Lumped-element tunable absorptive bandstop filter and its applications

Byung Guk Kim, Purdue University

Abstract

To avoid the cost, large size, and complexity of going off-chip between individually packaged components, it is desirable to integrate as many components as possible. For on-chip passive filter design, size constraints and the quality factor limit the amount of attenuation that can be achieved. This work demonstrates the use of absorptive bandstop filters which gives anomalously deep notches for a given Q-factor. A lumped-element-only topology enables a realization on a chip for the first time. For reconfigurable RF front-ends, a frequency-agile design is newly developed with Q-tunable resonators because an absorptive bandstop filter must balance both intrinsic Q of the resonators and the resonant frequency of the filter. Despite using small-size, low-Q resonators in the bandstop filter design, a large stopband attenuation with a capability of frequency tuning is achieved with potential to suppress potential interference or an image frequency signal. Higher-order absorptive bandstop filters which give higher selectivity are also demonstrated. The sensing of the unused bands is a pre-requisite and important function so that the cognitive radio system can track and use available frequencies. When the ultra-wideband ADC is utilized for sensing to find the unused bands or read the spectrum availability, both the high power interferences and small power signals are the signals we are interested, but the wideband ADC has a limited dynamic range. Since we have the signals with various frequencies and power levels, it is required to have something that can give different gains at different frequencies. This work proposes a frequency equalizer which gives selective attenuation at desired different frequencies, and absorptive bandstop filter with variable attenuation is proposed in this work. For a wide-band receiver or application, it is not typical for AGC to control different gain or attenuation levels at different frequencies. Using frequency selective attenuation, it is desirable in order to suppress a large signal before the signal compresses a wideband sampler, but still allowing us to receive and monitor the signal.

Degree

Ph.D.

Advisors

Irazoqui, Purdue University.

Subject Area

Computer Engineering|Electrical engineering|Electromagnetics

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