| 摘要 |
A photodiode (201) is positioned so as to detect a beam of light reflected from the surface of a spinning DVD. In response to the detection of incident light, the photodiode (201) generates a signal, which is input to a trans-impedance amplifier (203). The output of the trans-impedance amplifier (203) is input to a voltage amplifier (204), to generate an output signal for processing. The trans-impedance amplifier (203) is provided with a feedback arrangement comprising a resister (205) in parallel with a capacitor (206) and a diode (207), in this case embodied by a transistor (such as an MOS transistor) arranged to act as a diode. At an input voltage wherein the corresponding output voltage is equal to the maximum normal operating voltage, diode (207) begins to conduct and capacitor (206) becomes operative. As a result, the feedback conditions change, reducing the effective gain of the trans-impedance amplifier (203). As a result, outside of the normal operating ranges, the output voltage increases more slowly for a given increase in input voltage than in the normal operating range, thus a much larger input voltage can be tolerated without saturating the trans-impedance amplifier (203). |
