A HIGH PERFORMANCES CMOS MIXER DESIGN FOR 3.1-4.8 GHZ UWB MB-OFDM RECEIVERS Skandar Douss, Farid TOUATI and Mourad LOULOU Laboratoire d’Electronique et des Technologies de l’Information, Ecole Nationale d’Ingénieurs de Sfax, B.P. 3038 Sfax, Tunisie skandar.douss@tunet.tn ABSTRACT A design of active mixer intended for the “Mode 1” of ultra wideband multi-band OFDM receivers is presented. It is based on a doubly-balanced Gilbert cell type in which bleeding current sources are added in order to improve linearity and gain. Using an adequate input matching network and optimized device size, it was possible to obtain a good operation of the proposed mixer all over the 3.1-4.8 GHz band with AMS 0.35 μm CMOS process parameters. The simulated results show a conversion gain of 14.0 dBm, a noise figure of 7.7 dB and an input IP3 above 0 dBm, when the power consumption is 18 mW under 3V supply voltage. Index Terms— CMOS Mixer, analogue integrated circuit, Wireless receivers. 1. INTRODUCTION The rules defined by FFC, for marketing and operation of UWB products, permitted the appearance of other alternatives than the traditional impulse radio technology. Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM), which is an OFDM specification for UWB, has been stressed. After IEEE P802.15 TG3a has been withdrawn, the MB-OFDM specification is under control by ECMA International. ECMA standard [1] specifies the physical and MAC layers. The maximum transmitted power allowed by the FCC in this band is around -41.3 dBm/MHz (i.e. 75nW/MHz), which is similar to the power from unintentional radiators (TV, PC monitors, etc.). For this reason, receiver blocks need to have high signal amplification. In a UWB MB-OFDM receiver, a lot of trade-offs are posed in a mixer design. Firstly, the mixer has to meet wideband requirements over the ‘Mode 1’ band. An adequate input matching is then required. The basic trade-off is between gain and linearity. For a high gain, the linearity is less and vice-versa. The current bleeding technique, firstly proposed by Lee and Choi [2], allows improving simultaneously gain and linearity in the case of narrow band (fRF=900 MHz) single balanced mixers. The same technique was then used in [3] with the doubly balanced mixer topology for an operation from 1.056 to 1.584 GHz only. This work proposes a MB-OFDM down-conversion doubly-balanced Gilbert cell mixer that provides high and flat conversion gain and IIP3 and low noise figure, over all UWB bands of group # 1, and using the AMS CMOS 0.35 μm process parameters. 2. UWB MB-OFDM LINK ARCHITECTURES In a UWB MB-OFDM standard, the band spectrum from 3.168 to 10.560 GHz is partitioned to 14 sub-bands of 528 MHz band-width as illustrated in figure 1. Each band consists of 128 sub-channels of 4.125 MHz. The OFDM technique is employed in each band to transmit data rates as high as 480 Mb/s. Group#1 3432 3960 4488 5016 5544 6072 6600 7128 7656 8184 8712 9240 9768 10296 1 2 3 4 5 6 7 8 9 10 11 12 13 14 f (MHz) 528 MHz 128 subchannels ... f IEEE 802.11b/g, Bluetooth... 2400-2485 ISM-Band IEEE 802.11a, HiperLAN/2... Figure 1. frequency allocation of MB-OFDM UWB channels The down-conversion architecture of the receiver, shown in figure 2, is proposed to increase the integration level and hence foster SoC trend [4]. This scheme eliminates many bulky and expensive off-chip components such as image-rejection (no images) and channel-select filters [1]. As a result, this reduces the manufacturing cost, the power consumption, and improves circuit integration. The quadrature down-conversion mixer follows the LNA. Here, the LNA and mixer must show wideband characteristics over the band of interest. In fact, these blocks dominate the system linearity, noise performance