| 摘要 |
PURPOSE:To suppress the variation in the DC voltage caused by the change in the absorbing current of the differential amplifier, by controlling the power supply voltage for IF amplifier with the AGC voltage fed to the IF amplifier. CONSTITUTION:The IF signal fed to the input terminal 5 is controlled for the gain with the variable gain differential amplifiers 12,13 and is inputted to the next stage from the terminal 6. When the AGC voltage 4 is increased with a weak electric field input, the abosrbing current of the transistor Tr 31 is increased, and the collector voltage of Tr 25,26 is decreased. On the other hand, the current absorption amount of Tr 14 of the power supply voltage control circuit 10 is increased, lowering the base voltage of Tr 19 and increasing the base voltage of Tr 20, resulting that the current flowing to Tr 20 via the resistor 9 from the power supply 9 is decreased, the collector voltage of Tr 25,26 is increased, and the drop component due to the increase in the absorbing current is compensated. Taking that the impedance of resistors 22,23,16,17,18,24 as Z22,Z23,Z16,Z17,Z18,Z24, then the amount of compensation is optimized when the circuit 12 satisfies equation-(1). |
