JPS6271362A - Transmission and reception changeover circuit - Google Patents

Abstract

PURPOSE:To prevent missing speech head and tail of conversation by designing the titled circuit that the transmission loss of other signal line is decreased stepwise when the transmission loss of one signal line is increased stepwise in the hang-over state of the transition between the transmission and reception state. CONSTITUTION:A comparator circuit 13 brings an output to logical H when a transmission signal level is larger than a reception signal level and brings the output level logical L when the relation of the signal level is reverse. Time constant circuits 14a-14c consist respectively of diodes Da-Dc blocking the output signal of the comparator circuit 13, charging resistors R1a-R1c connected in series with the cathode of the diodes Da-Dc, capacitors Ca-Cc charged via the charging resistors R1a-R1c by the output of the comparator 13 and discharge resistors R2a-R2c connected in parallel with the capacitors Ca-Cc. The discharge time constant is set longer for the time constant circuits 14a-14c having a shorter charging time constant. Thus, the transmission/reception is attained at the same time in the hangover state and no howling takes place.

Description

[Detailed Description of the Invention] [Technical Field] The present invention uses a transmitting/receiving switching circuit, and more specifically, in a so-called hand-switching machine, etc., the transmission loss of the receiving signal line is increased when transmitting a call, and the transmitting/receiving signal line is increased when receiving a call. The present invention relates to a transmitting/receiving switching circuit that prevents sound from going around from the handset to the transmitter by increasing the transmission loss of the signal line, thereby preventing the occurrence of ringing.

[Background is important] In general, this type of transmitting/receiving switching circuit is constructed as shown in Fig. 5, and basically detects the level of the transmitting signal and the receiving signal. A transmitting/receiving control unit 1 outputs a control signal corresponding to the magnitude relationship between the signal levels of both signals, and variable loss circuits 21 and 22 inserted into the transmitting signal line and the receiving signal line respectively in response to the control signal. A transmission loss control unit 2 is provided for controlling the transmission loss of one signal line having a higher signal level to be smaller than the transmission loss of the other signal line. A pair of amplifier circuits 32, 33 for amplifying a transmission signal inputted from a microphone 31, which is a device, and a variable loss circuit 21 inserted between both amplifier circuits 32, 33 are arranged.
A pair of amplifier circuits 42 and 43 that adjust the level of the received signal and a variable loss circuit 22 inserted between the two amplifier circuits 42 and 43 are arranged on the receiving signal line, and the speaker 4 which is the receiver is arranged.
1, the audio corresponding to the received signal is output. Transmission signal sent to external line 3 and external #
It is separated from the reception signal input from the i-way 3 by the side sound protection circuit 4. The transmission loss control unit 2 includes a pair of variable loss circuits 21 and 22 each including an analog switch, and an inverting circuit 23 connected to the control input terminal of one of the variable loss circuits 22.
The input terminal of the inverting circuit 23 and the control input terminal of the other variable loss circuit vI21 are connected to the output terminal of the transmitter/receiver vi controller 1. The transmitting/receiving control unit 1 includes a pair of smoothing circuits 11.1.2 that smooth the transmitting signal and the receiving signal, respectively.
and a comparison circuit 13 that compares the output levels of both smoothing circuits 11 and 12 and outputs a control signal corresponding to the magnitude relationship;
It consists of a time constant circuit 14 that is charged and discharged by the output of the comparison circuit 13, and when the transmitting signal level is higher than the receiving signal level, the output level of the comparing circuit 13 is "
The output level of the time constant circuit 14 immediately becomes “H”.
"The variable loss element 21 inserted into the transmitting signal line
The amount of loss becomes approximately OdB, and the transmission loss in the variable loss element 22 inserted into the receiving signal line increases. Conversely, when the receiving signal level is higher, the output level of the comparator circuit 13 becomes "L". , time constant circuit 14
When the output level becomes "L", the relationship between the transmission losses of the transmitting and receiving signal lines is reversed. In this way, by increasing the transmission loss of the receiving signal line during transmitting and increasing the transmission loss of the transmitting signal line during receiving, the microphone 31 - amplifier circuit 32 - amplifier circuit 33 - side sound prevention circuit 4 (-recipient's telephone)-amplifier circuit 43-amplifier circuit u42-speaker 41-microphone 31 loop din is kept below 1 to prevent howling from occurring.

