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Record Setting Silicon Resonator Reaches 4.51 GHz
bibekpaudel brings news that researchers from Cornell University have developed a very small silicon microresonator that vibrates at the highest frequency ever recorded for such a device: 4.51 GHz. Typical quartz-crystal oscillators, commonly used in electronics as clock signals, are about a millimeter wide and operate in the KHz - MHz range. The newly developed microresonator measures 8.5 micrometers long and 40 micrometers wide, making it ideal for use in smaller circuits and microprocessing. Quoting:
"One of the advantages of silicon microresonators is that they can be integrated directly into microchips using conventional manufacturing techniques, making them cheaper to produce and easier to fabricate small. Also, multiple resonators of different frequencies could be put on the same chip, says Ville Kaajakari, an assistant professor of electrical engineering at Louisiana Tech University. In a cell phone, for example, high-frequency resonators could filter out interference from other sources of radio signals."
You don't do it with a CPU. You do it in hardware with a digital counter, like this:
http://www.play-hookey.com/digital/ripple_counter.html
Dividing by two is easy -- just take the output of one of the flip-flops. Dividing by other numbers can be done by connecting the flip-flop outputs and/or their complements to an AND gate. This requires some extra circuitry and wiring, but in an integrated circuit the overhead will be insignificant. Even in a discrete circuit, if you make the reference 2^32Hz (~4.2GHz), you're only looking at maybe two counter ICs to divide down to 1Hz, although no counter IC I know of can handle a 4GHz signal.
The real issue with using this would be whether your manufacturing process can make transistors fast enough for it. The quote in the summary suggests this will be popular in an analog role for high-frequency applications like wireless. Maybe we'll see discrete timing references too.
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The Q is an indicator of the short term accuracy of the resonator. The long term accuracy is usually discussed in terms of temperature drift. The absolute accuracy has to do with how accurately you can produce a resonator of the desired frequency.
The short term accuracy is referred to, by digital designers, as jitter and is a very important figure of merit in both digital designs and communication systems.
The Q of this resonator is quite good, athough it's not unusual for quartz crystals to havo a Q of 50000. What's truly amazing is that this resonator has a Q of 10000 @ 4.5 GHz. The high end on a quartz crystal is in the range of 20 to 40 MHz. It is very difficult to produce resonators with such a high Q at such a high frequency.
Absolute statements are never true
That is exactly correct. The Q of a resonator http://en.wikipedia.org/wiki/Q-factor#Electrical_systems/ or oscillator determines it's efficiency at turning electrical energy into a usable oscillation. The real significance of this new resonator is that it can be incorporated into the same piece of silicon that the electronic circuit is built on. Currently if a circuit needs a high quality clock or RF signal it uses an off chip crystal oscillator to generate a reference clock usually at 10s to 100s of MHz and then multiplies it up to the frequency needed on chip with an on chip Phase Locked Loop (PLL). PLLs work great, but they take up valuable area and power. Also they are one of the few analog circuits left on most modern microprocessors so it is expensive to keep specialized analog engineers (of which i am one) on staff to design the PLL. If this oscillator/resonator works as described and can truly be integrated into advanced CMOS manufacturing processes, it would eliminate the need for an off-chip quartz crystal and reduce the cost of the system. You probably have about 15 quartz crystals inside your computer now humming along at different frequencies to create the reference clocks of your cpu, memory, pci bus, cdrom, display, wireless, bluetooth, etc. These could potentially all be removed significantly reducing the cost of a computer system and other electronic gizmos. It could also reduce the size and increase battery life of handheld wireless devices. Whether it lives up to the hype that the researchers and reporters of technology review are creating is the big question. Martin