Tham khảo tài liệu 'ultra wideband communications novel trends system, architecture and implementation part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Frequency Synthesizer Architectures for UWB MB-OFDM Alliance Application 189 signals depending on a hop-control signal. The output of the LUTs drive 4 bit current steering DACs. Via SSB mixers it is then possible to generate 3960 4488 and 3432 MHz quadrature signals. Injection locked frequency divider ILFD The use of injection locked frequency dividers ILFDs for MB-OFDM application can also be found in literature Kim et al. 2007 Chang et al. 2009 . In both cases a divide-by-5 ring oscillator-based ILFD is implemented. In Kim et al. 2007 the divider consists of five cascaded CMOS inverters connected in ring oscillator configuration. The supply source and sink currents are controlled via two switches controlled by the input signal. ILFDs can also be constructed using LC-based oscillators resulting in better phase noise performance compared to ring oscillator-based ILFDs at the expense of a higher power consumption. In Chang et al. 2009 the ILFD consists of two ring oscillators whose supply is clocked by the input signal. In this case the two ring oscillators are coupled together via inverters in order to improve the quadrature phase accuracy. 3. DLL-based frequency multiplier for UWB MBOA Delay locked loops PLL-based frequency synthesis has been widely employed until recent times. Another approach drawing attention in this field is DLL-based frequency synthesis. DLL-based frequency synthesizers outperform their counterparts in terms of phase noise since they derive the output signal directly from a clean crystal reference with limited noise accumulation Chien Gray 2000 . Additionally the DLLs can be designed as a first-order system to allow wider loop bandwidth and settling times in the order of nanoseconds especially important in applications where fast band-hopping is required such as in MBOA-UWB Lee Hsiao 2005 2006 . The main challenge in designing DLL-based frequency synthesizers is limiting the fixed pattern jitter that result in spurious tones around
