Study On Front-End Circuit Of Visible Light Receiver Based On Diversity Receiving Technology

With rapid development of science and technology,the information age evolves into the era of big data.Due to the rapid growth of data volume and transmission rate,the available wireless spectrum becomes very limited.The visible light communication(VLC)technology utilizes the visible spectrum,thus becoming a potential solution for the problem of radio spectrum congestion,and it is one of the hot research topics of the next generation wireless communication.VLC uses low-cost LEDs as a light source,and realizes illumination and data transmission simultaneously.However,the light intensity of LED source is weak,and the signal is susceptible to the channel noise during transmission,these factors make the quality of communication decreasing.Since the diversity receiving technology overcomes the intersymbol interference by combining signals of different paths,thus it is possible to improve the signal-to-noiseratio of VLC.Based on TSMC 0.18?m CMOS process,a visible-light receiver based on diversity receiving technology was studied in detail in this thesis.The main contents include:1 In order to meet the requirements of low input impedance of optical receiver,a RGC transimpedance amplifier(TIA)was designed optimally.A common source amplifier is applied to form the feedback loop,and to reduce the input impedance.A cascaded output buffer stage is used to improve the load capacity of the circuit.When the chip input terminal connects with a commercial photodetector(C_PD=5 p F),the measured transimpedance gain is 62 d B?,-3d B bandwidth is 775 MHz,and the chip power consumption is 12.6 m W.2 To amplify the signals to the required level of digital decision circuit,an improved limiting amplifier(LA)was designed based on Cherry-Hooper structure.By increasing the feedback resistance,the equivalent resistance between the two stages is reduced and the bandwidth is expanded accordingly.An added load resistance provides bias current for the branch circuit,thus improving the output swing.The test results shown that the designed LA has a gain of 40 d B,and a-3d B bandwidth of 790 MHz.The chip power consumption is 27 m W.3 Based on the designed TIA and LA,a front-end analog circuit of visible light receiver with strong anti-noise ability was proposed and designed,which includes a RGC TIA,a modified LA with Cherry-Hooper structure,a dc offset elimination circuit and an output buffer.The input stage receives the signals of two paths,and combines them with equal gain.The layout,simulation,and optimization were carried out based on TSMC 0.18?m CMOS process,and the chip was fabricated and tested finally.The measurement results shown that the transimpedance gain of optical receiver is 98 d B?,and the-3d B bandwidth is 750 MHz.A date rate of 600 Mb/s was successfully realized under the condition of the error rate<3.8×10^-3.The overall chip area is 1.04 mm×0.99mm,and its power consumption is 50.4 m W.A comparative experimental study shown that the diversity receiving technology can reduce the bit error rate of VLC,thus improving the communication quality.