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Are you choosing a transducer because it is "cheap"?
I'm sure there are many readers of this article who say, "When selecting components for a board design, I choose ceramic resonators or quartz crystal resonators."
When we ask customers why they select a particular oscillator, we hear reasons such as the oscillator being specified by the MCU, or that they are accustomed to using it in the past.
However, if the reason is "because it's cheap," then there's nothing wrong with it, but you need to be a little careful.
The basic differences between resonators and oscillators are briefly touched upon in this article, so please take a look.
From here on, we will explain why it is good to have an option of "oscillators" when selecting clock components, even if you usually select "resonators."
We will provide an in-depth explanation from three perspectives: "Cost of matching evaluation," "Cost of EMI countermeasures," and "Reliability."
Three points to keep in mind when selecting clock components
① Cost of transducer matching evaluation
First, there are differences between the peripheral circuits of the resonator (left: Crystal) and the oscillator (right: Oscillator), as shown in the diagram below.
Reference material (source: SiTime Corporation)
First, the “oscillator” vibrates at any desired frequency when connected to an oscillator circuit in an SoC or MCU and voltage is applied.
Therefore, when designing the timing of a system, tedious "matching evaluation" is essential.
Many people are probably getting help from the manufacturer, but I'm sure there are many who have wondered, "Why does it take so long for a generic product?"
Don't you think engineers think it's a waste of time to spend hours or even days on matching evaluation?
One customer had a mismatch and it took 40 hours to troubleshoot it. Here is an example calculation of the labor hours:
Engineer man-hours (assuming 10,000 yen per hour)
・ 40 hours (0.25 man-months) × ¥10,000 = ¥400,000
⇒ Risks that cannot be understood by simply comparing unit prices of parts...
If the mass production volume is 5,000 units...
\400,000 ÷ 5,000 units = \80 per unit > Average price difference between a resonator and an oscillator: \35
*See prices on general websites such as DigiKey
In contrast, since an oscillator is modularized in a single package, there is no need for matching evaluation.
Do you understand how it is to the customer's advantage to take into account factors such as engineer man-hours and costs, which cannot be seen in a simple comparison of part prices?
2) Costs of EMI countermeasures
I think that many engineers use various methods to deal with EMI (electromagnetic interference) noise when designing.
Clock-related issues are no exception.
Since the oscillator is a passive component, it is not possible to implement such measures on-device.
Various measures are necessary, such as using shielding or adopting a clock generator with spectrum spread functionality.
Naturally, these measures also require time and effort, and delays in prototyping and evaluation of prototypes will result in costs for testing equipment, etc.
This could result in delayed product releases and lost opportunities.
In this regard, the oscillators released by SiTime include products with a spectrum spread function in the oscillator itself. (Lineup)
In addition, most general-purpose series allow you to adjust the rise and fall times of the signal.
This is a feature unique to SiTime's programmable oscillators.
This is the reason why our products are used by most domestic musical instrument and audio manufacturers.
⇒What specifications are programmable?
It is possible to order samples of several model numbers with different output drive/edge rates from the same product series and replace them for evaluation.
Macnica provides tools for writing to our products. Please feel free to contact us at any time to inquire about samples.
3) Reliability
SiTime's MEMS oscillators have a DPPM of less than 1 and an MTBF of over 2 billion hours.
This is several tens of times better than that of general crystal units and crystal oscillators.
*DPPM: Defective Parts PerMillion
*MTBF: Mean Time Between Failures
As those of you who have probably experienced it before probably know, quartz devices are extremely sensitive to vibrations and shocks.
Naturally, peripheral parts are also at risk of malfunction.
The resources required for analysis due to the reliability of the crystal unit (often involving more people involved within the same company), costs, and time
This is one of the reasons why you should not choose based solely on the superficial unit price of the parts.
At the end
This time, we proposed a new option for clock generation: "not just a resonator but also a MEMS oscillator."
For the reasons explained above, we hope you can see the benefits of adopting the new option of a "MEMS oscillator."
If you are having trouble selecting parts, please feel free to contact us. We will respond immediately, such as proposing alternative products.
In addition, we have listed some popular products that can be used for general-purpose purposes below, so please take a look if you are interested.
| Device type |
Recommended model number/series * Detailed specifications can be confirmed from the link for each product |
Features |
| oscillator (single-ended) |
・The simplest SPXO (general-purpose package oscillator) ・Many replacements from crystal oscillators (compatible) ・Support from 1 to 137MHz |
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