An apparatus includes an IC chip with a signal transmitter and an IC chip with a signal receiver, both chips being mounted on a printed circuit board and being connected via conductors on the board. The signal transmitter has a voltage-current converter and a high output impedance current amplifier. The signal receiver has a current-voltage converter. The voltage-current converter converts the voltage of the digital signal to current which in turn is amplified by the high output impedance current amplifier. The amplified current flows via the conductors in the receiver. The digital signal is transferred via the conductors on the current basis. Due to the transmission of the digital signal of current from the signal transmitter to the signal receiver via the conductors, signal spikes while transmitting are reduced and noise immunity is improved. Also, EMI (electromagnetic interference) emission is reduced and power dissipation is small.