This program receiver RF front-end system is designed and implemented based on software radio theory to achieve a goal of establishing a generalization, standardized, modular receiver RF front-end system simulation platform. To achieve low noise factors, small intermodulation distortions, large dynamic ranges and mirror suppression, good AGC, sufficient gain and correct selectivity, etc. The system modeling design and parameter simulation of the radio frequency circuit simulation software ADS is realized by the design of the design scheme of the receiver radio frequency front end and the use of RF circuit simulation software ADS. System performance of the receiver RF front-end circuit design.
With the development of DSP technology, the improvement of electronic devices production process, the sampling rate of A / D, D / A is getting higher and higher, and the digital processing in the radio station continues to advance, and the ability of channel reconstructing is constantly improving. The system can sample directly from the medium frequency, digital signal processing. This program receiver RF front-end system is designed and implemented based on software wireless telephonyism to achieve a goal of establishing a common, standardized, modular receiver RF front-end system simulation platform. To achieve low noise factors, small intermodulation distortions, large dynamic ranges and mirror suppression, good AGC, sufficient gain and correct selectivity, etc. The system modeling design and parameter simulation of the radio frequency circuit simulation software ADS is realized by the design of the design scheme of the receiver radio frequency front end and the use of RF circuit simulation software ADS. System performance of the receiver RF front-end circuit design.
Design and feasibility analysis of RF front-end system scheme
The main task of the radio frequency front end of this receiver is to filter signals, mix, and amplify the function, and suppress the mirror interference frequency of the system, intermodulation interference frequencies. The system function module mainly includes a filter, mixer, amplifier, and vibration. The system operating frequency range is 100 ~ 150MHz, where each 10 MHz bandwidth is used for frequency hopping modulation, using an ultra-extra-difference secondary mixing structure, and the design gain of the entire RF front end system is 110 dB, and the system noise is 3dB. The schematic block diagram is shown in Figure 1. As can be seen from Figure 1, the amplifier after the radio filter is a low noise amplifier (LNA), and the noise coefficient of the LNA has a decisive effect on the noise coefficient of the entire system. The balance between gain, noise factor, dynamic range, VSWR, stability, and other indicators. Level mixing passes through the PLL changed frequency to receive the radio frequency signal of different channels, and the reception signal is moved to the frequency band of 70 MHz and the frequency bandwidth is 10 MHz.
In this process, the mixer is a non-linear device that introduces a large number of interference components such that a large number of combined interference frequency points will occur after mixing, which causes serious interference to the useful signal to directly affect the performance of the receiver. The sound wave intermediate frequency filter is for mirroring frequency interference that the mixed frequency, performs high quality frequency selective filters of the intermediate frequency signal to improve the design objective of mirroring frequency suppression. The second stage mixed frequency band signal is moved to 10 to 20 MHz, as shown in Fig. 2 (the dashed line is a mixed mirror frequency, and the gray is the second mixing mirror frequency). Since the operating frequency is relatively low, the frequency band signal after the secondary mixing controls the gain control amplifier cascading, and its high gain is more easily realized, more stable.
Modeling and performance simulation and analysis of radio frequency front end system
RF front-end system modeling design
Using the ADS2008 software to model the receiver RF front end, each module parameter is set, and the selection filter is filtered for the input radio frequency signal 100 to 150 MHz. LNA noise coefficient 3dB, gain 24dB, and phase-locked loop output local oscillator signals are 175, 185, 195, 205, 215 MHz, respectively. The SAW intermediate frequency filter center frequency is 70MHz, and the frequency bandwidth is 10MHz. The mid-frequency amplifier generates 28DB and 72DB gain, respectively, respectively, as shown in Figure 3 after mixing and secondary mixing.
RF front end system frequency band selective simulation
The performance of the frequency band selective performance of the receiver RF front-end system is mainly determined by the radio front end of the radio frequency. With a conventional LC filter, by adjusting the input frequency of the grade vibration, the center frequency of the SEF network is changed, and the local oscillator is 195 MHz, and the lower frequency conversion processing of the 120 to 130 MHz radio frequency signal is realized. The simulation schematic of the grade mixing circuit module is set in ADS. As can be seen from Fig. 4, the receiver has a gain of 20.827 dB at 123 MHz, that is, the gain of the LNA minus the insertion loss of the filter. The selection filter can be suppressed very well on 240 to 290 MHz mirror interference signal.
RF front-end system channel selective simulation
The channel selection function is mainly completed by the spoke wave SAW intermediate frequency filter. The simulation circuit diagram is the schematic of the mixing system, wherein the intrusion frequency LO = 195 MHz. The channel selective simulation results are shown in Figure 5. As can be seen from Figure 5, the signal is a gain of about 13.46 dB at 120 MHz; the passband is 10 MHz, the gain is above 11 dB. The received signals are concentrated in the range of 10 MHz in the channel bandwidth, and the band fluctuations are small, avoiding the received signals to generate nonlinear distortion. Neighboring inhibition reaches around -43DB, meets the system design index.
Simulation of the influence of local oscillator output power on the performance of radio frequency front end system
The input signal power RF_PWR = -110dBm of the receiver RF front end system is provided. When a vibration power LO_PWR changes from -30 to 10 dBm (interval to 1 dBm), the relationship between the receiver output power and the LO_PWR is shown in FIG. As can be seen from Fig. 6, the output power level increases gradually as the increase in the power of the vibration is gradually increased, and when the intrinsic power is greater than -3dBm, the output power gradually tends to be stable. For the receiver, it is desirable to improve the vibration output power as much as possible to achieve a higher gain, but this is contradictory with the low power consumption of the system, which needs to design performance indicators as high-frequency output power and system as high as possible according to system design performance. Weighing between low power consumption.
RF front-end system power gain simulation
In order to be able to properly receive signals, the noise that the noise received and the noise generated by the receiver itself is submerged, requiring the receiver to produce a suitable output power level to make the device work normally. Considering the self-loss of the device, the overall power gain of the design system in this program is about 110 dB, as shown in Table 1. The system power gain budget simulation results are shown in Figure 7, and the power gain of the system machine is around 116 dB, meets the design indicator requirements.
Frequency domain response characteristics simulation of RF front end system
From the simulation results of Fig. 8, it can be seen that the spectrum of this scheme is expected to move the spectrum of the RF signal to the frequency band range of the frequency band in the system design, that is, the frequency domain response characteristics of the receiver RF front end system implement the design requirements. Figure 8 can intuitively see the power spectrum of the input frequency signal, the frequency spectrum output of the frequency output signal power spectrum and the receiver RF front end system. The frequency point frequency component of the intermediate frequency 15MHz output is single, the harmonics are well suppressed, and there is no interference to the desired signal.
In this paper, based on the theory of software radio system, the broadband receiver radio frequency front end system adopts an over-extra differential secondary mixing structure, established a generalized, standardized, modular receiver RF front-end system simulation platform. As can be seen from the performance simulation results, the program can be applied well in the software radio RF front-end circuit, which can achieve design requirements.
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Source: Wiku Electronic Market Network
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