Research And Design Of The CMOS Variable Gain Amplifier

With the rapid development of microelectronics technology, the variable gainamplifier becomes more and more widely used in TV tuners, hearing aids, wirelesscommunication systems and many other fields. In order to achieve single-chip andlow-cost, the highly improved performance of VGA is required. The current research ofthe VGA is moving towards high linearity, low-voltage low-power dissipation, wide gaindynamic range and so on. However, in China, VGA design is getting started now, so itbecomes a challenge.The thesis systematically discusses the design process of the VGA. Firstly, the designchallenges and the research of the VGA were introduced. Then, the performance index andthe common structures of the VGA were described. Finally, the thesis analyses the designprocess and simulation of the VGA. The amplifier cannot satisfy the specification for thelarge gain of the VGA, so six stages are cascaded. The first, the third and the fifth stagesare variable gain cell, the second and the fourth stages are attenuators, the sixth stage is abuffer, the fully differential degeneration amplifier (FDDA) is used, because the powerconsumption of FDDA is low for its simplicity in structure. Two attenuators are used inorder to obtain a wide dynamic range. The buffer is used to eliminate the DC offset andprovide exact differential signals to the ADC.The VGA is fabricated with TSMC0.18μm CMOS process. It’s3dB bandwidth is800KHz, it offers a varied gain from-12to64dB ranges in a3dB step, the circuit workson3V voltage, and the typical power consumption is1.2mW.