<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 />.

Use pcbTraceGap to request the edge-to-edge copper spacing between the two traces. The pad pitch can require a wider separation at the endpoints.

Quick start with trace names

Give each <trace /> a unique name, then reference those names from <differentialpair />.

export default () => (
  <board width="32mm" height="20mm">
    <connector
      name="J1"
      manufacturerPartNumber="TYPE-C-31-M-12"
      footprint="jlcpcb:C165948"
      pinLabels={{ pin8: "USB_DP", pin9: "USB_DM" }}
      pcbX={-10}
      pcbRotation={-90}
    />
    <testpoint name="TP_DP" pcbX={12} pcbY={3} padDiameter="1.2mm" />
    <testpoint name="TP_DM" pcbX={2} pcbY={-3} padDiameter="1.2mm" />

    <trace name="USB_DP" from=".J1 > .USB_DP" to=".TP_DP > .pin1" />
    <trace name="USB_DM" from=".J1 > .USB_DM" to=".TP_DM > .pin1" />

    <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.
• The large center meander makes the route-length correction visible.
• maxLengthSkew={0.05} allows an absolute routed-length difference of up to 0.05 mm.

The connector uses the real TYPE-C-31-M-12 footprint, but only one D+/D- contact pair is labeled and connected here. The testpoints stand in for downstream USB-device pins, so this is not a complete USB circuit.

Quick start with pin selectors

Use pin selectors when you want the pair declaration to identify each trace by a pin it connects to. Each selector must resolve to one pin that belongs to exactly one trace.

export default () => (
  <board width="32mm" height="20mm">
    <connector
      name="J1"
      manufacturerPartNumber="TYPE-C-31-M-12"
      footprint="jlcpcb:C165948"
      pinLabels={{ pin8: "USB_DP", pin9: "USB_DM" }}
      pcbX={-10}
      pcbRotation={-90}
    />
    <testpoint name="TP_DP" pcbX={12} pcbY={3} padDiameter="1.2mm" />
    <testpoint name="TP_DM" pcbX={2} pcbY={-3} padDiameter="1.2mm" />

    <trace name="USB_DP" from=".J1 > .USB_DP" to=".TP_DP > .pin1" />
    <trace name="USB_DM" from=".J1 > .USB_DM" to=".TP_DM > .pin1" />

    <differentialpair
      name="USB_DATA"
      positiveConnection=".J1 > .USB_DP"
      negativeConnection=".J1 > .USB_DM"
      maxLengthSkew={0.05}
    />
  </board>
)

Only one pin from each trace is needed. Here, .J1 > .USB_DP and .J1 > .USB_DM select named pins and resolve to the two existing traces. A component selector such as .J1 is not enough; select a specific pin.

Choosing trace names or pin selectors

Use	When to choose it	Example
Trace name	The trace has a unique name.	positiveConnection="USB_DP"
Pin selector	The selected pin connects to exactly one trace.	positiveConnection=".J1 > .USB_DP"

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.

If a selected pin connects to multiple <trace /> elements, use a trace name to avoid an ambiguous match. In phased autorouting, the routingPhaseIndex prop assigns a <trace /> to a phase. Both traces in a pair must use the same value.

Route a pair through several pads

Give each two-pad section a positive and negative trace name. The example routes a connector through an ESD device and test points to an IC. Each polarity keeps its electrical net across all three sections. Each phase routes one pair and sees the copper from the preceding phase.

export default () => (
  <board width={24} height={12} schematicDisabled routeRemaining={false}>
    <pinheader name="J1" pinCount={2} pcbX={-8} pcbRotation={90} />
    <chip name="D1" footprint="sot23" pcbX={-4} />
    <testpoint name="TP1" footprintVariant="pad" pcbX={1} pcbY={1.5} />
    <testpoint name="TP2" footprintVariant="pad" pcbX={1} pcbY={-1.5} />
    <chip name="U1" footprint="soic8" pcbX={7} />
    <autoroutingphase name="USB0" phaseIndex={0} autorouter="auto_local" />
    <trace name="P0" path={["J1.pin1", "D1.pin1", "net.USB_P"]} routingPhaseIndex={0} />
    <trace name="N0" path={["J1.pin2", "D1.pin2", "net.USB_N"]} routingPhaseIndex={0} />
    <differentialpair name="PAIR0" positiveConnection="P0" negativeConnection="N0" pcbTraceGap={0.2} />
    <autoroutingphase name="USB1" phaseIndex={1} autorouter="auto_local" />
    <trace name="P1" path={["D1.pin1", "TP1.pin1", "net.USB_P"]} routingPhaseIndex={1} />
    <trace name="N1" path={["D1.pin2", "TP2.pin1", "net.USB_N"]} routingPhaseIndex={1} />
    <differentialpair name="PAIR1" positiveConnection="P1" negativeConnection="N1" pcbTraceGap={0.2} />
    <autoroutingphase name="USB2" phaseIndex={2} autorouter="auto_local" />
    <trace name="P2" path={["TP1.pin1", "U1.pin1", "net.USB_P"]} routingPhaseIndex={2} />
    <trace name="N2" path={["TP2.pin1", "U1.pin2", "net.USB_N"]} routingPhaseIndex={2} />
    <differentialpair name="PAIR2" positiveConnection="P2" negativeConnection="N2" pcbTraceGap={0.2} />
  </board>
)

Properties

Property	Type	Description
name	string	Optional name for the differential pair.
positiveConnection	string	Exact positive trace name or port selector.
negativeConnection	string	Exact negative trace name or port selector.
maxLengthSkew	number	Maximum absolute difference between the routed lengths, in millimeters. Accepts any non-negative distance and defaults to 0.1 mm.
pcbTraceGap	number | string	Requested copper edge-to-edge gap between the pair. A number is in millimeters.