JPH0282859A - Modem equipment - Google Patents

Abstract

PURPOSE:To suppress the change in a control state due to effect of noise more than the case with a conventional equipment by discriminating the stage to be momentary interruption when a correction command by a prescribed small gain correction is changed into a correction command by a prescribed large gain correction and fixing the control state of an equalizer to the state at that point of time. CONSTITUTION:A reception signal amplitude discrimination section 6 outputs a control data (f) of high speed AGC UP when the output of an AGC1A is not recovered even when many number of times of the control data (f) of the low speed AGC UP. In this case, the AGC1A outputs a momentary interruption detection signal i' and gives it to a DSSP15. An error signal switching section 7A of the BSSP15 uses the momen tary interruption detection signal i' to give difference information of 0 to an equalizer and phase control section 3 as control coefficient information (g). Then the section 7A receiving the FCD signal (i) ON from the reception signal amplitude discrimination section 6 gives the difference information outputted from an error detection section 8 to the equalizer and phase control section 3 as control coefficient information (g). Since the momentary interruption is coped with earlier than the control based on an FDC signal in this way, the change in the control state due to the effect of noise is suppressed more than that of a conventional equipment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a modem device used in a line such as a telephone line where instantaneous signal interruption is unavoidable.

(Prior Art) When transmitting a digital signal via a communication line, a modem device modulates the digital signal, sends it out, and demodulates the signal on the receiving side to obtain the original digital signal. By the way, as shown in FIG. 5, the modem reception section includes an auto gain control circuit (hereinafter referred to as AGC) 1, a demodulation section 2, an equalizer and phase control section 3, a code determination section 4, and an audio signal control section ( It consists of a digital speech processor (hereinafter referred to as DSSP) 5.

DSSP 5 includes a received signal amplitude determination section 6 and an error signal switching section 7.
, an error detection section 8, etc.

The AGCI outputs a signal by controlling the gain of the received signal a so that it is at an appropriate level according to its level fluctuation, and when it receives control digital data from the DSSP 5, it adjusts the gain by the amount corresponding to the data. The above data can be changed, such as low speed AGC up, low speed AGC down, high speed AGC up, and high speed AGC.
There are 4 types of down modes available. When receiving data indicating a low-speed AGC up mode, increase the gain by a predetermined value, for example, equivalent to 1 dB, and when receiving data indicating a low-speed AGC down mode, increase the gain by a predetermined value, for example, by an amount equivalent to 1 dB. For example, if you receive data indicating a high-speed AGC up mode, you may want to lower the gain by an amount equivalent to 1 dB, for example, 1 odB.
In order to increase the gain by a corresponding amount, high-speed AG
When it receives data indicating the C-down mode, it has a function of amplifying and outputting the received signal by controlling the gain so as to lower the gain by a predetermined amount equivalent to, for example, 10 dB. The demodulator 2 demodulates the signal output from the AGCI. Furthermore, the equalizer and phase control unit 3 is for keeping the signal distortion within the tolerance value and correcting the phase distortion, and it performs control according to the control coefficient given from the DSSP 5. .

Further, the sign determination unit 4 determines whether the signal C output from the equalizer and phase control unit 3 corresponds to rHJ or rLJ of the digital signal, and depending on the determination result, rHJ or rLJ This signal (digital signal) is output as e and given to the terminal.

The received signal amplitude determination unit 6 in the DSSP 5 compares the ACCI output at a predetermined period (for example, 100 ops) using a predetermined threshold level as a reference value, and determines the A
When the output of the GCI is below the reference value, control data for low-speed AGC up is output, and even if the control data for low-speed AGC up is output a predetermined number of times, when the output of the AGCI is below the reference value, the GC is increased to high speed. When the AGCI output exceeds the reference value,
Control data for low-speed AGC down is output at the predetermined period, and when the output of AGC1 exceeds the reference value even after the control data for low-speed AGC down is output a predetermined number of times, high-speed AGC is output.
In addition to the control function of switching to down control data and outputting it, it also has a control function of turning off the FCD signal (early carrier detection signal) i when the maximum output signal level of AGCl is below the reference value for a predetermined period of time. It is something. Further, the error detection section 8 takes the signal level difference between the output d of the equalizer and phase control section 3 and the output e of the sign determination section 4, and outputs the difference information. 7 usually gives this difference information as control coefficient information g to the equalizer and phase control section 3, and while receiving the FCD signal, it is set to 0.
It has a function of providing difference information as control coefficient information g to the equalizer and phase control section 3.

