OpenSerDes: An Open Source Process-Portable All-Digital Serial Link

Over the last decade, the growing influence of open source software has necessitated the need to reduce the abstraction levels in hardware design. Open source hardware significantly reduces the development time, increasing the probability of first-pass success and enable developers to optimize software solutions based on hardware features, thereby reducing the design costs. The recent introduction of open source Process Development Kit (OpenPDK) by Skywater technologies in June 2020 has eliminated the barriers to Application-Specific Integrated Circuit (ASIC) design, which is otherwise considered expensive and not easily accessible. The OpenPDK is the first concrete step towards achieving the goal of open source circuit blocks that can be imported to reuse and modify in ASIC design. With process technologies scaling down for better performance, the need for entirely digital designs, which can be synthesized in any standard Automatic Place-and-Route (APR) tool, has increased considerably, for mapping physical design to the new process technology. This work presents a first open source all-digital Serializer/Deserializer (SerDes) for multi-GHz serial links designed using Skywater OpenPDK 130nm process node. To ensure that the design is fully synthesizable, the SerDes uses CMOS inverter based drivers at the transmitter, while the receiver front end comprises a resistive feedback inverter as a sensing element, followed by sampling elements. A fully digital oversampling CDR at the receiver end recovers the transmitter clock for proper decoding of data bits. The physical design flow utilizes OpenLANE, which is an open source end-to-end tool for generating GDS from RTL. Cadence Virtuoso has been used for extracting parasitics for post-layout simulations, which exhibit the SerDes functionality at 2 Gbps for 34 dB channel loss while consuming 438 mW power. The generated GDS and netlist files of the SerDes, along with the required documentation, are uploaded in a GitHub repository for public access.