High Frequency Crystal Oscillators

The heartbeat of an electronic system is the timing component. For the past 50 years, the timing reference in all electronics has been based on a quartz crystal. Components such as crystal resonators and crystal oscillators (also known as quartz oscillators) have been extensively used. Tens of billions of these devices are shipped every year.

In spite of their popularity, there are some significant limitations to crystal resonators and crystal oscillators. The most basic limitation is that typically, a crystal resonator cannot resonate at higher than 75 MHz in fundamental mode. To overcome this limitation for high frequencies, there are three alternatives:

* Use overtone mode – such as 3^rd overtone, 5^th overtone, etc. In this case, the oscillator operates at a frequency that is the third or fifth harmonic of the fundamental frequency. The disadvantage of this mode is that the costs are higher, and startup is not guaranteed over the entire temperature range.

* Use Phase Locked Loops to multiply the frequency – this is a very popular mode for MEMS-timing companies, but is not very popular with the crystal-based companies as they do not have analog circuits expertise. The benefits of this mode are that the intelligence is now in the electronics, leading to more features and higher performance at lower cost.

* Use Surface Acoustic Wave (SAW) technology – in which the crystal device operates differently than a standard AT-cut crystal.

Below is a comparison of the key parameters between SAW oscillators and MEMS Oscillators

SAW oscillators

* Frequency Range- Each device has to be cut to operate at a unique frequency

* Frequency Stability - Generally, 50 PPM, occasionally 25 PPM

* Package & Size – Large, 5032 and 7050 packages only

* Power Consumption- Typically more than 40mA

*1.8V Operation - Limited availability

* Aging - ± 3 PPM per year

* Shock & Vibration sensitivity – Sensitive, can break easily. Typical shock resistance is 2,000 to 5,000G

* Available Add-on features – Varies with part and frequency. Very few standard options available.

MEMS Oscillators

* Frequency Range- Programmable up to 800 MHz

* Frequency Stability - Can support as good as 0.5 PPM over industrial temperature range

* Package & Size - Small 2520 and 3225 in addition to 5032 and 7050 packages

* Power Consumption- Typically more than 20mA

* 1.8V Operation – Easily available

* Aging -Typically less than ± 1 PPM per year

* Shock & Vibration sensitivity – Extremely robust – 50,000G shock

* Available Add-on features - VCXO, SSXO (spread-spectrum) available in all frequencies and voltages, programmable drive

As can be seen from the above comparison, MEMS oscillators can offer superior characteristics compared to SAW crystal oscillators for high frequency applications.

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Clock Generator

Voltage Controlled Oscillator

Silicon Oscillator – Benefits of Silicon Oscillator

Today, the high-end Silicon Oscillators that are based on MEMS technology are fast replacing the conventional Crystal and Quartz oscillators. These Silicon oscillators are completely built on Silicon wafers and contain no quartz crystals. They typically use a MEMS resonator which is married to an analog silicon clock IC that generates the electrical clock signal.Today, Silicon Oscillators are used to replace all kinds of legacy clock components which are based on crystal or quartz technology. Because of the benefits that they offer, these Silicon Oscillators based on MEMS technology are rapidly replacing legacy components. Notable advantages that these new age oscillators provide users consist of robustness to vibration, humidity and shock that makes them an apt solution for products and goods that needs to be operated in tough environments.

Notable Silicon Oscillator component providers are now offering ultra performance oscillators that offer 600 femtoseconds of integrated RMS phase jitter and ±10ppm frequency stability across various temperature ranges, including industrial (-40 C to 85C), thus surpassing the rigorous SONET clocking requirements. All these MEMS-based Silicon Oscillators have been designed using MEMS technology and and with their innovative features, they are gaining in popularity as the timing components of choice in storage, networking, wireless and telecom applications.

Additional benefits of these devices are listed below:

* Offers greater design margin for high temperature applications

* Allows improved product robustness in rough environments

* Lengthens product life in rough environments

* Easily customizable for best possible system performance

* 100% drop-in replacement of crystal oscillators

* Broad product portfolio, which enables supply chain consolidation and reduction of vendor base

* 6 decimal places of frequency accuracy

* Large frequency range, up to 220 MHz for LVCMOS and 800 MHz for differential.

These Silicon Oscillators can also be used in other fields such as medical, aerospace, automotive and industrial.

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Voltage Controlled oscillators

Temperature Compensated Oscillators (VCTCXO)

MEMS Oscillator – Benefits of MEMS Oscillator

Over the past decade, Micro-Electro-Mechanical Systems (MEMS) have been very widely adopted in electronics. While they started out as life-saving components in the Automotive industry (air-bag sensors, tire pressure monitoring systems), they have recently been adopted by many consumer electronic devices such as SmartPhones, Tablets, Digital Cameras, gaming systems, etc. Typical components that are used in such systems include sensors, gyroscopes, and microphones.

Over the past five years, MEMS Oscillators have been replacing quartz crystal oscillators in electronics applications. MEMS oscillators offer the benefits of more features, higher performance, faster availability, higher robustness and reliability and lower cost, and hence their adoption is accelerating.

The advent of MEMS oscillators in electronic devices started with consumer electronic and computing devices such as laptops, DVRs, set top boxes and digital cameras. Recently, with the introduction of higher performance devices such as the Encore-based platform from SiTime, MEMS oscillators are penetrating higher performance applications such as:

* Telecom infrastructure - core routers based on SONET and Synchronous Ethernet and optical networking systems require very stable devices, such as MEMS TCXOs (Temperature Compensated Oscillators) for their high performance applications.

* High performance storage applications such as Storage Area Networks and RAID systems based on SATA, SAS and FibreChannel protocols have also recently adopted the use of differential MEMS oscillators to replace high frequency SAW (Surface Acoustic Wave) crystal oscillators.

* Wireless Applications, such as cellphone base-stations and repeaters are also adopting the usage of differential and single-ended MEMS oscillators which require very high robustness and reliability, as well as very low phase noise. MEMS VCXOs (Voltage Controlled Oscillators) provide a level of pullability and fine-tuning that is required for synchronization of clock signals, and are also used in such applications.

Benefits of MEMS Oscillators

* Can be programmed for any signaling level such as LVPECL, LVDS, CML, HCSL, or LVCMOS, supporting a variety of different products and applications

* Programmable for any frequency within the operating range, which allows for performance optimization and flexibility.

* Production lead times of 3-5 weeks, which enables better inventory control and management, flexibility in meeting upsides and simplified supply chain.

* Programmable for any of the standard operating voltages such as 1.8V, 2.5V, 2.8V and 3.3V, to interface with a wide variety of SOCs and ASSPs.

* Frequency stability as low as 10 PPM for better system timing margin and reliability, leading to longer life electronics. Better stability also offers improved immunity against low frequency environmental noise that comes from power lines, fluorescent lights and transformers.

Robustness and reliability as high as 50,000 G of shock resistance and 70 G of vibration resistance and 500 Million hours of Mean Time Between Failure is ten times better than quartz.

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Clock Generator

VCXO