JPH0113781B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a loudspeaker telephone device that compares a transmitted signal and a received signal and controls loss circuits in the transmitting and receiving systems inserted to prevent howling. It is something.

(Configuration of conventional example and its problems) As shown in FIG. , speaker amplifier 6, speaker 7,
It is composed of a transmitting call detection rectifier circuit 8, a receiving call detecting rectifier circuit 9, and an audio switch control circuit 10.

That is, in this device, in order to prevent howling, loss circuits 3 and 5 are inserted into the transmission and reception communication paths, and the audio switch control circuit 10 adjusts the output of the transmission detection rectifier circuit 8 and the output of the reception detection rectification circuit 9. The loss circuits 3 and 5 are controlled by comparing the sizes.

Here, the detection rectifier circuits 8 and 9 for transmitting and receiving are configured to operate in proportion to the difference between the transmitting and receiving audio signals.
As shown in the figure, it is composed of a logarithmic conversion circuit 11 mainly composed of diodes D ₁ and D ₂ and an operational amplifier 12, and a rectification circuit 13. The problem with this detection rectifier circuit is that the input/output characteristics of the transmitting and receiving detection rectifier circuits 8 and 9 are influenced by the electrical characteristics of the diodes D ₁ and D ₂ . It is necessary to make the characteristics uniform, and when using a general diode, the dynamic range in terms of logarithmic characteristics is narrow, around 40 dB.
Furthermore, since the characteristics of the diode change greatly depending on the temperature, the output voltage and the slope of the input/output characteristics also change greatly. Due to these influences, a malfunction occurs when the difference between the transmitted and received signals is determined and compared, and correct control is not performed.

(Object of the Invention) The present invention solves the problems of the conventional example described above, and aims to extend the dynamic range of logarithmic conversion so that the voice switch operation can be performed stably. .

(Structure of the Invention) In order to achieve the above object, the present invention uses a microprocessor (hereinafter abbreviated as CPU), a ladder resistor, and a comparator, and uses the CPU's ROM or
A/D conversion is performed while referring to a logarithm table prepared in RAM.The output of the ladder resistor is divided into two by a resistor, and these two output voltages and the detected and rectified output of the transmitting or receiving signal are Each is compared by a comparator, and the CPU receives this output.
It performs A/D conversion and numerical calculations internally, thereby expanding the dynamic range of logarithmic conversion with a simple configuration and without taking into account the dispersion of conventional logarithmic elements.

(Description of Embodiment) The present invention will be described below with reference to an embodiment shown in FIG. In Fig. 3, 14 is a ladder resistor that converts the output of the CPU 15 into voltage magnitude, R ₁ ,
R ₂ is a dividing resistor that divides the output of the ladder resistor 14;
Reference numerals 16 and 17 represent the outputs A and B of the ladder resistor 14, respectively, and a detection rectifier circuit that converts the signals into DC voltages. As an example, if we obtain a dynamic range of 60 dB, the ratio of resistors R ₁ and R ₂ is 30 dB, which is 1/2 of this dynamic range (for example, if point A is 3 V, point B is 0.1 V). Set it so that Here, in the ROM or RAM of the CPU 15, hexadecimal numbers that change every 1 dB are set in the contents from 0 to 30 as shown in FIG. First of all, CPU
When the contents of addresses 15 to 0 are output to the ladder resistor 14, if the output voltage of the detection rectifier circuit 18 is 0.1V or higher, the outputs of the comparators 16 and 17 will be high level, and if it is lower than 0.1V, only the output of the comparator 16 will be low. level.

For this reason, comparators 16 and 17
Observe the output of the input channel CH ₁ and CH ₂ of the CPU 15,
When CH ₁ is large, A/D conversion is performed while comparing the output of the detection rectifier circuit 18 and the output A of the ladder resistor 14 with the comparator 16, and then the CPU 15
Add 30 within. In other words, when comparing with point A of the ladder resistor 14, the A/D conversion value is 30~
60dB, when compared with point B of ladder resistor 14, it is 0 to 30dB, and the dynamic range is 60dB.
will be expanded to.

To summarize the characteristics of the present invention, the present invention has the following features:
The detection rectifier circuit 18 output is sent to the first comparator 16
and the second comparator 17, it is determined whether the output of the detection rectifier circuit is in the range of 0 to 30 dB or 30 to 60 dB, and if it is in the range of 0 to 30 dB, the output of the comparator 17 is set to A. If it is within the range of 30 to 60 dB, the output of the comparator 16 is A/D converted and a predetermined value is added.

(Effects of the Invention) As explained above, according to the present invention, the logarithmic characteristic is set in the ROM or RAM of the CPU and the logarithm value is set, so it is no longer necessary to take into account the variation of elements as in the past. Furthermore, since the dynamic range is also calculated by the CPU, stable operation of the voice switch can be obtained, and a loudspeaker telephone device with excellent characteristics can be provided with a simple configuration.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional loudspeaker telephone device, Figure 2 is a specific circuit diagram of the detection rectifier circuit shown in Figure 1, and Figure 3 is a diagram of the configuration of a conventional loudspeaker telephone device.
The figure shows an A/D conversion circuit for logarithmic conversion of a public address telephone device according to an embodiment of the present invention, and FIG. 4 is a table for logarithmic conversion. 14...Ladder resistance, 15...CPU, 16,17
...Comparator, 18...Detection rectifier circuit.

Claims (1)

[Claims] 1. A loss circuit for howling prevention inserted into the transmitting system and the receiving system, respectively, an audio switch control circuit that controls the loss circuit according to the level difference between the transmitting signal and the receiving signal, and the audio switch control circuit. a detection rectifier circuit, a microprocessor, a ladder resistor for converting the output of the microprocessor into a voltage level, and a first voltage waveform obtained by dividing the output of the ladder resistor into two by a dividing resistor. 1 output (total voltage) and a second output (divided voltage) and the output voltage of the detection rectification circuit, the output of the detection rectification circuit is compared with the output voltage of the detection rectification circuit. 2, the output of the second comparator is A/D converted by the microprocessor with reference to the logarithmic table, and the output of the detection rectifier circuit is made larger than the first and second outputs. A loudspeaker telephone apparatus characterized in that if the output of the first comparator is large, the output of the first comparator is A/D converted by the microprocessor with reference to a logarithm table and a predetermined value is added.