Biography
Enrollment Date: 2011
Graduation Date：2014
Degree：M.S.
Defense Date：2014.05.27
Advisors：Dongmei Li
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Design of Power Management Units for Low Power Audio CODEC
Abstract:
The CODEC of one hearing aid is the interface between the outer analog audio signal and the subsequent DSP. In the input signal path, it amplifies the weak signal from the microphone at frst, digitailizes the analog signal through the ADC and sends the digitalized signal into the subsequent DSP for signal processing. Meanwhile, in the output signal path, it translates the processed digital signals into anlog format and broadcasts the anlog signal to the user. To prolong the life of the used battery in the portable hearing aid as well as to meet with the requirement of the decreasing supply voltage in the advanced CMOS technology, the aim of my thesis is to study and design a low voltage low powe CODEC for a hearing aid.
This thesis introduces the system definition of the CODEC SoC and the requirement of every individual module at first and then follows the details of low noise high linearity PGA design. After that he PMU design including a now LDO, BJT based bandgap reference, reference generating circtuis. A low volage low power high precision bandgap reference is analyzed in detail aftereards. In the last two parts, the measurement results and the conclusion are made and drawn respectively.
In the circtuit design level, a PGA wih a transconductance input stage is proposed which achieves low power low noise high linearity operation. It works under the supply voltage of 1V while consuming 42uW power and the simulated input refered noise is less than 3uV. Besides, a low power (10uW) high PSRR (achieving -60dB in the audio band) is proposed by introducing an active LHP zero for frequency compensation. In addition, a high precision (7.5ppm/℃ on average) bandgap voltage referece operational as low as 0.65V is proposed. The current consumption is 238nA at room temperature when supplied by 1.2V.
In the system design level, all the modules propsed above are integrated into the Soc combing with the available ΔΣ ADC and class-D DAC designs in our group. The designed chip has been measured and the results show that the PMU, PGA works significantly with theΔΣ ADC and Class-D DAC.