Research On Broadband DB-linear Variable Gain Amplifier For 5G Mobile Communication

In recent years,with the rapid development of mobile communication technology,RF integrated circuit,as the core of modern communication system,has been paid more and more attention.The characteristics of high speed,low delay and massive interconnection of 5G communication system require the RF transceiver to have larger bandwidth and higher dynamic range.Variable Gain Amplifier(VGA)is one of the core components of RF transceiver.Its performance parameters,such as the dynamic range of gain,bandwidth,linearity and additional phase shift,have important effects on the scanning accuracy and dynamic range of the system.Among them,the dB-linear gain control technology of VGA can achieve constant settling time and uniform transient response,and can better adjust the gain amplitude of RF transceiver,which has important research value.Therefore,according to the above background and requirements,this thesis studies the variable gain amplifier applied to the intermediate frequency transceiver chip in the integrated millimeter-wave RF transceiver system compatible with C-band.The main research contents are as follows:(1)An analog baseband VGA applied to Sub 6GHz transceiver is designed.Large gain dynamic range is realized by cascading unit-cell VGA with dB linear gain.The unit VGA is loaded by transistors working in the sub-threshold region,and the pseudo-exponential approximation between the control voltage and gain is realized by using the exponential relationship between the voltage and current.In view of the bandwidth compression characteristics of cascading,an improved gate peaking and third-order interleaving feedback technology are used to expand the bandwidth.A third-order interleaving positive and negative active feedback structure applied to variable gain unit is proposed.Compared with the third-order interleaving negative and positive feedback interleaving structure,it has less damage to gain amplitude and flatness while maintaining the broadband effect.(2)The intermediate frequency VGA applied to Sub 6GHz transceiver is designed.The input stage adopts a single-end to differential noise cancellation structure,and the variable gain unit based on the common source and common gate structure is used as the intermediate stage,and the bandwidth is expanded by capacitive neutralization technology.The gate voltage of the transistor is controlled by a 5-bit digital-to-analog conversion circuit to achieve 32 gain states,and the gain step is 1dB.The two kinds of VGA designed in this thesis are developed based on TSMC 65 nm CMOS process,and the simulation results show that the two kinds of VGA designed in this thesis meet the design indicators.The measured results show that the dB-linear gain range of the analog baseband VGA is 5~23dB,the gain error is less than 0.6dB,the minimum bandwidth of-3dB is 2.6GHz,the input and output matching are below-10 dB,and the maximum input compression point of 1dB is-9.9dBm.