Research And Design Of Low Noise High Speed Variable Gain Amplifier Based On SiGe Process

Analog front ends(AFE)are used for amplifying,filtering and frequency conversion processing of the original analog signals,which play an important role in the electronic systems.Variable gain amplifier(VGA)is one of the most important components of the analog front end circuit,which predominantly determines the overall performance of the AFE circuits.It is widely applied in wireless transceiver systems,audio processing,remote sensing and ultrasonic imaging systems.In order to meet the specifications of these applications at the same time,the VGA has to achieve low noise,high speed,accurate dB-linear gain,and high linearity,which may bring some challenges to VGA circuits design under the traditional process.Compared with CMOS devices,SiGe devices have the advantages of low parasitic resistance and high cut-off frequency.Therefore,in this paper,a low noise high speed variable gain amplifier based on SiGe technology is introduced.The VGA core circuit is implemented based on gain interpolation,which can achieve both high dynamic range and low gain error.Moreover,it also has the advantage that the bandwidth does not change with the gain.At the input of the VGA,a low noise amplifier(LNA)is integrated to get lower noise.Additionally,a post amplifier(PA)is added to the output to ensure high linearity.The three-stage architecture,LNA+VGA+PA,can improve the performance of the whole VGA effectively.The chip is designed and fabricated in Tower Jazz 180 nm SiGe process.The test results show that the total gain range is 48dB and the gain error is less than 0.27 dB.The measured-3 dB bandwidth is 122.1 MHz,which is independent of the control voltage.The input referred noise is 0.9 nV/?Hz when the VGA gain reaches its highest.The best noise figure without impedance matching is only 2.7 dB,while that with 50?impedance matching is 4.07 dB.The measured output 1 dB compression point is about12.5 dBm,and the output third-order intercept point is 33 dBm.The second-order and third-order harmonic distortion is-53.6 dBc and-54.2 dBc,respectively.Each channel consumes 30.2 m A current and occupies a die area of 1.15 mm~2.Compared with the state-of-the-art researches,the proposed VGA features ultra-low noise and high bandwidth,achieves high accuracy and high linearity as well,which meets all the specifications above and the requirements of most applications.