Biography
Enrollment Date: 2011
Graduation Date：2014
Degree：M.S.
Defense Date：2014.06.26
Advisors：Dongmei Li
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：The Study and Implementation of Automatic Gain Control Amplifier for Audio CODEC
Abstract:
Nowadays, as people’s living standards is unceasingly improving, demand for portable electronics, such as medical and consumer use electronics, increases rapidly. CODEC is widely used in digital audio signal processing systems such as digital hearing aid. This paper focuses on the research and implementation of automatic gain control amplifier(AGC) used in digital hearing aid CODEC.This paper summarizes the structure, principle and advantages and disadvantages of common AGCs and VGAs. The structure of the source degeneration were deeply studied and the VGA based on this structure is proposed. Low noise and low voltage design techniques are used to optimize the noise and power performance the circuit. The resistor array, and the realization of the gain control method is studied, in order to reduce the mismatch of the resistor and increase the gain accuracy. Non-ideal factors of the circuit and causes of nonlinearity and noise are analyzed in detail, in order to improve the performance.Based on UMC180nm CMOS process, a low noise high linearity fully-differential VGA, supplied by 1V, is implemented. The VGA is composed of two stages, which are based on the structure of source degeneration. The second-stage VGA is implemented in two methods. Simulation results show that the VGA consumes about 70mW. The two methods provides a gain range of 32~64dB and 16~64dB, respectively, and the gain error of both methods is less than 0.6dB. The equivalent integrated input noise in the audio range is less than 2.8mV. The total harmonic distortion (THD) is below -50dB with a 0.2-Vpp differential output.