| 摘要 |
<p>PROBLEM TO BE SOLVED: To obtain a low-noise and accurate operation, regardless of the magnitude of current generated in a photo diode. SOLUTION: When a signal current Ii, inputted into a first transistor 1 by means of a photo diode 20, satisfies Ii<VBE3/Rf1, where VBE3 is the base-to- emitter voltage of a third transistor 3 and Rf1 is the resistance value of a first feedback resistor 4, the third transistor 3 will not operate. When Ii>VBE3/Rf1, the third transistor goes into a conducting state, supplying a negative feedback current to the signal input terminal 11 side via the third transistor 3. Unlike the conventional case, even if a large optical current is generated in the photo diode 20, the photo diode 20 is prevented from being turned into a solar battery mode, so as to secure stable and accurate operations.</p> |
