Patent ID: 6989717
Filing Date: 2006-01-24
Classification: H03F,H03G,H04B

Abstract:
1. A gain switching circuit for a pre-amplifier, which amplifies an output current of a photodetector, which converts a burst optical signal into an electrical signal, to generate an electric voltage signal, the pre-amplifier including a parallel connected operation amplifier and a feedback resistor, wherein a first serial circuit including a first resistor and a first switch is connected in parallel with the pre-amplifier, and a second serial circuit including a second resistor and a second switch is connected in parallel with the first serial circuit, comprising: an arrangement to receive the electric voltage signal, close the first switch at a specific bit position within a burst of the electric voltage signal, close the second switch at an other specific bit position within the burst of the electric signal, upon occurrence of a situation that the second switch is to be closed, provided that the first switch is closed, wherein the arrangement includes a signal generating unit that determines an output level of the electric voltage signal, checks whether the output level exceeds a first reference voltage, and if the output level exceeds the first reference voltage, generates a first gate signal at the specific bit position and generates a second gate signal at the other specific bit position.