See a side-by-side comparison of SiTime’s Elite TCXOs and leading Quartz TCXOs as they face off to show which performed better under environmental stresses including a heat gun test and air flow test.
Hi, it's Brett back to cover part two of the advantages of MEMS timing technology.
We are going to get started by showing some comparisons of the new Elite devices. The screenshot shown on this slide is an excerpt from a video showing side-by-side testing of one of the industry's best Quartz TCXOs versus an Elite MEMS TCXO.
In this screen capture, the frequency transient resulting from hot air from a heat gun is shown. This heat gun induces a very fast thermal transient of 86 degrees Celsius per minute as measured by a temperature sensor on the printed circuit board. The 50 ppb Quartz TCXO responds immediately to this thermal stress and deviates to negative 450 ppb, which is 9 times the datasheet specification.
By contrast, the MEMS frequency response is flat with small deviations of less than or equal to 3 ppb. The air gun also has a secondary effect of inducing some vibration on the board. This outstanding MEMS performance is the result of the design and construction principles as mentioned in the last two slides. Very tight thermal coupling between the temp sense and temp-flat MEMS in the high bandwidth TDC.
You can watch the full video on YouTube where it shows response to vibration and airflow as well. This screenshot shows the results of an airflow test using a small PC fan blowing directly on top of the test fixture containing the Quartz TCXOs versus the elite MEMS TCXO. In this test, turning on the fan lowers the temperature on the PCB but also induces some vibration on the board.
The temperature transient observed on the PCB was not as severe as in the heat gun experiment, but the Quartz TCXO, nevertheless, exceeded its datasheet specification with a 60 ppb frequency jump. MEMS's resilience to various environmental stresses as observed in the video also yields benefits to telecom standards testing. Time deviation or TDEV is a measure of clock face stability over a given time interval.
The telecom standard GR1244 specifies the maximum allowed TDEV for averaging times from 0.1 seconds to 100 seconds. The left graph in the slide shows TDEV under a still air condition and the right graph shows TDEV under airflow from the fan inside the oven chamber. Since TDEV is a measure of phase instability which causes clock wander, lower numbers are better.
Under the airflow condition, SiTime MEMS TCXO shows significant benefit of the 20 times better than Quartz TCXO. Frequency slope is an important parameter, especially for the IEEE 1588 applications when the maximum time error per node may be significantly less than 1 microsecond. Frequency transients due to temperature changes will be directly translated to time error between synchronization update messages.
Another parameter which can shift the oscillator output frequency is the output load. The graph on the slide shows the frequency shift of varying 15 peak of error nominal load by ±10%. The SiTime Elite oscillator has virtually no frequency shift because the resonator is completely isolated from the load by the PLL and output driver. In Quartz-based oscillators which do not use PLL technology, the frequency shift resulting from the load variation is greater.
This concludes the two-part series. Remember, the SiTime MEMS devices have many advantages to that of Quartz technology. Vibration, airflow, and extreme temperatures are a few key areas where SiTime stands out as the leader in timing technology.