Abstract
In this thesis, a variable gain low noise amplifier (VG-LNA) is designed and integrated into the RF front-end for 2.4-GHz ISM band applications. By setting the VG-LNA gain inverse proportional to the input power level, the maximum input swing of the mixer is reduced so that the RF front-end linearity is improved. To appropriately set the VG-LNA gain, an automatic gain control (AGC) loop is added as well. It consists of a clock generator, AGC enable circuit, and digital control logic circuit. By using the IF signal as the trigger source of the clock generator, there is no need of any external clock source. Moreover, when the input RF signal is small enough, there is no clock generated from the clock generator so that the AGC loop is disabled. Therefore, the noise performance of the RF front-end is not affected by the AGC loop. All designed circuits are realized in TSMC 0.18_μm mixed-mode CMOS technology and the chip area of the RF front-end with AGC is 1.184 × 1.218 mm2. According to the simulation results, the total gain range is around 7.3~36 dB with 4.1 dB step. The noise figure for the maximum gain setting is 4.6 dB. The P1dB for the minimum gain setting is -7.9 dBm. The setting time of the AGC loop is less than 19.7 μs. The total power consumption including output buffer is 32 mW under 1.8 V power supply.