1.2-Gb/s true PECL 100K compatible I/O interface in 0.35-μm CMOS

This paper describes the design and the implementation of input-output (I/O) interface circuits for serial data links in the gigabit-per-second range. The cells were implemented in a 3.3-V 0.35-μm CMOS technology in a couple of test chips. The transmitter is fully compatible (DC coupling) with 100K positive emitter-coupled logic (PECL) systems and it is based on the voltage-switching principle in order to allow different termination schemes besides the canonical ECL termination, i.e., 50-Ω toward (V_DD-2) V. The addition of some circuit techniques such as dynamic biasing and strobed current switching boosts the dynamic performance of the basic voltage-switching scheme and relaxes the requirements for a high bias current and large-size output devices at the same time. Moreover, thanks to the developed reference circuit, using both feedforward and feedback controls, the output levels are within the 100K tolerance over the full range of process, supply voltage, and temperature (PVT) variations without resorting to external components or on-chip trimming. The receiver cell is based on a complementary-differential architecture providing high speed and low error on the duty cycle of the CMOS output signal. The integrated receiver-transmitter chain exhibits a maximum toggle frequency of 1 GHz, while a chip-to-chip transmission link using the developed I/O interface was tested up to 1.2 Gb/s