| Following the rapid expansion of the wireless LAN and the military communication system, the receiver RF front-end system was promoted more flexible and mobility, at the same time, miniaturization low cost and high quality performance trend to inevitable requirement.The RF front-end design method is discussed, focused on the design and production of the RF module applied in IEEE802.11.b/g WLAN receiver. Centering on the system goal, layout design and debugging of the RF modules constitute the transceiver system is elaborated. Including microwave circulators, frequency selection filter, low noise amplifiers, local oscillator maked up by phase-locked loop circuit. Also, Down-conversion receiver circuit topology is described, based on the results of the system-level behavior simulation the parameter is confirmed.In passive module, automatic computing software is used for designing of the ferrite circulator, based on electromagnetic model and optimisation, the insertion loss of the sample is lower than-1.5dB, the isolation is higher than20dB;Butterworth lowpass prototype is selected for the designing of band-pass dual-band filter. Using parallel coupled microstrip lines, as well as the size is reduced. The stepped impedance resonator and enhanced coupling design is proposed, and feed structure is improved. The insertion loss is-2.8dB, return loss is less than-20dB.Active part of the circuit, DC tracing and bias circuit of LNA is presented, matching input and output circuit, the gain is14dB, noise figure is1.6;Digital divide combined with voltage-controlled oscillator. The crystal reference frequency is10MHz ADIsimPLL is empolied for designing a third-order low-pass loop filter. Local oscillator gain is3.1dB, phase noise is better than-85dBc@10kHz.Front-end module is tested after integration, The results is consistent with the pre-simulation, the system gain more than18dB, considering IF amplifier up to about50dB, receiving frequency range is2.39～2.49(GHz) with the high band rejection. |
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