JPH08107464A - Base band device - Google Patents

Abstract

PURPOSE: To improve the sound quality of the base band device and to accelerate communication speed. CONSTITUTION: When a changeover switch 33 is connected to the side of nc and a MODEM 6a is operated as a high-speed MODEM, a data input signal Din is converted into a modulated signal S6A by the MODEM 6A and inputted to an LPF 27. The modulated signal S6A is outputted through an adder 3A to an output terminal 4 as a MODEM signal S27 after its unwanted high frequency component higher than 2100Hz is removed by the LPF 27. In this case, the adder 3A passes only the MODEM signal S27 but does not pass any voice signal S22. On the reception side, the unwanted high frequency component of a received input signal Min higher than 2100Hz is removed through an LPF 29 and it is converted into the digital data of a received data signal Dout by the demodulating part of the MODEM 6A and outputted to an output terminal 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a baseband device used for mobile phones and the like for transmitting and receiving voice signals and data signals.

[0002]

2. Description of the Related Art Conventionally, techniques in such a field include:
For example, some documents were described in the following documents. Reference: Japanese Patent Laid-Open No. 63-198466 FIG. 2 is a configuration block diagram showing an example of the configuration of the conventional baseband device described in the above reference. This baseband device includes an input terminal 1 for inputting a voice input signal Ain for transmission. The input terminal 1 is a band elimination filter (BEF) 2
Of the BEF2 is connected to the first input side of the adder 3, and the output side of the adder 3 is connected to the output terminal 4 which outputs the output signal Mout for transmission.

An input terminal 5 for inputting a data input signal Din for transmission is a modulator / demodulator (modulator demodulator,
The output terminal of the modulation unit of the modem 6 is connected to the input side of a band pass filter (hereinafter, referred to as BPF) 7, and the output of the BPF 7 is connected. The side is connected to the second input side of the adder 3. The BEF2 and the BPF7 are designed so that their frequency bands do not overlap. Received signal Min
The input terminal 8 for inputting is input to the input side of the BPF 9 and the input side of the BEF 10. BPF
The output side of 9 is connected to the input terminal of the demodulation section of the modem 6,
The output terminal of the demodulation section of the modem 6 is connected to the output terminal 11 which outputs the received data signal Dout. The output side of the BEF 10 has an output terminal 12 for outputting an audio output signal Aout.
It is connected to the. The BPF 9 and the BEF 10 are designed so that their frequency bands do not overlap. The modem 6
CCITT Recommendation V. 21 in accordance with the high group frequency (17
Frequency modulation of 50 ± 100Hz) is used.

Next, the operation of the baseband device shown in FIG. 2 will be described. The audio input signal Ain input to the input terminal 1 is B
It is input to the first input side of the adder 3 via EF2. or,
The data input signal Din is modulated by the modulator of the modem 6 and becomes a modulated signal, which is input to the second input side of the adder 3 via the BPF 7. The adder 3 outputs the output signal of BEF2 and the BPF.
7 and the output signal of 7 are added and the output signal Mout for transmission is output. On the other hand, the received signal Min input to the input terminal 8 is
The received data signal Dout is output from the demodulator of the modem 6 after being input to the demodulator of the modem 6 via the BPF 9 and demodulated. Further, the received signal Min becomes the audio output signal Aout via the BEF 10.

[0005]

However, the conventional baseband device has the following problems. That is, since the voice input signal Ain passes through the BEF2 and the BEF10 until the voice input signal Ain becomes the voice output signal Aout, the required band 1750 ± 150 Hz of the modem signal in the voice band (300 Hz to 3.0 kHz) of the voice input signal Ain. However, there is a drawback that the frequency component of is removed and the sound quality is deteriorated.
Further, the baseband device of FIG. 2 is an optimum device for wired communication, but an optimum modem is not used for wireless communication. Further, in the above-mentioned baseband device, the data communication speed is 300 bps, but depending on the situation, if only data communication is to be carried out at a higher speed, it is necessary to prepare a high-speed modem separately from the modem 6. However, there is almost no part where the high-speed modem can be used also as the modem 6, and there is a drawback that the size of the device becomes large. Further, when the confidential function is added to the baseband device shown in FIG. 2, the frequency band of 1750 ± 150 Hz removed by BEF2 is converted into the frequency band of 1550 ± 150 Hz by the restoration circuit. That is, when the confidential talk function is added, the conventional baseband device has a drawback that the frequency band removed from the audio signal changes, and the sound quality is different between when passing through the secret talk circuit and when bypassing.