In such a configuration, upon receiving the received signal a, the AGC
I responds to received signal a according to its level fluctuation.

The signal is then amplified with a set gain value received from the DSSP 5 at that time to return it to its proper original level and then output. That is, assuming that the level of the output of AGCl is decreasing, the received signal amplitude determination section 6 of the DSSP 5 determines the amplitude of A at a predetermined period.
Since we are checking the GCI output level, the AGCI
When it is detected that the output level of is lower than the reference value, control data f for low-speed AGC up is output each time the above check is performed. As a result, the AGCI increases the gain by, for example, 1 dB each time it receives the low-speed AGC-up control data f. Conversely, when the output of ACCI exceeds the reference value, control data f for slow AGC down is output each time the above check is performed. As a result, the AGCI lowers the gain by, for example, 1 dB each time it receives the low-speed AGC down control data f. In this way, the AGC 1 controls the received signal a so that the maximum amplitude value becomes a predetermined level.

Furthermore, if the level does not recover even after outputting the control data f for low-speed AGC up a predetermined number of times, the received signal amplitude determination section 6 outputs the control data f for high-speed AGC up from the next time. Become. Then, the AGCI receives, for example, 10
Increase the gain by dB. The high-gain amplified output signal of AGCl is demodulated by a demodulator 2 and then input to a phase controller 3, where it is equalized and phase-controlled. Then, the output d of the phase control unit 3 passes through the sign determination unit 4, and the sign determination unit 4 determines rHJ, r
It is converted into a LJ signal and becomes a digital signal e. Here, in the DSSP 5, the error detection section 8 calculates the signal level difference between the output d of the phase control section 3 and the output e of the sign determination section 4, and outputs the difference information. This difference information is input to the error signal switching section 7, and the error signal switching section 7 normally supplies this difference information to the equalizer and phase control section 3 as control coefficient information g. The phase control section 3 performs equalization control and phase control on the input signal C, such as distortion->a, according to the control coefficient information g, and supplies the input signal C to the sign determination section 4. As a result, even if there is a level fluctuation or distortion in the received signal a, it is possible to correct this, convert it into a target digital signal, and provide it to the terminal.

By the way, as shown in FIG. 6, even if the received signal amplitude determination unit 6 outputs the control data f for high-speed AGC
If the output does not recover, the FDC signal i is turned off (t2) after a predetermined time has elapsed (this is, of course, a certain amount of time after outputting the control data f for high-speed AGC up). When the error signal switching unit 7 receives the FCD signal signal f from the received signal amplitude determination unit 6, while receiving the FCD signal signal f, the error signal switching unit 7 uses the difference information of 0 as control coefficient information g to the equalizer and phase control unit. Give to 3.

Therefore, the equalizer and phase control unit 3 fixes the control condition to the state at the time t2 using the control coefficient information g of O.

Here, as mentioned above, when the maximum output of the AGCI is below the reference value even after the FCD signal predetermined time has elapsed,
This is turned off by the received signal amplitude determination unit 6, which checks the output level of the AGCI at a predetermined period, and when the output level of the ACCI falls below the reference value, the low-speed AGC is turned up each time the above check is performed. control data f
When the control data f for low-speed AGC up is output for a predetermined number of times, the control data f for high-speed AGC up will be output from the next time. This is a signal output from the received signal amplitude determination section 6 after a predetermined period of time has elapsed.

This FCD signal is used here as a momentary interruption detection signal.

