Research And Design Of Variable Gain Amplifier

Since now, the people pay more attention to Global Positioning System which is most popular Global Navigation Satellite System. It's a trend that whole GPS receiver chain becomes integrated in one chip as automobile and hand-holding application. But in our country, design of RFIC is just beginning. To accomplish the receiver chain industrialization of our country, the ability of RF front-end design must be improved.The variable gain amplifier embedded in an automatic gain control loop is an essential component of GPS receiver. With the feedback loop, it constitutes the automatic gain control circuit for ADC to provide constant power signal. Resistive negative feedback amplifier is proposed to design a gain range of 0~30db,precise process-independent 0.5db Gain Step, low in-band ripple and low-power intermediate frequency variable gain amplifier. Operational amplifiers with adjustable GBW and constant closed-loop -3db bandwidth are uses to minimize power consumption. Testing results based on 0.18 um CMOS technical indicates that IIP3 is 31dBm@0dB,while dissipating 3mA (containing DC-offset cancellation circuit and CMOS Source-Follower Buffer Circuit).In this thesis, the knowledge of advanced communication system and the different structures of VGA are studied at first because they are very fundamental. Secondly, roughly introducing GPS system architecture, frequency plan ,system specification. Finally, design process of the most important part, fully differential operational amplifier, is included in aimed to implement VGA and DC offset cancellation circuit to meet the specification.