JPS63222528A - Tone signal detecting circuit - Google Patents

Abstract

PURPOSE:To decrease a delay time and to simplify the constitution by using a band pass filter circuit where the full frequency band of all tone signals is used as the frequency pass band width. CONSTITUTION:A band pass filter circuit A where the frequency pass band width is set to all frequency bands of plural tone signals is provided and a demodulation signal from a reception system B is inputted to the band pass filter circuit A and its passing signal is outputted as a tone detection signal. Since each frequency has no meaning and the presence of line connection is discriminated by having only to detect the presence of the tone signal, the band pass filter circuit using the full frequency band for all the tone signals as the frequency pass band is used. Thus, the constitution is simplified, no cost-up is incurred and the delay time is reduced.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a circuit for detecting a tone signal (system tone) in an MCA (multi-channel access) system applied to mobile communications. .

(Prior Art) There is a control system called an MCA system as one of mobile communication systems in which wireless communication is performed between a control station <wb base station) and a plurality of mobile stations. This MCA' system allocates fewer channels than the number of mobile stations between one base station and multiple mobile stations, and has recently been widely used to make effective use of frequency resources. .

In such an MCA system, one tone signal having a frequency outside the voice band is assigned to each system in order to prevent overreach, control relays of base stations, and the like. Here, the overreach prevention described above uses tone signals to prevent repeated use of the same frequency in adjacent areas, and base station relay I control is performed only when a tone signal is detected. The details of this relay control are as follows. In other words, the mobile station constantly sends a tone signal to the III 10 station during a call, and the control station relays this as is to the other party's mobile station, but the mobile station immediately stops sending the tone signal when the call ends. When the tone signal is interrupted for a certain period of time fJ1 or more, the control station assumes that the call has ended and sends a call end signal to the other party's mobile station to perform muting. In this case, each time a call ends at the other party's mobile station, the speaker emits a data signal sound (II speech sound) based on the end-of-call signal, which makes the operator of the mobile station's radio extremely uncomfortable.

As a means to eliminate the above-mentioned discomfort, the following call procedure is generally adopted.

In other words, as part of the call termination procedure, the control station sends out a call termination signal after a certain period of time has elapsed since the tone signal was interrupted.
If the mobile station side detects the disappearance of the tone signal and mutes the audio signal at the same time as the detection, it is possible to prevent the unpleasant end-of-call sound from being emitted from the speaker.

Here, the circuit for detecting and muting the tone signal described above conventionally has a configuration as shown in FIG. That is, the intermediate frequency signal (IF and other signals) from the reception system of the mobile station radio (not shown) is demodulated from the IF signal input terminal 1 through the demodulation circuit 2, and as shown in FIG. A band pass filter in which f2, f3, and f4 can be adjusted by control signals described later, and Q is set extremely high.
It is input to the filter circuit (8/PF circuit) 3. This B-P-F circuit 3 can change its center frequency by a control signal given from a control signal input terminal 4 (based on a command from a control station to set a tone signal of a certain frequency). ), if the input III signal contains the tone signal of the center frequency set above, the signal is output from the B-P・F circuit 3, and the output is converted to DC through the rectifier circuit 5 and then connected to the analog gate. The demodulated signal is inputted to the circuit 6 and the gate is opened to supply the demodulated signal to the amplifier circuit 7, which drives the speaker 8 and generates sound.

This is an operation during a call, and when the call is ended and a tone signal is no longer sent to the other party's mobile station, and then a call termination signal is sent, the following operation occurs. That is, since the input 111 signal does not include the tone signal of the center frequency set above, no signal is output from the B-P-F circuit 3, and the analog gate circuit 6 closes the gate, so that the tone signal is not output. The end-of-call signal (demodulated signal) sent after the transmission is stopped is not supplied to the amplifier circuit 7.

Therefore, since the speaker 8 is not driven, no noise is emitted by the end-of-call signal.

In the above configuration, if the center frequency of the B-P-F circuit 3 is switched in advance to the frequency of the desired tone signal by the control signal applied from the control signal input terminal 4, only the desired tone signal wave is included. When the other IF signal is input to the IF signal input terminal 1, the presence or absence of the tone signal having the set center frequency can be determined based on the presence or absence of the passing signal.

However, this configuration has the following problems. That is, since a narrow-band B-P-F circuit 3 whose center frequency can be varied is required, the circuit configuration becomes complicated. Further, a control signal for switching the center frequency in accordance with the frequency of the tone signal is required, and a circuit for signal generation is required, making the circuit configuration complicated. In the glare,
Since the B-P·F circuit 3 has a high Q, the delay time becomes long. Further, since the band is similarly narrow, the frequency characteristics change due to changes in the environment such as temperature, and a shift in the center frequency makes it impossible to detect the tone signal.

Furthermore, in order to prevent the frequency characteristics from changing due to the aforementioned environmental changes, it is necessary to use highly stable components of the B-P-F circuit 3, leading to an increase in cost.

