An 1～14GHz Analog Predistorter Used In Radio-over-fiber System

Lately, data traffic patterns in access of networks have altered from simple voice and text services to more complex audiovisual and multimedia services owing to the notable growth in the number of intelligent phone users. The total mobile data traffics will increase greatly in the next years. To efficiently solve this problem, the access networks need an operative technology employing distributed processing and frequency reusing. Radio-over-fiber systems are becoming very attractive in wireless access network infrastructures because that RoF system potentially offers low cost, noteworthy flexibility and large capacity in access networks. However, optical subcarrier modulation based RoF systems are analog transmission, therefore intrinsically incredibly susceptible to nonlinear distortions. To linearize RoF systems, diverse linearization techniques have been proposed and applied for analog fiber-optic links. Overall, analog pre-distortion circuit is more promising for future Radio over fiber applications. This is because it is simple, of low cost, of low power consumption and more importantly broadband.This paper proposes a simple low-current consumption analog predistortion circuit for 1~14GHz, ADS software is used for modeling and simulation. 1.ADS is used to observe these diodes’third-order Intermodulation at different bias currents. Then check out how much contribution the junction capacitance and inductance etc. of the diodes does to the final signals. Finally, the way of choosing diodes is concluded.2. Comparing carefully with the reference, and point out the modifications: Firstly changes the anti-parallel structure into a back to transmission line model. Secondly, make it possible to tune both of the diodes separately by adding a power supply. Thirdly, we have changed the two-part transmission line into an single 50 ohm one, making it more easier for adding other opponents.3. We depict the data of the IMD3 of the electro absorption modulator with the predistortion circuit. Considering the compensation of the insertion loss, we finally made a amelioration of 30dBc.4. Sweeping frequency results demonstrate that enhancements of about 30 dBc in the IMD3 from 0.5 to 7 GHz and 20 dBc from 7 to 14GHz are achieved, and the insertion loss of 2.2dB from 0.5GHz to 14GHz is accomplished, as well.