全CMOS噪声抵消和增益优化的宽带LNA

MIXDES 2010, 17th International Conference "Mixed Design of Integrated Circuits and Systems", June 24-26, 2010, Wroc aw, Poland

MOSFET-Only Wideband LNA

with Noise Cancelling and Gain Optimization

Ivan Bastos, Luis B. Oliveira, João Goes

CTS-UNINOVA, Dep.º de Eng.ª Electrotécnica, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa

Monte da Caparica, Portugal {iib14351, l.oliveira}@fct.unl.pt

Abstract—In this paper we present a MOFET-only implementation of a balun LNA. This LNA is based on the combination of a common-gate and a common-source stage with cancelling of the noise of the common-gate stage. In this circuit, we replace resistors by transistors, to reduce area and cost, and minimize the effect of process and supply variations and mismatches. In addition we obtain a higher gain for the same voltage drop. Thus, the LNA gain is optimized and the noise figure (NF) is reduced. We derive equations for the gain, input matching and NF. We compare the performance of this new topology with that of a conventional LNA with resistors. Simulation results with a 130 nm CMOS technology show that we obtain a balun LNA with a peak 19.8 dB gain (about 2 dB improvement), a spot NF lower than 1.9 dB (0.5 dB reduction). SThe total power consumption is only 4.8 mW for a wide bandwidth higher than 6 GHz.

Index Terms—CMOS LNAs, MOSFET-only circuits, Noise canceling, Wideband LNA.

Manuel Silva

INESC-ID Lisboa Tech. University of Lisbon

Lisbon, Portugal manuel.silva@inesc-id.pt

In this paper our main goal is to design a very low area and low-cost LNA, and at the same time obtain less circuit variability, by implementing the resistors using transistors (MOSFET-only design) [6]. As it will be shown, this approach adds a new degree of freedom, which can be used to maximize the LNA gain, and, therefore, minimize the circuit noise figure.

We start by reviewing the basic amplification stages, common-gate (CG) and common-source (CS). For each circuit we derive equations, with different levels of approximation, for the gain, input matching and noise figure. By comparing the results obtained with the different equations with those obtained by simulation, we select the level of approximation required for the frequency range in which we are interested. For the complete LNA (combined CG and CS balun topology), we compare the conventional design with resistors, and the new MOSFET-only implementation optimized for gain and noise figure. Simulation results of a circuit example designed in a standard 130 nm CMOS technology validate the proposed methodology.

This paper is organized as follows. In section II we derive the equations for the basic CG and CS stages. In section III we present simulation results for the conventional LNA with resistors, which confirm the theory. In Section IV we present the MOSFET-only LNA and we describe the optimization of gain and noise figure. We compare performance of this LNA with others in the literature. Finally, a discussion and some conclusions are given in Section V.

MON-GATE AND COMMON-SOURCE STAGES

Figs. 1 and 2 show, respectively, the CG and CS stages, normally employed in RC LNAs. We derive equations using three different levels of approximation: a) transistors’ complete model including the parasitic capacitances; b) low frequency approximation; c) low-frequency approximation neglecting the transistors’ output resistance.

mon-Gate Stage

In the equations below gm1 and gmb1 are the transistor’s transconductance and body effect transconductance, respectively, and ro1 is the transistor’s output resistance. The capacitance CS represents the source-bulk and source-gate

I.INTRODUCTION

Nowadays, the demand for mobile and portable equipment has led to a large increase in wireless communication applications. In order to achieve full integration and low cost, modern receiver architectures (Low-IF and zero-IF receivers), require inductorless circuits [1 - 4]. The LNA, which is a key block in the design of such receivers, is investigated in this paper.

LNAs can be either narrowband or wideband [1, 2]. Narrowband LNAs use inductors and have very low noise figure, but they occupy a large area and require a technology with RF options to have inductors with high Q. Wideband LNAs with multiple narrowband inputs have low noise, but their design is complicated and the area and cost are high [1, 2]. RC LNAs are very simple and inherently wideband, but conventional topologies have large noise figures. Recently, wideband LNAs with noise and distortion cancelling [5] have been proposed, which can have noise figures below 3 dB.

Inductorless circuits have reduced die area and cost [4]. However, they are usually realized with MiM capacitors, which require an additional insulator/metal layer, and they use poly or/and diffusion resistors, which have large process and mismatch variations (typically ±25%).

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