Performance Advantages with MEMS Oscillators

The expanse of technology has by far exceeded our knowledge and perceptions. The days of slow electronic devices are no longer relevant. Time and again we have been awed by innovative technologies that help us overcome obstacles and reach our goals. Today is an era of speed and dazzling performance. Electronic devices such as digital cameras, gaming systems, tablets, laptops etc., have to be robust and reliable with advanced features that accelerate performance and provide quick accessibility in a cost-effective manner.

 

The simulated games are accompanied with high quality sensors and microphones to provide the customer a real-life experience.  Keeping all these requirements in consideration, those who deal with the design and manufacture of these electronic items have to implement components that incorporate the desired application qualities and provide the customers with a positive experience. Thus, there is great demand for next generation solutions that are feature-rich and provide a lower total solution cost.  When it comes to clocking choices, the newest and most promising technology is MEMS (Micro-Electro-Mechanical Systems) oscillators. MEMS solutions were quickly adopted into the automotive market.  Applications such as tire pressure monitoring systems and air bag sensors benefited from the precision, reliability, and total solution cost.

 

Now the MEMS oscillator is widely used in electronic applications for various computing and electronic purposes such as laptops, DVRs, set top boxes, etc. The MEMS oscillator is revolutionizing the traditional quartz-crystal oscillator as the next generation clock timing solution for a number of reasons, but most importantly because of the superior performance and lower solution cost. It provides optimal performance and flexibility due to its ability to be programmed for any frequency within the range. It provides a simplified and enhanced inventory control and management process for supply chains. It can interface with numerous SoCs and ASSPs and operate under any standard voltage condition.

 

In addition to the performance and cost advantages, the MEMS oscillator offers significantly higher reliability. It features 70kG shock and 50G vibration, which represents a 10-50x improvement compared to a quartz-crystal oscillator.  Furthermore, the MEMS oscillator eliminates any start-up issues and frequency dips that occur with quartz-crystal oscillators.

 

MEMS performance is now meeting the demands of the highest performance telecom and networking systems that could only be addressed with quartz-crystal oscillators in the past.  Specifically, frequency stability as low as 0.1ppb (parts-per-billion) and phase 0.5fs (femto-second) jitter performance, combined with the lower solution cost and improved reliability make the MEMS oscillator an ideal solution for network routers, wireless and wireline telecom infrastructure equipment, and enterprise storage applications.  All of these applications benefit from SiTime's single-ended and differential oscillators

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Learn more about :- Clock Oscillator ,  Voltage Controlled Oscillator

Programmable Clock Oscillators Provide the Right Reference Clock, Every Time

A reference clock oscillator in electronics has long been the domain of fixed-frequency devices. These devices have historically consisted of a quartz crystal, which has been cut and manufactured to operate at a precise, fixed frequency, married to an analog oscillator circuit, which operates at the same fixed frequency and a fixed voltage. The process of manufacturing these fixed-frequency oscillators has been optimized over time, and results in accurate clocking devices that are very inflexible in offering features.

 

With recent advances in semiconductor-based MEMS technology and analog circuits, these fixed frequency clock oscillators are rapidly being replaced by a programmable clock oscillator. Programmable clock oscillators use a fixed frequency MEMS resonator, married with a programmable analog circuit which can offer a host of features that are not available from fixed-frequency oscillators, such as

 

1. Any frequency within the operating range, achievable by using a highly accurate Phase Locked Loop (PLL) which can multiply the MEMS resonator frequency up to any desired frequency of operation. The output frequency is accurate up to 6 decimal places of accuracy (1 Hz). This is particularly useful in applications where non-standard frequencies are desired to improve performance and reduce error rates.

 

2. Ability to operate at any voltage between 2.5V and 3.3V, as well as 1.8V, which are the most common input-output voltages used in electronics.

 

3. Programmable drive strength control using SoftEdge technology, which allows the user to accurately match the output impedance of the clock oscillator with the trace impedance of the board, and thus reduces reflections. Higher drive strength can also be used for driving multiple loads, while lower drive strength can be used for reducing electromagnetic interference (EMI).

 

4. Ability to configure the output control pin into Output Enable or Standby

 

In the case of more-featured oscillators such as Voltage Controlled Oscillators (VCXOs) and Voltage-Controlled, Temperature Compensated Oscillators (VC TCXOs), the programmability of the device also allows easy configuration of the pull range.

