| 摘要 |
PURPOSE:To keep the fixed wave detection gain by varying the bias voltage to be applied to the wave detecting diode in accordance with the temperature and thus obtaining the constant bias current of the wave detecting diode. CONSTITUTION:The voltage of the reverse input terminal of operational amplifier 20 is set to the earth potential along with the voltage of terminal 21 and the value of resistance 23 set to 1V and 10kOMEGA respectively. As a result, the current of 0.1mA flows to resistance 23 and then to temperature detecting diode D2 since the input impedance of amplifier 20 is infinite. And the voltage of terminal 22 can be set to the bias voltage of wave detecting diode D1 through the inversion of polarity since it is turned into the forward voltage of D2. On the other hand, the analog adder circuit consisting of operational amplifier plus resistances 32-34 applies the voltage of terminals 22 and 31 to the bias circuit through terminal 35. And in this case, the voltage level of terminal 31 is set so that the current of 0.1mA may flow to load resistance 14 to secure the same result as in case the current of 0.1mA is flowed to D1 as the forward voltage. Thus a fixed value of current flows regardless of the temperature to always secure the fixed wave detecting gain. |
