Biography
Enrollment Date: 2013
Graduation Date：2016
Degree：M.S.
Defense Date：2016.05.31
Advisors：Zhihua Wang
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Research on Key Technologies for Gain Self-Calibrated Bluetooth Low Energy Transmitter with Two-point Modulation
Abstract:
Wireless body area network (WBAN) is a communication network attached to the body, which covers smaller area. In recent years, with the development of WBAN, it has been widely used in mobile medical and health monitoring service systems, sports and fitness, entertainment, intelligent home, and other fields. A miniaturized low-power wireless transceiver is the necessary condition for WBAN. Compared with traditional Bluetooth, the most prominent feature of the Bluetooth Low Energy (BLE) is low power consumption. Therefore, BLE with high energy efficiency is the best choice in the applications of lower data rate, such as WPAN.
This thesis is based on the BLE 4.0 protocols, and performs study of the two-point BLE modulator with automatic gain calibration. The modulator applies the fractional-N phase-locked loop based on Delta-Sigma Modulator. The two points for modulation are VCO and DSM, respectively. One of the advantages of this structure is reduction of the circuit, which brings about lower power consumption. Another advantage of two-point modulation is to overcome the limitation of the loop bandwidth on data rate. The modulation type is GMSK. The process of the digital baseband modulation is like this. The symbols to be transmitted are firstly through GMSK modulation. And then the signal is complex. The phase of the complex signal does the differential operation. The frequency modulation signal for two-point modulation is obtained. The modulation algorithm is finally verified in hardware (FPGA) circuit, and tested with the RF chip. In this paper, we implement the digital baseband GMSK (GFSK) modulation based BLE protocol with FPGA, and complete the transmitter demo from the PC to the digital baseband and RF chip, which includes the PC software platform and USB interface for communication. Finally, the communication from the transmitter to the receiver is verified successfully.
The difficulty for the two-point modulation technology is gain calibration. Because the modulator is finally used in a dual-mode (400M/2.4G) wireless transceiver, this paper proposes a new method for gain calibration, which reuses the 400M receiving circuit. In the calibration mode, the D/VCO output signal is a sine wave with single frequency closed to 2.4GHz. And this signal is received after division. Through mixing, filtering and ADC, the frequency can be measured by the improved CORDIC algorithm. Compared with the theoretical value, we can get the value for gain calibration.
Eventually, the measured EVMs for the transmitter system, when the data rate is 1Mbps, are 4.3% (GMSK) and 2.9% (GFSK). The circuit of this project is implemented in tsmc 65nm CMOS process with 1V voltage. The area is about 700um * 700um. The equivalent gates are about 165,000. And the global clock is 24MHz.