Sharif Digital Repository

We present a novel and simple method to calculate each Fourier series coefficient of ISFs in LC oscillators, analytically. This new approach explains the relationship between Fourier series coefficient of ISF and oscillator topology and parameters. This technique helps designers to obtain the great insight of how to decrease the output noise in oscillators. This method also can be used to derive the waveform of ISFs in time domain.Based on the features of our new technique and by presenting a general method to change the stationary noises to Cyclo-stationary ones, we suggest a step by step design guide which elucidates new ideas for designers to manipulate the oscillator parameters and... 

In this thesis, we first introduce the required biological preparations and popular models for modeling single neuron, synapse and cable. Then by introduction of limit cycle oscillators and the necessary prerequisites, investigations are limited to systems involving weakly coupled oscillators. As two examples of such models, famous Kuramoto and Wilson- Cowan models are described. In the following, we introduce some methods for reduction dimension of weakly coupled oscillators and finally we apply one of the expressed methods on the dynamics of cortical network  

In this thesis, a modified method based on frequency discriminator technique is presented for measuring phase noise of microwave oscillators. In the proposed method, we use two oscillators with similar phase noise, but their free running frequencies are different in the range of 10MHz~50MHz. Mixing these two oscillators results in the IF frequency, for which the phase noise power at each offset has been doubled.The delay line is used in IF frequency and a phase shifter at microwave or millimeter wave range is used to provide quadrarure condition. Hence the cable loss at IF frequency is low and the sensitivity of system will be very good. Comparison of the measured data at X-band (the... 

The maximum number of oscillation frequencies which can be generated in a linear integer order system at the steady state is the half of its inner dimension. In this thesis, we seek the using of fractional order delayed systems with minimum order to produce maximum number of oscillation frequencies. We found a relation between the system parameters and the oscillation frequency and then adjust the system’s coefficients so that all the roots of the characteristic equation, except the roots on the imaginary axis, lie on the left-hand side of the imaginary axis. Taking into account the diagonal and triangular lower for the state space matrices of fractional order systems with one delay, we... 

In this thesis, it is shown that by detuning the array peripheral elements, without using phase shifters, and locking the array to the common frequency there exists a phase difference between two adjacent elements which is constant along the array and is proportional to the amount of free running frequency detuning. By changing free running frequency and therefore resultant phase difference, one can control the array beam direction. Linear, ring, hexagonal and triangular array configurations have been analyzed so far. In this work we endeavor to explore a circular planar array with weak coupling. The aim is to yield an analytical relationship to determine the free running frequency of each... 

For decades Crystal Oscillators (XO) have been the unequaled references for stable and low noise frequency sources. This leadership is due to their high Q-factor. The resonant frequency of such crystal resonator is inversely proportional to the thickness of the quartz disk (the resonant cavity) and is today limited , by physical manufacturing constraints , to about 150 MHz . in order to avoid such limitation , the solution is to start with an oscillator at higher fundamental frequency. SAW technology on quartz offers this opportunity . with SAW the resonant cavity size is not linked to the thickness of the substrate and resonant frequencies up to the GHz range are achievable. In this thesis... 

This thesis revises the conventional design of oscillators and presents new methods for shaping and improving the phase noise curve of the oscillators. These methods are based on the position of the zeros and poles of transfer functions in the S-plane and choosing their orders also. This thesis shows that the position of the zeroes and poles of the transfer functions can affect the phase noise performance of the oscillators. The basic idea is maximizing the slope of the phase of the transfer functions. It is proved that the maximizing the slope of the phase can expectedly reduce the phase noise of the oscillators. Increasing the order of the transfer functions with the proper selection of...