| 摘要 |
PROBLEM TO BE SOLVED: To make the securing of a level setting precision of an optical input signal near to a gain switching level compatible with the reduction of a testing time. SOLUTION: This system for testing a receiving circuit 21 near to the gain switching level is provided with input signal forming parts 13, 14 and 15 for modulating burst-shaped input signals to the receiving circuit so that a range to be tested can become the modulation amplitude of a fixed cycle, a variable attenuating part 12 for attenuating modulated input signals to an arbitrary level and an attenuator control part 11 for integrating a digital gain select signal for selecting the gain of the receiving circuit, controlling the attenuation quantity of the variable attenuating part on the basis of the integrated result and making the average level of modulated input signals into gain switching level. |