 

With such a host of features available from programmable clock oscillators, it is no surprise that the devices are rapidly gaining in popularity and have already replaced a significant number of fixed frequency reference oscillators.

 

 

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Learn more about: - Silicon Oscillator , Crystal Oscillator, MEMS oscillator

What is a Differential Oscillator? Where can it be used in Electronics?

There are two major kinds of electrical signaling –Single-ended (LVTTL, TTL, LVCMOS, CMOS, etc.) and differential (LVDS, LVPECL, HCSL, etc.). Differential signaling makes the use of 2 signals that are exactly opposite in phase to each other, thus eliminating common mode noise and resulting in a higher performance system. Differential signaling is used by many high performance protocols such as SATA, SAS, FibreChannel, 10G Ethernet, etc.

Differential oscillators are usually used to provide higher frequencies in very high performance systems where single-ended clocks do not perform well, such as the examples listed above. Typically, differential oscillators are used at frequencies above 100 MHz, because the rise times of differential clocks are usually much faster, and can support these high frequencies. However, it is not unusual to see differential clocks at even 25 MHz. Differential oscillators can output frequencies as high as 1 GHz.

One of the main reasons why differential oscillators are used in electronic systems is that they offer more robustness against power supply noise (and therefore, a higher PSRR) and reduce common mode noise coupling in the system. This is especially crucial for very high speed circuits, typically above 6 Gigabits per second data rates.

Historically, LVPECL protocols have been very popular in differential signaling. However, recently, LVDSs signaling has started to gain in popularity, driven by the lower power consumption of this protocol.

Since the output frequencies of differential oscillators are very high, they have typically operated at 3.3V and higher voltages. However, newer differential oscillator devices from Silicon MEMS timing companies have offered differential oscillators at voltages as low as 1.8V.

Typical quartz-based differential oscillators are offered in industry standard, 6-pin footprints, either 7x5mm or 5x3.2mm. Silicon MEMS-based differential oscillators also fit in these footprints, ensuring that they can replace differential quartz oscillators with no changes in design or layout. Some newer devices are also available in extremely small, 3.2x2.5mm packages.

Silicon MEMS-based differential oscillators are usually programmable, i.e. their frequency, voltage, stability, drive strength, and other features can be customized exactly to the required specification, which is different than what quartz differential oscillators can achieve. The ability to customize is an extremely important feature that can be useful in a variety of scenarios –such as –reducing EMI, bit error rates, higher performance, higher throughput, etc

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Learn more about :- Voltage Controlled Oscillator, TCXO, MEMS oscillator

MEMS Based Oscillators Outperform Quartz-Based Oscillators

Precision clock sources such as an XTAL, XO, VCXO, or TCXO require some type of resonator in order to supply an accurate, specific frequency. For decades, cost-effective clock sources have been manufactured with a quartz-crystal slice as the resonator element. That is, a precision quartz-crystal slice is machined, polished, and plated such that it resonates at a specific frequency. The crystal is then packaged together with a CMOS IC that provides the sustaining circuit and a logic-compatible output. Though this approach has been main-stream for the last 80+ years, there are many limitations that clock system designers have been forced to live with simply due to the lack of any other alternative in the market. That is, until now!

There has been significant progress in the MEMS (Micro-Electromechanical Systems) oscillator alternative. As a result, the quartz-based oscillator has a new and significant competitor. One MEMS start-up innovator making an impact in the precision timing space is SiTime Corporation. SiTime's all-silicon MEMS oscillators have been able meet or exceed the performance of quartz-based oscillators and overcome quartz-based limitations. A basic key feature of any oscillator is frequency stability. When comparing standard oscillators, also called XO, the SiTime SiT8208 and SiT8209 guarantees less than 10 ppm (parts-per-million) over the -40°C to +85°C operating temperature range. This represents a 2x (100%) performance improvement compared to the crystal-based 20 ppm alternative. Similarly, the SiTime SiT5001TCXO family features 0.5 ppm stability over the -40°C to +85°C operating temperature range. This represents a 5x (400%) improvement compared to a 0.5 ppm crystal-based TCXO. And last, SiTime's MEMS Oscillators, VCXO, and TCXO long term aging and jitter performance are comparable to, or better than, quartz-based oscillators. As you can see, the performance barrier has been shattered.

