Driver circuit for differentially outputting data from internal circuitry of an LSI to outside the LSI

#The present invention relates to a driver circuit. More particularly, the present invention relates to a driver circuit for differentially outputting data from internal circuitry of an LSI (large scale integrated circuit) to the outside of the LSI.

#Recently, multimedia is rapidly becoming widespread. This raises a demand for high-speed, mass data transmission. Therefore, high-speed serial data interfaces such as IEEE1394 and Gigabit Ethernet® have attracted attention. In these interface technologies, a driver circuit differentially transmits data from internal circuitry of an LSI at a high speed such as 1 Gbit/s. As shown in FIG. 8, this driver circuit forms a current mirror by applying a bias voltage Vbn generated by a reference current circuit to the gate of a MOS (Metal Oxide Semiconductor) transistor M50, and generates a desired, constant drive current. Either a differential output terminal TD or NTD to which the drive current is to be applied is determined by MOS transistors M51, M52, whereby the driver circuit digitally drives a prescribed current. This drive current is driven to a receiving device as a desired output voltage through resistors R respectively connected to the output terminals TD, NTD.

#If the output differential data from the driver circuit of FIG. 8 do not cross at the center, a differential skew (difference between the respective medians of the differential data) is generated as shown in FIG. 9. A large differential skew would increase variation in cross point in the time direction when the drive current varies due to noises or the like. As shown in FIG. 10, provided that the differential data ideally cross at the center, the intersection p1 is shifted to p2 or p2′ as the gradient of the voltage with respect to time is varied. If there is a difference in switching time, t_diff, the intersection q1 is shifted to q2 or q2′ as the gradient is varied. Therefore, it can be appreciated that, provided that variation in gradient is the same, the displacement of the intersection with respect to time, i.e., (p2−p1) or (q2−q1), is increased if there is a difference in switching time. That is, (p2−p1)<(q2−q1). Accordingly, in a differential driver, variation in switching timing would increase jitter components of the time direction due to noises or the like, thereby causing reduction in margin for communications. Note that the difference in switching time, t_diff, is negative, the displacement of the intersection with respect to time is seemingly reduced. In the subsequent cycle, however, the differential potentials rise and fall in the opposite manner, whereby the difference t_diff becomes positive. In view of irregular disturbance such as noises, it is ideal to make the differential data cross at the center.

#FIG. 1 is a block diagram showing the structure of an electronic equipment according to a first embodiment of the present invention;

#FIGS. 2 and 3 show modifications of a driver circuit in FIG. 1;

#FIG. 4 is a block diagram showing the structure of an LSI in an electronic equipment according to a second embodiment of the present invention;

#Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the same or corresponding portions are denoted with the same reference numerals and characters throughout the figures, and description thereof will not be repeated.

#(First Embodiment)

#FIG. 1 is a block diagram showing the structure of an electronic equipment according to the first embodiment of the present invention. The electronic equipment 1 of FIG. 1 outputs differential signals from output terminals TD, NTD. The differential signals output from the output terminals TD, NTD are transmitted to differential cables 11 for communications through a connector 10. The electronic equipment of FIG. 1 includes a semiconductor integrated circuit (LSI) 100, resistors 8, 9, and output terminals TD, NTD.