Research And Design Of InGaAs Integrated Circuit Optical Receiver For 4G Radio Over Fiber Communication

As the third generation mobile communication system (3G) is commercially used all over the world, the IMT-Advanced (4G) system has become the focus of the research activities. According to the targets proposed by ITU (International telecommunication union), the data rate of the IMT-Advanced should achieve the range from 100Mbps to 1Gbps. Consequently, a series of new technologies will be used. A new networking method based on RoF (Radio over Fiber) technology can solve the high frequency signal propagation loss problem effectively by combining low loss and large bandwidth characteristic of optical fiber communication and flexible characteristic of mobile communication. Therefore, the RoF technology can improve not only the coverage but also the power efficiency. As a result, the researches on RoF technology facing the IMT-Advanced system are imperative. It is also the difficult part in the RoF technology.The IMT-Advanced system should support 1Gbps data rate at the best condition. Its frequency spectrum includes four discrete spectrums from low frequency to high frequency spectrum in all: 450MHz-470MHz, 698MHz-806MHz, 2300MHz -2400 MHz, and 3400MHz-3600MHz. Because of the fiber link, nonlinear exists in the RoF system. Consequently, optic electric interface used in RoF technology should have wide bandwidth and nonlinear distortion correction circuit. At present, commercial optic electric interfaces are designed for two-level digital signal, but the signal of RoF technology is multi-level signal and more like analog signal. The signal with high voltage level is vulnerable to be nonlinear compressed. So, to meet these requirements is a challenge for the circuit design.In this paper, considering the bandwidth and linearity requirements of RoF technology, an optical receiver with automatic gain control (AGC) function has been designed. This circuit is based on the 0.15um low power InGaAs pHEMT process provided by WIN semiconductors corp. in Taiwan. A Schottky barrier (MSM) photodetector compatible with standard InGaAs pHEMT process were designed and implemented. Meanwhile, in order to improve the performance, TPD- 1C 12-051 pthotdetector produced by TrueLight Corporation in Taiwan is used in this design. This optical receiver has better bandwidth and frequency characteristics profit from the advanced compound semiconductor technology. The automatic gain control amplifier can change its gain by detecting the output signal amplitude, thereby; it can offset the changes caused by the signal transmission loss. Finally, the output signal amplitude is almost unchanged; the purpose of eliminating nonlinear is achieved.