Features and Applications of MEMS Clock Generators

History of Clock Generators

Clock Generators are timing components which integrate the clock functionality of many different discrete devices into one semiconductor component. They offer the traditional semiconductor benefits of integration, lower cost, smaller size, and full customization with minimal additional expenses. Historically, the use of clock generators started with the expansion of the PC motherboard market in the early 1990s. At that time, the functionality of a PC motherboard was increasing dramatically – audio, networking, high-end-graphics, video and various interfaces were being added to a PC. Each of these additional components (in addition to the core processor and memory) required a clock, which necessitated the use of as many as 7 clocking devices on a single PC motherboard. Semiconductor companies started developing clock generators which integrated the clocking function of these 7 devices into one or two clock generators, which resulted in the benefit of lower cost and smaller footprint.

MEMS-based Clock Generators are completely Integrated

Every clock generator requires multiple PLLs (Phase Locked Loops) which are used to generate any specified frequency from a standard fixed frequency reference, which is usually an external clock source such as a quartz crystal or oscillator. With the advent of MEMS resonators (which are available in the form of semiconductor die and can be completely integrated inside a plastic package), the need for having an external crystal or clock source goes away. Thus, a MEMS clock generator provides a completely integrated solution with no external reference clocks. A MEMS clock generator also eliminates the matching of the crystal with the clock generator circuit, which is a time-consuming problem to solve and may sometimes affect the performance of the system.

Features and Benefits of MEMS Clock Generators

* Completely integrated solutions, no external components required. MEMS resonator die (reference) is integrated inside package with analog circuit.

* Functionality of 3 – 6 clock generators in one 7.0x5.0mm package, results in up to 66% board space savings.

* Independent operating voltage on each of the PLLs, eliminates the need for external level translators, thus reducing component count and cost

* Mixed differential and LVCMOS outputs in the same device, addressing the need for different clocking devices in complex systems.

* Available spread spectrum capability to reduce system EMI and pass compliance testing.

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