Firstly what are MEMs oscillators?
Put simply MEMs are to Quartz what IC’s are to transistors and take the whole concept of Frequency Control into the 21st Century. As drop in replacement for standard Quartz oscillators, they differ in using Micro Electro Mechanical System technology, (essentially a silicon resonator controlled by an on board ASIC) rather than a Quartz blank to derive the output frequency.
MEMS technology is well proven, the first MEMS devices were produced in 1967. The technology has been in use reliably for many years in projectors, accelerometers, microphones and printer heads but has more recently been developed to allow the use of the technology in timing devices.
MEMs oscillators have been available on the market for some time but have not really broken into mainstream use as a replacement to Quartz oscillators, why is this?
I believe this is predominately due to a lack of understanding of the technology and also concerns related to moving from long established Quartz technology, whilst quartz is a very mature technology it does have some significant limitations, mainly physical size and shock resistance, both of which are becoming more significant with the rate of miniaturisation and breadth of development in electronics today.
Do MEMs devices offer a direct alternative to Quartz Oscillators?
Most current Quartz Clock Oscillator applications can be replaced seamlessly with MEMs oscillators without any changes to the PCB or effect on the circuit operation, MEMs offer a comprehensive product range with a wide range of specifications, outputs and package sizes, more specifically:
Outputs: HCMOS, LVDS, LVPECL & HCSL
Packages: 7x5mm, 5×3.2mm, 3.2×2.5m & 2.5×2.0mm industry standard footprints
Temperature Ranges: -20oC+70oC, -40oC + 85oC, -40oC +105oC & -55oC+125oC
Overall Stability: +/-10ppm, +/-25ppm & +/-50ppm
What advantages do MEMs offer over conventional Quartz Oscillators?
MEMs oscillators do offer a number of considerable advantages over quartz devices and
can counter the main weaknesses in Quartz technology:
Size Advantage – The resonator in a MEMs device measures only 50 x 20 microns, this allows costs to reduce as package size reduces rather than increase as is the case with Quartz devices. New product development will allow 1.6×1.2mm oscillators to be released in Q4 2012
Shock and Vibration Advantage – Due to the inherent semiconductor construction MEMs oscillators are much more resistant to Shock and Vibration (30000G Shock and 50G Vibration) than quartz, in addition the parts offer improved MTBF and FIT performance over quartz.
Cost Advantage – MEMS oscillators are generally lower cost than the quartz equivalent, this is more pronounced in the Differential output devices where costs can be up to 50% lower.
Lead-time Advantage – MEMs oscillators are available on very short lead-times in comparison to quartz devices, lead-times are typically 24 hours for low quantities and samples and 2-3 weeks for production volumes, and this is applicable to all output types including differentials and all package sizes.
Power Supply Noise Rejection Advantage – MEMs oscillators typically offer between 5 and 10dB better PSNR that the equivalent Quartz oscillator.
What Disadvantages are there to using MEMs oscillators?
One reason designers have dismissed using MEMs technology in the past has been the technologies inferior jitter performance in comparison to Quartz.
However with the more recent product releases the Jitter performance of MEMs devices has improved considerably and in many cases is now on a par with the quartz alternatives.
Integrated phase jitter now offers sub pS performance once above 100kHz and in a number of customer trials the Bit Error Rate following the change from Quartz to MEMs has been improved.
Currently MEMs does not offer a solution to tighter stability reference oscillators with sub +/-10ppm temperature stability, however these products are in the process of being developed.
In conclusion the performance of the current MEMs oscillators available in the market such as the AEL DSC range gives designers and purchasers many advantages over the current quartz parts in use. AEL are starting to see a number of large customers look at this technology with much renewed interest. For any users of quartz oscillators it is worthwhile investigating MEMs product in more detail.
Should you consider MEMs as a replacement for quartz in your products, simply
AEL Crystals Limited
Unit 28, The IO Centre
RH1 5GJ – UK
Tel: +44 (0) 1293 789200
Fax: +44 (0) 1293 789490