Summary
DifferentialPairProps currently exposes only positiveConnection, negativeConnection, and maxLengthSkew. This allows length matching, but it cannot express the routing geometry required for a controlled differential pair.
Tested with:
@tscircuit/props 0.0.585@tscircuit/core 0.0.1468tsci 0.0.2112
Current API
<differentialpair
name="TX_PAIR"
positiveConnection="TX_POS"
negativeConnection="TX_NEG"
maxLengthSkew={0.1}
/>There is no prop for pair gap, pair-level width, routing layer, same-layer enforcement, maximum uncoupled length, or matched via transitions.
Reproduction / motivation
On a six-layer USB-C pass-through board, the autorouter can route the two members of a TX pair on different internal layers because the pair cannot require a common layer. For example, one generated route used top -> inner2 -> top while its partner used top -> inner1 -> top.
The reference design requires a 0.17 mm trace width, 0.28 mm differential-pair gap, and no more than 0.1 mm intra-pair skew. Only the skew can currently be represented by <differentialpair>.
Minimal shape of the problem:
<trace name="TX_POS" from=".J1 > .pin1" to=".J2 > .pin1" thickness="0.17mm" />
<trace name="TX_NEG" from=".J1 > .pin2" to=".J2 > .pin2" thickness="0.17mm" />
<differentialpair
positiveConnection="TX_POS"
negativeConnection="TX_NEG"
maxLengthSkew={0.1}
// No way to request a 0.28 mm gap or require both traces on one layer.
/>Proposed props
An initial API could look like:
<differentialpair
positiveConnection="TX_POS"
negativeConnection="TX_NEG"
traceWidth="0.17mm"
traceGap="0.28mm"
layer="inner1"
requireSameLayer
maxLengthSkew={0.1}
maxUncoupledLength="1mm"
viaGap="0.25mm"
requireMatchedVias
/>Possible schema additions:
traceWidth?: DistancetraceGap?: Distance (document whether this is edge-to-edge)layer?: LayerRefInputrequireSameLayer?: booleanmaxUncoupledLength?: DistanceviaGap?: DistancerequireMatchedVias?: boolean
Target differential impedance could be handled separately because it depends on stackup dielectric and copper data.
Expected behavior
These props should be validated by @tscircuit/props and made available for downstream core/autorouter implementations. Post-route DRC should eventually be able to report violations of gap, same-layer, uncoupled-length, skew, and matched-via constraints.
Summary
DifferentialPairPropscurrently exposes onlypositiveConnection,negativeConnection, andmaxLengthSkew. This allows length matching, but it cannot express the routing geometry required for a controlled differential pair.Tested with:
@tscircuit/props0.0.585@tscircuit/core0.0.1468tsci0.0.2112Current API
There is no prop for pair gap, pair-level width, routing layer, same-layer enforcement, maximum uncoupled length, or matched via transitions.
Reproduction / motivation
On a six-layer USB-C pass-through board, the autorouter can route the two members of a TX pair on different internal layers because the pair cannot require a common layer. For example, one generated route used
top -> inner2 -> topwhile its partner usedtop -> inner1 -> top.The reference design requires a 0.17 mm trace width, 0.28 mm differential-pair gap, and no more than 0.1 mm intra-pair skew. Only the skew can currently be represented by
<differentialpair>.Minimal shape of the problem:
Proposed props
An initial API could look like:
Possible schema additions:
traceWidth?: DistancetraceGap?: Distance(document whether this is edge-to-edge)layer?: LayerRefInputrequireSameLayer?: booleanmaxUncoupledLength?: DistanceviaGap?: DistancerequireMatchedVias?: booleanTarget differential impedance could be handled separately because it depends on stackup dielectric and copper data.
Expected behavior
These props should be validated by
@tscircuit/propsand made available for downstream core/autorouter implementations. Post-route DRC should eventually be able to report violations of gap, same-layer, uncoupled-length, skew, and matched-via constraints.