| 摘要 |
A circuit (4) for generating metering pulses (P) includes a multiplier circuit (MULT), a bandpass filter (BF), a comparison circuit (COMP) and a ramp signal generator (RAMP). A current (IC) from the ramp signal generator is multiplied (MULT) by an alternating voltage (VTXX) such as to form the metering pulse (P), which is transmitted, together with a speech signal (SP), to a subscriber (1) for registration. The output voltage (UF) of the bandpass filter (BF) is compared with a reference voltage (UR) in the comparison circuit (COMP). The output (9a) of the comparison circuit is electrically conductive only when the filter voltage (UF) exceeds the reference voltage (UR). When control signals (D) open a switch (SW), a capacitor (C1) is charged by a first current generator (10). The capacitor voltage (VC) increases linearly and controls proportionally the current (IC) of the ramp signal generator (RAMP). When the filter voltage (UF) reaches the reference voltage (UR), the voltage (VC) of the capacitor (C1) is held constant. This is effected by small charging and discharging of the capacitor (C1) for each period of the alternating voltage (VTTX) when the output (9a) of the caparison circuit shifts between non-conductive and conductive states. When the current switch (SW) is closed (D), the capacitor (C1) is discharged by a current (2 x IS) through a second current generator (11) until the metering pulse (P) ceases. <IMAGE> |
