A Study on Buffer Structures to Improve the Bandwidth of HBT LD Driver for Optical Communication

광통신용 HBT LD 구동 회로의 대역폭 개선을 위한 버퍼 구조에 관한 연구

In LD driver with HBT's. the speed characteristics of HBT's are deteriorated very much mainly due to the source resistance(Rs) of the signal applied to the LD driving HBT. We improved the bandwidth of LD driver by 2-5GHz with modifications of EF buffer. Because the modified buffers are composed of EF structure, their bandwidths are decreased rapidly as Rs is increased. When Rs is large these buffers decrease the bandwidth of the LD driver rather than increase it. To solve this problem, we propose a new buffer structure which contaings new charging and discharging path for the parasitic collector capacitance of the HBT. For Rs>100${\Omega}$, it shows superior characteristics of improving bandwidth to the EF buffers. It also shows good gain characteristics.