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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 49907 (05)
- University: Sharif University of Technology
- Department: Electrical Engineering
- Advisor(s): Fotowat Ahmady, Ali
- Abstract:
- Ultra-wideband (UWB) frequencies with low level of power spectral density, which is set by FCC standard, have long been utilized in many short range applications, namely sensor networks, indoor positioning and radar systems. As their name suggests, the ultra-wide bandwidth of this standard, covering frequencies from 3.1 to 10.6GHz, provides high data rate communications. Two of the most critical challenges toward UWB receiver design is narrow-band interference coexistence, including IEEE802.11a and jitter due to the very narrow width of the UWB pulse in time domain. General previously proposed solutions to receive these narrow pulses is based on correlation principle, which is very sensitive to jitter. Additionally, there are so many complexities toward their design in order to meet the required accuracy in positioning. In this thesis, a super-regenerative receiver (SRR), which is one of the practical ways to receive UWB narrow pulses with much less jitter sensitivity, is designed. This recently proposed solution is not optimized for narrow-band interference cancellation yet. Inevitably, to minimize the unwanted signal energy loss, n-path notch filters with high Q factor have to be utilized in order to cancel out the interference signal in high frequencies. However, in this case, so many challenges may appear, since n-phase tunable local oscillator signals have to be generated to adjust the center frequency of the notch filter, which in turns results in complexity and high power consumption. In this design, after going through the ultra-wideband LNA, by using a down-conversion mixer, all the operations is done in lower frequencies. By this way and by properly choosing the LO signal frequency equal to the interference center frequency, controlled by an injection locking oscillator, the interference center frequency converts to a dc level and can be canceled out by using a simple low-power gm-C high-pass filter with high Q factor, in such a way that system can tolerate in-band interference as large as 8dBm/MHz. The quench signal and the received pulse in the super-regenerative oscillator used in such systems need to be synchronized to maximize the gain, and in this design a synchronization loop is employed. In previously designed architecture, the UWB transmitted pulse is shaped in such a way that the null frequency can be tuned to the interference center frequency in signal spectrum, which has two significant effect. First, the noise floor of the other narrow-band systems is relaxed, and second, the blocker resistance in the proposed UWB system is enhanced and the signal reception is less vulnerable to desensitization as well as preventing the unwanted loss of energy. However, this tunability increases the complexity and cost of the transmitter implementation. Since the number of tags in a positioning system is much more that the fixed number of readers, they should be designed with the most possible simplicity and cost. Therefore, in the proposed solution, the null frequency is fixed and down-conversion may lead to an asymmetric overlap of the spectrum around the interference frequency, which in some cases can degrade the received signal energy. But according to the simulations, the operation of the proposed energy-detection system is not interfered and the overall accuracy is enough to position the tag location along with the simply-designed tags and low-power simple gm-C high-pass filter. The proposed system is designed and simulated in 180 nm CMOS technology, while consuming 28 mW power under 1.8 V supply
- Keywords:
- Ultra Wideband (UWB)Receiver ; Super-Regenerative Oscillator (SRO) ; Synchronisation ; N-Path Filter ; Dithering
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