Ultra Low Power Analog Circuits for Wireless Sensor Node System

This thesis will discuss essential analog circuit blocks required in ultra-low power wireless sensor node systems. A wireless sensor network system requires very high energy and power efficiency which is difficult to achieve with traditional analog circuits. First, 5.58nW real time clock using a DLL-assisted pulse-driven crystal oscillator is discussed. In this circuit, the operational amplifier used in the traditional circuit was replaced with pulsed drivers. The pulse was generated at precise timing by a DLL. The circuit parts operate in different supply levels, generated on chip by using a switched capacitor network. Its frequency characteristic along with power consumption were measured and compared to the traditional circuit. Next, a Schmitt trigger based pulse-driven crystal oscillator is discussed. Simulation results show that this structure can still sustain oscillation at different process corners and temperature. In the next chapter, a sub-nW 8 bit SAR ADC using transistor-stack DAC is discussed. To facilitate design effort and reduce the layout dependent effect, a conventional capacitive DAC was replaced with transistor-stack DAC with a 255:1 multiplexer. The control logic was designed with both TSPC and CMOS logic to minimize transistor count. The ADC was implemented in a 65nm CMOS process and tested at different sampling rates and input signal frequency. Its linearity and power consumption was measured. Also, a similar design was implemented and tested using 180nm CMOS process as part of a sensor node system. Lastly, a multiple output level voltage regulator using a switched capacitor network for low-cost system is discussed.