By the way, when the transmitting signal level becomes lower than the receiving signal level near the end of a word during transmitting, the output level of the comparator circuit 13 becomes "L", but the discharge time in the time constant circuit 14 is set to an appropriate length. By keeping time constant circuit 1
It is possible to keep the output level of 4 at an open "H" level for a while (hereinafter referred to as hangover), and during this time, the transmission loss of the transmitting signal line can be maintained at approximately OdB, so that the so-called The structure is designed to prevent word endings from being cut off. Conversely, even if the level of the received signal suddenly decreases, the transmission loss of the received signal MA path is maintained at approximately OdB for a certain period of time to prevent endings from being cut off. However, in a hangover state, the transmission loss of one signal line is large, so
If a call is in a hangover state when transmitting a call, the received voice cannot be heard, and in the opposite case, the transmitted voice cannot be sufficiently conveyed to the other party.

[Objective 1 of the Invention The present invention has been made in view of the above-mentioned points, and its main purpose is to enable simultaneous transmission and reception in a hangover state, and to prevent howling from occurring. An object of the present invention is to provide a transmitting/receiving switching circuit.

DISCLOSURE OF THE INVENTION J (Examples) Examples of the present invention will be described below based on the drawings. 1st
As shown in the figure, the basic configuration is the same as that of the conventional example, and a pair of amplifier circuits 32 and 33 amplify an audio signal input from a microphone 31 that is a transmitter.
A transmit signal is output to the external line 3 via I, and a receive signal input from the external line 3 via the side sound protection circuit 4 is amplified by a pair of amplifier circuits 43 and 42, and then output from the speaker 41. It is designed to output audio. To switch between sending and receiving calls,
A transmitting/receiving control unit 1 that detects the levels of a transmitting signal and a receiving signal and outputs a control signal corresponding to the magnitude relationship between both signal levels.
Variable loss circuits 21 and 22 are inserted into the transmitting signal line and the receiving signal line, respectively, and in response to the control signal, the transmission loss of one signal #X path having a higher signal level is reduced to the other signal line. The transmission loss side r to be smaller than the transmission loss of
This is performed by the B section 2.

The transmitting/receiving control unit 1 includes a first rectifying and smoothing circuit 11 that smoothes the transmitting signal after rectifying it, and a first rectifying and smoothing circuit 11 that smooths the transmitting signal after rectifying the receiving signal.
The output level of the second rectifying and smoothing circuit 12 that smoothes the smoothing is compared with the output level of the first rectifying and smoothing circuit 11 and the output level of the second rectifying and smoothing circuit 12, and outputs a control signal corresponding to the magnitude relationship. It is comprised of a comparison circuit 13 and a plurality of time constant circuits 14a to 14c, each having a different charging and discharging time constant, which charge and discharge according to the output level of the comparison circuit 13.

The comparison circuit 13 is a comparator circuit, as shown in Figure V&2, which sets the output level to "H" when the transmitting signal level is higher than the receiving signal level, and sets the output level to "H" when the relationship between the signal levels is reversed. is set to be "L". Further, each of the time constant circuits 14a to 14c includes a diode Da-Dc for blocking the reverse flow of the output signal of the comparator circuit 13, a charging resistor R+a-R+c connected in series to the cathode of the diode Da-Dc, and a comparator circuit 1
Capacitor Ca-Cc charged via charging resistors R, a-R, and c by the output of 3, and capacitor Ca-Cc
The discharge resistors R2a to R2c are connected in parallel to each other. Charging time constant τ of each time constant circuit 14&~14c
a to τC and the discharge time constant Ta-Tc are each time constant circuit 14a.
If the symbols of the elements constituting ~14c are the circuit constants of the elements, they are set as follows.

ra=R, a+ca Ta=R2a fist caτb=R
,b-Cb Tb=R2b-Cbrc=R,cc
c Tc=R2cmCc Here, the time constant circuits 14a to 140 having a short charging time constant are set to have a long discharging time constant. That is, Ta<rb τC ga Ta>”rb>
It is set as Tc.

