JPS6372249A - Transmission and reception switching circuit - Google Patents

Abstract

PURPOSE:To set the titled circuit into reception state with a reception input by giving a suitable bias to a comparator circuit comparing a signal level of a transmission signal line and a reception signal line even if a transmission noise level is high. CONSTITUTION:When the level of the transmission input is higher than that of the reception input, the output level of the comparator circuit 2 goes to 'H' and a switch element SW2 of a bias adjusting circuit 1 is conductive. Even if the transmission signal level is lowered tentatively in this state, if it is within a time setting by a resistor R9 and a capacitor C2 of the circuit 1, the switch element SW2 is kept conductive. When the reception input is detected by a comparator circuit 6 within the hang-over period, the state of variable loss elements 12, 22 is changed immediately into the reception state and the changeover to the reception state is facilitated.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a so-called hands-free telephone, etc.
By making the transmission loss of one of the receiving signal line and the sending signal line larger than the other signal line when transmitting and receiving calls, howling due to sound looping from the receiver to the transmitter does not occur. The present invention relates to a transmitting/receiving switching circuit as described above.

[Background Art] As shown in FIG. 3, this type of transmitting/receiving switching circuit that has been provided in the past has a pair of variable loss elements 12 and 22 inserted into a transmitting signal line and a receiving signal line, respectively. As shown in FIG.
A level detection signal corresponding to the magnitude relationship of the signal level is inputted to the variable loss element 12.22.
By controlling the transmission loss of the variable loss element 12.22 inserted into the signal line with the lower signal level, the transmission loss of the variable loss element 12.22 is made larger than that of the other signal line. In this way, the amplification factor in the transmission loop including the microphone 10, which is the transmitter, and the speaker 20, which is the receiver, is increased to 1.
from speaker 20 to microphone 1 as follows.
This prevents the occurrence of howling due to the sound looping around to 0.

By the way, the comparator circuit 2 sets the output level to "H" or "L".
A digital signal is output as a level detection signal, and the output level is set to ``H'' when the signal level of the transmitting signal line is higher than the signal level of the receiving signal line. , a time constant circuit 3 is inserted between the comparator circuit 2 and the variable loss element 12.22, and when the output level of the comparator circuit 2 becomes H, the comparative When the output level of the time constant circuit 3 becomes "H" after a short time and the output level of the comparator circuit 2 becomes "L", the output level of the time constant circuit 3 becomes "H" after a relatively long time set by the resistor R2 and the capacitor C5. The output level is set to "L". In other words, even if the signal level of the transmission signal line becomes temporarily low, the end of the transmission signal is not cut off. Hereinafter, this period will be referred to as a hangover period.

Since it has such a configuration, there is a problem that if the transmitting noise level is high, the transmitting state is set. However, there is a resistor R at the receiving side input terminal to the comparator circuit 2.
Connect a bias circuit 1'' consisting of s = R* to bias the quality side level, and set the bias level to such an extent that the transmitting state does not occur at the transmitting noise level, but switches to the transmitting state at the transmitting voice level. By setting this, it is possible to solve the above problem. However, if the transmitting noise level is quite large, the preset bias level will not be enough to cope with the problem, and the state will not be switched to the receiving state even if there is an excellent input.

On the other hand, the levels of the transmitting and receiving signal lines are detected between the variable loss elements 12 and 22 and the side sound protection circuit 4, and both levels are compared by the comparison circuit 6, so that the level on the receiving side is higher than the level on the transmitting side. When the output level is high, the output level of the comparator circuit 6 is set to 'H''.
A configuration can be considered in which the switch element SW is turned on to shorten the discharge time of the capacitor C7 of the time constant circuit 3. According to this configuration, when there is a receiver's power during the hangover period, the output level of the time constant circuit 3 is reduced. Immediately close the L”
You can switch to the receiving state.

However, if the resistors R, , R2 of the time constant circuit 3 and the resistor R3 connected to the switch element SW are set appropriately, the time constant By setting the output level of the circuit 3 to a level that can be considered as "L", it is possible to switch to the receiving state even when the transmitting noise level is high, if the receiver has the power. However, with this configuration, a problem arises in that when the reception noise level is high, the system does not switch to the transmitting state even if there is human power to transmit.

[Objective of the Invention 1 The present invention has been made in view of the above-mentioned points, and its purpose is to apply a bias to the receiving side input terminal of the above-mentioned comparison circuit and to adjust the level of the transmitting side to the receiving side. To provide a transmitting/receiving switching circuit that sets the bias to a high level when the level becomes higher than the side level, so that even if the transmitting noise level is high, the receiving state can be set as long as the receiver has power. be.

