Frequency domain optimization of equalizer for high-speed differential interconnection using active filter and reactive termination techniques

Abstract

The operational frequencies of digital systems have increased at such a rapid pace over the past few years that nowadays high performance printed circuit boards (PCBs) have to deal with digital signals whose spectral content can reach tens of GHz. To ensure reliable operation at such high data rate, there is a growing tendency to adopt a differential signaling scheme for critical signals. Differential signaling has been important in communications system for more than 50 years, and recent technological advances have pushed analog differential circuit performance limits into RF and low microwave frequencies. Now, it has been a popular choice for multi-gigabit digital applications such as FiberChannel, Infiniband, OIF, RapidIO, Serial-ATA and XAUI, etc. This is because differential signaling has the ability to reject common mode noise such as crosstalk, simultaneous switching noise (SSN), power supply and ground bounce noise. However, as the required frequency for future high-speed signaling increases steadily, the high-frequency characteristic if the channel for data transmission becomes the major factor of the limitation in signal bandwidth. The widely used cost effective substrate material has high dielectric loss resulting in filtering of high frequency signals in the broadband digital system. Moreover, as the ESD capacitance and device input capacitance add more high frequency loss, the received digital signal will suffer from distortion in its shape. Inter-symbol interference (ISI) is a typical effect of the signal distortion due to channel loss. So, researches on the equalization methods to compensate the high-frequency loss have been done to improve the signal integrity of multi-gigabit data transmission and lots of equalizer circuits in the transmitter are developed. It compensates the low-pass-filtering effect and maintains the balance of the total gain of the signal over the frequency range. However, the equalizer in transmitter has limitation in the...