Browsing by Subject "Software Defined Radio (SDR)"
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Item Implementation of a 1GHZ frontend using transform domain charge sampling techniques(2009-05-15) Kulkarni, Mandar ShashikantThe recent popularity and convenience of Wireless communication and the need for integration demands the development of Software Defined Radio (SDR). First defined by Mitoal, the SDR processed the entire bandwidth using a high resolution and high speed ADC and remaining operations were done in DSP. The current trend in SDRs is to design highly reconfigurable analog front ends which can handle narrow-band and wideband standards, one at a time. Charge sampling has been widely used in these architectures due to the built in antialiasing capabilities, jitter robustness at high signal frequencies and flexibility in filter design. This work proposed a 1GHz wideband front end aimed at SDR applications using Transform Domain (TD) sampling techniques. Frequency Domain (FD) sampling, a special case of TD sampling, efficiently parallelizes the signal for digital processing, relaxing the sampling requirements and enabling parallel digital processing at a much lower rate and is a potential candidate for SDR. The proposed front end converts the RF signal into current and then it is downconverted using passive mixers. The front end has five parallel paths, each acting on a part of the spectrum effectively parallelizing the front end and relaxing the requirements. An overlap introduced between successive integration windows for jitter robustness was exploited to create a novel sinc2 downsample by two filter topology. This topology was compared to a conventional topology and found to be equivalent and area efficient by about 44%. The proposed topology was used as a baseband filter for all paths in the front end. The chip was sent for fabrication in 45nm technology. The active area of the chip was 6:6mm2. The testing and measurement of the chip still remains to be done.Item Reduced Area Discrete-Time Down-Sampling Filter Embedded With Windowed Integration Samplers(2010-10-12) Raviprakash, KarthikDeveloping a flexible receiver, which can be reconfigured to multiple standards, is the key to solving the problem of embedding numerous and ever-changing functionalities in mobile handsets. Difficulty in efficiently reconfiguring analog blocks of a receiver chain to multiple standards calls for moving the ADC as close to the antenna as possible so that most of the processing is done in DSP. Different standards are sampled at different frequencies and a programmable anti-aliasing filtering is needed here. Windowed integration samplers have an inherent sinc filtering which creates nulls at multiples of fs. The attenuation provided by sinc filtering for a bandwidth B is directly proportional to the sampling frequency fs and, in order to meet the anti-aliasing specifications, a high sampling rate is needed. ADCs operating at such a high oversampling rate dissipate power for no good use. Hence, there is a need to develop a programmable discrete-time down-sampling circuit with high inherent anti-aliasing capabilities. Currently existing topologies use large numbers of switches and capacitors which occupy a lot of area.A novel technique in reducing die area on a discrete-time sinc2 ?2 filter for charge sampling is proposed. An SNR comparison of the conventional and the proposed topology reveals that the new technique saves 25 percent die area occupied by the sampling capacitors of the filter. The proposed idea is also extended to implement higher downsampling factors and a greater percentage of area is saved as the down-sampling factor is increased. The proposed filter also has the topological advantage over previously reported works of allowing the designers to use active integration to charge the capacitance, which is critical in obtaining high linearity. A novel technique to implement a discrete-time sinc3 ?2 filter for windowed integration samplers is also proposed. The topology reduces the idle time of the integration capacitors at the expense of a small complexity overhead in the clock generation, thereby saving 33 percent of the die area on the capacitors compared to the currently existing topology. Circuit Level simulations in 45 nm CMOS technlogy show a good agreement with the predicted behaviour obtained from the analaysis.