| 摘要 |
PROBLEM TO BE SOLVED: To prevent attenuation from changing due to a temperature change by making the increase/decrease direction of attenuation due to the temperature of a variable attenuation circuit the same as that of impedance due to the temperature of an impedance element. SOLUTION: When an AGC voltage V changes from a high voltage to a low voltage, current caused to flow to a 2nd pin-diode 6a gradually reduces and its equivalent resistance increases. Then, voltage drop of both ends of a resistance 11 becomes small, current caused to flow to 3rd and 4th pin-diodes 6b and 6c increases and their equivalent resistance reduces. Consequently, the attenuation of a variable attenuation circuit 6 turns out to increase. On the other hand, when the AGC voltage V changes from a high voltage to a low voltage, a low voltage changes to a high voltage at the output terminal of an operational amplifier 15. Then, current caused to flow to a 1st pin-diode 1 increases and its equivalent resistance reduces. Then, unfeedback quantity in a transistor 1 increases and amplification reduces.
|
