| 摘要 |
In an exchange line which is terminated by a transformer which is DC-decoupled from the line in the respective exchange junction circuit, an "electronic choke" is used instead of a conventional holding choke in order to allow loop current to flow. It is constructed as a bridge circuit which has a low-impedance (R1, T) and a high-impedance (R2, C2, R3) half. The diagonal which is not directly connected to the operating voltage contains, for the purpose of bridge calibration, a differential amplifier (DV), the output of which is coupled to the control connection of the electronic switch (T) arranged in the low-impedance half of the bridge. To suppress high-frequency signals coupled in, the operating voltage for the bridge circuit and/or for the differential amplifier (DV) is supplied via a low-pass section (R4, C3 and R5, C1). <IMAGE> |
