# A Low Cost BLE Transceiver with RX Matching Network Reusing PA Load Inductor for WSNs Applications
## 1 Introduction  
There has been an explosive growth recently in wireless sensor networks (WSN) [1], whose applications have been extended to autonomous health monitoring, remote or hazardous area monitoring, and emergency management. The sensor nodes in these networks are typically connected to multiple types of devices, including smartphones, wearables and PCs [2]. For the sake of flexibility, low cost and seamlessness, the communication among these nodes requires the use of a commonly or easily available wireless technique. Therefore, Bluetooth Low Energy (BLE) is a competitive candidate [3, 4] because of its already massive establishment in the mobile market.  
Due to the limited energy source (e.g., battery or harvested energy) of the sensor nodes, an ultra-low power (ULP) transceiver design for WSN applications is highly desirable. In addition, because of the stringent market requirements, there has been a strong drive in recent years to decreasethe cost and module area of wireless sensor nodes [5]. This can be achieved through shrinking the silicon area and reducing the external components. Therefore, the investigation on low power and low cost BLE transceivers is indispensable.  
For a conventional radio frequency (RF) front-end configuration [6] as shown in Figure 1, there are several external components: (1) the impedance matching network for the low noise amplifier (LNA); (2) the TRX-antenna switch; and (3) impedance matching network for the power amplifier (PA). This leads to an increase in the printed circuit board (PCB) area and cost. For a low cost BLE module, these external TRX-switches and matching networks [6; 7] are clearly not favorable. To achieve higher integration, an on-chip CMOS TRX-switch technique has been reported in [8], yet the non-linearity and insertion loss introduced by CMOS transistors will deteriorate the performance of the transceiver. In [9; 10; 11], an on-chip balun shared by the transmitter (TX) and receiver (RX) was used to convert the single-ended signal to a differential one, and eliminated the need of a separated TRX-switch through the principle of impedance conversion. However, the differential architectures for both LNA and PA is power-consuming for an ultra-low power transceiver. Meanwhile, the insertion loss of the on-chip balun will degrade RX noise figure (NF). In [12; 13], a TRX-switch and matching network were integrated using multiple inductors, which is area-consuming and thus not favorable in low cost design.  
To address the aforementioned issues, a low power and low cost transceiver for 2.4 GHz ISM band was presented in this work. Seeking a low-power implementation, a single-ended LNA and PA were employed in the transceiver. In order to further reduce the chip cost and module area, a front-end with a RX matching network reusing PA load inductor was proposed.  
This work is organized as follows: the front-end circuit implementation of the transceiver is described in Section 2. Section 3 shows other circuit implementations. The measurement results and discussion are described in Section 4, and conclusion is drawn in Section 5.