(Problems to be Solved by the Invention) As described above, in order to detect tone signals of a plurality of different frequencies using the conventional technology, a circuit with a complicated configuration is required, which also increases cost and increases the delay time. There was a problem with increasing the size. 'Therefore, an object of the present invention is to provide a tone signal detection circuit that has a simple configuration, does not increase cost, and can detect tone signals of a plurality of different frequencies with a reduced delay time.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems and achieve the objects, the present invention is constructed as follows. That is, as shown in Figure 1,
A band pass filter circuit A whose frequency pass band width is set to the entire frequency band of a plurality of tone signals is provided, a demodulated signal from the receiving system B is input to this band pass filter circuit A, and the passed signal is input to the band pass filter circuit A. The present invention is characterized in that it is configured to be output as a tone detection signal.

(Function) According to this configuration, the individual frequencies of the tone signals relayed from the control station to the mobile station to MC8 have no meaning, and if the presence or absence of tone signals can be detected, the line Focusing on the fact that it is possible to determine whether there is a connection, it is not necessary to tune the band pass filter circuit to each frequency of the tone signal. The tone signal is detected by using a band pass filter circuit with a pass band width.

(Embodiment) An embodiment of the tone signal detection circuit according to the present invention will be described below with reference to FIGS. 2 and 3.

FIG. 2 is a block diagram showing the configuration of this embodiment, and FIG. 2 is a characteristic diagram of the B-P-F circuit used in this embodiment.

In FIG. 1, an IF signal input terminal 1 receives an intermediate frequency signal < IF multiplied signal from the receiving system of the mobile station's radio, and
The signal is demodulated from the F signal input terminal 1 through the demodulation circuit 2. As shown in Figure 3, the center frequencies ft, f2, f3
, f4 as a frequency pass band width. Here, if the input demodulated signal contains a tone signal of any center frequency, the signal is output from the B-P-F circuit 9, and the output is converted into DC through the rectifier circuit 5 and converted into an analog signal. The signal is input to the gate circuit 6, and by opening the gate, the tI tone signal is supplied to the amplifier circuit 7, and the speaker 8 is driven to generate a normal call tone.

On the other hand, when there is no tone signal in the input demodulated signal, that is, when the other party's mobile station stops transmitting, 8-
No output is obtained from the P-F circuit 9, there is no DC component in the output of the rectifier circuit 5, the analog gate circuit 6 closes its gate, and the speaker 8 becomes muted. If the partner mobile station continues to stop transmitting for a certain period of time, the control station considers the call to have ended and sends a call end signal. At this time, the mobile station's speaker 8 is muted, so
An unpleasant data signal sound due to the end-of-call signal will not be emitted from the speaker 8.

According to this embodiment as described above, the following effects are achieved.

■ Focusing on the fact that the individual frequencies of the tone signals relayed from your station to the mobile station to MC8 have no meaning, and if you can detect the presence or absence of tone signals, you can determine whether the line is connected or not. Since it is not necessary to tune the B-P-F circuit 9 to each frequency of the tone signal, the B-P-F circuit 9 has a frequency pass band width of all frequency bands of all tone signals so that all tone signals can pass through. By using the F circuit 9, the tone signal can be detected.

■ Since the center frequency of the B-P-F circuit 9 can be fixed,
The circuit configuration is simple.

(2) Since the B-P-F circuit 9 with a low Q is sufficient, the delay time can be reduced.

(2) Since it is a high-bandwidth B-P-F circuit 9, tone signals can be detected even if there is some variation in component constants.

■B-P-F circuit 9 has center frequencies f1, f2°f3
．． Since it is possible to pass all of f', there is no need to perform frequency switching using a control signal, and no configuration for generating a control signal is required.

[Effects of the Invention] As described above, the present invention provides that the tone signal relayed from the MCA ill 611 station to the mobile station has no meaning at this particular frequency, and if the presence or absence of the tone signal can be detected, We are focusing on the fact that it is possible to determine whether or not a line is connected, so there is no need to tune the band bus filter circuit for each frequency of the tone signal. The tone signal is detected by using a band pass filter circuit whose frequency pass band width is the entire frequency band of
It is possible to provide a tone signal detection circuit that can detect tone signals of a plurality of different frequencies with a reduced delay time.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a tone signal detection circuit according to the present invention, FIG. 2 is a block diagram showing the configuration of an embodiment of the tone signal detection circuit according to the present invention, and FIG. 3 is a block diagram showing the configuration of a tone signal detection circuit according to the embodiment. -A characteristic diagram showing the characteristics of the P-F circuit, Fig. 4 is a block diagram showing the configuration of the conventional example, and Fig. 5 is the B in the conventional example.
- It is a characteristic diagram showing the characteristic of a P-F circuit. 1... IF signal input terminal, 2... demodulation circuit, 5...
- Rectifier circuit, 6... Analog gate circuit, 7... Amplification circuit, 8... Speaker, 9... B-P-F circuit. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In a circuit that detects tone signals of a plurality of different frequencies specific to a system used for relay control, overreach prevention, etc. in a multi-channel access system on the mobile station side, the frequency pass bandwidth is determined by A band pass filter circuit set for all frequency bands is provided, a demodulated signal from the receiving system is input to this band pass filter circuit, and the passed signal is output as a tone detection signal. tone signal detection circuit.