Process Variation Detection and Self-Calibration Method for High-Speed Serial Links

Transmitters' output signal correction is very important for high speed serial link standards such as Universal Serial Bus (USB), X Attachment Unit Interface (XAUI), Peripheral Component Interconnect (PCI), Double Data Rate (DDR) etc. Day by day interface speed is increasing so some requirements become more affluent. For example, previously there were not necessity to have exactly the same rise/fall times, exact 50% duty cycle however nowadays there are. A method of designing the transmitter output driver which has independence from process variations is presented in this paper. The proposed architecture provides the equality between rise and fall times. System checks differences of speeds between NMOS and PMOS transistors and adding or removing parallel transistor accordingly to slowest or fastest one. As a result, output signal of transmitter has exactly the same rise and fall times regardless of process.