| 摘要 |
Apparatus for controlling the amplitude of an analog signal comprises a first and second impedance transformer (X,Y) and a resistance network (R4) connected between the output terminal of the first impedance transformer and the input terminal of the second impedance transformer. To control the transmission properties of the resistance network, two semi-conductor switches (S,T) are connected in series between points of the network (namely the output of X, and earth, respectively) carrying a signal voltage with respect to each other, both of which points are connected to the earth potential by means providing a low resistance (the output impedance of X is low). The junction of the switches is connected to the input of the second impedance transformer by means (R5) providing a low resistance. <IMAGE> |
