The Design Of 2.5Gb/s Optical Receiver Front-end Amplifiers With Adaptive Equalization Function

Over the past years, the amount of information exchanging has been increasing, and the optical fiber communication systems and networks have been developing rapidly. Optical fiber communication with light wave as carrier and optical fiber as the transmission medium has become one of the important ways for people to exchange data information. In the long distance data communication channel, optical fiber communication has the advantages of low loss and high bandwidth, large capacity, has completely replaced the traditional electrical interconnection, to become one of the majority of Internet operators and customers preferred network access scheme. Therefore, the research and development of high-speed integrated circuits with independent intellectual property intellectual property, used for optical fiber communication is of great significance.In the optical fiber transmission system, the front end amplifier of the optical receiver is a very important circuit. This paper designed a 2.5 Gb/s monolithic optoelectronic receiverfront-end amplifier with adaptive equalization function for short distance optical communication, employing the standard 0.18 μm CMOS process. The front-end of the optical receiver mainly includes four modules:the optoelectronic diode detector, the transimpedance amplifier (TIA), the limiting amplifier (LA) and the adaptive equalizer. Among them, the TIA is used to convert the weak current of the photoelectric detector into the voltage signal. In this paper, the FCG structure is choosed to be the input stage TIA. FCG circuit has the advantages of small input impedance, large output swing and so on. The active negative feedback is adopted in the post stage of the TIA to improve the gain bandwidth product. LA is designed to enlarge the output voltage of the TIA up to 900mV. The bandwidth of the TIA is 0.8 times that of the transmission rate and the bandwidth of the LA is equal to the transimission rate to reduce the inter-symbol interference. The limiting amplifier is composed of five differential amplifier units with negative capacitance structure. In order to compensate the slow roll down characteristic of the photoelectric detector frequency response, and the adaptive compensation is according to different rolling characteristics, the adaptive equalizer is adopted in this paper. Among them, the equalizer filter unit is used with a high high-pass characteristic of the capacitor degradation structure, generating a zero, resulting in a slow roll up characteristic curve. Adaptive loop have thewith adaptive detection function, which to generate different control voltage according to input signal of the different loss. The different control voltage is used to adjust the variable tunable capacitor of the equalization filter unit source level, resulting in the change of zero, to accomplish the adaptive high frequency compensation.In addition, according to the requirements of each module, also a single end to differential end circuit, DC offset compensation circuit and output buffer are presented in this paper. Cadence is used to simulate theoptical receiver system. The post simulation results show that the front-end amplifier can get the transimpedance gain of 100dBΩ, the bandwidth of 2GHz. And the minimum input current is 10μA, the output swing peak reached 900mV.