The present invention relates to an improved semiconductor integrated circuit that can transmit data at high speeds with reduced power dissipation and also relates to a system including such a circuit.
Present-day semiconductor integrated circuits (like an IEEE 1394 physical layer LSI) are specially designed to transmit data from unit to unit at high speeds to implement a system that can process a tremendously large quantity of data as fast as possible to cope with multimedia applications, in particular. As a result of recent vigorous research and development, the state-of-the-art semiconductor integrated circuits can normally transmit data at as high a rate as 200 megabits per second (Mbps). Some integrated circuits have already doubled the transmission rate although those circuits are just samples up to now. Furthermore, an extremely-high-speed data transmission technique exceeding 1 gigabits per second (Gbps) has also been realized albeit experimentally.
In the IEEE 1394 physical LSI, data is sent as direct current from the transmitting end through a differential twisted pair of cables. A resistor is connected between the twisted pair, and a potential difference between the twisted pair, which is variable with the current flowing through the resistor, will be supplied to the receiving end. The IEEE 1394 physical layer LSI also adopts a data transmission technique termed "DS-Link". Specifically, in transmitting data, a pair of data lines and a pair of strobe lines are associated with each single port. The specifications of the IEEE 1394 standards are described in Draft Standard Vex. 8.4.
According to the IEEE 1394 physical layer LSI technology, however, a considerable amount of current is always consumed at the output ports because the direct current is output through the twisted pair. Particularly when an integrated circuit is provided with an increased number of output ports, the increase in current dissipation poses a serious problem. Moreover, although data is supposed to change its level on either the data line or strobe line pair in accordance with the DS-Link technique, the direct current is always flowing through the pair with no data transitions, thus also increasing the amount of currents consumed.