Microsoft Word - 2-Ma-ed.doc ETASR - Engineering, Technology & Applied Science Research Vol. 3, No. 6, 2013, 540-543 540 www.etasr.com Ma et al.: Current-mode CMOS Active Inductor with Applications to Low-Voltage Oscillators Current-mode CMOS Active Inductor with Applications to Low-Voltage Oscillators Minglin Ma Key Laboratory of Intelligent Computing & Information Processing of Ministry of Education, Xiangtan University, China minglin_ma@xtu.edu.cn Zhijun Li Key Laboratory of Intelligent Computing & Information Processing of Ministry of Education, Xiangtan University, China lizhijun_320@163.com Zili Yao Key Laboratory of Intelligent Computing & Information Processing of Ministry of Education, Xiangtan University, China yaozili@xtu.edu.cn Abstract— This paper investigates a current mode active inductor. In the proposed active inductor, three current mirrors have been connected to each other to realize the negative feedback. This active conductor has a two layer transistor structure. A 4.257 GHz, 1.2-V power supply non-inductive LC negative resistor oscillator, base on two of the proposed active inductors, is demonstrated. Keywords-active inductor; current mirror; low-voltage I. INTRODUCTION Wireless and mobile communications are two of the fastest growing microelectronics applications and have an enormous impact on everyday life. Driven by the insatiable demand for lower cost, lower power and higher data rates in wireless and mobile communications systems, a growing demand for CMOS wireless System-on-a-Chip(SoC) solutions is recorded. This trend has motivated the evolution and research on low voltage, low power, low cost RFIC designs [1, 2]. The oscillator is an important building block in RF transceivers. Inductive characteristics are critically needed in LC tank oscillators to realize frequency selection. Traditionally, passive inductors are off-chip discrete components. The need for off-chip communications with these passive components severely reduces the reliability, and increases the cost. CMOS active inductors have been widely used in the design of ring and LC tank oscillators because of their small chip area and wide tenability [3-6]. All these circuits [3-6] suffer from a tradeoff between low voltage and low cost. Here, we propose a LC oscillator based on the current mode active inductor. Current mode approach has several advantages, such as extended bandwidth, simple circuit structure, higher dynamic range, suitability of operation in reduced power supply environment, low power consumption, low voltage operation [7-12]. In the next section, the current mode active inductor is introduced and analyzed. In section III, an LC oscillator based on the active inductor is described. Section IV is the conclusion. II. THE PROPOSED ACTIVE INDUCTOR The active inductor proposed is depicted in Figure 1. It is based on three current mirrors (M1,2, M3,4, M5,6). IO is the bias current. Consider the equivalent network shown in Figure 2 where a current mirror can be equivalent to a trans-impedance (Ti) and a trans-conductance (gm). Go1 and GO2 denote the total conductances at nodes 1 and 2 respectively. Note that Go1 is due to the finite output impedance of the gm1 and the finite input impedance of Ti2. C1,2 are the parasitic capacitors. The following equations apply: 1 1 1 2 1 2 2 2 1 2 3 3 ( ) ( 1) (1) ( ) ( 2) m m i m in sC Go V V g node sC Go V V g T g I node          Fig. 1. Proposed current mode active inductor ETASR - Engineering, Technology & Applied Science Research Vol. 3, No. 6, 2013, 540-543 541 www.etasr.com Ma et al.: Current-mode CMOS Active Inductor with Applications to Low-Voltage Oscillators Fig. 2. equivalent network of the current mode active inductor The admittance looking into port 2 of the equivalent network is obtained from 2 2 1 12 1 2 3 3 1 2 3 3 1 (2)in m m i m m m i m I Y sC Go