JP2684299B2 - Mobile communication telephone and silent section detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication telephone and a silent section detecting circuit, and more particularly to a silent section detecting circuit used in a transmitting circuit for mobile communication such as an in-vehicle telephone and used in a TDMA control circuit. The present invention relates to a silent section detection circuit that generates a signal, and a mobile communication telephone.

[0002]

2. Description of the Related Art In mobile communication such as an on-vehicle telephone and a mobile telephone, a TDMA (time division multiple access) control system in which one master station and a plurality of slave stations communicate by time-sharing the same frequency by digital data compression Has been adopted. For example, in the "RCR STD-28" of the Radio System Development Center, which is one of the standards of that system, one slot of voice data, which is a unit of transmission / reception in one slave station, has a section time width of 5 ms. , 160 bits are allocated as the data amount. Therefore, if the analog audio signal is digitized with a sampling frequency of 8 kHz and a conversion accuracy of 4 bits, the audio signal is sampled 40 times corresponding to one slot.

FIG. 4 shows a transmission circuit of a slave station which employs a conventional silent section detection circuit. Here, 10 is a voice input circuit such as a receiver, 20 is a voice encoding circuit that encodes voice as digital data, and 30 is a TDMA that performs transmission control etc. by associating the encoded digital data with the assigned slot. The control circuit 40 is a transmission circuit (MODEM) that modulates transmission data with a carrier wave and wirelessly transmits it. Further, reference numeral 20a is a silent section detection circuit, which is added to the voice encoding circuit 20.

The voice of the speaker is input to the voice input circuit 10 and sent to the voice encoding circuit 20 as an analog voice signal A. In the voice encoding circuit 20, the analog voice signal A is subjected to analog-digital conversion at the timing of the sampling clock CLK to be a digital voice signal B, which is sent to the TDMA control circuit 30 as it is or after being encoded. Further, the silence section detection circuit 20a of the speech encoding circuit 20 receives the digital speech signal B, and the state where it is not at a significant level equal to or higher than the predetermined threshold value X, that is, the silence state is continuously for one slot (40 sampling) or more. When there is no sound, the silence detection signal C is sent to the TDMA control circuit 30.

The TDMA control circuit 30 which has received the digital voice signal B basically sends the transmission data D including the digital voice signal B via the transmission circuit 40 to a master station (not shown).
To wirelessly send to. However, when the silence detection signal C is also received, the transmission of the transmission data D is thinned out. So-called VOX control is performed. In this way, by decimating the transmission of slots that do not contain valid voice,
The battery consumption of portable handsets and the like is being reduced.

[0006]

As described above, in the conventional mobile communication telephone and the silent section detection circuit, the effective voice signal is applied to the voice signal over the time width of one slot for the VOX control in the TDMA control system. A silence detection signal is generated according to the detection result of whether or not is included. This detection is performed based on whether or not the level of the audio signal has reached a predetermined threshold value. However, the audio signal to be detected often contains an undesired DC component, so-called offset, sporadic noise, and the like. If there is an offset, the relationship with the threshold value relatively shifts, and one of the upper side and the lower side of the waveform of the audio signal is judged to be strict and the other is judged to be loose, and an erroneous silence judgment may be made. Further, even if there is no valid voice but only noise, a voice having an amplitude equal to or larger than the threshold value is detected as a significant voice level, so that the silence detection signal is not output.

In particular, if noise is superimposed on the side that is strictly determined by the presence of an offset, even a small amount of noise will immediately exceed the threshold value. Therefore, even a slot containing only such noise is targeted for transmission. For this reason, in practice, wireless transmission often occurs in response to a slight noise even if there is no speaker's voice, so the thinning efficiency of VOX control is not good. This is inconvenient because the battery saving effect is not improved. An object of the present invention is to solve the above problems of the prior art, and to realize a mobile communication telephone and a silent section detection circuit which are hardly affected by offset and noise.

