| With the continuous development of modern wireless communication technology,the continuous popularization of mobile and portable terminal equipment makes the explosive growth of wireless communication data exchange business and related industries.According to relevant agencies,by 2023,the capital market of mobile terminal related industries will reach 1.4 Trillions of dollars,we can see the prospect is huge.However,with the increasing number of mobile terminal users,a series of demands for data transmission rate and transmission quality are getting higher and higher.Now that 4G communication technology can no longer meet the needs of the market,5G has become the focus of current research.Currently,the fifth generation mobile communication technology(5G)under development is a development and extension of 4G technology.It is also a new generation of mobile communication system after 2020.Its technology development is still in the stage of exploration and research.Compared with 4G mobile communication system,generally we think 5G system capacity should reach 1000 times more than it,the transmission rate and spectrum utilization is 10 times,the peak transmission rate should be greater than 10Gb/s at low speed mobile state,high speed State of at least 1Gb/s[8].It can be seen,5G has a very high spectrum efficiency and information transfer rate,in the wireless transmission performance,transmission delay,user experience and information security has also been very significant improvements.Massive MIMO technology is one of the key technologies of 5G.The circuit studied in this paper is to provide LO signal for large-scale MIMO system.In most cases,we do not consider the influence of the phase difference of LO signal on the system transceiver link.For a large-scale MIMO system,the synchronization between channels is particularly important due to the large number of system channels.The background of this paper is precisely based on this issue,designed a local oscillator with phase self-calibration function,making the phase of the local oscillator signal provided to different channels consistent.Circuit design principle is:the use of multi-chip PLL chip to generate the required RF signal,demodulator at the RF output signal phase difference detection,through the analog to digital converter A/D and D/A converter Phase difference into a voltage value,as the phase-locked loop reference signal input phase shift network control voltage.Here reference signal phase-shifting circuit is a simple LC low-pass filter,the capacitor C varactor diode replacement,by changing the voltage across the varactor can achieve the purpose of phase-shift,thus forming a closed-loop feedback system,making the radio frequency output signal is synchronized.The higher the signal frequency,the faster its attenuation,capacitive inductors and other devices will appear parasitic inductance and parasitic capacitance,self-resonance and thus no longer maintain its original characteristics,the presence of these factors makes the RF signal frequency shift is more difficult Achieve,and the circuit structure is complex,the design cost is higher.The circuit designed in this paper proposes a new idea to solve the problem.The phase difference of the RF terminal is discriminated,the phase shift at the reference input is made,and a closed loop feedback loop is formed to realize the self-calibration of the signal phase.Finally,the test result shows that the phase difference is successfully calibrated from 120 degrees to less than 1 degree,and the phase synchronization is almost achieved.The output signal has excellent phase noise characteristics and can be used as a local oscillator of a large-scale MIMO system. |
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