Even if the AGCI output drops below the reference value, there may be a temporary drop due to fluctuations in the transmission system, so it is not necessarily a momentary line interruption, and therefore the AGCI output may drop below the reference value.
Since it is not possible to immediately conclude that a momentary power outage has occurred when the output of the FDC falls below the reference value, the FDC should monitor the gain-controlled output signal for a while and then notify the FDC of a no-signal state (momentary power outage). Conventionally, the signal of signal OFF is used for momentary power interruption detection. However, in this case, as shown in Fig. 6, this FC
Before the D signal turns off, a time Tb has elapsed, during which time sampling has been repeated several times and data from several high-speed AGC ups has been given to ACCI. Even if the time when AGC up occurs is tl, the gain has already been increased by the number of times the AGCI has received high-speed AGO up data for a period of time Ta, and the gain has become high even though there is no signal. The output of ACCI is only the amplified noise component. Therefore, even if g becomes 0 at time 12, the phase control unit 3 and other domains that have received the difference output from the error detection unit 8 as a control coefficient during that time will perform control using the control coefficient based on the amplified noise. Even if the control coefficient is fixed at the 12th point, the control coefficient will be a completely random control coefficient, and then the instantaneous interruption will be recovered and the received signal will be input normally. However, the phase control unit 3 cannot perform normal geometric ratio control and phase control. Therefore, the received data from the received signal after the momentary interruption becomes a mess, resulting in a communication error.

(Problem to be solved by the invention) When a modulated signal is received, the loss of the signal due to line conditions is called a momentary interruption, but it is difficult to avoid data loss in communication lines such as telephone lines where instantaneous interruptions in the transmission system are unavoidable. In conventional modem devices used for communication, as mentioned above, the receiving system adjusts the level of the received signal, demodulates it, equalizes and controls the phase using an equalizer and a phase control section, and then The code was determined and digitized. Then, the DSSP, which is the control center that performs various processing on such audio signals, monitors the AGC output at a predetermined cycle, and depending on whether it is lower or higher than a predetermined reference value, performs low-speed AGC at each cycle. If you give up or down control data to the AGC and it does not recover even after repeating this several times, give control data indicating the high speed AGC up or down mode and control the AGC gain much more than in the case of low speed. Set it high and control it to reach the desired level quickly. However, if it still does not recover, it is determined that there is no signal. During this time, the equalizer and phase control section are controlled in accordance with the input/output difference of the sign determination section when there is no signal, and the AGC is subjected to high-speed AGC up control, so the equalizer And the phase control section has to variable control the above control coefficient in response to a large noise level, and even if it is fixed to the control coefficient at that time when the instantaneous interruption is detected, this is based on high level noise, so it is not practical. The signal is far from that of the current signal, and normal operation cannot be expected when the instantaneous power outage is recovered.

In other words, the equalizer and phase control section must be made to function normally after the momentary signal loss recovers, but in conventional modem equipment, the equalizer and phase control section must function normally when the signal is interrupted. The control state at that point is maintained, and when the signal resumes operation after the signal is restored, the control operation is started from the control state held at the time of detection of this instantaneous interruption, and the determination of instantaneous interruption is made by having AGC at the front stage. Above, gain control by AGC is performed using FCD (early carrier detection signal), which is turned off when it is confirmed that the signal level does not recover even if gain control is performed, so the gain of AGC is large, etc. The equalizer and phase control unit have to perform variable control of the control coefficients based on a large noise level, and when the instantaneous power outage is detected, the control coefficients are fixed at that point, and when the instantaneous power outage is recovered, the equalization 9 is performed from this state. Even if phase control is started, normal operation cannot be expected.

Therefore, an object of the present invention is to enable instantaneous interruption detection to be performed quickly within a range that does not cause any hindrance, and thereby to reduce the amount by which the control coefficients of equalizers and the like are influenced by noise. An object of the present invention is to provide a modem device that enables normal operation after recovery from a power failure.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention is configured as follows. That is, the received signal is level-adjusted via an auto gain control circuit, demodulated by a demodulator, equalized by an equalizer according to the coefficients, and the signal after this equalization is sent to a sign determination means. In addition, the output of the auto gain control circuit is monitored and when the output level deviates from a predetermined level, a correction is commanded by a small predetermined amount of gain correction, and a predetermined number of times. If the correction command is not recovered even after repeating the correction command, the next correction command for the same correction direction is switched to a correction command that provides a large predetermined correction amount, and the level difference between the input/output signals of the sign determining means is monitored. In the modem device, the modem device includes a control function that generates a control coefficient according to the difference between the signals and applies it to the equalizer, and a carrier detect function that determines the presence or absence of a signal from a change in the level of a received signal. When a correction command giving the large predetermined correction amount is given as a command, the control coefficients of other domains such as those mentioned above are fixed to the state at that time, and when the carrier detect function determines that there is a received signal, It is configured by adding an instantaneous interruption control means for releasing this fixation.

