JPS6041850A - public address telephone equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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. 1, this loudspeaker telephone device includes a microphone, a microphone 1, a microphone amplifier 2, and a transmitting variable loss circuit 3.
, a hybrid transformer 4 , a receiving variable loss circuit 5 , a speaker amplifier 6 , a speaker 7 , a transmitting detection rectifier circuit 8 , a receiving detection 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 voice 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 circuit 3.5 is controlled by comparing the magnitude.

Here, the detection rectifier circuits 8 and 9 for transmitting and receiving are logarithmic circuits mainly composed of a diode Di r 02 and an operational amplifier 12 as shown in FIG. It is composed of a converter circuit 1 and a rectifier 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 90 are diodes DI and D2.
The diodes used in the transmitting and receiving detection rectifier circuits must have the same characteristics, and if ordinary diodes are used, the dynamic range with logarithmic characteristics is narrow (around 40 dB). It is.

Furthermore, the characteristics of the diode change greatly depending on the temperature, and the output voltage and the slope of the input/output characteristics also change greatly.

Due to these influences, erroneous operation occurs when comparing the difference between the sending and receiving calls, and correct control is not performed.

(Objective 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 switching operation can be performed stably.

(Structure of the Invention) In order to achieve the above object, the present invention uses a microcontroller (hereinafter abbreviated as CPU), a ladder resistor, and a comparator, and while referring to a logarithm table prepared in the ROM or RAM of the CPU. It performs A/D conversion, and the output of the ladder resistor is divided into two by a resistor, and these two output voltages are compared with the detected rectified output of the transmitting or receiving key signal using a converter. Upon receiving this output, the CPU performs numerical calculations along with the line conversion core.
This attempts to expand the dynamic range of logarithmic transformation with a simple configuration without considering the conventional variation in logarithmic intensifiers.

(Explanation of Examples) The present invention will be explained below with reference to an embodiment shown in FIG.

In FIG. 3, 14 is a four-layer ladder resistor that converts the output of the CPU 15 into a voltage level, R1+R2 are dividing resistors that divide the output of the ladder resistor 14, and 16 and 17 are the resistors of the ladder resistor 14, respectively. This is a detection rectifier circuit that converts outputs A and B and signals into DC voltage. where - as an example 60
If we decide to obtain a dynamic range of dB, now the resistances R and R.

The ratio is set to be 30 dB of this dynamic lens A (for example, if point A is 3V, point B is 1V).

Here, in the ROM or RAM of the CPU 15, hexadecimal numbers that change by 1 dB are set in the contents from 0 to 30 as shown in FIG. Here, first, when the content of address O is outputted from the CPU 15 to the ladder resistor 14, if the output 'lE voltage of the detection rectifier circuit 18 is above IVJR, the outputs of the comparator 16 and ]7 will be high level, and if it is smaller than IV Only the output of the comparator 16 becomes low level.

For this reason, the outputs of comparators 1.6 and 1.7 are viewed at the inputs CH, , CH2 of the CPU 15 (i+11).
When I L and CI are large, the output of the detection rectifier circuit 18 and the output A of the ladder resistor 14 are compared by the comparator 16 and then A/D converted, and then 30 is added in the CPU i S. That is, when comparing with point A of ladder resistor 14, the value of ADD conversion is 30 to 60 dB, and when comparing with point B of ladder resistor J4, it is 0 to 30 dB, expanding the dynamic range I''l: 60 dB. be done.

(Effects of the Invention) As explained above, according to the present invention, the logarithmic characteristic is CP
Since the logarithm value is set in the U's ROM or RAM, the dynamic range is also calculated by the CPU, without taking into account variations in elements as in the past, resulting in stable audio switch operation. This makes it possible to provide a public address telephone device with a simple configuration and excellent characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional loudspeaker telephone device, FIG. 2 is a specific circuit diagram of the detection rectifier circuit shown in FIG. 1, and FIG. Line conversion circuit, Figure 4 is a table for logarithmic conversion. 14... Ladder resistance, 15... CPU, 16.17.
... Comparator, 18... Detection rectifier circuit. Figure 1 Figure 2 Figure 3 - Figure 4

Claims (1)

[Scope of Claims] A loss circuit for preventing howling inserted in a transmitting system and a receiving system, respectively, and an audio switch control circuit that controls the loss circuit according to a level difference between the transmitting signal and the receiving signal,
A detection rectifier circuit provided with a logarithmic conversion function provided on the input side of the audio switch fm control circuit so that the level difference between the transmitting and receiving audio signals operates proportionally, and a micro 7
A first output (total voltage ) and a second output (divided voltage), and the outputs of the first and second converters are respectively compared with the micro 7° By inputting the input to the first and second input ports of the processor, A/D conversion is performed within the micro 70 processor, and numerical calculation is performed.
A loudspeaker telephone device characterized in that the dynamic lens of the logarithmic transformation is extended. (2) The microprocessor includes the first and second nests.
If the first comparator output is large, the output voltage of the detection rectifier circuit and the first output of the ladder resistor are compared with the first condenser output. Claim (1) characterized in that: A/D conversion is performed from the above, and thereafter, the parts of the dynamic lens divided by the dividing resistor are added within the microprocessor.
Loudspeaker telephone equipment as described in Section 1. (3) The A/D conversion is performed by referring to a logarithm table set in advance in the Micro 7 Rosenoza.
The loudspeaker telephone device described in section 2).