Signal improvement is an additional capability added to CAN FD transceiver that enhances the maximum data rate achievable in complex star topologies by minimizing signal ringing. Signal ringing is the result of reflections caused by impedance mismatch at various points in a CAN network due to the nodes that act as stubs. An example of a complex network is shown below.

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Figure 8-9 CAN FD Signal Improvement Topology

Recessive-to-dominant signal edge is usually clean as the bus is strongly driven by the transmitter. Transmitter output impedance of CAN transceiver is ~50Ω and matches to the network characteristic impedance. For a regular CAN FD transceiver, dominant-to-recessive edge is when the driver output impedance goes to approximately 60kΩ and signal reflected back experiences impedance mismatch which causes ringing. The TCAN146x resolves this issue by TX-based Signal Improvement Capability (SIC). The TCAN146x continues to drive the bus recessive strongly until t_{REC_START} so that reflections die down and the recessive bit is clean at the sampling point. In the active recessive phase, the transmitter output impedance is low (~100Ω). After this phase is over and device goes to passive recessive phase, driver output impedance goes to high-Z. This phenomenon is explained using Figure 7-17.