Gain Wide Dynamic Range Cmos Variable Gain Amplifier Design

With the development of the electronic and communication technologies, the variable gain amplifier (VGA) becomes more and more widely used in the disk drive circuits, TV tuners, wireless communication systems and many other fields, which plays an important role of changing the gain, adjusting the signal dynamic range and stabilizing the signal power. In order to achieve low-cost and single-chip of the mixed signal integrated circuits, the VGA must be implemented in CMOS technology. The current research of the VGA is moving towards low voltage low power dissipation, high linearity, wide gain dynamic range, low DC-offset, good temperature characteristics and so on.In this dissertation, a CMOS VGA with wide gain dynamic range is proposed which can be used in the low frequency and the intermediate frequency systems and has continuous gain adjusting. The whole circuit, which consists of a VGA core amplifier module, a exponential gain control module and a buffer, is designed using a single-stage way, and has the 3dB bandwidth of 310MHz, dB-linear gain range of 62dB and power consumption of 5.82mW. The design is developed in the Cadence environment under the standard SMIC 0.18μm CMOS process, 1.8V supply voltage, using Hspice for the circuit simulation and Virtuoso Layout for the layout design.First of all, the research and development of the VGA is introduced, and then the structure and principle of the VGA are summed up, as well as the exponential gain control methods in CMOS process, the design method of this dissertation is then giving. Based on the improved Gilbert cell, the VGA core amplifier is designed, which is the key to realize the gain adjusting. Two active loads with gain boosting capability are analyzed and simulated, and by contrast, the cross-coupled active load is applied in the VGA core amplifier, which has about 320MHz bandwidth and the gain control range more than 70dB. A CMOS V-V exponential control circuit with about 60dB exponential control range is proposed by CMOS pseudo-exponential, which is the key to realize the exponential gain control. Based on a parameter revised pseudo-exponential function which improves the level of the exponential similarity, the circuit gets a wider control range. The CMOS VGA with wide gain dynamic range is implemented by the combination of VGA core amplifier and the exponential control circuit, which has low power dissipation in single-stage way by the compare of some papers. Finally the layout design of this VGA is giving.