The transmission loss control section 2 is connected between the control input terminals of the variable loss circuits 21 and 22 inserted in each signal line and the variable loss circuit 22 inserted in the receiving signal line, and the output terminals of each of the time constant circuits 14a to 14c. Inversion circuits 23a to 2 inserted respectively in
3c.

As shown in FIG. 3, the variable loss circuits 21 and 22 include analog switches ASa-ASc and analog switches ASa.
A resistor R3a = R) c connected in parallel to -ASc, and a resistor R4a -R+ c whose one end is connected to the output side of the parallel circuit of the analog switch ASa-ASc and the resistors Rta to Rcoc and the other end is grounded. Three variable loss elements 24a to 24c are connected in series via a coupling capacitor Ca.

Each analog switch ASa- inserted in the transmission signal line
The output terminals of the time constant circuits 14a to 14c are connected to the control input terminal of the ASc, and the control input terminals of the analog switches ASa to ASc inserted in the reception signal line are connected to the output terminals of the time constant circuits 14a to 14c. Inversion circuits 23a to 23c
connected via. Therefore, when the input level of the control input terminal of each analog switch ASa-ASc becomes "H", the analog switches ASa-ASc become conductive and the transmission loss becomes approximately OdB, while the analog switches ASa-A
Sc's edict control and power friction 9 people level, ht''■'' input Makilog switches ASa-ASc become non-conductive and resistors Rzaw Rzaw R4aSRvbHR4bx R3el RI that constitute each loss amount variable element 24a to 24e
The signal is attenuated by an attenuation amount determined by c. Here, the amount of attenuation of each of the variable loss elements 24a to 24c is set to the same magnitude, and the signal level is attenuated by 20 dB in one stage of variable loss elements 124a to 24c.

(Operation) The operation will be explained below based on FIG. 4. In addition, S+-3s in FIG. 4 respectively indicate the signals of the corresponding parts in FIG.
The output level of the second rectifying and smoothing circuit 11 becomes higher than the output level of the second rectifying and smoothing circuit 12, and the output level of the comparator circuit 13 becomes "■(") as shown in FIG. Constant circuits 14a-14c are charged, but f
As shown in the pJA diagram (c), the output level of the first time constant circuit 14a whose charging time constants τa to τC are smaller first exceeds the threshold value Vs of the first 7-analog switch ASξ, and the transmitting signal is First analog switch A inserted into the line
Make Sa conductive. At this stage, the attenuation of the receiving signal line decreases from 60 dB to 40 dB as shown in FIG. 4(d). If the output level of the comparison M path 13 remains "H" for a longer period than the charging time constant of the third time constant circuit 1.4c, which has the largest charging time constant τa to τC, the second time constant The output level of the circuit 14b and the output level of the third time constant circuit 14c both become H", and as a result, all the analog switches ASa-ASc become conductive, and the attenuation amount of the transmission signal line becomes approximately 0clB. The transmitting state is maintained.

Here, even if the transmitting signal level becomes low at time t, ~t, and the output level of the comparator circuit 13 becomes 'L'', the comparison is made by comparing it with the discharge time constant Tc of the third time constant circuit 14c. Since the time during which the output level of the circuit 13 is "L" is short, the amount of attenuation of the transmission signal line is approximately OjB.
It is maintained. In this state, the amount of attenuation of the signal level of the receiving signal line is maintained at 60 dB.

Also, from time t4 to time t.

