Speech controlled telephonic communication channel - employing digital filters and comparators to set reception and transmission channel damping

摘要

The circuit overcomes the problem of correct input and output damping when both parties to a connection speak simultaneously. The microphone (M) output is amplified (MV) and, via the adjustable damping circuit (SD), fed to the transmitter amplifier (SV) and switching circuit (GS). A tapping from the microphone amplifier output goes to a null detector (SN). A comparable signal from the loudspeaker amplifier (LV) in the receive channel (EK) also goes to a null detector (EN). The null detections are all counted (SZ,EZ) and applied to a coincidence gate (KG). These items together form a correlation filter (KF). The filter output is integrated (IG) and ultimately placed in a memory (ROM) from where the null coincidence data is used to affect the setting of the damping circuits (SD,ED). Because the integration is not instantaneous, level detector circuits (SS,ES) setting of maximum or minimum damping. The feed from the receiving channel is time delayed (VG) by up to 250 microseconds.