JPH01258537A - Hand free circuit - Google Patents

Abstract

PURPOSE:To prevent a heading cut by cancelling the delay of the switching time of a gate circuit due to a comparing circuit by the delay of the writing and reading time to the FIFO memory of a transmitting signal or a receiving signal. CONSTITUTION:When the level of a transmitting signal inputted to a microphone 1 is higher than the level of the receiving signal, it is set to a transmitting condition by a comparing circuit 11. A gate circuit 4 is turned on, a gate circuit 8 is turned off, only a signal and read from an FIFO memory 3 is inputted to a D/A CODEC circuit 5 and sent to a trunk line. When the level of the receiv ing signal from the trunk line is higher than the level of a transmitting signal, the gate circuit 8 is turned on and the gate circuit 4 is turned off. Only a signal read from an FIFO memory 7 is inputted to a D/A CODEC circuit 9 and dis charged from a speaker 10. In this case, the writing and reading time to FIFO memories 3 and 7 is set longer than the delaying time of the comparing circuit 11.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a switching type hands-free circuit,
In particular, the present invention relates to a circuit that prevents the beginning of a word from being cut off when switching between sending and receiving calls using a switching function.

[Conventional technology]

Functional telephones with various special functions, button telephones for key telephone devices, intercoms, etc. are equipped with a hands-free circuit for loudspeaker calls, and taking a telephone as an example, the configuration is shown in the block diagram of Fig. 3. is commonly used.

That is, the transmission signal from the microphone 31 is amplified by a preamplifier (HA) 32, and is also passed through a variable loss circuit (
VLS) 33, is amplified again by the transmitting amplifier (TA) 34, and then the side sound prevention port! (HYB) 35, where it is prevented from going around to the receiving side and sent out to a two-wire telephone line (hereinafter referred to as line) 36. On the other hand, the reception signal from the line 36 is transmitted to the reception amplifier (RA).
) 37, the signal is amplified to a predetermined power by a variable power amplifier (PA) 39 via a variable loss circuit 38, and drives a speaker 40.

However, it is difficult to make the amount of crosstalk attenuation by the sidetone prevention circuit 35 to the transmitting amplifier 37 sufficiently large, and the occurrence of ringing due to acoustic coupling between the speaker 40 and the microphone 31 is prevented. Therefore, a control unit 41 is provided, which compares the levels of the transmitting signal and the receiving signal via the variable loss circuits 42 and 43, and determines the signal on the high level side, and if the transmitting signal is high, the variable loss circuit The loss of the variable loss circuit 33 is made small and the loss of the variable loss circuit 38 is made large, and the variable loss circuit 43 is controlled to exhibit a predetermined loss. On the other hand, if the level of the reception signal is high, the loss of the variable loss circuit 38 is made small, the loss of the variable loss circuit 33 is made large, and the variable loss circuit 42 is controlled to exhibit a predetermined loss. In this way, after setting the transmitting state or the receiving state with the high level side system as low loss and the low level side system as high loss, the microphone 31 - preamplifier 32 - variable loss circuit 33 - transmitting amplifier 34 is set. - Sidetone prevention circuit 35 - Receiving amplifier 37 - Variable loss circuit 38 -
The loop gain of the power amplifier 39-speaker 40 is limited to a certain value or less so that no noise occurs.

[Problem to be solved by the invention]

However, in the hands-free circuit configured as described above, a delay occurs in the output signal when switching the transmitting state from receiving to transmitting or from transmitting to receiving, and the beginning of the transmitting signal sent to the line 36 is cut off. , the beginning of the word of the received voice emitted from the speaker 40 is cut off, and the conversation becomes unnatural.
In addition, there was a problem in that the clarity deteriorated.

[Means to solve the problem]

The present invention has been made to solve these problems, and in analog lines, transmitting and receiving signals are converted into digital signals by an A/D codec circuit and temporarily stored in a FIFO memory. In parallel with this processing, a comparator circuit compares the levels of the transmit signal and the receive signal, turns on only the gate circuit for the higher input signal, and then outputs the FIFO signal.
The signal output from the memory is input to the codec circuit via the turned-on gate circuit, converted back into an analog signal, and then output to the transmission line or speaker.

In addition, in a digital line, the transmitting signal is converted into a digital signal by an A/D codec circuit, and the receiving signal is temporarily stored directly in a FIFO memory, and the stored information is read out and output. In parallel, the receiving signal via the transmission line converted into an analog signal by the codec circuit and the sending signal via the microphone are input to a comparison circuit, the levels of these signals are compared, and a gate circuit is applied to the higher input signal. The signal output from the FIFO memory is sent to the transmission line via the turned-on gate circuit, or converted into an analog signal by the codec circuit and then output to the speaker.

[For production]

The delay in the switching time of the gate circuit caused by the comparison circuit is offset by the delay in the writing and reading time of the transmit signal or the receive signal to the FIFO memory.