[Disclosure of the Invention] (Embodiment) As shown in FIG.
After amplification according to 1.13, the transmitting signal is output to the external line 5 via the side sound protection circuit 4, and the receiving signal input from the external line 5 via the side sound protection circuit 4 is output to a pair of amplification circuits. 2
After being amplified by 1.23, the sound is output from the speaker 20. Microphone 10 and side sound protection circuit 4
Both amplifier circuits 11゜1
A variable loss element 12 for varying the transmission loss of the transmitting signal line is inserted between 3, and both amplifier circuits 21 and 23 are inserted on the receiving signal line between the side sound protection circuit 4 and the speaker 20.
A variable loss element 22 is inserted between them to vary the transmission loss of the receiving signal line. Are variable loss elements 12 and 22 analog switches? It is composed of a switching element such as an E field effect transistor. The input end of a first transmitting level detection circuit 14 consisting of a rectifying and smoothing circuit is connected between the amplifier circuit 11 and the variable loss element 12 in the transmitting signal line, and the input end of the first transmitting level detection circuit 14 is connected between the amplifier circuit 21 and the variable loss element in the receiving signal line. 22, the input terminal of a first receiving level detection circuit 24 consisting of a rectifying and smoothing circuit is connected, and the signal levels of the transmitting signal line and the receiving signal line are detected as outputs of the respective level detection circuits 14 and 24. It is now possible to do so.

The outputs of both level detection circuits 14 and 24 are sent to the first comparison circuit 2.
The bias adjustment circuit 1 is inserted between the tjSl reception level detection circuit 24 and the input terminal of the comparison circuit 2. Bias '14 node circuit 1 is comparator circuit 2
A bias is applied to the input end of the receiving side of the device, and it has a series circuit of a pair of resistors R5, R, and a series circuit of a resistor R7 and a switch element SW2 made of a transistor is connected in parallel to one resistor R5. The control end of the switch element SW2 is connected to the output end of the comparator circuit 2 via a time constant circuit consisting of a diode D2, a pair of resistors Rs = Rs, and a capacitor C2. In addition, the first comparison circuit 2
The connection point of the resistors R, , R, is connected to the connection point between the receiver side input terminal of the receiver and the first reception level detection circuit 24. In the first comparison circuit 2, the level on the transmitting side and the level on the receiving side are compared and binarized into "H" and "L" corresponding to the magnitude relationship between the level on the transmitting side and the level on the receiving side. It is designed to output a level detection signal. The output of the first comparator circuit 2 is input to the time constant circuit 3. The time constant circuit 3 is composed of a diode D1, resistors R,, R, and a capacitor CI, and the charging time by the resistor R7 and capacitor C1. is relatively short, and the discharge time by resistor R2 and capacitor C8 is set to be relatively long. The output of the first comparison circuit 2 is input to the control end of the variable loss element 12 inserted in the transmitting signal line, and is also input to the control end of the variable loss element 22 inserted in the receiving signal line via the inverter 8. is input. The inverter 8 is provided here because each variable control element 12, 22 is set to reduce transmission loss when the input level of the control aii becomes "H". As described above, the transmission loss within the variable loss element 12.22 inserted into the signal line with a low signal level is made larger than that of the other, and the microphone 10 - transmission signal line 1 protection sidetone circuit 4 - ( The amplification factor in the transmission loop of the other party) - receiving signal line - speaker 20 - microphone 10 is set to 1 or less to prevent howling from occurring. Here, since the transmission loss of the signal line with a lower signal level is made larger than that of the other signal line, the necessary signal is transmitted at a sufficiently high level.

Variable loss element 12 and amplifier circuit 13 in transmitting Z branch line
The input terminal of a second transmitting level detection circuit 5 consisting of a rectifying and smoothing circuit is connected between the variable loss element 22 and the amplifier circuit 23 in the receiving signal line, and an ff12 consisting of a rectifying and smoothing circuit is connected between the variable loss element 22 and the amplifier circuit 23 in the receiving signal line. The input terminal of the reception level detection circuit 25 is connected. The output levels of both level detection circuits 15 and 25 are compared in a second comparator circuit 6, and the second comparator circuit 6 converts the output level to H" when the receiving level is higher than the transmitting level. The output of the second comparator circuit 6 is connected to the resistor R,
, R, and a switch element SW made of a transistor.A series circuit of the switch element SW and a resistor R is connected in parallel to the resistor R2 of the time constant circuit 3.

(Operation) Hereinafter, the operation will be explained based on FIG. 2 showing signals of each part in FIG.