[0008]

The mobile communication telephone of the present invention which achieves the above object comprises the following silent section detection circuit. The first configuration of the silent interval detection circuit of the present invention which achieves such an object is
With respect to the digital voice signal sampled to be transmitted in the TDMA control method, a silent period detection indicating that the voice to be transmitted is not included in the period of the constant time width corresponding to the slot of the TDMA control method. In a silent section detecting circuit for generating a signal, a maximum value detecting circuit for receiving the digital audio signal and detecting a maximum value of the digital audio signal in the section, and a digital value in the section for receiving the digital audio signal A minimum value detection circuit that detects the minimum value of the audio signal, a difference circuit that receives the maximum value and the minimum value, and outputs a difference signal whose value is the difference between these values, and the amplitude level of the digital audio signal is The difference signal is received when a predetermined threshold value for determining whether the level corresponds to a silent state or a voiced state is received. A comparison circuit value of No. outputs said silent interval detection signal when the a threshold or less, or less than,
It is provided with.

A second configuration of the silent section detection circuit of the present invention which achieves the above object is such that a digital voice signal sampled to be a transmission target in the TDMA control system is stored in a slot of the TDMA control system. In a silence interval detection circuit that generates a silence interval detection signal indicating that a voice to be transmitted is not included in a corresponding interval of a certain time width, with respect to the digital audio signal in the interval after receiving the digital audio signal A quasi-maximum value detection circuit for detecting a quasi-maximum value of the n-th (n is an integer greater than “1” and determined according to the frequency of noise occurrence), and the digital audio signal. And a quasi-minimum value detection circuit for detecting the quasi-minimum value of the n-th smallest value of the digital audio signal in the section. A difference circuit for receiving a value and the quasi-minimum value and outputting a difference signal having the difference between these values as a value; and a level where the amplitude level of the digital audio signal corresponds to either a silent state or a voiced state. A comparison circuit which receives a predetermined threshold value for determining whether or not the difference signal is output and outputs the silent section detection signal when the value of the difference signal is less than or equal to the threshold value or less than the threshold value. .

[0010]

In the silence interval detection circuit of the present invention having the above-described first structure, the value of the voice signal is not directly compared with the threshold value, but the value within the interval corresponding to one slot is The difference between the maximum and minimum values for the digital audio signal is compared against a threshold. Since a normal voice signal has a waveform that is locally almost vertically symmetrical, this difference indicates the maximum amplitude of the voice signal in the section. Therefore,
The level of the audio signal can be detected by comparing this difference with the threshold value. Moreover, since the DC components contained in the audio signal cancel each other out by taking the difference, the DC component does not remain in this difference. Therefore, since the offset is removed before the comparison with the threshold value, the influence of the offset is less likely to occur in the comparison detection of whether or not there is a silent state, and the influence of the noise superimposed on the offset can be reduced.

In the silent section detection circuit of the present invention having the second structure, the quasi-maximum value and the quasi-minimum value are used instead of the maximum value and the minimum value in the invention of the first structure.
Therefore, even if sporadic noise is superimposed on the audio signal, if the upper and lower sides of the waveform of the audio signal are less than n, the signal value of the noise portion is adopted as a signal value of comparison symmetry. Never. This also further reduces the influence of noise. Therefore, in addition to being less susceptible to the influence of the offset and the noise superimposed on the offset, it is possible to effectively reduce the influence of the sporadic noise. Also, the same effect can be achieved in the mobile communication telephone of the present invention.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the silent section detection circuit of the present invention.
As an example of application of the above embodiment, a transmitting circuit of a slave station of a mobile communication telephone is shown, and FIG. 2 shows a detailed circuit diagram of a first embodiment of the silent section detecting circuit of the present invention. Here, 10 is a voice input circuit such as a receiver, 200 is a voice encoding circuit that encodes voice as digital data, and 30 is a TDMA that performs transmission control and the like by associating the encoded digital data with an assigned slot. The control circuit 40 is a transmission circuit (MODE) that modulates transmission data with a carrier wave and wirelessly transmits it.
M). Further, 200a is a silent section detection circuit, which is added to the speech encoding circuit 200.

The silent section detecting circuit 200a includes a timing signal generating circuit 201 and a maximum value detecting circuit 2 which will be described in detail below.
02, a minimum value detection circuit 203, a difference calculation circuit 204, and a comparison circuit 205. Then, it is a circuit that receives the digital audio signal B, detects a silence state, and generates a silence detection signal C. Timing signal generation circuit 201
Is a circuit which receives the sampling clock CLK, divides it, and generates a timing signal T consisting of a pulse for each section of a time width corresponding to one slot. Upon receiving this timing signal T, each circuit in the silent section detection circuit 200a is initialized, and the silent detection signal C is also output in synchronization with this timing signal T.

