Industry Article

# How Choosing Oscillators over Crystals Reduces Time to Market and Project Costs

November 05, 2019 by Bruce Potvin, SiTime

## This article looks at the differences between crystal resonators and oscillators and presents examples that show when choosing crystals over oscillators could increase the total cost of a design.

This question of the actual cost of using a crystal versus a MEMS oscillator may not be at the forefront of a designer's selection process when the price of crystals seem so cheap—at least on the surface. But although the cost of crystal components is generally lower, once the total cost of design is calculated, the picture looks much different.

I have heard from many designers who have crystal design issues such as cold startup failures, oscillator circuit problems from mismatched crystals, or failure to pass EMI tests. These problems cause engineering cost overruns during development and can create costly quality issues. Plus delaying the product release date can cause costly lost opportunities. Described in this article are three situations where designers needed to decrease their overall cost of ownership when facing crystal design concerns.

## The Basics of Crystals and Oscillators

What is the difference between a crystal (XTAL) and an oscillator (XO)? A crystal (sometimes called a resonator) is a moving/resonating passive device that connects to the external oscillating circuit in the chip that it is timing, like an SoC, microcontroller or processor as shown on the left in Figure 1.

##### Figure 1. Comparing the design of a crystal resonator and an oscillator.

An oscillator, shown on the right in Figure 1, is an integrated timing solution that contains a resonator and an oscillator IC in one active device. For some oscillators, the resonator is based on silicon MEMS (micro-electro-mechanical systems) technology instead of the traditional quartz crystal. This architecture enables robust “plug-and-play” timing products that are flexible and very easy to design into a system.

## Conclusions Drawn from these Examples

In addition to direct costs, there are other factors that affect the cost of designing with crystals. For example, oscillators can drive multiple loads. That means one oscillator can replace multiple crystals, which can only clock one device.

MEMS oscillators that are based on a programmable architecture are readily available in any frequency, stability, and voltage within a very wide range. This provides great flexibility for designers in optimizing their design. In fact, such oscillators can be programmed by key distributors or even by customers in their own lab using Time Machine II.

##### Figure 4. An overview of the additional benefits of using MEMS oscillators.

Programmability can also reduce the cost of qualification efforts if specification changes are needed. This time-saving benefit is possible because a MEMS oscillator (before programming) can generate millions of part numbers and specification combinations—all with the same base part.

Perhaps one of the biggest indirect savings comes in the form of higher reliability and quality. Silicon-based MEMS oscillators can have higher reliability of over as much as one billion hours mean time between failure (MTBF) compared to typical quartz devices with about 25 million MTBF. These devices deliver less than two DPPM quality level which is about 30 times better than quartz devices, and they have much better survival rates against shock and vibration compared to quartz crystals. Using an oscillator in place of a crystal can provide benefits beyond cost as well (PDF).

The higher failure rates of quartz crystals can increase costs in many ways such as the added resource costs for root-cause analysis or extra service and replacement costs. When procurement is focused on lowering component costs, looking at the big picture can ultimately save in the long run.

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