①F=1/(Tr*π) F is the frequency (GHz); Tr(nanosecond) refers to the rise time and fall time of the signal.Usually when F > 100 GHz, it can be called high frequency circuit.
②The high frequency circuit depends on the rising edge and falling edge of the signal frequency. According to the formula, when the rising time is less than 3.183ns, it belongs to the high frequency circuit.
③High frequency circuit should be paid more attention to dielectric loss (DK) of board.
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