JPS6041851A - Loudspeaker telephone set - Google Patents

Abstract

PURPOSE:To expand the dynamic range through calculation and also to attain stable voice switch operation by deciding the logarithmic characteristic depending on a numeral set to a memory of a CPU. CONSTITUTION:A signal changed by 1dB each is outputted from an output port PTC of the CPU, a voltage A appearing at an output of a ladder resistor 14 and a detected rectifier output voltage B in response to a voltage at a signal input terminal 17 are compared by a comparator 16, and A/D conversion is conducted sequentially while supervising the output of the comparator 16 at a port PTA. When a switch element 21 is turned off and the output of the comparator 16 is at L level, i.e., an input signal is <=-30dB in this case, the switch element 21 is turned on to increase the gain of the detection rectifier circuit 18 to 30dB and the A/D conversion is conducted. When the output of the comparator 16 is at H conversely, the switch element 21 is turned off for the A/D conversion and the dynamic range is expanded by adding numeral 30 to the result of the conversion.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention compares a transmitting signal and a received signal... A loudspeaker telephone that controls loss circuits in the transmitting and receiving systems inserted to prevent ringing. It is related to the device.

(Configuration of conventional example and its problems) In general, as shown in FIG. It is composed of 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, a loss circuit 3.5 is inserted in the transmission and reception communication paths, and the voice switch control circuit 10 divides 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 magnitudes of .

Here, the detection rectifier circuits 8 and 9 for transmitting and receiving are mainly composed of diodes DI and D2, and an operational amplifier 12, as shown in FIG. 2, so that the difference between the transmitting and receiving audio signals operates proportionally. It is composed of a logarithmic conversion circuit 11 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 DI+D2, so the diodes used in the transmitting and receiving detection rectifier circuits have different characteristics. However, if a general diode is used, the logarithmic characteristic loses linearity as the input level becomes lower, and the dynamic range is 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, when the difference between the transmitted and received signals is determined and compared, malfunctions are likely to occur and correct control may not be 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 performs logarithmic A/D conversion of a transmitting or receiving signal.
Alternatively, refer to the logarithm table set in RAM, output the contents to the R-2R network (hereinafter abbreviated as ladder resistance), and use a comparator to compare the output voltage and the detected rectified output voltage of the transmitting or receiving signal. Predicate A/D conversion is performed without comparison. Furthermore, since the gain of the detection rectifier circuit is controlled, A
/D conversion and performs numerical calculations within the CPU to expand the dynamic range.This allows the dynamic range of logarithmic conversion to be expanded with a simple configuration without considering the variations in conventional logarithmic elements. be able to.

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

In Figure 3, 14 is a ladder resistor, 15 is a CPU, 1
6 is a comparator, 17 is an input terminal for a transmitting or receiving signal, and 18 is a detection rectifier circuit that converts the input signal into a DC voltage. As shown in FIG. 4, this detection rectifier circuit is mainly composed of an operational amplifier 20, and further includes a CPU.
A switch element 21 that is on/off controlled by a control signal 19 of
The gain can be varied.

In such a configuration, the operation for obtaining logarithmic transformation with a dynamic range of 60 dB will be described as an example.
First, the A/D conversion operation is performed using the cPU output, tr-PT
Voltage A that outputs a signal from C and appears at the output of ladder resistor 4 and detected rectified output voltage B that corresponds to signal input terminal 17
The comparator 16 performs a comparison with the output port PTC, and sequential A/D conversion is performed while monitoring this output using the boat PTA.However, the signal output from the output port PTC of the cPU is stored in advance in the CPU's ROM or as shown in Figure 5. is 1 in RAM
A hexadecimal value that changes every dB is set, and the contents of the specified address are output in sequence. therefore,
The output A of the ladder resistor 14 and the output B of the detection rectifier circuit 18 must be compared logarithmically, and the final A/D conversion value is determined by the fact that the ROM or RAM address is a logarithmic A/D value. Become. In Figure 5, the address size is 0 to 30, that is, 3
This means that logarithmic transformation of 0 dB is possible.

Next, we will describe the operation required to expand to 60 dB.

In FIG. 4, the values of resistors R1 and R2 are set so that the gain of this circuit is 30 dB when the switch element 21 is turned on, and O dB when it is turned off. However, here, the maximum level input to the input terminal 17 is OdB for convenience of explanation.
Think of it as.

Next, the content of address 0 shown in FIG. 5 is output to the PTC (output capo of the CPU shown in FIG. 3), and the voltage A appearing at the output of the ladder resistor 14 and the input terminal - The value of the resistor R connected to the ladder resistor 14 is set so that the output voltage B of the detection rectifier circuit 18 when a level of 30 dB is input is the same, and the voltage A at this time is set as the reference voltage.

In this setting state, a control signal is output from the CPU boat PTB so that the switch element 21 is turned off, and the controller output is monitored by the boat PTA. At this time, if the output is LOW, that is, the input signal is -30d
If it is below B, the switch element 21 is turned on, the gain of the detection rectifier circuit is increased to 30 dB, and A/D conversion is performed. Conversely, when the comparator output is HIGH, switch element 2
1 is turned off, A/D conversion is performed, and 30 is added to the value of the A/D conversion result. The flow of this series of operations is shown in FIG.

From the above, in this embodiment, the Guinamino clean can be extended by controlling the level of the transmitting or receiving system.

(Effects of the Invention) As explained above, according to the present invention, the logarithmic characteristic l1−
i: Since it is determined by the numerical value set in the CPU, stable characteristics can be obtained without considering variations in logarithmic conversion elements as in the past, and the dynamic range is also calculated by performing A/D conversion in the CPU. Since it can be expanded
It is possible to provide a loudspeaker telephone device with a simple configuration and excellent characteristics so that stable voice switch operation can be obtained.

[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. A/D
FIG. 4 is a specific circuit diagram of the detection rectifier circuit 18 in FIG. 3, FIG. 5 is a logarithmic table set in the CPU for logarithmic conversion, and FIG. 6 is a flowchart for expanding the dynamic range. 14... Ladder resistor, 15... CPU, 16... Converter, ]7... Signal input terminal, 18... Detection rectifier circuit, 21... Switch element. Figure 1 Figure 2 Figure 3 Figure 5 Figure 6

Claims (1)

[Scope of Claims] A loss circuit for howling prevention inserted in a transmitting system and a receiving system, respectively; 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 equipped with a logarithmic conversion function is provided on the input side of the audio switch control circuit so that the level difference between the transmitting and receiving audio signals operates proportionally, and has a switching element controlled by a microprocessor. , a detection rectifier circuit whose gain can be varied for on/off operation of the switching element, a ladder resistor which converts the output of the microprocessor into a voltage magnitude, and a comparator, and the output of the detection rectifier circuit and the output of the detection rectifier circuit. , the output of the ladder resistor is compared with the comparator, and the comparison output is input to the microprocessor to perform sequential A/D conversion, and the dynamic range of the logarithmic conversion is expanded. A loudspeaker telephone device featuring: (2) Output a set value from the microprocessor so that the output of the ladder resistor becomes a reference voltage, and also apply a control signal to the switch element that changes the gain of the detection rectification circuit so that the gain becomes small, and adjust the detection and rectification circuit. When the circuit output is higher than the reference voltage, the control of the switching element is set to the "IT" state, and when the output of the detection rectifier circuit is smaller than the reference voltage, the gain of the detection rectifier circuit is increased. A loudspeaker telephone device according to claim (1), characterized in that: (3) The loudspeaker telephone device according to claim (1) or (2), wherein the A/D conversion is performed by referring to a logarithm table preset in the microprocessor. .