Signal transmission circuit and endoscope system

A signal transmission circuit to which a signal of each of a reference level and a signal level is input as an input signal, the signal transmission circuit comprising:

• an impedance conversion circuit configured to receive a first current as an input and to output a second current according to the first current;
• a current-voltage conversion circuit configured to convert the second current output from the impedance conversion circuit into a voltage;
• and
• a switch disposed between the impedance conversion circuit and the current-voltage conversion circuit and configured to switch between on and off states of an electrical connection between the impedance conversion circuit and the current-voltage conversion circuit,
• the impedance conversion circuit including:
• a first current source configured to generate a reference current;
• and
• a current output circuit configured to output the second current according to a difference between the first current and the reference current or a sum of the first current and the reference current,
• wherein the switch is controlled to be off in a first period,
• the impedance conversion circuit is configured to convert the first current that is based on the input signal of the reference level into the reference current in the first period,
• the first current source is configured to hold the reference current converted by the impedance conversion circuit in the first period,
• the switch is controlled to be on in a second period after the first period, and
• the impedance conversion circuit is configured to output the second current according to the difference between or the sum of the first current that is based on the input signal of the signal level and the reference current held by the first current source in the second period.