C GoV s g g T g g g T g      Equation (2) can be represented by the RLC networks shown in Figure 3 with parameters given by: 1 1 2 2 1 2 3 3 1 2 3 3 1 , , , (3) p p s m m i m m m i m Go C R C C R L Go g g T g g g T g     Fig. 3. The admittance looking into port 2 The proposed circuit contains only three current mirrors that all are of a two layer transistor structure. The minimum voltage required for proper circuit operation is Vgs+Vdsat where Vdsat is the minimum Vds voltage required to keep a MOS transistor in saturation. The compactness of the circuit results in low voltage supply and low power consumption. The active inductor has been simulated in Cadence (5.10.41_USR6.12) using parameters for chartered 0.18 μm RF CMOS Process with VDD=1.2 V. All transistors have the same channel length of 0.18 μm. The width of the transistors and the value of Io were chosen as W1=10 ， W2=30 ， W3=40 ， W4=120 ， W5=30 ， W6=42.85 ， Io=3 mA. The simulated Im(Z) and Re(Z) is shown in Figure 4. QLmax=7.8 is achieved at 4.257 GHz. Fig. 4. Simulated Im(Z) and Re(Z) ETASR - Engineering, Technology & Applied Science Research Vol. 3, No. 6, 2013, 540-543 542 www.etasr.com Ma et al.: Current-mode CMOS Active Inductor with Applications to Low-Voltage Oscillators III. AN LC-TANK OSCILLATORS USING THE PROPOSED ACTIVE INDUCTORS The proposed low-voltage current mode active inductor is applied to LC oscillator shown in Figure 5. This LC oscillator consists of two active inductors. The capacitor of the LC tank is the parasitic capacitors of transistors. The negative resistor, which is used to cancel the input resistance of the active inductors, is realized by the cross coupling between M7 and M27. Fig. 5. Current mode LC oscillator based on the active inductor Figure 6 shows the output voltage of the LC oscillator shown in Figure 5. Its frequency is set to about 4.257 GHz. Spectre from Cadence design systems is used for the phase noise simulation. It is approximately -105 dBc/Hz (1 MHz frequency offset). Figure 7 shows the simulated phase noise. Table I lists the comparison of the performance of previous active inductors oscillators to the one proposed in this paper. Fig. 6. The output voltage of the proposed oscillator TABLE I. COMPARISON OF ACTIVE INDUCTOR OSCILLATORS PERFORMANCE Ref. Tech. (μm) Vdd Phase noise PDC (mW) F (GHz) [3] 0.18 1.8V -101~-118 6-28 3 [4] 0.18 1.8V 110 30 1.6 [5] 0.18 1.8V -122.9 ---- 1.6 [6] 0.18 1.8V -109.4 30.5 1.5 This work 0.18 1.2V -105 t 20 4.257 Fig. 7. The simulated phase noise at the oscillation frequency of 4.257GHz IV. CONCLUSION This paper proposes a current mode active inductor build with three current mirrors. A 4.257 GHz, 1.2-V power supply, LC negative resistor oscillator, based on the proposed active inductor, is also demonstrated. Considering that the phase noise of the oscillator is approximately -105dBc/Hz at 1 MHz frequency offset, it is hinted that it can be used in a current domain circuit or a voltage domain circuit with low-voltage supply and small size. ACKNOWLEDGMENT This work was financially supported by a subproject of the Nature Science Foundation of China (No. 11KH|KH01069), the Nature Science Foundation of China(No. 61176032), and a project supported by the Scientific Research Fund of Hunan Provincial Education Department (NO. 12C0417) ETASR - Engineering, Technology & Applied Science Research Vol. 3, No. 6, 2013, 540-543 543 www.etasr.com Ma et al.: Current-mode CMOS Active Inductor with Applications to Low-Voltage Oscillators REFERENCES [1] M. Saito, M. Ono, R. Fujimoto, H. Tanimoto, N. Ito, T. Yoshitomi, T. Ohguro, H. S. Momose, H. Iwai, “0.15-μm RF CMOS technology compatible with logic CMOS for low-voltage operation”, IEEE Transactions on Electron Devices, Vol. 45, No. 3, pp. 737 –742, 1998 [2] D. Wang, J. Ou, X. 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