The maximum value detection circuit 202 selects a comparator, which compares the current sampling value and the maximum value up to the present time point, and selects the larger one of the current sampling value and the maximum value up to the current time point according to the comparison result. And a latch that holds the maximum value up to the present time by latching the value selected by the selector. As a result, the maximum value of the audio signal B in the slot-corresponding section is detected and sent to the difference circuit 204 as the maximum value signal Bm.

The minimum value detection circuit 203 selects a smaller one of the current sampling value and the minimum value up to the present time according to the result of the comparison, and a comparator for comparing the current sampling value with the current minimum value. And a latch that holds the minimum value up to the present time by latching the value selected by the selector. As a result, the minimum value of the audio signal B in the section corresponding to the slot is detected and sent to the difference circuit 204 as the minimum value signal Bn.

The difference calculation circuit 204 receives the maximum value signal Bm and the minimum value signal Bn, and outputs a difference signal Bd having the difference between the values of these signals to the comparison circuit 205. Since the difference between the maximum value and the minimum value is thus taken, the DC components contained in the audio signal B cancel each other out. Therefore, the value of the differential signal Bd no longer contains the DC component contained in the audio signal B. That is, the influence of the offset is removed. In addition, the section corresponding to the slot,
For example, in the section of about 5 ms, the audio signal B has a substantially vertically symmetrical waveform. Therefore, the difference signal Bd indicates the maximum amplitude of the audio signal B in the section.

The comparison circuit 205 compares the threshold value Y corresponding to the amplitude level of the voice to be transmitted with the value of the difference signal Bd. Thereby, it is possible to detect whether or not the audio signal B contains the audio of the level to be transmitted. Therefore, according to the comparison result, “true” is adopted when the value of the difference signal Bd, that is, the maximum amplitude value within the section of the digital audio signal B is a value corresponding to the silent state, and otherwise it is “false”. A logic signal that takes a value is generated. And
If the value of this logic signal is "true" when receiving the timing signal T, the silence detection signal C is sent to the TDMA control circuit 30.
Send to The correspondence relationship of this logic is arbitrary.

Under such a configuration, the voice of the speaker is input to the voice input circuit 10 and sent as the analog voice signal A to the voice encoding circuit 200. In the audio encoding circuit 200, the analog audio signal A is subjected to analog-digital conversion by the A / D conversion circuit 21 at the timing of the sampling clock CLK to be a digital audio signal B, which is directly or encoded and then sent to the TDMA control circuit 30. Sent out. Furthermore, the silence section detection circuit 200a of the speech encoding circuit 200 receives the digital speech signal B, and when it is in the silence state within the section corresponding to one slot, sends the silence detection signal C to the TDMA control circuit 30.

The TDMA control circuit 30 which has received the digital audio signal B, when not receiving the silence detection signal C,
The transmission data D is wirelessly transmitted to the master station (not shown) via the transmission circuit 40. On the other hand, when the silence detection signal C is also received, the transmission data D is thinned out. Since this silence detection signal C is not easily affected by the offset and noise as described above, the thinning efficiency of the VOX control is improved. In addition, when the clear voice is recognized, the silence detection signal C is not output, so that the original call is not spoiled. In this way, for slots that do not contain effective voice, the transmission is efficiently thinned out, so that it is possible to effectively reduce the battery consumption of the portable handset or the like.

FIG. 3 is a detailed circuit diagram of the second embodiment of the silent section detecting circuit. The block diagram and the application example to the transmission circuit are the same as those obtained by replacing the maximum value detection circuit with the quasi-maximum value detection circuit in the block diagram of FIG. 1 and replacing the minimum value detection circuit with the quasi-minimum value detection circuit. Omit. As the quasi-maximum value and quasi-minimum value, a value having the nth magnitude or the smallest value from the maximum value and the minimum value is adopted.

For example, assuming a standard case in which the ratio of sporadic noise spikes mixed in is about 1% and the number of samplings in a section is 40, (40/10
The minimum integer value of 0 + 1) or more, that is, "2" is a specific value of n. The circuit of the second embodiment in FIG. 3 is an example corresponding to this n = “2”. Thereby, the influence of sporadic noise can be reduced. The operational effect of the second embodiment is the same as that of the first embodiment except for the replacement and effect of the detection circuit described above, and the detailed description thereof will be omitted.