[0006]

In order to solve the above-mentioned problems, the first invention is provided with the following means in a baseband device for transmitting and receiving a voice signal and a data signal. That is, a first high-pass filter (hereinafter referred to as HPF) that removes a frequency component lower than a predetermined cutoff frequency from a voice input signal for transmission.
A modulator for modulating a data signal for transmission at a frequency based on a clock to convert it into a modulated signal, and a cutoff frequency higher than the cutoff frequency of the first HPF is determined based on the clock, and the cutoff frequency is determined from the modulated signal. The first low pass filter (Low Pass) that removes frequency components higher than the cutoff frequency.
Filter (hereinafter referred to as LPF)) and a selection unit that selects either the output signal of the first HPF or the output signal of the first LPF based on a control signal from the outside and outputs it as a transmission output signal. It is provided. Furthermore, the first HP
The first HP from the received input signal composed of the output signal of F and the signal of the same frequency band as the output signal of the first LPF.
A second HPF for outputting a received voice output signal by removing a frequency component lower than the same cutoff frequency of F
And the first LPF higher than the cutoff frequency of the second HPF.
A cutoff frequency that is the same as the cutoff frequency of the second LPF, and a second LPF that removes a frequency component higher than the cutoff frequency from the received input signal, and an output signal of the second LPF that has a frequency based on the clock. And a demodulation unit that demodulates the received data and converts it into received data.

In the second invention, the first HP of the first invention is provided.
F, the modulator of the first invention, and a cutoff frequency lower than the cutoff frequency of the first HPF are determined based on the clock,
A first LPF that removes a frequency component higher than the cutoff frequency from the modulation signal, and an adding unit that adds the output signal of the first HPF and the output signal of the first LPF are provided. Further, the second HPF of the first invention and the second HPF
A cutoff frequency that is lower than the cutoff frequency of the first LPF and is determined based on the clock, and removes a frequency component higher than the cutoff frequency from the received input signal; A demodulation unit that demodulates the output signal of the LPF at a frequency based on the clock and converts it into reception data is provided. According to a third aspect of the invention, the baseband device according to the first or second aspect of the invention is provided with a variable clock generator that varies the frequency of the clock. According to a fourth aspect of the invention, the baseband device according to the first, second or third aspect of the invention is subjected to a predetermined confidential communication process for a voice input signal.
Of the second HPF that has been subjected to the predetermined confidential processing, and a restoration circuit that performs predetermined restoration processing on the output signal of the second HPF.

[0008]

According to the first aspect of the invention, since the baseband device is constructed as described above, the voice input signal is the first HPF.
Thus, frequency components lower than the predetermined cutoff frequency are removed. The data signal is modulated by the modulator at a frequency based on the clock and converted into a modulated signal. The modulated signal is
The first LPF removes frequency components higher than the cutoff frequency. Further, either the output signal of the first HPF or the output signal of the first LPF is selected by the selection means based on the control signal from the outside and is output as the transmission output signal. On the other hand, the reception input signal has a frequency component lower than the cutoff frequency removed by the second HPF and becomes a reception voice output signal. The frequency component higher than the cutoff frequency is removed from the received input signal by the second LPF. The output signal of the second LPF is demodulated by the demodulation section at a frequency based on the clock and converted into reception data. Therefore, since the frequency band of the output signal of the first HPF overlaps the frequency band of the output signal of the first LPF, the speed of data communication by the modulation unit and the demodulation unit is made faster than before.

