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Filtro Gm-C Para Aplicaciones de Comunicaciones con Sintonía Adaptativa del Factor de Calidad Q Independiente de la Sintonía de la Frecuencia Central


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Este artículo muestra la propuesta de un filtro gm-C de segundo orden con control independiente total de la frecuencia central y el factor de calidad diseñado para aplicaciones inalámbricas multiestándar. Se presenta asimismo el diseño de los lazos de control adecuados para hacer la correcta sintonía del filtro tras una breve descripción de las ventajas e inconvenientes de las propuestas encontradas en la bibliografía. El trabajo se completa con una propuesta de mejora del lazo de control del factor de calidad que permite aumentar la rapidez del lazo y disminuir el error de rizado de la señal de control. Postprint (published version)
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Conference Paper
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A fully reconfigurable channel select filter is presented which is used as a part of a multi mode direct conversion receiver. The filter supports different modes including GSM, IS-95, and UMTS. A 4<sup>th</sup> order Butterworth filter is realized in a g<sub>n</sub> C filter topology. The filter circuit is implemented in a standard 0.35 μm CMOS process. The filter is able to handle large input signals up to 600mVpp at a supply voltage of 2.7V. The circuit has a low current consumption of 620μA, whereas the needed die size is only 530520μm.
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A third-order G<sub>m</sub>-C Butterworth low-pass filter implementing G<sub>m</sub>-tuning and G<sub>m</sub>-switching to maximize the tuning range is described. This filter is intended to be used as a channel-selection/anti-aliasing filter in the analog baseband part of a zero-IF radio receiver architecture for multimode mobile communications. Its G<sub>m</sub>-switching feature allows extending the tuning range and adapting the power consumption. The filter's cutoff frequency ranges from 50 kHz to 2.2 MHz. An Input IP3 of up to +18 dBV<sub>p</sub> is achieved, for a total worst-case power consumption of 7.3 mW for both I and Q paths, and an effective area of less than 0.5 mm<sup>2</sup> in a 0.25-μm SiGe BiCMOS process. A new figure of merit is introduced for comparison of published low-pass tunable filters including noise, linearity, and tuning range.
We present programmable, fully differential G<sub>m</sub>-C second-order sections (SOS) showing tunability over a wide range of frequencies. The SOSs use floating-gate operational transconductance amplifiers (FG-OTAs) to realize tunability. We present two FG programmable OTAs. The OTAs have a pFET input stage and employ current mirror topology. An FG common-mode feedback (CMFB) circuit as well as a conventional CMFB circuit is described for use with these OTAs. Their performance is compared. Expressions are derived for the differential and common-mode frequency response of the OTAs. Typical simulation and experimental results are shown for prototypes fabricated in a 0.5-mum CMOS process available through MOSIS. The prototypes operate from a single 3.3-V supply with typical bias currents in the 10-100-nA range. We present experimental results showing frequency-and Q-tuning for a low-pass SOS (LPSOS) and a bandpass SOS (BPSOS) designed using these FG-OTAs also fabricated in a 0.5-mum CMOS process. Measured 1-dB compression for LPSOS and BPSOS are -15 and -11 dBm, respectively
A tuning scheme for continuous-time high-Q biquad filters is presented. An improvement over the existing implementation of the modified-LMS Q-tuning scheme is proposed and efficiently combined with the frequency tuning based on phase-locked loops. The proposed scheme takes much less area without compromising the accuracy achieved previously. The proposed unified Q- and f<sub>0</sub>-tuning scheme does not require the Q-tuning loop to be slower than the f<sub>0</sub>-tuning loop. The optimal case is to have equal speeds for both loops. Also, a low-voltage pseudo-differential operational transconductance amplifier with inherent common-mode feedforward is introduced. The structure is fully symmetric and suitable for high-frequency applications. An experimental test chip is fabricated in standard CMOS 0.5-μm technology, with a bandpass filter of center frequency 100 MHz and Q of 20, along with the proposed tuning scheme. The measured Q-tuning error is around 1%. Expected and experimental results are in good agreement.
The state of the art of continuous-time filter design is reviewed. Several techniques are discussed and compared in terms of performance and implementation feasibility in different fabrication technologies. This review does not aim at historical completeness, but rather emphasizes techniques that have proven their worth in commercial applications. Brief mention is also made of experimental work which, in the opinion of the author, shows promise for the future
Diseño CMOS de un filtro de tiempo continuo con sistema de sintonía automáticaA Loss-Control Feedback Loop for VCO Indirect Tuning of RF Integrated Filters
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