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This work elaborately investigates the possible circuit techniques to overcome the temperature and supply voltage sensitivity of fully integrated time references for ultra-low-power wireless communication in WSN. In a first step, the basic needs to build a frequency reference are studied. Furthermore, a closer look at the short-term as well as the long-term frequency stability of integrated oscillators is taken. This results in a design strategy, which is applied to six different oscillator design cases. All six implementations are subject to a study of phase noise and long-term frequency
stability. The first two implementations are respectively a temperature- and a supply voltage-independent Wien bridge oscillator. The temperature independence is obtained by using a novel feedback amplifier topology of which the output resistance only depends on a temperature stable resistor. This requires advanced circuit techniques and a highly-stable amplitude regulation circuit. The second Wien bridge implementation makes use of two nested regulators, resulting in an ultrahigh supply voltage stability over a wide voltage range. The third design case makes use of a high-quality bondwire LC tank. A novel pulsed driving technique is developed to decrease the power consumption of the high-frequency oscillator circuit. This driving technique reduces the impact of the oscillator circuitry on the output frequency and therefore also on the temperatureand supply voltage stability of the oscillator. To better understand the application field of the pulsed oscillator topology, the noise performance is analyzed as well. The processed implementation is a unique combination of power consumption and long-term frequency stability. Next, two injection-locked oscillator implementations are discussed. Apart from a stable output frequency, a high absolute accuracy is also obtained due to the locking to a wirelessly received RF signal. The first design uses the received 2.4 GHz carrier frequency as a time reference. Despite its simple system topology, this approach has several drawbacks in terms of selectivity and power consumption. The second implementation locks to the envelope of the received RF signal. Therefore, the oscillator can run at a low frequency, drastically diminishing the power consumption. A second improvement is the addition of a network coordination
receiver. For this purpose, a novel ultra-low-power receiver topology and demodulation technique are developed. As a result of the addressability, the overall power consumption in the network is reduced. The last design case is a temperature- and supply voltage-independent oscillatorbased sensor interface. Since the challenge in this design is rather the stability of the output value than the frequency stability, a different design strategy is used. It is shown that the matching of different oscillator delay stages can be applied to obtain a stable and highly-linear digitalization of a sensor input. The wirelessly injection-locked oscillator, the coordination receiver, the sensor interface, and a transmitter are combined into one highly-flexible wireless tag. The content, the scrambling code, and the length of the transmitted data burst can be adapted freely, depending on the application. The developed tag can therefore be used in a wide range of applications, with different accuracy requirements and energy constraints. Finally, an elaborate comparison between the developed oscillator designs and the state of the art is performed. It is shown that the free-running implementations as well as the injection-locked designs improve the state of the art. This discussion results in several suggestions for possible future work