Differential transmission substrate and power-over-differential data communication device

A differential transmission board that superimposes DC power on a differential data signal from a transmission/reception IC and then transmits the signal to a cable, the differential transmission board comprising:

• a first differential transmission line including two wiring patterns;
• a second differential transmission line including two wiring patterns;
• a third differential transmission line including two wiring patterns;
• two DC transmission lines that transmit the DC power;
• two capacitor elements that cut off the DC power and pass only the differential data signal;
• and
• two inductor elements that cut off a radio-frequency component that is the differential data signal and pass only a DC component,
• wherein the first differential transmission line and the third differential transmission line are connected in series,
• the third differential transmission line and the second differential transmission line are connected in series,
• the two capacitor elements are connected in series to the second differential transmission line,
• the second differential transmission line and the DC transmission line are connected via the two inductor elements,
• a characteristic impedance in a differential mode of the first differential transmission line, a characteristic impedance in the differential mode of the second differential transmission line, and a characteristic impedance in the differential mode of the third differential transmission line are substantially equivalent, and characteristic impedances in an in-phase mode of the second differential transmission line and the third differential transmission line is higher than a characteristic impedance in the in-phase mode of the first differential transmission line,
• the third differential transmission line has a microstrip line or strip line structure having a GND layer on an upper side, a lower side, or upper and lower sides of a wiring layer of a signal line of the third differential transmission line, and
• a GND plane or a pattern equivalent thereto immediately below the second differential transmission line is removed.

A differential transmission board that superimposes DC power on a differential data signal from a transmission/reception IC and then transmits the signal to a cable, the differential transmission board comprising:

• a first differential transmission line including two wiring patterns;
• a second differential transmission line including two wiring patterns;
• two DC transmission lines that transmit the DC power;
• a common-mode choke coil having a low impedance in a differential mode and a high impedance in an in-phase mode;
• two capacitor elements that cut off the DC power and pass only the differential data signal;
• and
• two inductor elements that cut off a radio-frequency component that is the differential data signal and pass only a DC component,
• wherein the first differential transmission line and the second differential transmission line are connected in series,
• the common-mode choke coil and the two capacitor elements are connected in series to the second differential transmission line,
• the second differential transmission line and the DC transmission line are connected via the two inductor elements, and
• a characteristic impedance in a differential mode of the first differential transmission line and a characteristic impedance in the differential mode of the second differential transmission line are substantially equivalent, and a characteristic impedance in an in-phase mode of the second differential transmission line is higher than a characteristic impedance in the in-phase mode of the first differential transmission line.