A 0.7dB Insertion Loss CMOS – SOI Antenna Switch with more than 50dB Isolation over the 2.5 to 5GHz Band Carlo Tinella Jean Michel Fournier Didier Belot * Vincent Knopik * Institut de Microélectronique Electromagnétisme et Photonique (IMEP) UMR CNRS/INPG/UJF ENSERG 23, Avenue des Martyrs BP 257 38016 Grenoble - Cedex 1 France * STMicroelectronics 850, rue Jean Monnet F38926 Crolles Cedex France Tel: +33(0)76856034, Fax: +33(0)76856080, email: tinella@enserg.fr Abstract Taking full advantage of the high resistivity substrate and underlying oxide of SOI technology, a high performance CMOS SPDT T/R switch has been designed and fabricated in a partially depleted, 0.25μm SOI process. The targeted Bluetooth class II specifications have been fully fitted. The switch over the high resistivity substrate exhibits a 0.7dB insertion loss and a 50dB isolation at 2.4GHz; at 5GHz insertion loss and isolation are 1dB and 47dB respectively. The measured ICP 1dB is +12dBm. 1. Introduction Thanks to continuous scaling, CMOS technology is moving up the frequency ladder, making the use of MOSFETs for circuits operating in the low gigahertz band very attractive [1-2]. This scenario becomes even more promising as the technologies are scaled in the very deep sub-micron domain [3]. In such context, CMOS appears to be the best solution for the integration of RF, IF and Baseband blocks on the same die, allowing semiconductors suppliers to deliver a complete low cost and low power radio-on-a-chip solution. In TDD (Time Division Duplex) communication systems, the block that best expresses the trade off between losses and isolation is the T/R switch. Several works have recently pointed out the feasibility of T/R switches for the 1-2.4GHz range with classical CMOS bulk technologies [12-16]. Nevertheless, although satisfactory low losses have been achieved, the isolation at 2.4GHz remains below 25dB. Demonstrating the potential of CMOS-SOI, this paper describes the design and presents the experimental results of a T/R switch integrated on a 0.25μm – 2.5V CMOS SOI process on standard (20Ohm*cm) and high resistivity (>1kOhm*cm) substrates. To the author’s knowledge, this is the first CMOS reflective switch achieving a loss of 0.7dB while keeping isolation as low as 50 dB at 2.5GHz. The results demonstrate the use of high resistivity substrate maintaining an excellent trade off between losses and isolation up to 5 GHz 2. The advantage of SOI Process High-level RF-Baseband integration in CMOS is mainly limited by the low resistivity of the substrate. To prevent latch-up, CMOS-bulk technologies use low resistivity silicon substrates that, at high frequency, drastically increase the losses in integrated passive (mainly inductors) and active devices. As a consequence, to preserve good performances (i.e. gain, NF) at very high operating frequencies more power must be dissipated. Furthermore, the use of low resistivity substrates increases the cross-talk between the noisy digital circuits and the sensitive analog-RF part. SOI offer the opportunity to design integrated circuits on high resistivity substrates leading to reduced losses as well as improved substrate insulation [4-7], without latchup. These key RF advantages, together with the smaller parasitic capacitance (vs. CMOS-bulk) [8-9], the floating body speed enhancement [10] and the lower subthreshold-swing factor in the fully depleted case [11], make CMOS-SOI technology the most promising candidate for the integration of wireless systems on a chip. 3. Switch Structure A typical application of SPDT (Single Pole Double Throw) switches is the sharing of the antenna between receiver and transmitter when the system uses a TDD access. However, a multi-throw switch could also be used to regulate the access time to multiple antennas. Fig. 1 shows the schematic of the CMOS SPDT in a series (M1, M2) – shunt (M3, M4) configuration. As explained later, shunt transistors (M3, M4) are added to improve isolation while gate resistors help to increase both isolation and linearity. Since the impedance of the 483 ESSCIRC 2002