Research And Design Of Frequency Synthesizer In C Band RF Receivers

C-band(4-8GHz)is widely utilized in Satellite Television,Radar Communication,Military Communication,and also covers 802.11AC(5.8GHz),which has been planned to be the fifth generation mobile communication(5G)R&D test frequency band by the Ministry of Industry and Information Technology for many times since 2016.Frequency usage plan in 3000-5000 MHz frequency range(middle frequency band)of 5G system clears 3300-3400 MHz,3400-3600 MHz and 4800-5000 MHz as the working frequency channels of 5G system.C-band transceiver has broad market prospect and application space in 5G Mobile Communication,Base-station Communication,Internet of Things(IOT)and Satellite Television,as well as positive significance in Transceiver Module(TRX)Research and Frequency Synthesizer(SX).The main work of this paper is to study and realize the frequency synthesizer of C-band 3000-6000 MHz RF broadband receiver,whose phase noise index is better than-100 d Bc/Hz @10KHz.By researching and analyzing several classical system architectures of RF receivers,this paper firstly analyses frequency and bandwidth requirements of frequency synthesizer,and difficulty of phase noise implementation in each frequency conversion scheme,then determines the frequency conversion scheme,as well as the local oscillator design scheme,with comprehensive demonstartion;finally implements the detailed design and demonstration of broadband first local oscillator and narrowband second local oscillator.3000M-6000 M bandwidth receiver usually needs 3000 M bandwidth VCO to realize local oscillator for frequency conversion.In this paper,superheterodyne secondary frequency conversion scheme is adopted,which means that the traditional first intermediate frequency is changed to two first intermediate frequencies with different frequencies.This improvement saves 1232 M VCO bandwidth requirement,and enhances VCO frequency utilization rate to 169%.Its realization is downconverting to intermediate frequency of 1024 MHz when the receiver RF frequency is3000-4600 MHz while necessary frequency of local oscillator VCO is1976-3576 MHz,and downconverting to 2256 MHz when the receiver RF frequency is 4600-6000 MHz while necessary frequency of local oscillator VCO is 2344-3744 MHz.Through the usage of two different first intermediate frequencies,VCO spectrum is folded,and bandwidth is saved,and broadband PLL is efficiently implemented.This methodology can be utilized in the design of many broadband receivers and transmitters,especially when RF microwave frequency is in very high high-frequency section.Due to the high cost of broadband VCOs and PLL,the increased intermediate frequency filter cost is much less than that of VCOs and PLL at the usage of frequency spectrum compression,but phase noise performance may be an order of magnitude difference.First local oscillator has been optimized and improved during design & tuning phase.Initial scheme is to use a PLL chip HMC704 and a broadband VCO chip DCMO190410-5 to tune at high and low frequencies and phase noise index reaches-102 d Bc/Hz,while improved scheme is to use PLL chip HMC830 of integrated VCO to carry out simulation analysis and demonstration.While second local oscillator generates two frequency points,the two first intermediate frequencies should separately convert to second intermediate frequency of 70 MHz,so second local oscillator uses a PLL chip to phase-detect the two narrow-band VCOs separately.In the design of broadband transceiver frequency conversion scheme,multiple VCOs can be used in parallel at different time,when phase detector has a relatively high bandwidth while VCO bandwidth is relatively narrow.Specific circuit implementation is relied on the usage of PLL chip ADF4107,VCO SMV1000A-LF generating 1094 MHz output to 1024 MHz intermediate frequency while converting frequency to second intermediate frequency 70 MHz later,and VCO SMV2070A-LF generating 2186 MHz output to 2256 MHz intermediate frequency while converting frequency to second intermediate frequency 70 MHz later.Within expectation,phase noise indicator has reached-102 d Bc/Hz after tuning.