I. Halkhams A CMOS 0.35 μm High Quality Factor Active Filter 77 Revue Méditerranéenne des Télécommunication Vol. 4, N° 2, October 2014 Mediterranean Telecommunication Journal A CMOS 0.35 μm High Quality Factor Active Filter Imane Halkhams 1 ,W. El Hamdani, M. El Bekkali, S.Mazer, LTTI laboratory,University Sidi Mohammed Ben Abdallah Fez, Morocco ; 1 imane.halkhams@usmba.ac.ma Abstract__In this work we describe the topology of an active filter using active inductor principle with a high quality factor in CMOS technology. This filter shows a resonant frequency at 6.4 GHz. A negative resistor circuit and Q- enhancement techniques such as channel width and current and voltage optimisation of the transistors compensated serial and parallel loss. S21 parameters were studied in two frequencies 6 GHz and 12 GHz according to the value of a capacitance that tunes the frequency of the filter. Keywords- active filter; active inductor; frequency tuning; Q- enhancement; CMOS 0.35μm I. INTRODUCTION Recently, telecom researches have known a great evolution, in particular in the implementation of RF bandpass filters, widely used in band selection and imaging. These systems usually require the use of highly selective filters with a high quality factor Q. Active inductor based filters have lots of benefits such as electronic frequency tuning, simplicity of integration and minimizing size. However, the intrinsic losses of the transistors limit the quality factor and the energy consumption remains significant. To remedy, many studies have been made proposing different resistance topologies [1][2]. The addition of a negative resistance does not only allow the reuse of the inductor current and thus saving energy but also improved the quality factor from 1.12 to 650. In this paper a study of the active inductor is first treated. Thereafter, serial and parallel losses are compensated through quality factor improvement techniques. Finally, active filter based on active inductor is presented at the end of this document. II. ACTIVE INDUCTOR The active inductor treated in this study (Figure 1(a)) [3][4] consists of a common source transistor M1, in feedback with a second transistor connected in common gate M2. The current source Iind is an active load. The two transistors form a gyrator which transforms Cgs1, the input capacitance of M1 to an inductor. Figure 1: (a) Active inductor topology (b) equivalent resonator The active inductor is equivalent to a resonator circuit (Figure 1(b)). The input impedance calculated from the small signal circuit is given by: Zin = gds1 gm1×gm2 + p Cgs2 1×2 + 1 gm1 + 1 p Cgs1 (1) Where gdsi et gmi i(1,2) are respectively the output conductance and the transconductance of transistor i. With : Rs = gds1 gm1×gm2 (2) L= Cgs2 gm1×gm2 (3)  = 1 gm1 (4) Cp = 1 (5) Simulation results show that the active inductor resonates at f = 8.46 GHz. Below the latter we have an inductive effect and above this frequency we have a capacitive effect, thus there is a parallel RLC circuit with a quality factor of 1.12, hence the need for Q-enhancement techniques. (a) (b) Iind