چكيده به لاتين
In this thesis, a new and efficient structure is presented with regard to design and implementation of 8-point DFT circuit in the form of current-mode analog with differential input. This circuit is used to overcome interferences (jamming) in GPS receiver. An anti-jamming block is placed in GPS receiver prior to AGC to detect jamming frequency range and then attenuates it as much as possible. There are different methods to overcome jamming. As an efficient method, the received signal can be transformed into a frequency-domain by Fourier transform and after calculating the threshold limit, all spectral energy exceeding that threshold can be removed to obtain the desired signal. Then using reverse Fourier transform, the modified spectrum is returned to the time domain. Here, the main core of mitigation block is the discrete Fourier transform processor. As GPS is more used in portable equipment, therefore, special attention should be paid to power consumption. The main focus of this thesis is on presenting an 8-point analog Fourier transform circuit with low power consumption and high speed to mitigate the interferences.
Two structures for implementing 8-DFT circuit are proposed in this thesis. In one of the methods, area and power consumption have been minimized and the other method has a higher response rate. It should be noted that the both proposed structures are superior to the common butterfly model with regard to all parameters including the area and power consumption, speed and error rate, and accuracy. In addition, using low voltage NMOS cascode current mirror and low voltage PMOS cascade load, the proposed design can support a wide range of the input current very accurately.
In addition, design stages were investigated through simplifying DFT relations. Simulations were performed using ADS in 0.13μm TSMC technology and MATLAB software. The simulation results show that, the proposed 8-point DFT in complex differential mode is able to reach a response rate of 3.98ns, with a time reduction of about 5 times, and power consumption of 37.57mW and error mean about 1% in a wide range of input current changes between 0 to 100µA. additionally, 8-DFT power consumption in complex differential mode is equal to 37.67mA fed from 1.2V supply voltage.
Keywords: Global Positioning System, Analog Fast Fourier Transform, 8-Point FFT, Butterfly Model, Current-Mode, Voltage-Mode, Interference Mitigation, Jamming, Current Mirror
