Sep. 09, 2024
Consumer Electronics
The power and performance of quartz oscillators is easy to describe. Quartz oscillators offer superior frequency solutions that help them stand out in a crowded field of lesser options. Their low power usage, stability, longevity, versatility and more make them the most desirable choice for engineers in the design community who require a frequency component for their applications.
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There are, of course, plenty of technologies that have tried to rival quartz oscillators as a frequency solution. However, these alternatives cannot compete, and they tend to fall by the wayside when measured against quartz crystals. Whether a product designer is considering ceramic resonators, MEMs or other frequency-based alternatives to quartz, they may discover what attributes make these products different, but not reasonable replacements.
When an engineer is given the opportunity to see the advantages and disadvantages of the various frequency solutions on the market today, they will be able to make a more confident decision when ordering quartz crystal oscillators and more. With comprehensive knowledge about frequency solutions in hand, getting in touch with the ECS Inc. sales team today has never been an easier decision.
Ceramic resonators create a frequency based on their shape. A ceramic resonator has a cavity which resonates at a specific frequency. Some engineers consider using this product when a stable frequency does not necessarily matter.
For example, if your frequency-based application does not offer a crucial, essential function &#; and does not require a strong, stable, clean frequency &#; ceramic resonators might be useful.
However, in the case of an application that requires very low frequency drift and must ensure stability, efficiency, durability and high performance, frequency from a quartz crystal oscillator is a better choice. Quartz crystal oscillator circuits tailored to your application are available now from ECS Inc.
Surface acoustic wave (SAW) resonators filter out unwanted frequencies. These products are silicon based, so they are readily available and can be ordered at a low cost. SAWs are sometimes preferred over ceramic resonators, and yet they still require compensation to work as effectively as quartz.
If an engineer is looking for an affordable solution that may not guarantee the fidelity or performance of quartz crystal oscillators, SAWs may be an alternative. Keep in mind that corrections for frequency control will need to be applied to this component. Even then, however, a SAW resonator&#;s performance will not match a quartz oscillator circuit in quality, reliability or effectiveness.
MEMs vs. Quartz Oscillators as Frequency Solutions
Microelectromechanical oscillators are often held up as a competitor to quartz. Unfortunately, many of the touted benefits of MEMs turn out to be marketing language, as opposed to useful rationales.
Engineers may read that MEMs are easy to produce at a low cost and promise short lead times. MEMs manufacturers may also claim improved phase-noise and jitter when used over a long period of time (and perhaps longer than the application would even be useful). The durability of MEMs is also often cited. However, the benefits of MEMs often fail to include information that engineers should know in advance of seeking this product:
Read the ECS Inc. white paper comparing MEMs to quartz oscillators.
When high performance, quality, efficiency and effectiveness are required, engineers should consider choosing quartz oscillator circuits over other frequency products. While SAWs, ceramic resonators and MEMs offer some positive attributes &#; as any frequency-based solution should &#; quartz oscillators provide the most versatile, well-rounded group of measurable performance indicators on the market today.
Most applications that require a timing solution need more than just average effectiveness or advantages that will not necessarily matter in the long run. Engineers want key characteristics that matter now and offer a guarantee that their products will succeed.
ECS Inc. is dedicated to your application&#;s success. Explore ECS Inc.&#;s parametric search tool to find the solution you&#;re looking for, as well as our vast list of sales representatives and authorized distributors. ECS Inc. quartz oscillators for frequency control are available for order today, so your use case can benefit from everything this component has to offer.
Every electronic system needs a timing device. And crystal (XTAL) resonators are often the go-to solution. However, oscillators, which pair a resonator with an oscillator IC into one complete integrated timing device, offer several benefits compared to XTALs. These benefits are further extended with MEMS timing technology. System designers no longer need to work around the limitations of XTALs and accept the headaches and risks of designing with crystals.
