degree termination is also within spec. Why?
USB termination requirements are quite lenient. For example, a 0 to 3.6V signal input into a 51.75 line with a 28 source termination will swing between 4.6 and -1.0V-this is where the voltage levels in figure 7-1 of the 1.1 spec come from. In practice, most USB devices are underterminated, sometimes egregiously. The IF recommends sizing the series termination resistors to create a 44O termination. While not enough to perfectly terminate the device when its connected to an ideal cable, it does bring the terminations well within the standard 15% impedance tolerance-most modern processes are well controlled, so the internal impedance of USB drivers is quite consistent from wafer to wafer. It is, of course, wise to characterize the drivers’ impedance range and perform sampling of production parts. 8. Section 7.1.14 isn’t clear. How long can dribble and an EOP be? A: Dribble is between 0 and 15ns per hub and the change in delay for the drive to J at the end of the EOP to -0/+15ns. If the de
