Contents I. Introduction
Optical detectors, or optical sensors, are electronic devices used to sense the specific ambient light, such as infrared, and widely used in many applications, like as medical instrumentation, position and proximity sensors, smoke detector etc. Optical detector presented in this paper is designed for optocoupler application, which is known as optical isolators. They are used to realize communication between two isolated systems through emission and reception of light. The transmitter end may operate in a crucial environment, such as voltage surge induced by lighting, electrostatic discharge or ultra-high supply voltage. In order to prevent entire communication or data transfer system from damage of large voltage spike, optocouplers are useful devices to exchange signals but remain electrically isolated. They are widely used in applications such as automotive signal isolation interface, automotive sensor/control and optical communication. Most of the existing high speed optocouplers can only operate at data rates up to 10Mb/s. A few exceptions can reach speeds of 40Mb/s but at the penalty of power consumption and optical sensitivity [1]. A traditional TIA (Transimpedance Amplifier) depicted as Fig. 1 consists of an operational amplifier with gain A and a large feedback resistor RF to turn weak photocurrent signal into sufficient large voltage. The parasitic capacitances on node Vx and large input impedance of TIA lower the bandwidth. To achieve high speed operation, the bandwidth of OP and photocurrent must be enlarged and make the chip consume more power.
