CMOS RF switched capacitor bandpass filter tuned by ring VCO

Abstract

A new RF switched capacitor bandpass filter and its command circuit made up of a ring voltage controlled oscillator with 'XOR' gates are proposed. Implemented in a standard 0.35 m CMOS technology, this circuit is intended to be used in a subset of professional mobile phone applications . Experiments carried out on a prototype show a tunable center frequency range of 260 MHz [240-500 MHz], with a quality factor that can be as high as 300.

Design of switched capacitor Q-enhanced filter in 0.18µm CMOS technology for applications in UHF band

“…The command signals are applied to the N switches (X 1(t) to XN(t)) which are successively closed with a switching period TO, during a slot time equal to TOIN (Fig. 2), thus the N paths of this comb filter are successively activated during TOIN [6][7].…”

“…Then it can be applied whatever this number [6][7]. Moreover, this YCO can be fully integrated with the switched capacitor filter to ensure interne command signals.…”

“…The Q-factor of the switched capacitors filter used in this paper is given by: Equation (1) shows that selectivity depends directly on the number of cells and the resistor. In LC switched capacitor filter [6][7] the quality factor depends mainly on the inductor value. So, to obtain a higher Q-factor it appears evident that the inductor value should be higher as possible, but for values that can provides a good quality factor the limitation constraint of integration [13] still the major inconvenient of the LC switched capacitor filters particular for UHF applications [6].…”

“…Unlike passive filters, which have high insertion losses and are off-chip with prohibitive manufacturing costs [4][5], switched capacitors filters can be fully integrated in low cost CMOS technology which increase the operating frequency [6][7]. The remarkable characteristic of filters based on CMOS technology industry is that their performances increase and their cost decreases as their size is reduced, for designers this has been a great challenge for few years [7], [8][9]. This paper would like to prove the feasibility of an UHF Ease of Use integrated and tuned RC switched capacitor filter with 900 MHz as an operating frequency.…”