[China Instrument Network Instrument Development] Japan's Tokyo Institute of Technology and Japan's Information and Communications Research Institute (NICT) have developed a circuit technology that enables wireless communication circuits to no longer use crystal oscillators, using MEMS (micro-Nano-electromechanical systems) Technology and other oscillators integrated in the chip.
Existing wireless communication circuits use a crystal oscillator in an LO (local oscillation circuit) that provides a reference frequency of an RF (Radio Frequency) signal. For example, an LO transmitting hundreds of MH to several GHz of RF signals is composed of a PLL circuit capable of multiplying the output of a crystal oscillator such as 40 MHz. With this technology, the necessary high-precision and expensive 40MHz crystal oscillator can be omitted. However, there is a need for a clock composed of a 32 kHz crystal oscillator that is used in many embedded devices.
Ito Hiroshi, associate professor at the Institute of Future Industrial Technology, Tokyo Institute of Technology, said that instead of removing the 32 kHz crystal oscillator, the RF signal crystal oscillator is because "the crystal oscillator for RF signals is still a subject in the design of wireless communication circuits." . The 32-kHz crystal oscillator is used in many devices such as MCUs and is inexpensive, so that future R&D that can be integrated into an IC or built into an IC package is also in progress.
Using a piezoelectric vibrator This time, in order to remove the 40 MHz crystal, a vibrator that is made of MEMS technology and can be integrated into the IC is used. The vibrator prototype uses an external piezoelectric element with a resonant frequency of several GHz.
The newly developed circuit consists of a piezoelectric vibrator and a two-stage clock circuit using a 32 kHz crystal oscillator. The first stage is a clock generation circuit formed by a piezoelectric vibrator, and also has a function of detecting the frequency fluctuation and phase displacement of the piezoelectric element based on the 32 kHz clock source. The next stage is a clock adjustment circuit that compensates for frequency fluctuations and phase shifts. The frequency variation and phase displacement are controlled within the requirements of the wireless communication circuit.
Another advantage of using a piezoelectric vibrator is that it is easy to obtain the low phase shift (phase noise) required for wireless communication circuits. Since the frequency of the crystal oscillator output signal (resonance frequency of the resonator) depends on the shape, it is not easy to increase. When used for RF signals such as several GHz and tens of GHz, it is necessary to increase the multiplication ratio so that the accuracy (phase noise) may deteriorate. On the other hand, MEMS products such as piezoelectric vibrators can easily achieve a GHz level of resonance frequency, and signal degradation due to multiplication can be suppressed.
The prototype piezoelectric vibrator was commercially available. The two-stage clock circuit uses TSMC's 65nm process product.
(Original title: The use of MEMS technology for wireless devices does not require the use of a crystal)
Existing wireless communication circuits use a crystal oscillator in an LO (local oscillation circuit) that provides a reference frequency of an RF (Radio Frequency) signal. For example, an LO transmitting hundreds of MH to several GHz of RF signals is composed of a PLL circuit capable of multiplying the output of a crystal oscillator such as 40 MHz. With this technology, the necessary high-precision and expensive 40MHz crystal oscillator can be omitted. However, there is a need for a clock composed of a 32 kHz crystal oscillator that is used in many embedded devices.
Ito Hiroshi, associate professor at the Institute of Future Industrial Technology, Tokyo Institute of Technology, said that instead of removing the 32 kHz crystal oscillator, the RF signal crystal oscillator is because "the crystal oscillator for RF signals is still a subject in the design of wireless communication circuits." . The 32-kHz crystal oscillator is used in many devices such as MCUs and is inexpensive, so that future R&D that can be integrated into an IC or built into an IC package is also in progress.
Using a piezoelectric vibrator This time, in order to remove the 40 MHz crystal, a vibrator that is made of MEMS technology and can be integrated into the IC is used. The vibrator prototype uses an external piezoelectric element with a resonant frequency of several GHz.
The newly developed circuit consists of a piezoelectric vibrator and a two-stage clock circuit using a 32 kHz crystal oscillator. The first stage is a clock generation circuit formed by a piezoelectric vibrator, and also has a function of detecting the frequency fluctuation and phase displacement of the piezoelectric element based on the 32 kHz clock source. The next stage is a clock adjustment circuit that compensates for frequency fluctuations and phase shifts. The frequency variation and phase displacement are controlled within the requirements of the wireless communication circuit.
Another advantage of using a piezoelectric vibrator is that it is easy to obtain the low phase shift (phase noise) required for wireless communication circuits. Since the frequency of the crystal oscillator output signal (resonance frequency of the resonator) depends on the shape, it is not easy to increase. When used for RF signals such as several GHz and tens of GHz, it is necessary to increase the multiplication ratio so that the accuracy (phase noise) may deteriorate. On the other hand, MEMS products such as piezoelectric vibrators can easily achieve a GHz level of resonance frequency, and signal degradation due to multiplication can be suppressed.
The prototype piezoelectric vibrator was commercially available. The two-stage clock circuit uses TSMC's 65nm process product.
(Original title: The use of MEMS technology for wireless devices does not require the use of a crystal)
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