Research And Design Of Ultra Wideband Variable Gain Amplifier Based On BiCMOS Process

Ultra-wideband(UWB) variable gain amplifiers are widely adopted in vector-sum phase shifters, radio communication transceivers, phased arrays, millimeter-wave imaging systems and optical communication systems, and are used to maximize the gain dynamic range of overall systems. Silicon–germanium heterojunction bipolar transistor(Si Ge HBT) Technology combines transistor performance competitive with III–V technologies with the processing maturity, integration levels, yield, and hence, cost commonly associated with conventional Si fabrication thanks to advances in the Si-based semiconductor fabrication process, which make it possible for low cost commercial phased arrays to come true.First of all, this paper classifies variable gain amplifiers from three angles, at the same time, elaborates main performance indexes of VGAs and their importance. By theoretically analyzing, a conclusion was drawed that d B linear characteristic of VGAs is the sufficient condition in which settling time of automatic gain control(AGC)loops can keep constant. Optimization techniques of three key performance indexes of d B linear characteristic, linearity and Phase Variation are discussed by studying articles published in the recent years. With many metrits of large gain dynamic range, excellent RF performance, input impedance unchanged with control signal varies and so on, current steering topology was chosen to be core topology structure of the RF front-end UWB variable gain amplifier designed in this paper. Improvement in the traditional current steering topology is needed for required performance indexes. Adding the control voltage producer in the circuit broaden the d B linear gain dynamic range of a typical current steering topology and introducing the emitter degeneration capacitor broaden the bandwith of a typical current steering topology. Secondly, based on Tower JAZZ 0.18?m Si Ge Bi CMOS process, the RF front-end UWB variable gain amplifier is designed using the improved current steering topology. Digital-to-Analog Conventer(DAC) circuit is designed for digital control and input/output matching circuits are designed for testing. Finally, based on profound understanding of layout design rules, post-layout simulation was achieved after layout design, DRC check, LVS check and parameter extraction. By pre-layout simulation and post-layout simulation's proceeding iteratively, design parameter and layout were optimized until post-layout simulation results was satified. In addition, based on Tower JAZZ 0.18?m Si Ge Bi CMOS process again, a new d B-linear variable gain amplifier interfacing the baseband section is proposed in the paper, which use the gain control mechanisms of variable transconductance and variable load, and has many metrits of compactness, d B linear characteristic, small size, good robustness and large gain dynamic range.The RF front-end UWB variable gain amplifier used in RF front-end and designed in this paper was fabricated in the Tower JAZZ 0.18?m Si Ge Bi CMOS process. The measurement results show that the variable gain amplifier designed achieves a gain dynamic range of 31 d B stepped by 1d B, input and output return loss <-10 d B, output P1 d B of-17.8d Bm at 12 GHz in the highest gain state, Phase Variation lower than 24°.