a system that transmits signals through a communication channel . during operation , the system receives a sequence of bits for transmission through the communication channel . while transmitting a given bit , the system determines if the given bit has the same state as the previously transmitted bit . if so , the system uses a voltage - mode driver to drive a signal through the communication channel . otherwise , the system uses a current source coupled to the voltage - mode driver to boost the drive - level of the voltage - mode driver . note that the current source supplies a current to the communication channel without changing the impedance of the voltage - mode driver . in this way , the present invention compensates for frequency dependant losses in the communication channel without sacrificing impedance matching and without substantially increasing power consumption .