How to Design High-Speed Nano-scale CMOS Mixed-voltage Digital I/O Buffer with Reliable Slew Rate Insensitive to PVTL Variation
Ever since the reliability issues caused by I/O (input/output) compatibility among chips fabricated using different processes were raised by cellular phone makers during mid-2000, onsilicon mixed-voltage I/O buffer with wide voltage tolerance was considered better solution than using signal level converters to shrink PCB size, number of discrete, and power consumption. However, various external voltages on I/O pad result in body effect, leakage, hot-carrier degradation, and gate-oxide overstress in stacked transistors of mixed-voltage I/O. What even worse is that slew rate (SR) was also found deteriorated by PVT (Process, Voltage, Temperature) variations. Therefore, many design techniques for CMOS mixed-voltage I/O buffer design using nano-scale CMOS processes will be introduced and analyzed, including Clamping Dynamic Gate Bias Generator, Dynamic Biasing, and Leakage Detection, such that these I/O buffers will be able to transmit and receive digital signal with 2x or even 3x VDD voltage swing. Moreover, the reliability design consideration for the digital I/O buffers, including ESD, PVT detection, and slew rate (SR) auto-adjustment will also be discussed as well. Moreover, the maximum data rate can be drastically enhanced to meet the latest I/O interfacing protocol requirements.