The low-noise amplifier (LNA) of th

The low-noise amplifier (LNA) of the SX1261/2 is designed with differential inputs for the benefit of common mode rejection and immunity against noise and interferers.The LC network in front of the differential inputs serves both functions of a balun to convert the single-ended to differential signals and impedance transformation. As shown in Figure 15, this network consists of two capacitors (C11, C12) and one inductor (L6). C13 is an optional element which could be used to provide additional rejection against undesired interferers.In a similar way to the transmitter, the primary objective of impedance matching on the receiver front-end is to transform the ideally 50-ohm impedance at the RF switch output to the desired optimal impedance (Zopt) of the SX1261/2 differential LNA inputs.The steps to identify the optimal source impedance and simulating/implementing the matching network are similar to the ones deployed on the transmitter. A source pull was first conducted to identify the optimal impedance which delivers the lowest noise figure, as shown in Figure 18. In the case of SX1261 at 915 MHz, the optimal differential source impedance is 74 + j134.