[0022]

As can be understood from the above description, in the present invention, the difference between the maximum value (or quasi-maximum value) and the minimum value (or quasi-minimum value) in the section corresponding to one slot is calculated. The calculation is performed so that the offset (or offset and sporadic noise) component included in the audio signal is not included in the amplitude value to be compared. Then, the amplitude value is compared with a predetermined threshold value, and a silence detection signal is generated according to the comparison result.
Therefore, even if the offset (or offset and single / sporadic noise) component is included in the audio signal,
The effect is reduced, and the silence interval detection signal is not suppressed by itself. As a result, the thinning efficiency in the VOX control of the TDMA control system is improved, and the battery consumption of the device adopting the circuit of the present invention can be effectively saved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a transmission circuit to which a first embodiment of a silent section detection circuit of the present invention is applied.

FIG. 2 is a detailed circuit diagram of the first embodiment of the silent section detection circuit of the present invention.

FIG. 3 is a detailed circuit diagram of a second embodiment of the silent section detection circuit of the present invention.

FIG. 4 is an application example of a conventional silence section detection circuit.

[Explanation of symbols]

 10 voice input circuit 20 voice encoding circuit 20a silence section detection circuit 21 A / D conversion circuit (A / D) 30 TDMA control circuit 40 transmission circuit (MODEM) 200 voice encoding circuit 200a silence section detection circuit 201 timing signal generation circuit 202 maximum value detection circuit 203 minimum value detection circuit 204 difference calculation circuit 205 comparison circuit

Claims (3)

(57) [Claims] 1. A digital voice signal sampled to be a transmission target in a TDMA (Time Division Multiple Access) control system, to be transmitted within a fixed time width section corresponding to a slot of the TDMA control system. In a mobile communication telephone having a silent period detection circuit for generating a silent period detection signal indicating that the maximum value of the digital voice signal in the period is detected by receiving the digital voice signal. A value detection circuit, a minimum value detection circuit that receives the digital audio signal and detects a minimum value of the digital audio signal in the section, receives the maximum value and the minimum value, and sets a difference between these values as a value. A differential circuit that outputs a differential signal, and a level at which the amplitude level of the digital audio signal corresponds to either a silent state or a voiced state. And a comparison circuit that receives a predetermined threshold value for determining whether the difference signal is equal to or less than the threshold value and outputs the silence section detection signal when the value of the difference signal is less than or equal to the threshold value. A mobile communication telephone having a circuit. 2. A digital voice signal sampled to be a transmission target in a TDMA (Time Division Multiple Access) control system, to be transmitted within a period of a constant time width corresponding to a slot of the TDMA control system. In a silence interval detection circuit for generating a silence interval detection signal indicating that the digital audio signal is not included, a maximum value detection circuit for detecting the maximum value of the digital audio signal in the interval, the digital A minimum value detection circuit that receives an audio signal and detects a minimum value of the digital audio signal in the section, and a difference that outputs a difference signal that receives the maximum value and the minimum value and has a difference between these values as a value. And a circuit for determining whether the amplitude level of the digital audio signal corresponds to a silent state or a voiced state. And a difference circuit that receives a constant threshold value and the difference signal and outputs the silence section detection signal when the value of the difference signal is less than or equal to the threshold value or less than the threshold value. 3. The digital voice signal sampled to be transmitted in the TDMA control method does not include a voice to be transmitted within a fixed time interval corresponding to a slot in the TDMA control method. In the silent section detection circuit for generating a silent section detection signal, the nth section (n is an integer larger than “1” and the frequency of noise occurrence) for the digital sound signal in the section upon receipt of the digital sound signal. Is a number that is determined according to the above), and a quasi-maximum value detection circuit that detects a quasi-maximum value of a large value, and a n-th smallest value of the digital audio signal in the section that receives the digital audio signal. A quasi-minimum value detection circuit that detects a quasi-minimum value, and outputs a difference signal that receives the quasi-maximum value and the quasi-minimum value and that has a difference between these values as a value. A difference circuit that receives the difference signal and a predetermined threshold value for determining whether the amplitude level of the digital audio signal is a level corresponding to a silent state or a voiced state. A comparison circuit that outputs the silence interval detection signal when the value is less than or equal to the threshold value or less than the threshold value.