When the power supply voltage is ■, if the switch element SW2 of the bias gtff1 circuit 1 is a non-conducting concept, the comparator circuit 2
The bias voltage ■ to the receiving side input terminal of is V + =
V x R4/ (Rs + Rs), and if the switch element SW2 is completely conductive, the bias voltage ■2 is V2=VxRs/[1RsRs/(Rs+Re)l+R
s]. Therefore, Vl<V2.

In FIG. 2(a), the solid line is the comparison circuit 2 of fjIJl.
The input signal on the transmitting side is shown by the broken line, and the broken line indicates the input signal on the receiving side.If the level of the human power of the transmitter is higher than that of the receiver, as shown in FIG. 2(b), the first comparator circuit 2 The output level of becomes ``H'', and after a delay time set by the resistor R3 and capacitor C2 of the bias adjustment circuit 1, the switch wire SW2 of the bias adjustment circuit 1 becomes conductive, and the bias voltage becomes ``2.'' This state Even if the transmitting signal level temporarily decreases and the transmitting side signal level to the comparator circuit 2 becomes lower than the receiving side signal level, the bias adjustment circuit 1's resistor R and capacitor C2 maintain the same level. If the time is up, the switch element SW2 is maintained in a conductive state.However, when the transmitting noise level is large and there is no receiver power, the switch element SW2 is maintained in a conductive state and the bias voltage is higher than ■1. In other words, if there is human power on the part of the speaker, the bias level will be raised accordingly and the level on the receiving side will be raised, and if there is manpower on the receiving side, even if the level is relatively small, The output of circuit 2 is inverted.

The output of the first comparator circuit 2 is repeatedly inverted as shown in FIG. 2(b) due to a temporary drop in the transmitting side signal level, but as shown in FIG. 2(e), Since the output level of the time constant circuit 3 is maintained at "H" during the change within the hangover period set in the variable loss element 12.3.
The state of 22 does not change. Furthermore, during the hangover period, when the second comparator circuit 6 detects the receiver's power, the state of the variable loss points X12 and 22 immediately changes to the receiving state, making it easy to switch to the receiving state. It is something. On the other hand, when the receiver is in the receiving state due to reception noise, the bias level is at a low level, so if there is human power to speak, the level detection signal that is the output of the first comparator circuit 2 will set the transmitting state. It is.

[Effects of the Invention] As described above, the present invention includes a variable loss element that is inserted into a transmitting signal line and a receiving signal line to vary the transmission loss of each signal line, and a transmitter, a receiver, and each variable loss element. A first comparator circuit outputs a level detection signal corresponding to the magnitude relationship of the signal level between the transmitting side and the receiving side. The signal level is compared between the time constant circuit that maintains the transmitting state, each variable loss element, and the side sound protection circuit, and when the receiving side level becomes higher than the transmitting side level, the hangover period of the time constant circuit is shortened. It comprises a second comparison circuit and a bias adjustment circuit that applies a bias to the receiving side input terminal of the first comparison circuit and sets the bias to a high level when the transmitting side level becomes higher than the receiving side level. It operates as described above, and even if the transmitting noise level is high, if there is human power to speak, it will be set to the receiving state, and even if the receiving noise is high, if there is human power to speak, it will be set to the transmitting state. This has the advantage that malfunctions in switching between transmitting and receiving can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of the same operation, FIG. 3 is a block diagram showing a conventional example, and FIG. 4 is an explanatory diagram of the same operation. 1 is a bias adjustment circuit, 2 is a first comparison circuit, 3 is a time constant circuit, 4 is a side sound prevention circuit, 5 is an external line, 6 is a second comparison circuit, 7 is a receiving priority circuit, 12°22 is It is a variable loss element.

Claims (1)

[Claims] (1) Variable loss elements inserted into the transmitting signal line and the receiving signal line to vary the transmission loss of each signal line, and the magnitude relationship of the signal level between the transmitter and receiver and each variable loss element. a first comparison circuit that outputs a corresponding level detection signal; and a time constant circuit that maintains the variable loss element in a transmitting state during a hangover period of a predetermined time from the time when the level on the transmitting side becomes lower than the level on the receiving side. , a second comparison circuit that compares signal levels between each variable loss element and the side sound prevention circuit and shortens the hangover period of the time constant circuit when the receiving side level becomes larger than the transmitting side level; A transmitting/receiving switching circuit comprising: a bias adjustment circuit that applies a bias to a receiving side input terminal of a comparison circuit and sets the bias to a high level when a transmitting side level becomes higher than a receiving side level.