Signal transmission circuit and signal transmission system

A signal transmission system, comprising:

• a communication unit that transmits a signal;
• and
• a control unit that is connected to the communication unit by a signal wiring and receives the signal transmitted from the communication unit via the signal wiring,
• wherein
• the control unit includes
• a direct-current supply unit that outputs a direct current with a variable output voltage, superimposes the direct current on the signal, and supplies the direct current to the communication unit via the signal wiring,
• a signal reception unit that receives the signal from the communication unit, and
• a signal processing unit that performs signal processing based on the signal received by the signal reception unit,
• the signal reception unit has an equalizer function that adjusts a waveform of the signal to compensate for attenuation due to the signal wiring, and
• the output voltage is controlled based on an equalizer setting value used for control of the equalizer function.