| With the development of modern communication technology, the old low-speed narrowband transmission has been difficult to meet the needs of users, so the high-speed wideband transmission will be the main trend of the future. As a core part of the RF front-end, the performance of UWB LNA determines the overall performance of the wideband system, so researching and optimizing the wideband CMOS LNA is meaningful.First of all, this paper analyzes and compares several common wideband input structures, and designs a three-order butterworth high-pass filter after considering the effective bandwidth, the number of components and the transmission effect. Secondly, in the view of the contradictory relationship between the noise and the matching, this paper uses the resistive-feedback solution in stead of the method of paralleling capacitor between the gate and the source, and studies the influence of the feedback element on the input network.Then, this paper investigates the characteristics of the direct matching and the source follower in the matching, the noise and the gain respectly. After that, this paper presents the output network using two stage cascade structure, which can relase the gain pressure of the primary stage. Meanwhile, in order to use less large inductor, this paper uses the shunt peaking structure and the serial to parallel equivalent to optimize two-order high-pass filter. In addition, as to the gain roll-off, this paper uses the method of inserting inductor which will resonate with the gate-source capacitor in the middle of stages to raise the high-end gain. This solution can optimize the high-frequency gain and the gain flatness.Finally, the wideband LNA is designed under TSMC 0.18?m RF CMOS process, and the Spectre RF simulation show that, using 1.8V power supply and working in 0.8~2.5GHz, the S11 and S22 are less than-12 dB, NF is less than 3dB, S21 is more than 16.5dB, the gain flatness is within 1.75 dB, IIP3 at 1.6GHz is-5.05 dBm. |
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