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本文对长波长HPT(异质结光电三极管)在数字光纤通信系统中应用进行理论方面的研究。理论推导是根据至今国外已研制出来的IaGaAs/InP异质结、小面积、高速光三极管的特性进行的。这种HPT采用光的直流偏置而不采用电的直流偏置,避免了接触电容,以提高码速;它的截止频率可达几个GHz。本文主要是从数字光纤接收机采用HPT为前置放大器的观点出发,应用D.R.Smith的简化理论,对HPT的特性提出要求,并指出HPT的适用范围。理论推导是在a>1条件下进行,a的条件表示集电极直流偏置和信号成份之比必须大于1。接收机的灵敏度可用a来表示,以指出理论的适用范围。理论推导得到的结果指出:减小HPT的输入电容和增加HPT的电流增益,将改善接收机功能,同时也指出,减小基一集漏电流,特别在低位周期区域,也有利于功能的显著改善。本文中的关键性公式与K.Tabatabaie等人论文中对应公式极为相似,但本文考虑了更多的因素,因此得到的结果更为精确。HPT的一个突出的优点是接收机灵敏度随位速率线性地变化,而不像PINFET那样随位速率的3/2次变化。从近期得到的数据可以看出HPT在长波长波段中,工作在1Gb/s或更高的位速是可以考虑的一种新器件。
In this paper, the long wavelength HPT (heterojunction phototransistor) in the digital optical fiber communication system for theoretical research. The theoretical derivation is based on the characteristics of IaGaAs / InP heterojunction and small area, high speed phototransistor that have been developed abroad so far. This HPT uses a DC bias of light instead of an electrical DC bias, avoiding contact capacitance and increasing code speed; it has a cut-off frequency of several GHz. This paper is mainly from the point of view of digital fiber receiver adopting HPT as preamplifier, applying the simplification theory of D.R. Smith, putting forward the characteristics of HPT and pointing out the applicable range of HPT. The theoretical derivation is performed under a> 1 condition, where a indicates that the DC bias of the collector and the signal component ratio must be greater than one. Receiver sensitivity can be used to indicate a, to point out the scope of application of the theory. The theoretical deduction shows that reducing the input capacitance of the HPT and increasing the current gain of the HPT will improve the receiver function while also noting that reducing the base-set leakage current, especially in the low-cycle region, also contributes to significant function improve. The key formulas in this paper are very similar to the corresponding formulas in K.Tabatabaie et al’s paper, but more factors are taken into account in this paper, so the result is more accurate. An outstanding advantage of the HPT is that the receiver sensitivity varies linearly with bit rate, unlike the 3/2 variation of bit rate with PINFET. From the data available recently, it can be seen that HPT is a new device that can be considered for operation at 1 Gb / s or higher in the long wavelength band.