If the period during which the output level of the comparison circuit 13 is "L" is longer than the discharge time constant Tc of the third time constant circuit 14c and shorter than the second time constant circuit 14b, then the transmission The transmission loss of the speaking signal line temporarily becomes 20 clB, and at this time the transmission loss of the receiving signal line decreases from 60 t (B to 40 dB).Furthermore, as shown from time t6 to ta, the transmission signal is at a low level for a period of time. Therefore, as the time period during which the output level of the comparator circuit 13 remains "L" longer than the discharge time constant Ta of the first time constant circuit 14a, the transmission loss of the transmission signal line gradually increases by 20 dB. 60 at the end
It becomes dB. Here, as the transmission loss of the transmitting signal line gradually increases, the transmission loss of the receiving signal line gradually decreases, and the transmission loss of the transmitting signal line increases by 2.
At 0 dB, the transmission loss of the receiving signal line is 40 dB,
When the transmission loss of the transmission signal line is 40 dB, the transmission loss of the reception signal line is 20 dB. Furthermore, even if the transmit signal level increases for a short time during reception, such as from time t7 to time t, the transmission loss in the transmit signal line decreases by 20 dB, and the transmission loss in the receive signal line increases by 20 dB. , it hardly interferes with the intelligibility of the received voice. Furthermore, since the transmission loss changes stepwise when transitioning from the receiving state to the transmitting state, it is possible to prevent the end of the received voice from being cut off, and also to prevent the beginning of the transmitted voice from being cut off.

Due to the second operation, when the transmitting signal level decreases near the end of a word during transmission, the transmission loss of the transmitting signal line increases step by step to prevent the end of the word from being cut off, and As the transmission loss of the signal line increases, the transmission loss of the reception signal line gradually decreases, and the reception voice gradually becomes more audible. Conversely, when the received signal level decreases while receiving a call, the transmitted voice is gradually conveyed better. Microphone 31 - amplification circuit 32 - amplification circuit 33 - side sound protection circuit 4 - amplification circuit 4
In the loop of 3-amplifier circuit 42-speaker 41-microphone 31, the f transmission loss due to both variable loss circuits 21 and 22 is maintained at 60clBl: J2, so huffing can be effectively prevented as in the conventional system. It is.

[Effects of the Invention 1] As described above, the present invention includes a comparison circuit that compares the levels of the transmission signal and the reception signal and outputs a digital signal corresponding to the magnitude relationship, and a comparison circuit. It consists of multiple time constant circuits that are charged and discharged according to the output level of the circuit, and each time constant circuit is set so that the longer the charging time, the shorter the discharge time, and the variable loss circuit is inserted in series with each signal line. Since the transmission loss is controlled by the output of each time constant circuit, the transmission loss of one signal line is gradually reduced in the hangover state during the transition between the transmitting state and the receiving state. When the transmission loss of the other signal line increases, the transmission loss of the other signal line is set to gradually decrease accordingly, which has the advantage of preventing the beginning and end of a conversation from being cut off. In addition, as the transmission loss of one signal line decreases, the transmission loss of the other signal line increases, so the loop din including both signal lines can be kept at a constant value, and the loop din can be kept below 1. By setting this, LF howling can be prevented.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing a specific configuration of a comparison circuit and a time constant circuit used in the same, and Fig. 3 is a circuit diagram showing a specific configuration of a comparison circuit and a time constant circuit used in the same. FIG. 4 is a circuit diagram showing a specific configuration, FIG. 4 is an operation explanatory diagram showing signals of each part in FIG. 3, and FIG. 5 is a circuit diagram showing a conventional example. 1 is a transmission/reception control section, 2 is a transmission loss control section, 13 is a comparison circuit, 14a to 14c are time constant circuits, and 21 and 22 are variable loss circuits.

Claims (1)

[Claims] (1) A transmitting/receiving control unit that detects the level of the transmitting signal and the receiving signal and outputs a control signal corresponding to the magnitude relationship between the two signal levels, and a variable speed control section inserted in the transmitting signal line and the receiving signal line, respectively. and a transmission loss control section that controls the loss circuit in response to a control signal so that the transmission loss of one signal line with a higher signal level is smaller than the transmission loss of the other signal line. In the transmitting/receiving control unit, the transmitting/receiving control unit includes a comparing circuit that compares the levels of the transmitting signal and the receiving signal and outputs a digital signal corresponding to the magnitude relationship, and a plurality of circuits that are charged and discharged according to the output level of the comparing circuit. Each time constant circuit is set such that the longer the charging time, the shorter the discharge time, and the variable loss circuit is inserted in series with each signal line and controlled by the output of each time constant circuit. A transmitting/receiving switching circuit comprising a plurality of loss variable elements.