High Frequency Crystal Oscillators

High Frequency Crystal Oscillators
The heartbeat of an electronic system is the timing component. For the past 50 years, the timing reference in al
electronics has been based on a quartz crystal. Components such as crystal resonators and crystal oscil ators (also
known as quartz oscil ators) have been extensively used. Tens of bil ions of these devices are shipped every year.
In spite of their popularity, there are some significant limitations to crystal resonators and crystal oscil ators. 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:
1. Use overtone mode - such as 3rd overtone, 5th overtone, etc. In this case, the oscil ator 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.
2. 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.
3. 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 oscil ators and MEMS Oscil ators
SAW oscillators
1. Frequency Range- Each device has to be cut to operate at a unique frequency
2. Frequency Stability - Generally, 50 PPM, occasional y 25 PPM
3. Package & Size - Large, 5032 and 7050 packages only
4. Power Consumption- Typically more than 40mA
5. 1.8V Operation - Limited availability
6. Aging - 3 PPM per year
7. Shock & Vibration sensitivity - Sensitive, can break easily. Typical shock resistance is 2,000 to 5,000G
8. Available Add-on features - Varies with part and frequency. Very few standard options available.

MEMS Oscillators

1. Frequency Range- Programmable up to 800 MHz
2. Frequency Stability - Can support as good as 0.5 PPM over industrial temperature range
3. Package & Size - Smal 2520 and 3225 in addition to 5032 and 7050 packages
4. Power Consumption- Typically more than 20mA
5. 1.8V Operation - Easily available
6. Aging -Typical y less than 1 PPM per year
7. Shock & Vibration sensitivity - Extremely robust - 50,000G shock
8. Available Add-on features - VCXO, SSXO (spread-spectrum) available in al frequencies and voltages,
programmable drive


As can be seen from the above comparison, MEMS oscil ators can offer superior characteristics compared to SAW
crystal oscil ators for high frequency applications.
Learn more about :- Clock Generator , Differential Oscil ator , TCXO & Voltage Control ed Oscil ators

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