: "USB_DM" }}
      pcbX={7}
      pcbY={2}
    />

    <trace
      name="usb_dp"
      from=".U_HOST > .USB_DP"
      to=".U_DEVICE > .USB_DP"
    />
    <trace
      name="usb_dm"
      from=".U_HOST > .USB_DM"
      to=".U_DEVICE > .USB_DM"
    />

    <differentialpair
      name="USB_DATA"
      positiveConnection="usb_dp"
      negativeConnection="usb_dm"
      maxLengthSkew={0.05}
    />
  </board>
)

In this example:

• usb_dp and usb_dm create the electrical connections.
• <differentialpair /> groups those connections for length matching.
• maxLengthSkew={0.05} allows an absolute routed-length difference of up to 0.05 mm.

Supported autorouters try to add length, often as a meander, to the shorter route. Routing can fail when there is no valid segment or enough room to meet the tolerance.

Choosing trace names or pin selectors

Use	When to choose it	Example
Trace name	The same circuit defines and names the traces.	positiveConnection="usb_dp"
Pin selector	A reusable component knows its differential pins, while its parent creates the traces.	positiveConnection=".USBC > .DP1"

You may use a trace name for one connection and a pin selector for the other. Each value must ultimately resolve to exactly one trace in the same board or autorouted subcircuit.

Properties

Property	Type	Description
name	string	Optional name for the differential pair.
positiveConnection	string	Exact positive trace name or pin/port selector.
negativeConnection	string	Exact negative trace name or pin/port selector.
maxLengthSkew	number	Maximum absolute difference between the routed lengths, in millimeters. Accepts 0 through 1; defaults to 0.1 mm.