(Function) In such a configuration, the control means monitors the output of the auto gain control circuit, and when the output level deviates from a predetermined level, the control means commands a correction by a small (1 predetermined gain correction amount) and If the correction command is not recovered even after repeating this correction command a predetermined number of times, the next correction command for the same correction direction is switched to a correction command that provides a large predetermined correction amount, and the signal level input to the demodulator reaches the reference value. The input/output of the sign determining means is controlled so as to be maintained.
A level difference between the output signals is monitored, a control coefficient corresponding to the difference is generated, and the control coefficient is supplied to the equalizer to perform equalization control corresponding to the control coefficient. When an instantaneous interruption occurs, the level does not recover even if a correction command for a predetermined gain correction amount is executed several times, so the control means changes the correction command to a correction command that gives the large predetermined correction amount. . As a result, the instantaneous interruption control means fixes the control coefficient of the equalizer to the state at that time, and releases this fixation when the gear 1 nor detect function in the control means determines that there is a received signal. In this way, a momentary interruption is determined at the stage of switching from a correction command for a small predetermined gain correction amount to a correction command for a large predetermined gain correction amount, and the control state of other domains is fixed to the state at that point. Therefore, since the state of the other domain can be fixed at a stage where the gain of the auto gain control circuit is small, changes in the control state due to the influence of noise can be suppressed more than before. Therefore, according to the present invention, instantaneous power outage detection can be performed quickly without any hindrance, and as a result, the amount of movement of the control coefficients affected by noise can be suppressed to a smaller value than in the past. Therefore, it is possible to provide a modem device that can operate normally after recovery from a momentary interruption.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. As shown in FIG.
It is composed of an IA1 demodulation section 2 (referred to as AGC), a phase control section 3, a code determination section 4, and an audio signal control section (digital φ speech processor; hereinafter referred to as DSSP) 15.

The DSSP 15 includes a received signal amplitude determination section 6, an error signal switching section 7A, an error detection section 8, and the like.

The A G CIA outputs a signal by controlling the gain of the received signal a to return it to the proper original level according to the level fluctuation, and outputs the signal from the DSSP 15 using digital data for control (hereinafter referred to as control data). When received, the gain characteristics and gain can be changed according to the data, and the above data can be used in four types of modes: low speed AGC up, low speed AGC down, high speed 〇〇 up, and high speed AGC down. . When receiving data indicating the mode of low-speed AGC up, a predetermined setting such as 1 d
If data indicating a mode of 〇〇down to low speed is received, the high-speed AGC is set so that the gain is increased by an amount equivalent to 1 dB. When receiving data indicating an up mode, increase the gain by a predetermined amount equivalent to, for example, 10 dB, and when receiving data indicating a high speed AGC down mode, increase the gain by a predetermined amount, for example, 10 dB. It has a function to amplify and output the received signal by controlling the gain so as to reduce the gain by a corresponding amount, and when it receives data indicating the high-speed AGC up mode, it sends this to the DSSP15 as an instantaneous interruption detection signal i'. It has a function to output. Moreover, the demodulator 2 uses this A G CIA
This is to demodulate the signal output from the The phase control unit 3 is for keeping the signal distortion within the allowable value and correcting the phase distortion, and this is done according to the control coefficient given from the DSS P 15. Implement specific controls. Further, the sign determination unit 4 determines that the signal C output from the phase control unit 3 is a digital signal r.
It is determined whether the signal corresponds to HJ or rLJ, and depending on the determination result, it is output as a signal (digital signal) e indicating whether it is rHJ or rLJ and is given to the terminal.

The received signal amplitude determining unit 6 in the DSS P 15 compares the output of the A G CIA with a predetermined threshold level as a reference value at a predetermined period (for example, 100 as), and determines whether the output of the A CCIA is the reference value. When the value is lower than the value, low-speed AGC up control data is output, and even if this low-speed AGC up control data is output a predetermined number of times, A
When the G CIA output falls below the reference value, it switches to high-speed AGC up control data and outputs it, and also outputs the A
When the output of A exceeds the reference value, the control data of 〇〇down to low speed is output at the above-mentioned predetermined period, and this low-speed AG is
In addition to the control function of switching to high-speed AGC down control data and outputting it when the A G CIA output exceeds the reference value even if C down control data is output, the A G CIA output signal is output for a predetermined period of time. FCD signal (early carrier detection signal) i when the maximum level value is below the reference value
It has a control function to turn off the Further, the error detection section 8 takes the signal level difference between the output d of the equivalent signal and phase control section 3 and the output e of the sign determination section 4, and outputs the difference information. 7A usually supplies this difference information as control coefficient information g to the equalizer and phase control section 3, and when it receives the instantaneous interruption detection signal i', the difference information becomes 0 as a control coefficient until the FCD signal turns on. information g
It has a function to provide to the equalizer and phase control section 3 as described above.

