What is clock recovery?

Clock recovery is a critical process in high-speed digital signal testing that extracts clock signals from a serial data stream which does not include a separate, embedded clock. This recovered clock enables accurate signal timing analysis, triggering, and jitter measurement, which are essential for validating the performance of high-speed interfaces such as USB, PCIe, and Ethernet. Many modern digital communication systems transmit data without a dedicated clock signal. Instead, the receiver must infer timing information from the transitions in the data stream. This is where clock recovery comes in. It reconstructs the timing reference needed to properly interpret and analyze the signal. Ensuring accurate clock recovery is vital for minimizing jitter, achieving reliable measurements, and maintaining compliance with industry standards. Whether you're testing USB, HDMI, or other high-speed protocols, robust clock recovery capabilities are essential for effective electronic design validation.

Why is clock recovery needed during transmitter testing?

Many common digital communications signals do not include clock information in the signal itself. The receiver must recover the clock signal to interpret the signal. Oscilloscopes, acting as “ideal receivers” during device validation and compliance testing, often need some form of clock recovery, either internal or external, to properly interpret the signals. While some oscilloscopes have internal clock recovery features, many digital standards compliance specifications require external clock recovery for testing.

How do I choose the right clock recovery solution?

Developers should ensure that their clock recovery solution meets the requirements of the digital data signals they are testing, or of the data standards compliance specifications that they are validating their device to. Some features and attributes to keep in mind: Data rate range: Most clock recovery units only support a specific range of data rates. If testing a 112 Gb/s PAM4 signal, ensure that you are using at least a clock recovery unit that supports 64 GBd data rates. Another consideration is determining whether your oscilloscope supports different modulation formations, such as NRZ or PAM4. Signal compatibility: Ensure that your clock recovery supports the signals you need to analyze. Some clock recovery units support electrical inputs only, while others include optical-to-electrical converters for recovering clocks from optical signals. When considering optical clock recovery, consider whether you need single-mode or multimode optical coverage.

Clock Recovery

Required timing extraction for standards conformance testing

Clock recovery units improve the accuracy of high-speed optical and electrical measurements by extracting timing from data signals. You need a precise clock signal to reduce jitter and improve the quality of high-speed signal integrity analysis of your devices. IEEE 802.3 Ethernet and OIF-CEI standards require external clock recovery during compliance testing to ensure accurate measurements. Select these clock recovery units when you plan to perform compliance tests on these classes of digital communications devices. Choose one of our popular configurations or configure one specific to your application.

NRZ and PAM4 support

Minimize timing errors and gain clearer visibility into a broad range of high-speed signals with data rates up to 64 GBd for non-return-to-zero (NRZ) and pulse amplitude modulation 4-level (PAM4).

Extended test coverage

Optical / electrical solutions integrate electrical clock recovery with an amplified O/E, enabling support for both optical and electrical applications.

Jitter spectrum analysis

Optional jitter spectrum analysis provides insight into the magnitude and distribution of low-frequency jitter for troubleshooting root cause for excessive jitter.