Tunable RF Filters Research Articles

RF CMOS Varactors for 2 GHz Applications

CMOS varactors are important components for the integration of tunable RF filters and VCOs. This paper presents a performance evaluation and comparison of three different types of CMOS varactors based on measurements. The tested varactor types are: (i) {p}^+-to-n-well junction, (ii) standard mode nMOS, and (iii) accumulation mode nMOS. The performance of each varactor type with respect to capacitance ratio and quality factor Q is evaluated at 2 GHz. Further, it is shown how these varactor types must be configured in LC-tank circuits for optimum performance. Finally, the three varactor types are compared and it is concluded that the Standard Mode nMOS type seems to the best choice for RF applications.

Optical fiber Fabry-Perot cavities and recirculating delay lines as tunable microwave filters

The radio frequency or microwave responses of single-mode fiber Fabry-Perot cavities and recirculating delay lines are studied. It is shown that fiber Fabry-Perot cavities may be used as bandpass filters and the recirculating delay lines as bandstop filters at radio or microwave frequencies. These electric filters are tunable by electrooptic effects since the bandpass or bandstop characteristic changes when the cavity or the delay line length is varied by a few tenths of an optical wavelength. The ultimate limit on speed of tuning is set by the coherence time of the light source. The dependence of the filter responses on the spectral purity of light is studied. Examples are given to illustrate the tunability of these electric filters. The availability of various components required to build the tunable RF or microwave filters is reviewed. >

Tunable electrooptic rf filter

A real time tunable electrooptic rf filter is demonstrated using a multichannel total internal reflection modulator to spatially filter the output of a Bragg cell. The demonstrated filter has a bandwidth to resolution ratio of 28. This ratio can potentially be increased to over 5000 with a like number of individually resolved frequencies.