Biography
Enrollment Date: 2013
Graduation Date：2016
Degree：M.S.
Defense Date：2016.05.30
Advisors：Woogeun Rhee
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Ultra-Wideband Transmitters for Low-Power Body-Range Wireless Communication
Abstract:
With the advent of Internet of Things (IoT), ultra-low power (ULP) short range radios for wireless body area network (WBAN) and wireless sensor network (WSN) have received great attention these days. Smartphone-based IoT applications drive a strong momentum in the design of the ULP radio. As CMOS technology advances, the power consumption of analog baseband and DSP circuits takes less portion of the whole SoC, while the power consumption of RF front-end circuits is not scaled down well with the technology. Even though transceiver designs based on Bluetooth Low Energy (BLE), ZigBee, or IEEE802.15.6 standards have difficulty in satisfying the power requirement for ULP sensors and radios.
On the other hand, the ultra-wideband (UWB) technology has great advantage in low power applications. Traditional impulse radio UWB (IR-UWB) transceivers and frequency-modulated UWB (FM-UWB) transceivers have both advantages and disadvantages. The IR-UWB transceiver achieves low power consumption with aggressive duty cycled operation but suffers from the bit-level synchronization problem by the baseband. What is more, the output spectrum of the IR-UWB transceiver exhibits slow spectral roll-off, leading to a low spectrum efficiency. The FM-UWB transceiver features a good spectrum roll-off and high spectrum efficiency. However, the FM-UWB transceiver operates with continuous modulation, resulting in high power consumption. The chirp-UWB transceiver, combing the merit of the IR-UWB and the FM-UWB together, shows a good spectrum roll-off with high spectrum efficiency and achieves low power.
For IoT applications, secure wireless transmission is an important factor. Public key encryption increases hardware complexity and power consumption. Existing wireless standards such as Bluetooth or WiFi have difficulty in satisfying the requirement of secure applications. Near-field communication (NFC) systems require a bulky inductor and only provide low data rate transmission. By adopting the UWB technology, accompanied with frequency hopping and pulse position modulation methods, a high secure wireless transmission is achieved.
This thesis covers the UWB research works for two transceiver systems.
Based on the existing results, a multi-channel chirp-UWB transmitter is proposed. To achieve an optimum duty-cycle control, burst-mode transmission and steep digital gradient generation techniques are employed. A 5-to-9GHz chirp-UWB transmitter is implemented in 65nm CMOS for multi-channel operation with a channel bandwidth of 500MHz. The transmitter achieves 1Mb/s data rate, consuming 0.5mW from a 1V supply.
Aiming at secure proximity communication, a pulse-based UWB transmitter is proposed. The transmitter achieves high security by utilizing a pseudo-random scrambling method for both frequency hopping in frequency domain and pulse position modulation (PPM) in time domain. In addition, the low transmitted power of -70dBm/MHz not only makes it difficult for other receivers to detect the signal but also makes the transmission worldwide compliant with existing wireless standards. A prototype 3-to-4GHz proximity transmitter is implemented in 0.18m CMOS. The transmitter achieves 1Mb/s data rate with 0.3mW power from a 1.8V supply