According to the second invention, since the frequency band of the output signal of the first HPF does not overlap with the frequency band of the output signal of the first LPF, transmission / reception of the voice signal and data communication by the modulator and demodulator are performed. And are performed simultaneously by frequency division. According to the third invention, the frequency of the clock of the first or second invention is varied by the variable clock generation unit.
Therefore, the frequency band of the output signal of the first HPF and the first
The frequency band of the output signal of the LPF is set to the case where it overlaps and the case where it does not overlap, and the same baseband device functions as both the baseband device of the first invention and the baseband device of the second invention. With. According to the fourth invention, the baseband device of the first, second, or third invention is provided with a confidential circuit and a restoration circuit, and the frequency band of the data communication by the modulator and the demodulator is set to the frequency of the voice signal. Since the frequency is lower than the lower limit frequency of the band, the sound quality does not differ when the secret circuit is passed and when it is bypassed. Therefore, the above problem can be solved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a block diagram showing a configuration example of a baseband device showing a first embodiment of the present invention, in which elements common to those in FIG. Is attached. This baseband device is provided with an input terminal 1 for inputting a voice input signal Ain for transmission, as in the conventional FIG. The input terminal 1 is connected to the input side of the first HPF 22.
The HPF 22 is a circuit that removes a frequency component lower than the cutoff frequency from the audio input signal Ain and outputs the audio signal S22. The output side of the HPF 22 is connected to the first input side of the adder 3A which is the selection means, and the output side of the adder 3A is connected to the output terminal 4 which outputs the output signal Mout for transmission. The input terminal 5 for inputting the data input signal Din for transmission is connected to the input terminal of the modulator of the modem 6A. The modulator of the modem 6A uses the data input signal Din
Has a function of generating a modulated signal S6A. The output terminal of the modulator of the modem 6A is the first LPF2.
7 is connected to the input side. The LPF 27 removes a frequency component higher than the cutoff frequency from the modulated signal S6A,
This is a circuit for outputting the modem signal S27. The output side of the LPF 27 is connected to the second input side of the adder 3A. The adder 3A has a function of selecting either the audio signal S22 or the modem signal S27 based on the control signal CONT and outputting the output signal Mout.

On the other hand, the input terminal 8 for receiving the reception input signal Min is connected to the input side of the second LPF 29 and the input side of the second HPF 30. LP
F29 is a circuit for removing a frequency component higher than the cutoff frequency from the received input signal Min, and HPF30 is a received signal M
It is a circuit that removes a frequency component lower than the cutoff frequency from in and outputs an audio output signal Aout. The output side of the LPF 29 is connected to the input terminal of the demodulation section of the modem 6A. The demodulation section of the modem 6A has a function of demodulating the output signal of the LPF 29 and generating a reception data signal Dout. The output terminal of the demodulation section of the modem 6A is connected to the output terminal 11 which outputs the received data signal Dout. HP
The output side of F30 is connected to the output terminal 12 that outputs the audio output signal Aout. The input terminal 31 for inputting the clock signal ck is connected to the input side of a 1 / N frequency divider 32 that divides the clock signal ck into a frequency of 1 / N (N; natural number), and the normal of the changeover switch 33. It is connected to the close side (hereinafter referred to as nc). 1 /
The output side of the N frequency divider 32 is connected to the normally open (hereinafter referred to as “no”) side of the changeover switch 33. Common of changeover switch 33 (hereinafter referred to as c)
The side is connected to the clock input terminals of the modem 6A, the LPF 27, and the LPF 29. The 1 / N frequency divider 32
The changeover switch 33 constitutes a variable clock generator.

Further, the LPFs 27 and 29 are composed of switched capacitor filters (hereinafter referred to as SCFs), and the SCF clock for determining their cutoff frequencies is supplied from the c side of the switch 33. It is created from the clock signal ck. Next, FIG.
Operations (1) and (2) of the baseband device shown in FIG. (1) When the modem 6A operates as a high-speed modem In this case, the changeover switch 33 is connected to the nc side. The modem 6A is widely used for wireless data communication, for example, minimum shift keying (Minimum Shift Keyi).
ng, hereinafter referred to as MSK) type modem, and the communication speed is 1200 bps. Frequency band used is 1500 ±
Since it is 600 Hz, it is not possible to send a voice signal and a modem modulation signal at the same time. This is the same method as the conventional baseband device. In FIG. 1, the data input signal Din
Is converted into a modulated signal S6A by the modem 6A and the LPF2
Input to 7. The modulation signal S6A is output by the LPF 27 21
Unnecessary high frequency components of 00 Hz or higher are removed and output as a modem signal S27 to the output terminal 4 via the adder 3A. In this case, the adder 3A passes only the modem signal S27 and does not pass the voice signal S22. On the receiving side,
The received input signal Min is 2100 Hz via the LPF 29.
The above-mentioned unnecessary high-frequency component is removed, the demodulation section of the modem 6A converts it into digital data which is the received data signal Dout, and outputs it to the output terminal 11. The main clock signal ck of the modem 6A is supplied from the c side of the switch 33.