On the surface, oscillator design using quartz crystals might seem straight forward, especially considering the maturity of this technology. But there are a myriad of design parameters to consider when matching a crystal to an oscillator circuit. Among these parameters are crystal motional impedance, resonant mode, drive level, and oscillator negative resistance which is a measure of oscillator gain. Additionally, load capacitance must be considered for parallel resonant mode crystals and it should account for the PCB parasitic capacitance and potentially the on-chip integrated capacitance included in the oscillator circuit.
All of these parameters must be carefully considered to ensure reliable start up and operation of the circuit. Because an oscillator circuit requires close matching of the resonator to the oscillator circuit, crystal vendors cannot guarantee startup of the crystal. By contrast, oscillators are a completely integrated solution. The oscillator manufacturer matches the quartz resonator to the oscillator circuit, thus relieving the board designer of this burden. Because matching errors are eliminated, oscillator start-up is guaranteed by SiTime. In short, oscillators are a plug-and-play solution that greatly simplifies system design.
The oscillator circuit must have enough gain and phase shift to meet the Barkhausen criterion for oscillation. Of particular importance is the motional impedance (ESR) of the crystal and the negative resistance (equivalent to gain) of the oscillator. If the oscillator has insufficient gain to overcome the motional impedance of the quartz resonator, the circuit may not start up. These issues are eliminated with the use of oscillators.
Quartz crystals can resonate in either series or parallel resonant mode, but they are typically calibrated for only one of these two modes. If calibrated for parallel resonance, they require a specific load capacitance which is usually specified. However, the proper capacitance is not used, the frequency error may exceed the datasheet specifications. The oscillator IC may or may not have integrated chip capacitance which must be taken into account along with any parasitic capacitance from the printed circuit board connections, bond wires and lead frame of the oscillator IC to ensure the best frequency accuracy.
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In contrast, MEMS oscillators integrate the resonator and oscillator/PLL IC into one package, eliminating the need for an external capacitor to tune the resonant frequency.
Care must be taken to ensure the oscillator circuit does not overdrive the crystal resonator. Overdriving the resonator can lead to accelerated aging of the crystal resonator and at extreme levels, it can damage the crystal. In contrast, MEMS resonators do not experience aging.
Quality and reliability are critical &#; not only are company reputations at stake, but re-work can be costly and time consuming. Moreover, systems that are deployed outdoors and exposed to environmental stresses must be especially robust. Quartz resonators, while a mature technology, involve a rather complicated manufacturing process in which each individual resonator is tuned to the desired frequency, usually by ablating the metal electrode with an ion beam. This step occurs before the crystal is encapsulated and causes the resonator to be susceptible to contamination. This process, along with other quartz manufacturing complexities, result in the mean time between failures (MTBF) of quartz to be as low as 14 to 38 million hours. The defective parts per million (DPPM) is up to 50 for the best quartz manufacturers and as high as 150 for tier 2 quartz suppliers.
In contrast to the specialized manufacturing processes of quartz crystals, MEMS oscillator manufacturers use standard semiconductor batch mode techniques. This includes wafer level production of resonators and oscillator ICs, and die bonding to standard lead frames with plastic encapsulation. SiTime MEMS resonator die are made from a single mechanical structure of pure silicon. During the manufacturing of SiTime MEMS, an Epi-Seal process is used to clean the resonator, after which polysilicon is deposited to seal the structure. The ultra-clean hermetic vacuum seal ensures the resonator structure is protected and free of contamination, eliminating aging mechanisms.
As a result, the DPPM and MTBF of SiTime oscillators are about 30 times better than quartz, providing a very reliable technology platform that endures severe environmental stresses and delivers a high quality product for the end user.
Oscillators are a completely integrated solution and do not require external components such as power supply decoupling caps. SiTime&#;s 1.5 mm x 0.8 mm () footprint is smaller than the smallest quartz crystal footprint at 1.6 mm x 1.2 mm. And when taking into account load capacitors that are needed for the 32 kHz quartz crystal, the total board area or the XTAL solution is over three times larger.
