Introduction

An inductor is one of the basic components of electronic circuits. It is often used for filters, oscillators, low noise amplifiers, matching circuits and so on. However, using a inductor in an integrated circuit has a significant drawback. Even though a CMOS process has been developed rapidly and its minimum gate width becomes deep sub-micron, a spiral inductor in the integrated circuit occupies very large chip area. For example, required chip area of on-chip inductor whose inductance is 10 nH is about 450 ${\rm\mu m}~\times$ 450 ${\rm\mu m}$ according to the estimation proposed in Ref. [1]. Furthermore, $Q$ of an on-chip inductor is relatively low. Obtaining an on chip inductor with high $Q$ is very difficult. Its typical value is about 10.

There are a lot of literatures which deal with this problem[2]. Using active inductors is one of the most successful approach to overcome these problem. An active inductor is a circuit block whose input impedance is the same as that of a passive inductor [3]-[6]. This approach is often used in base band filter design. An active inductor occupies very small chip area compared with a spiral inductor because it consists of only MOSFETs and its parasitic capacitors. Furthermore, $Q$ of an active inductor is higher than spiral inductor. On the other hands, it is well known that the disadvantages of a active inductor are nonlinearity, power consumption and noise characteristics. Relation between an input voltage and in input current of most active inductors is not linear because of nonlinearity of MOSFETs. Their linearity is decreases as an input voltage swing becomes larger. Input signal level is limited by the linearity of active inductor.

In this paper a novel distortion reduction technique for active inductors is proposed. Low distortion active inductors using the proposed technique are introduced and its performances are confirmed.