〔Example〕

Next, a case where the present invention is applied to a hands-free circuit of a telephone will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the invention according to the first claim of the present application, in the case where the office line is an analog line.

In the figure, 1 is a microphone that inputs a transmission signal;
2 is a first A/D codec circuit that converts the A word from this microphone 1 from an analog signal to a digital signal, and 3 is a destination for sequentially storing the digital signals converted by the first A/D codec circuit 2. A first FIFO (first-in-first-out) memory that reads out information stored in the FIFO memory 3; 4 is a gate that has the function of switching output No. 43 read out from the FIFO memory 3 and allows the signal to pass through when it is in the on state; The circuit 5 is a first D/A codec circuit that converts the signal from the gate circuit 4 from a digital signal to an analog signal and sends it to the office line. A/D codec circuit 2. FIFO memory 3. The gate circuit 4 and the codec circuit 5 constitute a circuit of a transmission system.

Further, 6 is a second A/D codec circuit which inputs a reception signal from the office line and converts it from an analog signal to a digital signal, and 7 is a second A/D codec circuit which sequentially stores the digital signal converted by the second codec circuit 6 and stores it first. The second step is to read out the stored information.
8 is a gate circuit that has the function of switching the output signal read out from the FIFO memory 7 and allows the signal to pass when it is in the on state. 9 is a gate circuit that converts the signal from the gate circuit 8 from a digital signal to an analog signal. 10 is a second D/A codec circuit that outputs
This is a speaker that receives the output signal of the A/D codec circuit 9 and emits audio as audible sound, and is similar to the above A/D codec circuit 6. FIFO memory 7, gate circuit 8. The D/A codec circuit 9 and the speaker 10 constitute a receiving system circuit.

As shown in the diagram, clock signals of two different frequencies are input to each circuit of the transmitting system and the receiving system, and the 8 KHz clock signal sets the sampling rate, and the 64 KHz clock signal The signal sets the transfer rate.

In addition, 11 inputs the transmitting signal from the microphone 1 and the receiving signal from the office line, compares the levels of these signals, and turns on the gate circuit connected to the system for the input signal with a higher level signal. and the FIF of that system
This is a comparison circuit that outputs a signal read from O memory. Further, the comparator circuit 11, together with the gate circuits 4 and 8, has a function of preventing the generation of sound due to acoustic coupling between the speaker lO and the microphone 1, similar to the conventional hands-free circuit. In other words, after setting the transmitting state or receiving state with the high-level side system of the input signal as low loss and the low-level side system as high loss, the loop gain of the loop circuit formed in the circuit of the transmitting/receiving system is set. is limited to below a certain value so that no noise occurs.

In such a configuration, an analog input signal, which is a transmission signal from the microphone 1, is converted into a digital signal by the codec circuit 2 and temporarily stored in the FIFO memory.

A reception signal from the office line is also input and converted from an analog signal to a digital signal by the codec circuit 6.
It is temporarily stored in the IFO memory 7. In parallel with this, the transmission signal from the microphone 1 and the reception signal from the office line are input to the comparison circuit 11, and their levels are compared. As a result of the comparison, the gate circuit of the system for the input signal with the higher level is controlled to be in the on state.

In other words, when there is an audio input to the microphone l and the level of this transmitting signal is higher than the level of the receiving signal, the comparing circuit 11 sets the transmitting state, and the transmitting state is selected from the comparing circuit 11 to the gate circuit 4. The signal turns the gate circuit 4 on and the gate circuit 8 off, and only the signal read out from the FIFO memory 3 and output is input to the codec circuit 5, where it is converted back into an analog signal and sent to the central office line. be done.

Further, when the level of the reception signal from the office line is higher than the level of the transmission signal, the reception selection signal from the comparator circuit 11 to the gate circuit 8 turns on the gate circuit 8 and turns the gate circuit 4 on. The codec circuit 9 is turned off, and only the signals read from the FIFO memory 7 and output are sent to the codec circuit 9.
is input into
0, it is emitted as an audio signal.

In this way, the process of controlling the gate circuit 4.8 by the comparator circuit 11 and the process of temporarily storing the input transmitting and receiving signals in the FIFO memories 3 and 7 and further reading them are executed in parallel. . Moreover, this FIFO memory 3,
The writing and reading times to and from the gate circuit 7 are set in advance to be somewhat longer than the delay time that occurs when the comparison circuit 11 controls the gate circuit. Therefore, the delay time caused by the comparator circuit 11 is offset with the write and read time by the FIFO memory 3.7, and the FIFO memory 3.
．． 7 outputs a signal to the codec circuit 5.9. Therefore, the beginning of a word is prevented from being cut off, which conventionally occurs due to the delay time caused by the comparison circuit 11.

FIG. 2 is a block diagram showing an embodiment of the invention according to the second claim, in which the office line is a digital line. Note that the same reference numerals as in FIG. 1 represent the same or corresponding parts, and the explanation thereof will be omitted.

