Research And Design Of Digital-Controlled Silicon-Based Variable Gain Amplifier

With the continuous development of communication systems,people have proposed miniaturization,portability,and high performance for communication systems.In order to meet these requirements,integrated circuits come into existence as the situation requires.In existing integrated circuit manufacturing technologies,silicon-based process is attracting attention due to its low cost,low power consumption,and high integration.Variable gain amplifier(VGA),that is,the gain of an amplifier varies with an externally controlled variable such as voltage or current.It is widely used in many aspects such as medical equipments,telecommunication systems,hearing aids,disk drives and analog front end of transceiver in wireless communication.Among them,the application in the transceiver is the most concerned.In order to stably amplify the received signals of different amplitudes,the transceiver needs automatic gain control(AGC)loop circuit.The important part of the AGC loop circuit is the variable gain amplifier.The variable gain amplifier determines the overall performance of the automatic gain control loop.Variable gain amplifier specifications include gain variation range,gain step,gain error,supply voltage,power consumption,bandwidth,linearity,noise and so on.This thesis introduces the development of the variable gain amplifier all over the world and the classification of the VGA,and also elaborates and exemplifies various indicators of variable gain amplifier.Then the design structure of the variable gain amplifier is summarized,and two commonly used structures,open-loop structure and closed-loop structure are introduced respectively.In this thesis,two variable gain amplifiers based on silicon-based technology are designed.In order to facilitate the system,both of them use digital control to control the gain variation.The first variable gain amplifier is a digital control variable gain amplifier with dB-linearity based on SiGe BiCMOS technology,the variable gain amplifier completes the dB linear structure through the triode in the process.The exponential current converter circuit based on the inherent exponential characteristic of the triode itself is proposed for the first time.The exponential current converter is used to convert the linear current into an exponential current.In addition,based on the analysis of this design principle,various methods for constructing dB linearity are summarized.Finally,through the schematic,the layout and post-layout results of the VGA,the gain variation range is 27 dB and the gain error is less than 1 dB,which means acceptable good dB linearity.The-3dB bandwidth of the entire variable gain amplifier is up to 5 GHz.Another focus of this thesis is a digitally controlled variable gain amplifier based on CMOS technology.The VGA completes the dB linearity by using the subthreshold region characteristics of the MOSFET transistor.Through the Cadence Virtuoso to accomplish the schematic,simulation and layout,and the simulation and layout are completed with Cadence Virtuoso.From the simulation results,the variable gain amplifier has a gain range of-7.7 dB to 15 dB,and its-3dB bandwidth reaches about 1 GHz.In addition,the variable gain amplifier has low power consumption due to designing in sub-threshold region,the power consumption of the VGA core is approximately 0.72 mW.The digital control modes of the two variable gain amplifiers are both realized by the switching circuit,which makes their digital control simple and convenient,which therefore reduces the circuit area and power consumption.