In recent years, there has been a growing need for Successive Approximation Register (SAR) Analog-to-Digital Converter in medical application such as pacemaker. The demand for long battery life-time in these applications poses the requirement for designing ultra-low power SAR ADCs. This thesis work initially investigates and compares different structures of SAR control logics including the conventional structures and the delay line based controller. Additionally, it focuses on selection of suitable dynamic comparator architecture.  Based on this analysis, dynamic two-stage comparator is selected due to its energy efficiency and capability of working in low supply voltages. Eventually, based on these studies an ultra-low power 10-bit SAR ADC in 65 nm technology is designed. Simulation results predict that the ADC consumes 12.4nW and achieves an energy efficiency of 14.7fJ/conversion at supply voltage of 1V and sampling frequency of 1kS/s. It has a signal-to-noise-and-distortion (SINAD) ratio of 60.29dB and effective-number-of-bits (ENOB) of 9.72 bits. The ADC is functional down to supply voltage of 0.5V with proper performance and minimal power consumption of 6.28nW.

In this thesis, the circuits are designing with TSMC.18£gm CMOS process and 1.8V of supply voltage. The speed and resolution of ADC are 150MS/s and 12-bits individually. In order to achieve a high speed, low power consumption pipelined ADC. The proposed pipelined stage is replaced Flash ADC by SAR ADC and add an extra comparator to determine one additional bit in sampling phase of pipelined stage. This technique reduces large number of pipelined stage and opamp which is energy-hungry in the pipelined ADC. Second, the SAR ADC provides inherent sample-and-hold mechanism so that the front-end sample-and-hold amplifier circuit is non-need. Third, the SAR ADC can achieve rail-to-rail input signal swing and improve the conversion accuracy rather than Flash ADC. The dynamic comparator is used for lower power consumption for whole circuit. Furthermore, this pipelined ADC implement under a supply voltage as low as 1.8V. The bootstrapped switch is used for controlling the sampling in the front-end. It can reduce the impacts of linearity for operating under low supply voltage. The operation amplifier implement by the partially switched-opamp technique to reduce more power consumption. Finally, the output codes are translated by digital correction circuit, it enhance the comparators input offset error tolerance.

Rapid evolution of integrated circuit technologies has paved a way to develop smaller and energy efficient biomedical devices which has put stringent requirements on data acquisition systems. These implantable devices are compact and have a very small footprint. Once implanted these devices need to rely on non-rechargeable batteries to sustain a life span of up to 10 years. Analog-to-digital converters (ADCs) are key components in these power limited systems. Therefore, development of ADCs with medium resolution (8-10 bits) and sampling rate (1 MHz) have been of great importance. This thesis presents an 8-bit successive approximation register (SAR) ADC incorporating an asynchronous control logic to avoid external high frequency clock, a dynamic comparator to improve linearity and a differential charger-distribution DAC with a monotonic capacitor switching procedure to achieve better power efficiency. This ADC is developed on a 0.18um TSMC process using Cadence Integrated Circuit design tools. At a sampling rate of 1MS/s and a supply voltage of 1.8V, this 8-bit SAR ADC achieves an effective number of bits (ENOB) of 7.39 and consumes 227.3uW of power, resulting in an energy efficient figure of merit (FOM) of 0.338pJ/conversion-step. Measured results show that the proposed SAR ADC achieves a spurious-free dynamic range (SFDR) of 57.40dB and a signal-to-noise and distortion ratio (SNDR) of 46.27dB. Including pad-ring measured chip area is 0.335sq-mm with the ADC core taking up only 0.055sq-mm

A digital system is often required to operate under a specific frequency. A ring oscillator can be helpful in this circumstance because it can generate a signal with a specific frequency. However, a ring oscillator is also sensitive to the environment temperature. With the increasing requirement of accuracy and stability, many approaches appear worldwide to make a temperature-insensitive ring oscillator. This thesis project presents an approach to compensate the temperature effect on a Current Starved Ring Oscillator(CSRO). More concretely, we researched how to achieve temperature compensation for CSRO in a digitally-controlled configuration. A Phase Frequency Detector (PFD) block is adapted to sense the frequency difference between the reference frequency and CSRO frequency. Two Charge Pumps (CP)are used to quantify the difference in voltage signal. A Dynamic Comparator block compares the signals from CPs. A following Bidirectional Counter block can count up or down to change the current in CSRO by a four-bit signal. In the end, the CSRO can generate an oscillating signal at the appropriate frequency after some adaptation time. This proposed circuit was realized with AMS 0.35 um CMOS technology and simulated using the Cadence tools. Power consumption, temperature compensation analysis and voltage supply compensation analysis under different temperatures are also performed in the project.