(2) When the modem 6 operates as a low speed modem In this case, the switch 33 is connected to the no side. Here, for example, N = 10 will be described. The frequency divider 32 works as a 1/10 frequency divider, and the communication speed and frequency band used by the modem 6A are 1/10 of those of the high speed modem of (1) above.
Becomes That is, the communication speed is 120 bps and the frequency band used is 150 ± 60 Hz. Also, the SCF clock of LPF27 and LPF29 is 1 for high-speed modems.
/ 10, and the cutoff frequencies of these LPFs 27 and 29 also become 1/10. In this case, the data input signal Din is
The modulated signal S6A is converted by the modem 6A and input to the LPF 27. The LPF 27 removes frequency components of 210 Hz or higher, and outputs the result to the output terminal 4 via the adder 3A. On the other hand, the audio input signal Ain input to the input terminal 1 is input to the HPF 22, the frequency component of 300 Hz or less is removed to become the audio signal S22, which is added to the modem signal S27 by the adder 3A and output to the output terminal 4. It

That is, as the output signal Mout, any one of the following (a) to (c) is output. (A) Only the modulation signal S27 of the modem 6A having a communication speed of 1200 bps or 120 bps. (B) Only the audio signal S22. (C) A signal obtained by adding the modulation signal S27 and the voice signal S22 of the modem 6A having a communication speed of 120 bps. On the other hand, on the receiving side, the LPF 29 removes unnecessary high frequency components of 210 Hz or more from the received input signal Min input to the input terminal 8 and converts it into digital data which is the received data signal Dout in the demodulation section of the modem 6A. It is output to the output terminal 11. At the same time, the received input signal Min is
In F30, the frequency component of 300 Hz or less is removed and output to the reception voice output terminal 12.

FIG. 3 is a spectrum diagram of the baseband device when the modem 6A in FIG. 1 is operated as a low speed modem, in which the vertical axis represents power density and the horizontal axis represents frequency. As shown in this figure, the voice signal S22 and the modem signal S27 do not overlap in spectrum. As described above, in the first embodiment, the following advantages (i)
Have (vi). (I) When the changeover switch 33 is connected to the nc side and the modem 6A is operated as a high speed modem, data communication by the modem can be performed at high speed. (Ii) When the switch 33 is connected to the no side and the modem 6A is operated as a low speed modem, the HPF 22 sets 300H.
Remove the frequency component below z and 210Hz with LPF29
Since the above frequency components are removed, the audio signal S22
And the modem signal S27 are transmitted at the same time, the LPF29
The voice signal Ain does not leak into the output signal of, and the bit error rate of the modem 6A is not deteriorated. (iii) Since the LPF 27 removes the frequency component of 210 Hz or more and the HPF 30 removes the frequency component of 300 Hz or less, the modem signal S6A does not leak into the audio output signal Aout and the sound quality is not deteriorated. This is the audio signal S2
2 and the modem signal S27 are frequency-divided and used. (Iv) Since the HPF 22 and the HPF 30 that pass the voice signal pass all of the voice band of 300 Hz to 3.0 kHz, the deterioration of the sound quality which is the conventional problem is solved. (V) Since an MSK modem can be used as the modem 6A, it is resistant to the fading phenomenon that is a phenomenon unique to wireless communication. (Vi) A low-speed modem for simultaneously performing data communication and voice communication and a high-speed modem for only data communication can be realized by simply switching the switch 33. Therefore, most of the circuit can be shared and the scale of the device can be increased. Can be made smaller. That is, the size of the chip when the baseband device of this embodiment is integrated can be reduced.

