Radio-Frequency Integrated Circuits (RFIC) and Microwave Devices Laboratory
RRF-CMOS front-end, LNA (Low-noise amplifer),
PA(Power amplifier) ,
mixer, VCO(Voltage-Controlled Oscillator),
Advanced matching circuit ,
Microwave filter ,
Miniaturized antenna ,
Optical switch, Optical router, Superconducting device,
Planar antenna, Slot antenna, UWB antenna, array antenna, adaptive array, film antenna, THz-antenna on a chip and array antenna, energy harvester .
Cellular Phones, Wireless LAN, Bluetooth, Ultra Wideband(UWB), IMT2000, Satellite communication, Broadband transmission,
Sensor, Body area network, Medical application, Opt.-THz high speed communication, THz imaging, energy harvesting.
Design of RF-CMOS Front-End
⇒ A wireless RF front-end may consist of ampliefiers ( LNA, PA), mixers, Voltage-controlled Oscillator (VCO) with phase-locked loop (PLL) and impedance matching circuits inconnecting them or at the input terminal. We are now focusing to design all theese components using the newly proposed theory based on the microwave design rules on a single chip. The design of RFIC components differs from the conventional low-frequency analog circuits because they often demand high gain, low noise and low energy consumption, low loss (high Q-factor) at higher frequencies.
The integration technology has recently been reduced to nanometer (nm) range and this heavily results in significant reduction of chip size occupied by digital and low frequency analog circuits. However, the reduction in transistor's gate width does not help in anyways to reduce the chip size occupied by RFIC components or passive devices because spiral inductors are indispensable in designing amplifiers, mixers, VCOs, or impedance-matching circuits. Therefore, RFIC designers and engineers have working very hard to put impedance matching circuits and microwave filters inside an LSI chip for on-chip realization but the success story using conventional design theory has not been reported yet. Therefore, the void due to the lack of a new design theory for miniaturization of each components using microwave circuit design rules has been felt for a long time for on-chip realization.
Here, we proposed a new design theory using Coplanar Waveguides (CPW) lines instead of spiral inductors for RFIC components such as LNA, PA, mixers, VCO and impedance-matching circuits in interconnecting them. One of the advantages of the proposed theory is that it can save more than 50% on-chip space than those of the conventional theory.We use the state-of-the-arts technology, cutting-edge design tools, fabrication techniques and measurement equipments. We are working in collaboration with SoC R&D project called Fukuoka Innovative Cluster Project called Design Method for Low Energy and Mobile System LSIs.
Design of Miniaturized Filter and Matching Circuit
⇒Microwave filters such as BPF (Bandpass filter) with high frequency selectivity is another key component in wireless technology. Microwave filters are usually realized in passive structures such as microstrip or coplanar lines whose size is directly proportional to the wavelengths of interest. Low spurious responses and realization of attenuation poles near the passband to realize the sharp skirts are always in the demand of microwave filter regime. We were successful to fabricate those filters with improved characteristics and downsizing them by LSI technology for on-chip design, and study on their further characteristics improvement is now going on. On the other hand, matching circuits are necessary in RF-front end for interconnecting each components such as LNA and mixer or PA and mixer. Recently, spiral inductors have widely been used instead of resistors in the design of matching circuits to enhance the thermal noise performance of a wireless transceiver. However, such elements usually have low quality factor (Q) and may encounter the self-resonance in microwave-frequency band which permits its use in higher frequencies, and on the other hand, they occupy the large on-chip space. In this research, a new design theory for the impedance-matching circuits for a single-chip receiver front-end is presented. The presented matching circuits are composed of conductor-backed coplanar waveguide (CPW) meander-line resonators and impedance (K) inverter. The prototype front-end receiver is designed, fabricated and tested. A few of the advantages of the proposed method is not only the small on-chip space than the spiral inductors that they occupy, but a BPF can be realized by matching circuits.
Design of Electrically Small Antennas
⇒Miniaturization of electronic systems has accelerated over the last few decades and this process feeds expectations for even smaller components and systems in each new generation of equipment. Antennas have not been exempt from this pressure to be made smaller. Often, the result has been the use of antennas that are reduced in size without regard to their performance. This has led to needlessly poor system efficiency and reduced range.
Antenna performance is fundamentally a function of size measured in wavelengths at the operating frequency. "Electrically small" antennas are those that are small compared to the wavelength. In this research, we discuss the limitations on small antenna performance, possible tradeoffs, recent developments, detailed design and optimization.
We designed and fabricated miniaturized antennas, and possible applications of these antennas would be found in RFID and wireless LAN for commercial purpose. The future purpose of this research is to design a highly improved but very small antenna over a chip for SoC. We use Momentum, HFSS and circuit simulator driven by very strong mathematical feedback.
Design of High-Performance Optical Switch & Router
⇒Optical Switch is the key device, which changes the route of optical signal without electro-optic conversion. In the high-speed optical communications, external optical switches using a LiNbO3 and semiconductor devices have been using. There have still been great demands for realizing higher speed and lower power optical switch for small networks, i.e. router rather than main networks. With such background, we have been studying optical switch of high speed and low-power driver circuit connected to the open-end of transmission line in order to realize the high speed. In order to obtain the high output voltage and low power dissipation, we designed the stand-by power less driver circuit by using stacked CMOS inverters. In order to transmit high-speed pulses, the gates of CMOS inverters are divided and connected with transmission line like a distributed-type amplifier. Switching speed of our proposed CMOS driver has 31.5% faster than that of a standard one.
Study on microwave surface impedance of HTS