In such a configuration, when receiving signal a is received, A C
The CIA receives the received signal a from the DSSPL 5 at that time, amplifies it with a set gain value, and outputs the amplified signal to an appropriate level according to the level fluctuation.

In other words, if the level of the output of the A G CIA is decreasing, the received signal amplitude determining section 6 of the DSSP 15 checks the output level of the A G CIA at a predetermined period, so the output level of the A G CIA is equal to the reference value. If it is detected that the value is lower than the above value, control data f for low-speed AGC up is output each time the above check is performed. As a result, A.G.C.
The IA increases the gain by, for example, 1 dB each time it receives the control data f for slow AGC up.

Conversely, when the output of the AG CIA exceeds the reference value, the control data f for slow AGC down is output each time the above check is performed. From this step 1, the A G CIA lowers the gain by, for example, 1 dB each time it receives the low-speed AGC down control data f. In this way, the AG CIA controls the received signal a so that the maximum amplitude value becomes a predetermined level.

Furthermore, if the level does not recover even after outputting the control data f for low-speed AGO up a predetermined number of times, the received signal amplitude determination section 6 outputs the control data f for high-speed AGC up from the next time. Become. For example, each time ACCIA receives high-speed AGC up control data f,
Increase the gain by OdB. The high-gain amplified output signal of the AG CIA is demodulated by the demodulator 2 and then input to the phase controller 3, where it is equalized and phase-controlled. Then, the output d of the phase control section 3 passes through the sign determination section 4, and the sign determination section 4 outputs "H" according to the frequency of the input signal d.

It is converted into an "L" signal and becomes a digital signal e.

Here, in the D S S P 15, the error detection section 8 calculates the signal level difference between the output d of the phase control section 3 and the output e of the sign determination section 4, and outputs the difference information. This difference information is input to the error signal switching section 7A, and the error signal switching section 7A normally supplies this difference information to the equalizer and phase control section 3 as control coefficient information g. The phase control unit 3 performs equalization control and phase control on the input signal C for the amount of distortion, etc. according to the control coefficient information g, and provides the result to the sign determination unit 4. As a result, even if there is a level fluctuation or distortion in the received signal a, it is possible to correct this, convert it into a target digital signal, and provide it to the terminal.

By the way, as shown in FIG. 2, even if the received signal amplitude determination section 6 outputs the low-speed AGC up control data
When the GCIA output does not recover, control data f for high-speed AGC up is output (time t1 in FIG. 2).

When this high-speed AGC up control data f is received, A
G CIA outputs instantaneous interruption detection signal i' and DSSP15
Therefore, the error signal switching unit 7A of the DSSP 15 uses this instantaneous interruption detection signal i' to provide difference information of 0 to the equalizer and phase control unit 3 as control coefficient information g. Then, when the received signal amplitude determination section 6 subtracts the FCDCD signal, the difference information output from the error detection section 8 is again given to the equalizer and phase control section 3 as control coefficient information g.

Therefore, the control state of the phase control unit 3 is fixed at the time (tl) when the high-speed AGO up control data f is output, and the control state is based on the control coefficient information g output from the error detection unit 8 upon recovery from the instantaneous interruption. Move to control.

