Publication: Noise improvement in differential low noise amplifier for wideband code division multiple access
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Date
2007-05-01
Authors
Wong, Lung Sing
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Abstract
Low Noise Amplifier (LNA) is the backbone of any RF (radio frequency) communication receiver to increase the signal level. The noise figure which is the critical characteristic of LNA and need to be emphasized in the design of LNA. A 2.14GHz differential cascode low noise amplifier (LNA) for the Wide-band Code Division Multiple Access (WCDMA) application was designed with a suitable topology that can minimize the noise. Noise figure of the differential LNA should be less or equal to 3dB. A technique for substantially reducing the noise of a CMOS LNA implemented in the inductive source degeneration topology was presented. The inductive source degeneration topology was chosen because it does not bring with it the thermal noise of a resistor, since pure reactance is noiseless. The effects of the gate induced current noise on the noise performance were taken into account, and the total output noise was reduced considerably by inserting a capacitance of appropriate value in parallel with the G and S to amplify the MOS transistor of the LNA. The main problem faced while doing this project was to adjust the trade-offs between the specified parameters. The design specifications of this project were outlined as followed: a gain or S21 bigger than 8dB, a noise figure which was less than 3dB and in a good reverse isolation (S12) as well as the input (S11) and output reflection coefficient (S22) which were less than -10dB respectively. The results obtained how the design were noise figure=1.9138dB, S21 =13.22dB, 1dB compression point=-4.10965dB, IIP3=-1.95473dBm S11=-10.32dB, S22 =-10.11, and IDC =7.77mA. Overall, the performance of the designed differential LNA is within the specification requirement. In this project, results had shown that the linearity of the circuit had been slightly increased with the added capacitor, Cd without changing the noise. Anyway noise figure obtained from this topology does not show much improvement if compare with the noise figure from normal differential cascode LNA topology. Therefore, further research on the noise improvement should be carried out.