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Understand the basic concepts of SERDES and quickly enter high-speed system design
SERDES (Serializer-Deserializer) hard cores are now commonly integrated into high-end FPGAs from leading manufacturers. For example, Altera’s Stratix IV GX family includes SERDES channels that support data rates ranging from 600 Mbps to 8.5 Gbps. The Stratix IV series also features high-speed differential interfaces operating from 150 Mbps to 1.6 Gbps, with enhanced Dynamic Phase Alignment (DPA) functionality. Xilinx’s Virtex II Pro features embedded SERDES channels supporting data rates from 622 Mbps to 3.125 Gbps, while the Virtex II Pro X offers higher speeds, up to 10.3125 Gbps. Lattice’s SC series FPGA integrates SERDES channels supporting data rates from 622 Mbps to 3.4 Gbps, and their FPSC (Field Programmable System Chip) devices include various SERDES channels capable of handling data rates from 400 Mbps to 10.709 Gbps.
Embedding a hard core like SERDES into an FPGA significantly increases data throughput, reduces power consumption, and improves overall performance, making FPGAs essential in high-speed system designs. This technology is especially useful for applications requiring fast and reliable data transmission, such as backplane communication.
This article explores the basic concepts of SERDES, focusing on the architecture of the Stratix IV GX device and its DPA feature. It also presents real-world examples of high-speed system design and discusses key considerations in designing high-speed PGB (Parallel-to-Serial) systems, helping readers gain a deeper understanding of high-speed digital design.
Understanding the fundamentals of SERDES is crucial for anyone working with high-speed communication systems. Key terms include eye diagrams, jitter, pre-emphasis, equalization, 8B/10B encoding, and more. These concepts help evaluate signal integrity and ensure reliable data transmission.
SERDES stands for Serializer and Deserializer. As the name suggests, it consists of two main components: the serializer, which converts parallel data into a high-speed serial stream, and the deserializer, which recovers the original parallel data from the serial stream. The deserializer often includes a Clock and Data Recovery (CDR) unit to extract the clock signal from the incoming data stream.
A typical 10:1 SERDES configuration takes ten parallel 100 MHz signals and converts them into a single high-speed serial stream. The clock is embedded within the data stream, allowing the receiver to reconstruct both the data and the clock. This approach reduces the number of required I/O pins, saves board space, and improves system stability, making SERDES a vital component in high-speed system design.
An eye diagram is one of the most important tools for evaluating the quality of a high-speed signal. It visually represents the signal's integrity by displaying the overlapping waveform of multiple bits. A well-formed eye diagram indicates a stable and clean signal, while a closed or distorted eye may suggest issues such as noise, jitter, or signal degradation.
The eye diagram template serves as a reference for measuring signal quality. Common templates include diamond-shaped and hexagonal-shaped patterns. These templates define acceptable limits for signal amplitude and timing, ensuring that the received signal meets the required standards.
In an eye diagram, the vertical axis represents the signal amplitude, typically measured in millivolts (mV), while the horizontal axis shows the time interval, usually in UI (Unit Intervals) or picoseconds (ps). A larger eye opening indicates better signal quality, with less jitter and a higher probability of correct data recovery.
Understanding these concepts is essential for designing robust and efficient high-speed systems, whether in telecommunications, networking, or industrial automation. By mastering SERDES and related technologies, engineers can build more reliable and high-performance digital systems.