The differences in the circuit configurations between FIG. 2 and FIG. 1 are as follows. In other words, the hands-free circuit shown in Figure 2 is
First, the central office line is a digital line. Second,
The reception signal from the office line is converted from a digital signal to an analog signal by the D/A codec circuit 21, and then input to the comparison circuit 11, and this reception signal is directly input to the FIFO.
This point is stored in the memory 7. Third, gate circuit 4
The transmitting signal output from the station is directly sent to the central office line.

The operation of this circuit is almost the same as that of the circuit shown in FIG. Since the incoming signal is a digital signal, it is directly stored in the FIFO memory 7. In parallel with this process, an analog signal obtained by converting a reception signal from the office line by the codec circuit 21 and a transmission signal from the microphone 1 are input to the comparison circuit 11, and the levels of these input signals are compared. be done.

As a result of the comparison, the gate circuit of the system corresponding to the higher level input signal is turned on as described above. As for the signals read out from the FIFO memories 3 and 7, when the level of the transmitting signal is higher, the signal is sent as is to the office line, and when the level of the receiving signal is higher, the signal is sent as is. The codec circuit 9 converts the signal into an analog signal and outputs it, and the speaker 10 emits it as an audible sound.

In the circuit shown in FIG. 2, as in the circuit shown in FIG. FI after confirming that it is on
A signal is now outputted from the FO memory 3.7 to the codec circuit 5.9, and truncations at the beginning of words are prevented.

[Effects of the Invention] As explained above, the present invention temporarily stores the transmitting signal and the receiving signal in the FIFO memory, and in parallel with the processing of reading out and outputting the stored information, the transmitting signal and the receiving signal are By comparing each level with the input signal and turning on the gate circuit of the system for the input signal with the higher level, the delay in switching time of the gate circuit due to the comparison circuit is reduced by the FIFO memory of the transmit signal or the receive signal. offset by delays in write and read times. For this reason, these signals are output only after the switching for switching between sending and receiving calls has been confirmed, which prevents the beginning of a word from being cut off, which was previously caused by the delay time caused by the comparison circuit, and allows for clear and natural sound. It has the effect of being able to make phone calls.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the invention according to the first claim of the present application, FIG. 2 is a block diagram showing an embodiment of the invention according to the second claim of the present application, and FIG. The figure is a conventional block diagram. ■... Microphone, 2.6... A/D codec circuit, 3, 7... FIFO (first in first out) memory, 4.8... Gate circuit, 5
, 9... D/A codec circuit, 10... Speaker, 11... Comparison circuit. Patent applicant: Tamura Electric Manufacturing Co., Ltd. Representative: Masaki Yamakawa (2 persons)

Claims (2)

[Claims] (1) A microphone that inputs a transmission signal, a first A/D codec circuit that converts the transmission signal from the microphone from an analog signal to a digital signal, and a first A/D codec circuit that converts the transmission signal from the microphone from an analog signal to a digital signal. A first FIF that sequentially stores digital signals and reads out the information stored first.
O memory, a first gate circuit that switches the output signal of the first FIFO memory, and when the first gate circuit is in an on state, inputs the output signal of the first FIFO memory and converts the digital signal into an analog signal. a first D/A codec circuit that converts the signal into a signal and sends it to the transmission line; a second A/D codec circuit that converts the received signal via the transmission line from an analog signal to a digital signal;
A second FI that sequentially stores the digital signals converted by the A/D codec circuit and reads out the information stored first.
An FO memory, a second gate circuit that switches the output signal of the second FIFO memory, and when the second gate circuit is in an on state, inputs the output signal of the second FIFO memory and converts the digital signal into an analog signal. A second D/A codec circuit that converts the signal into a signal and sends it to the speaker; inputs the transmitting signal via the microphone and the receiving signal via the transmission line; compares the levels of these signals; and inputs the one with the higher level. A hands-free circuit for an analog transmission line, comprising a comparison circuit that turns on the gate circuit for a signal and turns the other gate circuit off. (2) A microphone that inputs a transmission signal, an A/D codec circuit that converts the transmission signal from this microphone from an analog signal to a digital signal, and a sequential storage of the digital signal converted by this A/D codec circuit. a first FIFO memory that reads out previously stored information;
A first gate circuit that switches an output signal from this first FIFO memory to a transmission line, a first D/A codec circuit that converts a received signal via the transmission line from a digital signal to an analog signal, and this transmission line. a second FIFO memory that sequentially stores reception signals transmitted through the line and reads out information stored first;
a second gate circuit that switches the output signal of the memory; and a second gate circuit that switches the output signal of the memory;
a second D/A codec circuit that inputs the output signal of the IFO memory, converts it from a digital signal to an analog signal, and sends it to a speaker;
a comparison circuit which inputs the receiving signal converted into an analog signal by the /A codec circuit, compares the levels of these signals, and turns on the gate circuit for the input signal with a higher level and turns off the other one. Hands-free circuit in digital transmission line.