Integrated Circuits and Systems

Sangmin Yoo | |


Research in the Integrated Circuits and Systems Laboratory includes analog/mixed-signal circuits; radio-frequency (RF); wireless transceivers; circuits for communication; low power sensor interface.

Tremendous opportunities exist in broad areas of biomedical, health care, wearable, automotive, and communication systems of the future. Low power consumption and small form factor are critical features in the systems, as can be seen in examples such as smart glasses or implantable devices. Analog/RF/mixed-signal integrated circuit (IC) is one of the key technologies for high performance, low power, and small form factor systems. Research encompasses a wide range of topics in analog, mixed-signal, and RF circuits and systems that will enable innovations in the future. More specifically, research topics include analog/mixed-signal integrated circuits, such as data converters, amplifiers and filters, and RF circuits like mixers and power amplifiers in CMOS or other semiconductor technologies.

Wireless Transceiver with a Small Footprint and High Efficiency

A wireless transceiver with a small area and high efficiency is a key technology for modern mobile devices. It becomes increasingly more important because internet and connectivity are extended to everything in life. IC with small area and low power consumption is one of the crucial elements because the battery life and small form factor are very critical for portable, wearable, implantable, or sensor applications. Power consumption in radio could easily explain a significant portion of power budget in mobile systems, and transmitter usually occupies a big part of power consumption in the radio because it has many building blocks to process the signal to be transmitted to antenna. Transmitters consist of many building blocks such as digital-to-analog converter (DAC), filter, mixer, driving amplifier, and power amplifier that occupy a very large area and consume high static current in many amplifiers. High-efficiency RF PA is a very crucial circuit block because it consumes very high current to transmit high-power signal with linearity and accuracy required in advanced wireless communication standards.

All Digital Transmitter

All digital transmitter has a great potential for low-power small-area wireless transmitter.  With the advancement in modern fine-line CMOS process that features a myriad of transistors operating at very high speed with lower consumption, new technologies and architectures have been proposed and employed in analog/mixed-signal/RF circuits and systems. All-digital transmitter based on switched-capacitor power amplification (SCPA) technique, a very high energy-efficiency RF DAC topology, shows significant potential for wireless transceivers with very low power consumption and small chip area. It shows a great energy efficiency as RF power amplifier. In addition, it can also save a significant amount of energy and chip area by eliminating all other circuit blocks in transmitter chain because SCPA inherently contains the functions of DAC, mixer, and power amplifier. The SCPA technology could significantly reduce the power consumption and chip area of a whole transmitter by replacing all analog circuit blocks with a single mixed-signal RF block based on SCPA. In order to realize the full capabilities and maximize the impact, high resolution and accuracy are desired while delivering high Pout with spectral purity. All digital transmitter based on SCPA architecture could also be seen as an RF digital-to-analog converter that directly converts digital signal into RF signal.

Transmitters based on SCPA technology started to obtain worldwide attention from academia and industry as shown in International Solid-State Circuits Conference (ISSCC), the most prestigious international conference in IC design, in 2017. Many high-performance wireless transmitters presented at ISSCC 2017 employed SCPA architecture proposed by Dr. Yoo, and it started to get significant attention due to its superior linearity and efficiency. Many exciting opportunities exist in the future communication systems based on SCPA. Dr. Yoo’s research team is working toward true innovation and breakthrough.

Examples of previous projects include 6b SCPA, class-G 7b SCPA, high-efficiency class-AB RF PA, 802.11ac wireless transmitter, and high-performance ADCs. Research starts with identifying challenges and difficulties. Engineers come up with creative ideas to solve problems and lead to innovations. The research process includes circuit design, physical layout, chip fabrication, and performance evaluation. Innovations to tackle challenges can often be implemented in the design phase. For example, we have developed a SCPA circuit that consists of arrayed capacitors and switches. The circuit design is verified through intensive simulations using circuit and EM simulation tools. The design is implemented in layout using CAD tools such as Cadence Virtuoso, and then it is physically fabricated in advanced CMOS processes.