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Analysis and System-Level Design of a C-Band Signal Generator with High Spectral Purity

Heydari, Hossein | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50049 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Nayebi, Mohammad Mahdi; Medi, Ali
  7. Abstract:
  8. In this project a high spectral purity C-band (4.25-5GHz) frequency synthesizer has been analyzed and designed and implemented in CMOS 0.18μm technology. This synthesizer has been embedded in TX path of a transceiver module as a frequency translator for digital phased array system applications. The system includes Phase Locked Loops (PLLs) and Direct Digital Frequency Synthesizer (DDFS). Due to desired Low spur level (90 dBc) in C-band, system level design, frequency plan, choosing proper PLL topology and etc. have been considered in details. One of the important challenges in system design is the signal spectrum purity. In other words, the system should produce minimum phase noise. Output signal impurity (high phase noise and spur level) makes interference for other receivers. In this work, a frequency synthesizer based on dual-loop offset PLL structure has been developed. The mixer used in the proposed structure produces residual spurs. Because of this, an improved dual-balanced mixer has been exerted. There is a need for Voltage Controlled Oscillator (VCO) with low Kvco. It contains controlling bits to have control over the phase noise and the output spur level. In order to cover the frequency range, a dual polarity Phase Frequency Detector (PFD) and a DDFS have been applied. Calibration circuits have been designed to assure proper modes for oscillators. Lock-time of the synthesizer should be lower than 10 µs, then two high speed and normal speed modes are considered. The circuit first enters high speed mode to follow the output frequency, then enters normal mode. This makes it possible to lock in 10 µs. The system has two different states: Constant Wave (CW) and Linear Frequency Modulation (LFM). The current injection in loop filter improves the chirp linearity
  9. Keywords:
  10. Phase Noise ; Linear Frequency Modulated (LFM)Signal ; Direct Digital Synthesizer (DDS) ; SPURS ; Offset Phase Locked Loop ; Spectral Purity

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