# A 2.4-GHz Fully-Integrated GaAs pHEMT Front-End Receiver for WLAN and Bluetooth Applications
## 1 Introduction  
The requirements of high-quality and low-cost wireless local area network (WLAN) applications cause strong efforts for the development of radio frequency (RF) front-end modules (FEMs). As an essential part of the RF FEM, the receiver low-noise amplifier (LNA) generally integrates a single-pole double-throw (SPDT) switch for transmitting and receiving paths because the WLAN standards are time division duplex (TDD) communication systems [1; 2]. Furthermore, to emerge short-range wireless communication markets, such as WLAN and Bluetooth, the feasibility of integrating a single-pole triple-throw (SP3T) switch into a front-end receiver has been pointed out for the 2.4-2.5 GHz frequency range [3; 4]. Among various process technologies, silicon-based CMOS processes are desirable for the WLAN front-end receiver due to their lower cost and better integration capability. The study in [5] shows that an LNA realized by a bulk CMOS technology has a gain of 14.8 dB and a noise figure (NF) of 3.6 dB with an input third-order intercept point (IIP3) of \(-\)2.7 dBm for WLAN application. In [6], a 0.13 \(\upmu\)m silicon-on-insulator (SOI) CMOS LNA shows a peak voltage gain of 18.2 dB, minimum NF of 3.4 dB, and best IIP3 of \(-\)1.46 dBm over 0.1-3.4 GHz. However, poor NF and linearity performance are the critical drawbacks. Gallium-arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) technology progressively emerges in WLAN market of the radio receiver due to its lower noise, higher cut-off frequency and higher breakdown voltage characteristics compared to silicon-based CMOS processes. Many low-cost and superior performance solutions have been realized by pHEMT technology for short-range wireless communication applications [7; 8]. A GaAs pHEMT LNA had achieved a gain of 16 dB and an NF of 2.1 dB with an IIP3 of 2 dBm reported in [9]. The study in [10] shows that a S-band LNA fabricated using a 0.15 \(\upmu\) GaAs pHEMT process for satellite communication system has a gain of 22 dB and a NF of 1.4 dB. However, the previous designs have the disadvantages that they requireextra control function and stable power supply made in CMOS or other technologies for multiple operation modes. To obtain good RF performance and high integration, a fully integrated RF front-end receiver in WLAN system, including a LNA and a SP3T switch with logic controller incorporated for 2.4 GHz WLAN and Bluetooth applications, as shown in Figure 1, is proposed. The WLAN system has a transmitting path and a receiving path. A power amplifier (PA) is used in the transmitting path to amplify the signal from the inside system and send it via the antenna, while the LNA is used to receive a signal from the air space through antenna to inside the WLAN system. The SP3T switch is used to connect the antenna to the WLAN transmit-and-receive functions as well as Bluetooth functions in TDD from-end transceivers. As explained above, TX is the output port of the PA and one of the input ports of the SP3T switch. BT is the interface that is used to connect the antenna to the Bluetooth transmit-and receive-functions. ANT is a common port that is used to transmit and receive signals for both WLAN and Bluetooth systems. The proposed receiver is capable of switching into four operating modes, including receive high gain, bypass, transmit switch and Bluetooth switch modes. The logic controller is used to convert the logic control signals and provide enable signals to the receiver for different operation modes. The truth table and interfaces for different operation are shown in Table 1, where \"1\" equals to 3.3 to 5.0 V and \"0\" equals to 0 to 0.2 V. In both high gain and bypass modes, the system is in the WLAN receiving state, then the signal comes from ANT to RX. In transmit switch mode, the system is in the WLAN transmitting state, then the signal comes from TX to ANT. In Bluetooth switch mode, the system is in the Bluetooth transmitting and receiving state, then the signal can be from BT to ANT and ANT to BT.