Research And Design Of Ultra Wideband Digitally Controlled Variable Gain Amplifier

In recent years, the performance of SiGe process in the radio frequency field ismore and more close to GaAs process with the rapid development of semiconductortechnology. The MMIC using SiGe process has become a popular researchpoint.Variable gain amplifier (attenuator) is widely used as an amplitude control circuitin phased array and other kinds of RF transceiver system. The bandwidth, linearity, gainflatness and gain control characteristics of variable gain amplifier affects theperformance of the receiver.Based on the analysis of the current situation of research on ultra-wideband variablegain amplifier, this thesis presents the design requirements of ultra wideband digitalcontrolled variable gain amplifier according to its key performance index andimplementation methods. According to the characteristics of UWB VGA, currentsteering structure is used to implement the variable gain unit of VGA. With thetechnology of inductive shunt peaking and emitter capacitance negative feedback areadopted to enhance the bandwidth, two kinds of ultra-wideband variable gain unit aredesigned. According to the characteristics of compression gain at high gain, the des ignof a gain compensation circuit with dB linear gain control characteristics is completed.Then a DAC circuit using the cascode current mirror is designed to complete the digitalcontrol of ultra-wideband variable gain amplifier. The simulation results show that thetwo kinds of ultra-wideband variable gain amplifier and each module’s circuit designedin this thesis perform good. Finally, the emitter capacitance negative feedback basedVGA layout design optimization and circuit post simulation are completed.This design is based on JAZZ0.18μm SiGe BiCMOS process, The results of postsimulation show that ultra-wideband digitally controlled variable gain amplifier canoperate across a wide range frequency including X band and Ku band. The design has adynamic gain range of31dB, gain step is1dB, gain flatness less than1.6dB, inputmatching less than-16dB, output matching less than-13dB and input1dB compressionpoint greater than-5.37dBm.