Top Five Reasons to Replace your Quartz Oscillator

A quartz oscillator (also known as a crystal oscillator) has been the reference clock of choice in the electronics industry for many decades. Recently, this legacy device has been under attack by a host of clock devices that use a newer, more advanced technology – Silicon MEMS. Here are the Top Five reasons why you should replace your quartz oscillator with a Silicon MEMS device.

1. Higher Performance:  
Silicon MEMS oscillators offer higher performance across a wide spectrum of parameters. A quartz oscillator has been optimized for specific parameters – such as phase noise at a particular frequency and operating voltage and does extremely well. Silicon MEMS oscillators not only perform extremely well on these specific parameters – but they also offer high performance other parameters, such as:

a. Stable and reliable startup over temperature (which is an inherent problem in quartz oscillators due to the activity dips of crystals)
b. Full frequency range available at 1.8V, which is not commonly available from quartz devices
c. Oscillator stability as good as 10 PPM, which is not commonly available from quartz devices (MEMS TCXOs offer stability as good as 0.1 PPM)

2. More Features:  
Silicon MEMS oscillators offer many more features than a quartz oscillator.  Some of these features are listed below

a. Any frequency, up to 6 decimal places of accuracy. This capability is useful for generating higher performance or lower error rates from systems.
b. Drive strength control for better impedance matching, ability to drive multiple loads, or reduced EMI.
c. Thinner packages for thinner electronics.
d. Operation at custom voltages between 2.5V and 3.3V.

3. Better availability:
Production lead times of Silicon MEMS oscillators are 3-5 weeks, while that of a quartz oscillator is 6 – 16 weeks. This reduction of lead time ensures that Silicon MEMS oscillators can reduce inventory and cost of ownership.

4. Better robustness and reliability:
Silicon MEMS oscillators are based on Silicon, and use no quartz. They offer 10 times more robustness (ability to withstand shock and vibration) than quartz oscillators, as well as ten times better reliability.

5. Better cost trajectory:
Silicon MEMS oscillators have a better cost trajectory than quartz oscillators because they are based on Silicon and leverage the semiconductor industry infrastructure.

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Learn more about :- differential oscillator ,  Voltage Controlled Oscillator

The Unique Features and Benefits of Silicon MEMS Differential Oscillators

A differential oscillator is used as reference timing sources in very high performance electronic systems. Typically, differential oscillators have a frequency in excess of 100 MHz, though frequencies below that are also occasionally used.

 There are a couple of reasons why differential oscillators are used in electronic systems. First – a differential output eliminates common mode noise, which is important in very high performance, high-speed systems. Another reason for using a differential oscillator is that it offers more robustness against power supply noise – and therefore, offers a higher Power Supply Rejection Ratio (PSRR). These two capabilities are especially useful in serial data protocols that transfer data in excess of 6 Gigabits per second.

 Historically, a differential oscillator is made of a quartz resonator, married to a fixed frequency analog circuit (oscillator). The quartz resonator operates in either fundamental or overtone mode, and generates resonance at the target frequency of oscillation. The clock output from the oscillator goes through output conditioning, and appears as LVPECL, LVDS, CML or HCSL outputs on the device. LVPECL and LVDS are the most popular signaling standards in differential oscillators, with LVDS getting more adoption in the recent past because of its lower power consumption.

 A Silicon MEMS differential oscillator uses a MEMS resonator operating at a fundamental frequency of resonance, which is married to an analog circuit consisting of an oscillator, a PLL and various other functions. Most of the Silicon MEMS differential oscillators are programmable, i.e. their frequencies, voltages, stabilities, output signaling type and control pin can be configured exactly to the customer's specification. Because Silicon MEMS timing companies use the fabless semiconductor model, samples of these customized devices are available in less than a week, and production is available in 3-5 weeks, both of which are very important for accelerating time to revenue.

 Another unique advantage of Silicon MEMS differential oscillators is its ability to offer very high frequencies and stabilities at very low voltages, without resorting to overtone and SAW technology. Therefore, they eliminate the startup issues that are associated with overtone oscillators, and they offer significantly better stability than SAW oscillators, as low as 10 PPM, which is not available from SAW. In addition, their aging is also significantly better than SAW oscillators.

 With all these benefits, it's no wonder that Silicon MEMS differential oscillators are gaining significant traction against quartz oscillators and are replacing the latter in storage, networking and telecom applications.

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Learn more about :- Voltage Controlled Oscillator , TCXO , Crystal 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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Learn more about :- MEMS Oscillator , Silicon Oscillator