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

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What is a Differential Oscillator? Where can it be used in Electronics? Powered By Docstoc
					         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.

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

				
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Description: 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