| 摘要 |
A preamplifier converting an input current signal into a voltage signal and outputting the voltage signal, comprises a voltage amplifier, a feedback resistor connected in parallel between an input and an output of the voltage amplifier, and a plurality of diodes (7a,7b) which are connected in series to each other and are connected in parallel with the feedback resistor (3b) so that an anode side of the diodes is connected at an input side (4) of the voltage amplifier (2) and a cathode side the diodes is connected at an output side (6) of the voltage amplifier. In this construction, a voltage drop by the feedback resistor for turning on the diodes increases in proportion to the number of diodes with relative to a case where a single diode is connected in parallel with the feedback resistor, thereby changing the input signal level at which a substantive feedback resistance value is switched. Against the diodes, a fuse may be connected in parallel with each of them, or a bonding pad may be connected to each of an input side and an output side of each of them, or an FET (21a,21B) may be connected in parallel with each of them, so as to enable short-circuiting each of the diodes. Thereby, an increased input dynamic range is obtained considering a sensitivity of the amplifier (an output voltage amplitude) and an amplification factor. <IMAGE> |
