Many engineers wonder whether a crystal oscillator alone can provide clocks for an entire system. In reality, a crystal oscillator typically outputs
only one frequency and can drive a limited number of loads. Modern systems often require multiple clock frequencies for components such as
CPUs, DDR memory, PCIe devices, USB interfaces, and Ethernet PHYs. In addition, clock signals can degrade over long PCB traces, leading to increased
jitter and signal integrity issues.
To address these challenges, clock ICs are commonly categorized into two types:
Clock Generators
Clock generators use PLL (Phase-Locked Loop) technology to convert a low-frequency reference clock into one or more higher-frequency outputs. They can generate multiple clock frequencies and support various output formats, including CMOS, LVDS, LVPECL, and HCSL.
Typical applications include:
• CPU and GPU reference clocks
• DDR memory clocks
• PCIe reference clocks
• Ethernet PHY clocks
• ADC/DAC sampling clocks
Representative models: SYKB23F04, SYKG1042E/Q5
Clock Buffers
Clock buffers receive a single clock input and distribute it to multiple outputs while maintaining signal integrity. They help drive multiple loads,
compensate for signal attenuation, and preserve fast clock edges.
Typical applications include:
• Multi-channel ADC systems
• PCIe clock distribution
• Server motherboards
• Industrial control systems
Conclusion
While crystal oscillators provide a stable frequency reference, clock generators and clock buffers are essential for frequency synthesis, clock distribution,
and signal conditioning. Together, they ensure accurate timing and reliable operation in high-speed digital systems.
