Biography
Enrollment Date: 2011
Graduation Date：2014
Degree：M.S.
Defense Date：2014.05.27
Advisors：Baoyong Chi
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Research on Key Techniques of Low Power WiFi Transmitter
Abstract:
Recently with the widespread application of Wi-Fi in our daily life and work, the design of a low power single-chip Wi-Fi transceiver, which can operate at several frequency bands, has been brought into attention of the counterparts at home and abroad.
This thesis presents a 180nm low-power transmitter using direct-conversion architecture for Wi-Fi application. The transmitter’s baseband section consists of a current DAC、a transresistance biquadratic section (TI-LPF) with adjustable bandwidth and a passive low-pass filter .The current DAC with 10-bit resolution is used to realize the conversion between the digital signals and the analog current signals. The TI-LPF can filter out the aliasing signals generated by the DAC and also modify the trans-resistance gain. The passive low-pass filter makes a contribution to attenuating the out of band noise, which reduces its power. The transmitter’s RF section includes two parts, each of which operates in a frequency band of 2.4~2.5GHz and Sub-GHz separately. The 2.4~2.5GHz part consists of a passive voltage mixer and a power amplifier. The mixer is driven by 50% duty-cycle LO due to the limitation of the 180nm technology. The Sub-GHz part also consists of a passive voltage mixer and a power amplifier. Unlike the 2.4~2.5GHz mixer, the Sub-GHz mixer is driven by 25% duty-cycle LO .An average efficiency improvement technique of RF power amplifier based on the envelope detection is proposed. The technique utilizes an on-chip envelope detector to detect input signal strength and dynamically configures the size of the power transistors as well as optimizes the load by adjusting the output impedance matching network, so that the efficiency at low output power level is improved and the average efficiency improvement for the PA could be achieved.
The power amplifier has been implemented in 0.18um CMOS .The post-layout simulations show that the TI-LPF realizes a gain range of 0-25 dB, and the -3dB bandwidth can be adjusted among 1.5M、2.5M and 4M.For the 2.4~2.5GHz PA which can operate at 2 modes: high output power mode and low output power mode. The output P1dB at the high output power mode is15.3 dBm with 30.5 % PAE, and the output P1dB at the low output power modes are 10.5dBm with 17.7% PAE .For the Sub-GHz PA which can operate at 3 modes: high output power mode、medium output power mode and low output power mode. The output P1dB at the high output power mode is 18.3dBm with 30.2% PAE, and the output P1dBs at two low output power modes are 14.9dBm with 24.11% PAE and 11.1dBm with 17.1% PAE, respectively. The die area is 4x2 mm2.