An oscillator is an active circuit with an output driver usually capable of driving 2 to 3 loads depending on the drive strength. This allows the oscillator to replace several crystals and their associated capacitors, further reducing BOM, system cost, and board area.
Electromagnetic energy, which is common in most systems, can be picked up by exposed PCB traces that connect the crystal resonator to the IC containing the oscillator circuit. This noise can be coupled into the oscillator circuit and passed to the output, potentially adding jitter and noise to the system. However, integrated oscillators have no exposed PCB connections between the resonator and oscillator IC, and the bond wires or balls that connect the MEMS resonator to the IC are extremely short. This makes MEMS oscillators much less sensitive to EMI. As shown in the following table and plot, SiTime oscillators are up to 11.3 dBm less sensitive (134x on a linear scale) than crystal resonators.
This test was performed per IEC -2 standard that injects electromagnetic energy into a transverse electromagnetic (TEM) cell where the device under test (DUT) is mounted.
Some systems that require a very stable frequency, such as wireless base stations and small cells, can experience system failure and service interruptions due to vibration.
MEMS oscillators are vibration resistant because the mass of a MEMS resonator is approximately 1,000 to 3,000 times lower than the mass of a quartz resonator. This means a given acceleration imposed on a MEMS structure, such as from shock or vibration, will result in much lower force than its quartz equivalent and therefore induce a much lower frequency shift. The figure on page 5 shows that SiTime MEMS oscillators are more than 10 times lower (better) in vibration sensitivity compared to quartz oscillators. Note this figure is based on measurements of quartz oscillators rather than passive crystal resonators, but comparable results are expected on quartz crystal resonators.
The quartz supply infrastructure has several constraints which can result in long lead-times, on the order of 12 to 16 weeks or even longer. One constraint is the limited number of ceramic package suppliers. Another constraint is the limited availability of frequency options. With quartz products, every frequency needs a different crystal cut unless a programmable phase locked loop (PLL) is used. Therefore, lead-times for non-standard frequencies can be very long.
In contrast to crystal resonators, MEMS resonators are based on a standard resonator configuration. The output frequency of MEMS oscillators is generated by programming the PLL to different multiplication values. This enables a very wide frequency range with six digits of accuracy. In addition, silicon MEMS oscillators are manufactured using standard semiconductor processes and packaging. Because MEMS oscillator vendors leverage the very large semiconductor industry infrastructure, capacity is virtually unlimited.
MEMS oscillator samples can be programmed and available within one day, even for non-standard frequencies. By using SiTime&#;s low-cost Time Machine II programmer and field-programmable oscillators, designers can instantly program oscillators in their lab to create a device with any frequency, any supply voltage and any stability within the device&#;s operating range. Production lead-times are only 6 to 8 weeks.
Qualifying components for end-use (system) conditions can consume significant time and resources. However, qualification efforts can be reduced with MEMS oscillators. SiTime products are based on a programmable platform which allows each device within a base product family to generate a wide range of frequencies, supply voltages and stabilities. If for example, resources have been invested in qualifying a SiTime device at a particular output frequency and a new board design requires a different frequency, the existing qualification data may be extended to a part with a new frequency.
In contrast, each XTAL frequency requires a different quartz blank. And if a design requires frequencies above 60 MHz, a different technology other than fundamental mode quartz is often used. Third overtone quartz crystals are often used for higher frequencies. This mode can introduce additional challenges to ensure reliable start up (i.e. higher motional impedance and different oscillator circuit than fundamental mode) which requires qualification.
Despite inherent limitations, crystals have been the standard in electronic timing for several decades. SiTime&#;s MEMS oscillators overcome these limitations and offer many benefits compared to traditional quartz crystal resonators. Designers no longer need to accept the headaches and limitations associated with XTALs.
The top 8 reasons to replace XTALs with MEMS oscillators are:
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