Controlling Impedance

An ideal transmission line has a characteristic impedance that matches the intended signal's transmitter and receiver. If the characteristic impedance of the matched transmission line is perfectly maintained, the receiver sees the transmitter's full signal at the end of the trace. There is no reflection or signal attenuation.

To control impedance, you need to control three features of the circuit’s geometry:
  • The trace width.
  • The spacing between the signal return path and the signal trace.
  • The dielectric coefficient of the material surrounding the trace.
You can calculate these values using a trace impedance calculator. Work with your PCB manufacturer during your PCB layout design for these impedance calculations.
Additionally:
  • Route high-speed signals using a minimum number of vias and corners to reduce signal reflections and impedance changes.
  • To route a 90° turn, use two 135° turns or an arc instead of a single 90° turn. This method reduces reflections on the signal by minimizing impedance discontinuities.

The following table shows the typical high-speed trace impedance for the Titanium™ MIPI interface.

Table 1. MIPI Trace Impedance
Parameter Min Typ Max Units
MIPI D-PHY RX or TX differential impedance 90 100 110 Ω
MIPI D-PHY RX or TX single-ended impedance 45 50 55 Ω