Design Of An Active Digital Controlled Phase Shifter

As the electromagnetic wave signal received by phased array is divergent in all directions,it is too weak for the circuit to apply.As a key module in phased array systems,phase shifter is the main component that controls and changes the phase shift of the electromagnetic wave.With the rapid development of microwave and RF integrated circuits based on silicon-based technology,it is imperative to manufacture low-cost,low-loss,highly integrated phase shifters.However,the traditional passive phase shifter which has a high insertion loss and a large area cannot meet the current requirement,so a new structure is needed.Active phase shifter adopts active structure,which is based on the Si Ge Bi CMOS technology compatible with the silicon-based technology,it can not only has a high precision,but also has a low cost,low insertion loss and high integration.So,based on the Si Ge Bi CMOS technology,a 5-bit active digital controlled phase shifter adopting the vector-modulation method is proposed.In this paper,a new vector modulation method is used to study and design the active phase shifter,its core circuit includes input and output active balun,quadrature signal generator,four 3-bit sub-phase shifters and synthesis circuit.The input active balun converts the RF single-ended signal into a double-ended differential signal;the quadrature signal generator generates both in-phase and quadrature signals;four sub-phase shifters use these two orthogonal signals for vector synthesis to achieve 3-bit accuracy;the synthesis circuit employs the output signals of the sub-phase shifter as input signals,quadratic vector synthesis to complete the overall 5-bit accuracy.Based on the theoretical analysis of the every modules of the overall circuit,the design and optimization of the overall circuit is realized.The input active balun circuit uses a two-stage active structure,achieved the conversion from RF single-ended signal to differential signal in X-band,and provides a differential signal for the quadrature signal generator circuit,while achieves 50 W impedance matching at the input port;The quadrature signal generator circuit employs a two-stage RC passive multiphase network,it can not only provide a smaller error of the orthogonal signal,but also has a smaller insertion loss and a smaller chip area;The overall phase shifter circuit has four 3-bit sub-phase shifter modules,each sub-phase shifter bring switch tubes to control its input tubes and tail current tubes on the basis of the Gilbert cell circuit,through the effective control of the switch states to achieve 8 phase shifting states with a step of 45°respectively,at the same time the emitter follower is introduced instead of spiral inductor to reduce the chip area;The output signal of the four sub-phase shifters is used as the input signal of synthesis circuit,synthesis circuit use the basic differential amplifier circuit structure to complete the second vector synthesis,or the phase shifter achieves 32 phase shifting states with a step of 11.25°in the range of 0~360°;The bandgap reference and logic control circuits provide stable bias and efficient control for the entire phase shifter circuit.Based on this structure,the phase shifter circuit is designed based on JAZZ 0.18μm Si Ge Bi CMOS technology,and completed the drawing of the layout.The simulation results show that in the X-band operating frequency range,the RMS phase error of the designed phase shifter is less than 2.74°,which meets the accuracy requirements of the five phase shifters;The RMS gain error of the 32 phase-shifted states is less than 0.42 d B,and the flatness of the gain is maintained throughout the operating frequency band;The input reflection coefficient S11<-11 d B,output reflection coefficient S22<-12 d B,the phase shifter provides a 50Ω impedance matching port for other circuit modules of the phased array system.