JPS6128259B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sound switch type loudspeaker telephone device that compares the transmitting level and the receiving level and controls a loss circuit inserted in the transmitting and receiving systems to prevent howling. The purpose of this is to switch the detection position of the listening level between the talking state and the receiving state to facilitate interrupts.

FIG. 1 shows a conventional loudspeaker telephone device. In the figure, 1 is a receiving microphone, 2 is an amplifier, 3 is an audio switch control circuit, 4 and 5 are loss circuits, 6 is a speaker, 7 is a power amplifier, 8 is a volume variable circuit, 9 is an AGC circuit, and 10 is a transmitter. A speech output terminal, 11 a reception input terminal, 12 a hybrid transformer, and 13 a line.

During the transmitting state, this device is designed to prevent malfunctions due to side noise β caused by the hybrid transformer 12, etc., between points A and B.
Interruption is improved by comparing the levels at points A and C and adjusting them respectively to prevent malfunctions due to acoustic feedback α when receiving a call.

However, in order to compensate for line loss etc. in the receiving system,
When the AGC circuit 9 is inserted, the static characteristics of the interrupt will be as shown in FIG. As is clear from the figure, malfunctions occur in the region where the transmission and reception interrupt curves intersect. In order to prevent this malfunction, there is a method of adjusting the transmitting interrupt level as shown in FIG. 3, but in this case, transmitting interrupting becomes difficult.

In order to solve the above-mentioned drawbacks, the present invention inserts a circuit that operates reciprocally with the receive AGC circuit into the receive level detection system during the receive state, thereby further improving interrupts. This will be explained below along with examples.

In FIG. 4, blocks corresponding to the apparatus in FIG. 1 are given the same reference numerals. A is an AGC reciprocal circuit that operates reciprocally with the receiving and AGC circuits.

Here, the reception AGC circuit 9 will be explained. FIG. 5 shows its detailed structure, in which 13 is an operational amplifier, 14 is a rectifier circuit, and 15 is a semiconductor element such as a transistor or a field effect transistor, which is controlled by the output of the rectifier circuit 14.

If the resistance of the semiconductor element 15 is _Rx , the gain _G1 of this circuit is expressed by the following equation.

G _{1 =} R _{X / ( R O} + _R In the figure, 17 is a semiconductor element 15.
It is a semiconductor element equivalent to the semiconductor element 15, and is controlled via the terminal T by the output of the rectifier circuit 14, similar to the semiconductor element 15. If the resistance of this element is R _x ', the gain G ₂ of this circuit is as follows.

G ₂ =R _O ′+R _X ′/ _R

G ₌ G ₁ × _{G 2 =} R _X /R _O + _{R X}・R _{O ′} +R _X ′/ _R G ₁・G ₂ =G ₀ , and the input/output characteristics of this system change linearly.
Therefore, the interrupt static characteristics with this configuration are as shown by the dotted line in FIG. Such AGC circuit 9, AGC
By providing the reciprocal circuit A, it is possible to prevent the switching operation of the audio switch from being performed incorrectly.

As is clear from the above explanation, according to the present application, by inserting a circuit that automatically operates in opposition to the receive AGC in the receive signal detection system, malfunctions can be prevented without sacrificing transmit interrupts, and call performance can be further improved. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional loudspeaker telephone device, FIGS. 2 and 3 are interrupt static characteristic diagrams of FIG. 1, FIG. 4 is a block diagram of a loudspeaker telephone device according to an embodiment of the present invention, and FIG. The figure and FIG. 6 are detailed wiring diagrams of the main parts. 3... Audio switch control circuit, 4, 5... Loss circuit, 9... AGC circuit, A... Reciprocal AGC circuit.

Claims (1)

[Claims] 1 A transmitting system that passes the microphone output through a microphone amplifier and a loss circuit on the transmission side to obtain a transmission output, and a speaker amplifier that passes the reception input through an AGC circuit and a loss circuit on the reception side to drive a speaker. In the transmitting state, the output of the microphone amplifier and the receiving input are determined by the magnitude relationship between the output of the microphone amplifier and the receiving input, and in the receiving state, the input of the speaker amplifier is routed through an AGC reciprocal circuit having characteristics contradictory to that of the AGC circuit. The loudspeaker telephone device is configured to control the amount of loss in the transmission and reception loss circuits by an audio switch control circuit in accordance with the transmission or reception state according to the magnitude relationship with the output of the microphone amplifier.