This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS 1 Compact Variable Gain Amplifier for a Multistandard WLAN/WiMAX/LTE Receiver Raul Oneţ, Marius Neag, Member, IEEE, István Kovács, Marina Dana Ţopa, Member, IEEE, Saul Rodriguez, Member, IEEE, and Ana Rusu, Member, IEEE Abstract—This paper presents a novel single-stage VGA archi- tecture that employs two Gm cells, a voltage-controlled current at- tenuator, resistors and capacitors. The gain can be changed in three large steps by using digital controls, and continuously within these steps. The VGA bandwidth and output-related IP3 and 1dBCP are independent of the gain setting; the bandwidth can be programmed through a digitally-controlled capacitor array placed at its output. The proposed architecture was employed to realize the VGA for a WLAN/WiMAX/LTE radio receiver. Die area and power con- sumption were reduced by implementing the two Gm cells with one instantiation of a high-linearity Gm-core and scaled outputs; also, the current attenuator was implemented with a simple differ- ential current steering circuit; finally, the load resistors were also used to sense the output common-mode level. The VGA was fab- ricated in 0.15 um standard CMOS process. Measurement results show the gain varying between 5 dB to 30 dB and the max band- width surpasses 60 MHz; input referred noise; O1dBCP of 8.6 dBm while taking 4.2 mA from a 1.8 V supply; it settles within 20 ns after a min-max step-change of the gain; it oc- cupies 0.05 . Index Terms—LTE, multistandard receiver, programmable bandwidth, variable gain amplifier, WiMAX, WLAN. I. INTRODUCTION I N recent years the complexity of mobile communication systems has radically increased, driven by the continuous evolution of the broadband wireless communication standards and by the need to integrate more and more functionality into mobile devices. Multistandard transceivers targeting Wireless Local Area Networks (WLAN), Worldwide Interoperability for Microwave Access (WiMAX) and Long Time Evolution (LTE) standards combine the high-data rate connectivity avail- able near hot-spots and the high mobility and coverage area of cellular networks [1]. WLAN (IEEE 802.11n), WiMAX and LTE transceivers are capable of utilizing multiple-input multiple-output (MIMO) diversity [2]–[4]. Recently, several proposals for transceivers that can support multiple standards, based on programmable and reconfigurable blocks, have been Manuscript received May 30, 2012; revised February 20, 2013 and May 06, 2013; accepted May 21, 2013. The work was supported in part by two programs: “Ph.D. in advanced technologies-PRODOC” POSDRU/6/1.5/S/5 ID 7676 and “PNII-IDEI” 2534/2008. This paper was recommended by Associate Editor A. Demosthenous. R. Oneţ, M. Neag, I. Kovács, and M. D. Ţopa are with the Technical Univer- sity of Cluj-Napoca, Romania (e-mail: raul.onet@bel.utcluj.ro). S. Rodriguez and A. Rusu are with the Royal Institute of Technology (KTH), Stockholm, Sweden. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TCSI.2013.2268324 Fig. 1. The block diagram of the envisaged multistandard radio receiver. presented in the literature: WiMAX and LTE [2], [5], WiMAX and WLAN [1], [6], [7]. Another strong driver for developing multistandard receivers is the software defined radio concept [8]–[10] and cognitive radio [11], [12]. Fig. 1 presents the block diagram of the multi-standard re- ceiver, able to handle WLAN, WiMAX and LTE broadcasts, envisaged in this paper. The Zero-IF architecture is the preferred solution for WLAN/WiMAX/LTE radio receivers [1], [2], [8], [13], as its well-known drawbacks—sensitivity to both DC (and near DC) offsets and the 1/f noise—are less critical for OFDM WLAN systems, where the near-DC subcarriers are not used [14]. The signals received by one or more antenna are amplified by several narrow-band Low-Noise Amplifiers (LNA) or a single multi-band LNA [1], [2], [5]. The radio-frequency (RF) signal is then down-converted directly into the baseband by a quadrature mixer so that the baseband analog blocks—the channel filters and the variable-gain amplifiers (VGA)—need to deal only with half the channel bandwidth at RF [13]. This paper focuses on the VGA placed before the Analog-to-Digital converter (ADC) in order to use more efficiently the ADC dynamic range. The linearity and bandwidth of most VGAs proposed in the literature depend strongly on the gain settings; quite often, the VGA bandwidth is not controlled, its value being only kept large enough as to have no significant impact on the frequency charac- teristics of the baseband path set by the channel filter. However, there are at least two good reasons to control the VGA band- width: i) the VGA can also implement a section of the channel filter and ii) the noise bandwidth can be limited/optimized ac- cording to each channel bandwidth. The VGA described here addresses these points by targeting wide gain range and very good linearity, independent of the gain setting, as well as fast response to gain changes and well-con- trolled and programmable bandwidth. 1549-8328/$31.00 © 2013 IEEE