Linear Equalization and PVT-Independent DC Wander Compensation for AC-Coupled PCIe 3.0 Receiver Front End

Abstract

An alternating current (ac)-coupled high-speed receiver analog front end is capable of shifting the input direct current (dc) level without extra current consumption and signal degradation at high frequencies. However, the dc wander due to the high-pass characteristic of the ac-coupled front end may degrade the receiver performance because it equivalently modulates the sampling threshold voltage of the sampler. While this modulation may be negligible for highly dc-balanced input, it shows observable degradation in Peripheral Component Interconnect Express (PCIe) 3.0 receivers operating at 8 Gb/s. In addition, analog equalization is generally required for a PCIe 3.0 receiver front end. This paper presents techniques to add linear equalization and dc wander compensation into an ac-coupled receiver front end. The proposed linear equalization scheme attenuates the low-frequency energy and keeps the high-frequency energy. The proposed dc wander-compensation method is independent of process, voltage, and temperature; therefore, there is no need for calibration or compensation. The proposed schemes have very low power consumption and very good linearity because only passive and linear components are utilized in the main signal path. The proposed schemes were confirmed by simulation.