| 摘要 |
PURPOSE:To make it possible to improve a noise factor by dividing an amplifier performing the automatic gain control into multi-stage amplifier circuits and connecting them in multiple stages and providing detectors at outputs of amplifier circuits respectively and performing independently the automatic gain control by the output of this detector. CONSTITUTION:The high frequency amplifier circuit performing the automatic gain control is divided into circuits which are provided with multi-stage amplifier circuits A1 to A3 and attenuators ATT1 to ATT3, and they are connected in multiple stages. Then, detectors X1 to X3 are provided at output terminals A, B and C of these circuits respectively, and the attenuation quantity of attenuators ATT1 to ATT3 which attenuate outputs of amplifier circuits A1 to A3 respectively is controlled by the output of detectors X1 to X3. Then, the attenuation quantity of attenuators ATT1 to ATT3 is controlled correspondingly to the noise factor of the output of amplifier circuits A1 to A3, thereby improving the noise factor as the whole. |
