| 摘要 |
PURPOSE:To eliminate completely the temperature fluctuation of the attenuation of a variable attenuator by using an output of a voltage generating circuit utilizing a temperature sensor as an input voltage of a logarithmic amplifier and using an output of the logarithmic amplifier as a bias of a variable attenuator. CONSTITUTION:The voltage generating circuit 1 outputs a voltage proportional to temperature and gives it to an operational amplifier 4. An inverse amplifier comprising resistors 5, 6 and an amplifier 4 provides a temperature dependancy with an optional rate of change with respect to temperature change to the left end voltage of a resistor 10 by changing the gain. When the same kind of PIN diodes 8, 12 are used, the current flowing to the diode 12 is a ratio of the left end voltage across the resistor 10 to the resistance of the resistor 10 at all times independently of the temperature. In this case, since linear relation exists in the impedance of the diode in driving the diode by a constant current, the voltage has a linear relation to the temperature so as to avoid the impedance change against the temperature. The complete temperature compensation is attained by avoiding the fluctuation of the impedance thereby preventing the fluctuation of attenuation.
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