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 Silicon Oscillator - Features and Benefits

Micro-Electrical Mechanical Systems (MEMS) have been greatly expanding in popularity over the past decade. While the automotive industry found MEMS vital for vehicle safety applications (tire pressure monitoring, air bag sensors, etc), these MEMS components have more recently been put to use in systems including sensors, gyroscopes, and microphones. These systems are used in high end electronics devices like Smartphone's, Digital cameras, tablets, gaming devices, etc.

In the past five years, MEMS-based Silicon oscillators have been replacing quartz oscillators in electronic applications. MEMS-based Silicon oscillators have numerous advantages over quartz including more features, higher performance, faster availability, higher robustness and reliability, along with a lower cost.

MEMS-based Silicon oscillators were first used in consumer electronics in such devices as laptops, DVRs, digital cameras, stereos, etc. But since SiTime has recently released a much higher performance MEMS–based Silicon Oscillator, these devices are being used in high performance applications like:

Telecom infrastructure – highly stable MEMS-based Silicon Oscillators, such as MEMS TCXOs (Temperature Compensated Oscillator) have been designed in by companies developing core routers based on SONET and Synchronous Ethernet and optical networking systems.

Differential MEMS-based Silicon oscillators have also replaced high frequency SAW (Surface Acoustic Wave) crystal oscillators, leading to their usage in Storage Area Networks and RAID systems based on SATA, SAS and FibreChannel protocols.

MEMS-based Silicon Voltage Controlled Oscillators provides a level of pullability and precision-tuning that is crucial in synchronization of clock signals. This leads to wireless applications, such as cell-phone base-stations and repeaters to start adopting the usage of differential and single-ended MEMS-based Silicon oscillators, which are well-known for their robustness, reliability, and low phase noise.

The addition of programmable signaling levels makes customizing your oscillator for any product or application easy. Available signaling levels include LVPECL, LVDS, CML, HCSL, or LVCMOS on various Silicon oscillator devices. Frequency is another customizable feature to enhance your system performance. Operating voltage is also a programmable feature, with options of 1.8V, 2.5V, 2.8V, and 3.3V, allowing interface with a wide variety of SOCs and ASSPs.

The long lead time for crystal oscillators is another disadvantage in which Silicon Oscillators have a solution. Lead times of 3-5 weeks enables better inventory control/ management, flexibility in meeting upsides, and simplified supply chain.

Because of a superb frequency stability, as low as 10PPM, the system timing margin and reliability of your electronics will increase greatly. Better stability also offers improved immunity against low frequency environmental noise from power lines, fluorescent lights and transformers.

With a robustness and reliability as high as 50,000 G of shock resistance, 70 G of vibration resistance, and 500 million hours of mean time between failure, MEMS-based Silicon oscillators are 10 times more reliable than quartz.

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