SiTime's MEMS oscillators simplify system designs and open the door to new applications. First, standard crystal-based oscillators do not operate at frequencies beyond approximately 70 MHz. Beyond that frequency, crystal oscillators use different techniques that sacrifice accuracy (such as Surface Acoustic Wave (SAW) oscillators) and reliability (Overtone Mode). SiTime's single-ended LVTTL/CMOS compatible oscillators operate at any frequency up to 220 MHz without any frequency holes and the differential oscillator family expands the frequency to 800 MHz. Second, crystal-based oscillators cannot support any frequency that the customer may want. Instead, they are available in standard, pre-set frequencies already defined by the cut of the crystal. Any non-standard frequency requires the crystal oscillator manufacturer to develop a new device and make it manufacturable in higher volumes, and the lead time for the non-standard frequency is typically 16-weeks. As a result, the high selling price is usually prohibitive for mid-to-high volume applications. This limitation goes away with the MEMS-based approach. SiTime's oscillators are all programmable to any frequency within their operating range as previously described, samples are shipped within 48 hours, and the price is similar to any standard frequency.

And last, MEMS-based oscillators are significantly more rugged and reliable. Shock and vibration are two standard figures of merit. SiTime's MEMS-based oscillators feature 50,000 G and 70 G tolerance to shock and vibration, respectively. This represents a 7-10x improvement compared to crystal-based oscillators with their shock and vibration tolerance of only 5,000 G and 10 G, respectively.

In summary, the SiTime's MEMS-based oscillators meet or exceed the performance of crystal-based oscillators plus they include the advantages of any frequency between 1-to-800 MHz without any delivery delay, improved reliability, and no price premium for non-standard frequencies!

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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 3rd overtone, 5th 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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Voltage Controlled Oscillator - Usage of Voltage Controlled Oscillators

A voltage controlled oscillator is a timing component that allows the fine tuning of a clock frequency within an electronic system, thus allowing a receiving system to be synchronized with a transmitting system that is not at the same location. The fine-tuning (pulling) of the output frequency can be controlled with an analog voltage input that is offered on one of the pins. Voltage controlled oscillators (VCXO) are generally made of quartz crystals, though recently, all silicon oscillators that utilize MEMS technology have also begun to offer VCXO devices.

Today's programmable and MEMS-based Voltage Controlled MEMS Oscillator that are flexible and provide innovative solutions for various applications such as telecom clock synchronization, wireless networking, FPGA-based systems, instrumentation, audio and video. Two main categories of Voltage Controlled Oscillators are the Differential VCXO and High Performance LVCMOS VCXO. The salient features and benefits are listed below-

Differential VCXO

* 100% compatible with quartz crystal VCXOs

* Provide a differential clock output, at LVPECL, LVDS and other popular signaling levels.

* Excellent jitter and frequency stability allows designers to resolve timing margin concerns and increase system reliability. Increased timing margin translates into fewer system errors and higher long-term reliability

* Programmable differential VCXOs are easily customization and can be optimized for the system application for the best system performance.

* Extremely short lead times (3-5 weeks for production volumes) minimize inventory overhead and reduce cost

* Better availability reduces shortage risk.

High Performance VCXO

* LVCMOS signaling levels, with frequencies up to 220 MHz

* 100% drop in replacement for quartz crystal VCXOs.

* Excellent jitter and frequency stability allows designers to resolve timing margin concerns and increase system reliability. Increased timing margin translates into fewer system errors and higher long-term reliability

* Programmable high performance VCXOs are easily customization and can be optimized for the system application for the best system performance. Best linearity results in simpler loop monitoring in software controlled system PLL

* More reliable PLL bandwidth over operating range

* Quicker lock time and calibration

* Decrease in of modulation harmonics

* Tighter PLL bandwidth and simpler system design

Voltage controlled oscillators have a number of uses, for instance in clock functions to control computer processes. They are also used to give out electronic signals in stationary as well as wireless devices like radio receivers, radio transmitters, routers, modems, game consoles and television. In addition to that, it can be also located on function generators and electronic jamming equipment.

 

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Learn more about :- Silicon Oscillator