In this way, to set the AGC gain, the DSSP
When the output level of the AGC deviates from the standard, a correction command corresponding to a small predetermined gain correction amount is issued, and if the AGC output does not recover even after repeating this several times, the large predetermined correction is issued as the correction command. We focused on changing the correction command to a correction command that gives a certain amount of gain, and found that when an instantaneous interruption (at time tO) occurs, the level does not recover even if the correction command for the small predetermined gain correction amount is executed several times, and eventually the DSSP When the modification command changes to a modification command that gives the large predetermined modification amount (tl), the control coefficients of the equalizer and phase control section are fixed to the state at that time, and when the FDC signal is turned on, This fixation is released. In this way, there is an instantaneous interruption at the stage of switching from a correction command for a small predetermined gain correction amount to a correction command for a large predetermined gain correction amount, and the control state of the other domain is fixed to the state at that point. Since the state of other domains can be fixed earlier than the time point (t2) when the FDC signal is generated, and at a stage when the gain of the auto gain control circuit is small, it is possible to deal with instantaneous interruptions earlier than with control based on the FDC signal. Therefore, changes in the control state due to the influence of noise can be suppressed more than before. Therefore, according to the present invention, instantaneous power outage detection can be performed quickly without any hindrance, and as a result, the amount of movement of the control coefficients affected by noise can be suppressed to a smaller value than in the past. Therefore, normal operation is possible after recovery from a momentary interruption.

In the above embodiment, the A G CIA is configured to generate an instantaneous interruption detection signal i'' based on high-speed AGC up data, and the DSSP'15 is configured to generate an F upon receiving this instantaneous interruption detection signal i.
Although the configuration includes an error signal switching section 7A that sets the control coefficient to 0 until the DC signal is turned on, the AGC remains the same as the conventional configuration as shown in FIG. 3, and the received signal amplitude determination section 6 It is also possible to provide a function of generating an instantaneous interruption detection signal i- together with high-speed AGC up data.Also, as shown in Fig. 4, the basic configuration is the same as the conventional example shown in Fig. 5, and the reception High-speed AGC output from signal amplitude determination section 6
Instantaneous interruption detection circuit 2 that detects instantaneous interruption when receiving uploaded data
1 and the output signal of the instantaneous interruption detection circuit 21 sets the control coefficient information g to 0, and when the control coefficient information g output from the error signal switching section 7 changes from 0 to a value other than 0, the error signal A configuration may also be provided in which a switch 22 for selecting the control coefficient information g output from the switching section 7 and providing it to the other domain and the phase control section 3 is attached externally.

〔Effect of the invention〕

In this way, the present invention causes an instantaneous interruption at the stage of switching from a correction command for a small predetermined gain correction amount to a correction command for a large predetermined gain correction amount, and fixes the control state of the other domain to the state at that point. Therefore, the state of other domains can be fixed when the gain of the auto gain control circuit is small.
Since instantaneous interruptions can be dealt with earlier than in control based on FDC signals, changes in the control state due to the influence of noise can be suppressed more than before. Therefore, according to the present invention, instantaneous power outage detection can be performed quickly without any hindrance, and as a result, the amount of movement of the control coefficients affected by noise can be suppressed to a smaller value than in the past. Therefore, it is possible to provide a modem device that can operate normally after recovery from a momentary interruption.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a receiving section of a modem device according to the present invention, FIG. 2 is a time chart for explaining its operation, and FIGS. 3 and 4 are block diagrams showing other embodiments of the present invention. 5 is a block diagram showing a conventional example, and FIG. 6 is a time chart for explaining its operation. 1. LA...Auto gain control circuit (AG
C), 2... demodulation unit, 3... etc. and phase control unit, 4... code determination unit, 5.15... audio signal control unit (digital speech processor, DSSP), 8
．． 6A...Received signal amplitude determination unit, 7.7A...Error signal switching unit, Error detection unit, 21...Momentary interruption detection circuit, 22...Switcher. Figure 3

Claims (1)

[Claims] The received signal is level-adjusted via an auto gain control circuit, demodulated by a demodulator, equalized according to the coefficients by an equalizer, and the signal after this equalization is converted into a digital signal by a sign determination means. The output of the auto gain control circuit is monitored, and when the output level deviates from a predetermined level, a small predetermined gain correction amount is commanded, and this correction command is issued a predetermined number of times. If the recovery does not occur even after repeating this, the next modification command for the same modification direction is switched to a modification command that provides a large predetermined modification amount, and the level difference between the input/output signals of the sign determining means is monitored and a control function that generates a control coefficient according to the difference and applies it to the equalizer;
and a modem device equipped with a control means having a carrier detect function that determines the presence or absence of a signal based on a level change of a received signal, when a modification command giving the large predetermined modification amount is given as the modification command, the equalization 1. A modem device comprising: a momentary interruption control means for fixing a control coefficient of a device at a current state and releasing the fixation when the carrier detect function determines that there is a received signal.