Ultra low power and high gain switched CMOS $g_m\mathrm{-}\mathrm{boosted}$ current reused mixer for wireless multi-standard applications

Abstract

An ultra low power and low voltage down conversion mixer is presented in this paper for the frequency band of 1.8–2.4 GHz. Designed in $0.18\mathrm{\mu }\mathrm{m}$ CMOS technology, the double balanced proposed mixer is composed by two cascaded stages. The first one is based on cross coupled capacitors technique in current reused topology providing a high voltage gain, while the second one employs a current reused transducer coupled to LO driven inverters to perform the down conversion. All the devices operate on moderate inversion for better trade-off between gain, linearity, and low power consumption. The post layout simulation shows a 23 dB of voltage gain conversion, an IIP3 of −2 dBm, with $300\mathrm{\mu }\mathrm{W}$ of power consumption under 0.9 V voltage supply.

Introduction

According to the recent advances in CMOS transceivers, multi-standard idea is the key solution to figure out the dilemma between the rapid growth of communication standards and high level of integration needs of RF system architectures [1]. Besides, low power and low cost transceiver designs are highly recommended and encouraged by the market for an effective competitiveness. However, most of the building blocks in the RF section are known by their high power consumption and large silicon area. Therefore, sharing the hardware remains to be an important suggestion to reach low power and low cost purpose for such sections [2]. In this context, up and down conversions, which are mainly based on mixers as building blocks, are the two functions essentially used to perform the frequency translation in the transmission and receiving operation modes, respectively. In down conversion mode, the mixer of receiving path is always in post-position of low noise amplifier circuit. A shared mixer in this configuration is undoubtedly a challenging design to achieve frequency translation under multi-standard requirements including GSM (DCS1800, PCS1900), 3G (UMTS), Bluetooth and WLAN b/g.

As mixer topology, the double balanced configuration is more used then the single one for its benefit in terms of common mode unwanted signals cancellation such as a common mode noise. For such topologies, Gilbert cell is a conventional double balanced one that provides gain [3]. In general, a moderate gain could be necessary to reach front-end requirements when a differential LNA precedes the mixer. However, a high gain mixer performance is more appreciated to increase the whole front end gain. Besides, the high gain needs an appropriate biasing leading to high power consumption and low linearity performances. Therefore, mixer design is still challenging to make trade-off between those performances. For instance, lowering the supply voltage to reduce the power is challenging task due to stacked stages of Gilbert cell. In pseudo differential mixers, the stacked stages are reduced to three to operates at low supply voltage [4]. However, it is often combined with a bleeding technique for a high gain purpose leading to additional current consumption.

Switched transconductors represent a good alternative to the conventional Gilbert cell by employing LO driven inverters instead of commuting stages [5]. As inverters operate in linear mode, less headroom is needed even for three stacked stages. In [6], the same technique is reported using a current reuse configuration to achieve a high gain conversion. All transistors operate in weak inversion inducing some benefits on linearity as shown in Section 3.3. This mode of operation becomes more attractive for best trade off between gain and power consumption. However, the frequency response is poor compared with the strong inversion mode [7]. Obviously, the moderate inversion mode seems the best choice for the best gain and power dissipation compromise.

Moreover, some other techniques were reported to reduce power consumption in front-end circuits for wireless applications. For instance, a cross coupled mixer is presented in [8]. A cross coupled LNA combined with current reuse is also used in [9]. In [10], the transconductance of common gate LNA is boosted using cross coupled technique.

In this work, a multi-standard switched transconductance mixer is addressed to operate in range frequency of 1.8–2.4 GHz. Operating in moderate inversion mode, the proposed mixer is based on two cascaded stages. The first one consists of the cross coupled current reused capacitor providing a high voltage gain. The switching operation is performed in the second stage, also based on the current reuse providing an additional gain conversion.

This paper is organized as follows: the second section describes the employed current reused and g_m boosted techniques. The mixer design is presented in Section 3. The simulation results and discussion are presented in Section 4.