| 摘要 |
PURPOSE:To reduce the gain of a variable gain circuit by a control signal generated in accordance with the sending of a dial pulse and to suppress a dial pulse sending tone from a speaker properly by cascade-connecting the variable gain circuit to an amplifier for amplifying a dial signal. CONSTITUTION:At the on-hook dialing of a functional telephone set, a dial signal is amplified by a receiving amplifier RA and a power amplifier PA to drive a speaker SP. Variable gain control circuits VG1, VG2 are cascade-connected among the amplifier RA, a hybrid circuit HYB and a remote detecting circuit RMD to control the circuit VG2 by a control circuit GCT. Control signals HRON1, HRON2 are inputted to the circuit VG1 and the control circuit GCT in accordance with the on-hook dialing operation of a telephone line. The gain of the circuit VG1 is reduced on the basis of the input of the signal HRON1, the quantity of attenuation is increased and the time constant of the control circuit GCT is increased. Consequently, a high-level dial signal tone is suppressed, a gain control time is extended and the discharge of the dial signal tone from a speaker SP is interrupted. |
