| With the lack of spectrum resources becoming a factor restricting the development of wireless communication technology,visible light communication systems have become a hot research topic in the industry due to their large channel capacity,high communication efficiency and good confidentiality.As one of the most essential part,the LED intensity modulator has always restricted the development of the visible light communication system.The most important reason is that the visible light communication system has high requirements on the LED intensity modulator,such as speed,output power,linearity.This paper will design a 10-bits LED current steering intensity modulator for visible light communication systems with optical feedback circuits.The input of the modulator is a digital signal,which is converted into a current signal after being modulated by the modulator to directly drive the LED to complete the function of the transmitter in the visible light communication system.If the LED intensity modulator operates in the closed-loop mode,the optical feedback circuit converts a part of the emitted light into an electrical signal through the photoelectric conversion circuit and feeds back to the transmitter,so that the negative feedback structure can suppress the illumination nonlinearity of the LED,and the transmitter is realized self-equilibrium function.The 10-bit LED current steering intensity modulator with optical feedback circuits described above uses TSMC18rf CMOS technology to design schematics and layouts in the Cadence Virtuoso development environment and complete simulation of relevant performance.After using Cadence software for post-simulation,the measured maximum output current of the 10-bit LED current steering intensity modulator is 23 mA.The SFDR is guaranteed to be greater than 60 dB at 500 MHz sampling rate,and the static conversion characteristics are good,which can satisfy the visible light communication system for transmitter requirements. |
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