| 摘要 |
PURPOSE:To amplify an antenna input without cross modulation distortion, by providing a means, which uses a semiconductor junction capacity to change the attenuation degree according to the level of the input signal, at the input end of an aperiodic amplifier. CONSTITUTION:The variable attenuator consisting of varicap diode CV is connected to the input end of aperiodic amplifier 20 through capacitor Ct. When the level of input signal EA is low, transistor (TR)Q2 becomes conductive because input voltage VB is near 0V, and applied voltage VC to diode CV becomes a high value near power source +B. THerefore, the capacity of diode CV becomes small, and attenuation of the signal dependent upon the path of capacitor Ct and capacity CV of diode CV is almost none. When the input signal level becomes high, voltage VB becomes high, and voltage VC is lowered, and capacity CV becomes large, and the input signal level to the gate of TR Q1 is lowered due to the voltage division effect dependent upon capacitors Ct and CV. Consequently, the antenna input can be amplified without cross modulation distortion. |
