The linearity improvement of LNA for W-CDMA

While an LNA (low noise amplifier) has several requirements (high gain, low noise figure, low in out VSWR, and high stability), it is difficult to satisfy the desired specifications all together. Moreover, W-CDMA (wideband code division multiple access) receiving systems require high linearity to have good sensitivity, and the portable communication devices have low power consumption. It is important to select an appropriate transistor and have some trade offs among the required specifications to satisfy and optimize various specifications. We designed and fabricated an LNA which can be used in a W-CDTWA receiving system. For improving the input VSWR and stability an inductance composing of series feedback was added to the emitter, and for acquiring high-linearity at low DC bias current the by-passing method was used. The fabricated LNA had a power gain of 15.33 dB, NF 2.17 dB, S₁₁ 9.53 dB, S₂₂ 35.91 dB at 2.16 GHz, and IIP₃ +5.34 dBm with 10 MHz channel spacing. We think that this LNA can be applied to a W-CDMA receiving system.