A robust, load-insensitive pad driver

A new approach to implement load-insensitive integrated pad drivers in monolithic integrated circuits is presented. The design utilizes a source follower topology along with a simple negative feedback approach to fix and control both rise and fall times independent of loading capacitance. This novel technique was used to implement a differential output pad driver for Universal Serial Bus design in a standard 0.35-/spl mu/m/3-V CMOS technology. The two drivers occupy less than 0.15 mm/sup 2/ of die area and can handle a capacitive load of 0-100 pF and 0-800 pF for 1.2- and 1.5-Mbps data rates, respectively. Measured transition times for 1.2 Mbps (with 50 pF) and 1.5 Mbps (with 350 pF) data rates were 17 and 250 ns, respectively.