A signal transmission circuit is provided. The signal transmission circuit includes a first driving circuit including a first differential output pair, a plurality of input/output units and a calibration module. The first differential output pair includes a positive and a negative ends. The plurality of input/output units receive a positive and a negative control signals and generate a first superimposed current at the first differential output pair. The calibration module transmits a calibration signal to the first driving circuit. The calibration module sets operation of each of the input/output unit in the first driving circuit, and generates the first superimposed current flowing to a first external resistor according to the positive and the negative control signals.