Second Embodiment FIG. 4 is a block diagram showing a configuration example of a baseband apparatus showing a second embodiment of the present invention, which is common to the elements in FIG. 1 showing the first embodiment. Elements are given common reference numerals. In this baseband apparatus, a confidential circuit 41 is provided between the input terminal 1 and the HPF 22 shown in FIG. 1 according to the first embodiment, and further, an output signal of the confidential circuit 41 and a voice input signal Ain are provided. A switch 42 for selecting one of them and supplying it to the HPF 22 is provided. That is, the input terminal 1
Is a confidential circuit 4 that performs confidential processing for the voice input signal Ain.
1 is connected to the input side of the switch 42 and is connected to the no side of the switch 42, and the output side of the confidential circuit 41 is connected to the nc side of the switch 42. HPF on the c side of the switch 42
22 is connected to the input side. Further, a restoration circuit 43 is provided between the HPF 30 and the output terminal 12, and the H
A switch 44 that selects one of the output signal of the PF 30 and the output signal of the restoration circuit 43 and outputs the selected signal to the output terminal 12.
Is provided. That is, the output side of the HPF 30 is connected to the input side of the restoration circuit 43, and the n of the switch 44 is
connected to the o side, and the output side of the restoration circuit 43 is the switch 4
4 is connected to the nc side. The c side of the switch 44 is connected to the output terminal 12.

FIG. 5 is a schematic circuit diagram showing an example of the configuration of the confidential communication circuit 41 shown in FIG. The confidential circuit 41 has, for example, a frequency reversal confidential circuit configuration. That is, the confidential circuit 41 has the input terminal 51 for inputting the voice input signal Ain.
have. The input terminal 51 is connected to the inverting input terminal of the operational amplifier 53 via the resistor 52,
Is connected to the inverting input terminal of the operational amplifier 53 via the resistor 54. The confidential circuit 41 has a clock signal input terminal 55. The input terminal 55 is connected to the control input terminal of the switch 56 and the input side of the inverter 57. The output side of the inverter 57 is connected to the control input terminal of the switch 58. The input terminal 51 is connected to the non-inverting input terminal of the operational amplifier 53 via the switch 56. Operational amplifier 5
The non-inverting input terminal 3 is connected to the ground via the switch 58. The output terminal of the operational amplifier 53 has a cutoff frequency of 3.3 kHz from the output signal Rev of the operational amplifier 53.
It is connected to the output terminal 60 via the LPF 59 that removes frequency components of z or higher.

FIG. 6 is a time chart showing the operation of FIG. 5, in which the voltage V is plotted on the vertical axis and the time t is plotted on the horizontal axis. In FIG. 6, while the clock signal CK having a frequency of 3.3 kHz is at a high level (hereinafter referred to as “H”), the audio input signal Ain and the output signal Rev have the same phase, and the clock signal CK is at a low level (hereinafter, “H”). Term "L"),
It is shown that the audio input signal Ain and the output signal Rev have opposite phases. FIG. 7 is a spectrum diagram of the audio input signal Ain in FIG. 5, in which the vertical axis represents power density and the horizontal axis represents frequency. In FIG. 7, the voice input signal Ain
Has a frequency of 1.4 kHz. FIG. 8 is a spectrum diagram of the output signal Rev in FIG. 5, with the vertical axis representing the power density,
And the frequency is plotted on the horizontal axis. The output signal Rev is
The LPF 59 removes frequency components of 3.3 kHz or higher, and leaves only the 1.9 kHz component.

Next, the operation of the baseband device shown in FIG. 4 will be described. Since the confidential circuit 41 is provided in the path of the transmission voice signal Ain and the restoration circuit 43 is provided in the path of the reception voice signal Aout, the confidential function is realized. Furthermore, since the switches 42 and 44 that bypass the confidential circuit 41 and the restoration circuit 43 are provided, it is possible to select whether or not to use the confidential function. In the confidential circuit 41 and the restoration circuit 43, assuming that the inverted clock frequency is fr and the input frequency is fi, the output signal frequency fo
Becomes fo = fr-fi. That is, the inversion clock frequency fr is set to 3.3 kHz.
Then, when the frequency of the input voice signal Ain is 1 kHz, the frequency of the output signal OUT of the confidential circuit 41 is 2.3 kHz.
z. This 2.3 kHz signal is input to the input terminal 8 of the reception input signal, and is restored to 1 kHz by the restoration circuit 43.

FIG. 9 is a spectrum diagram of the voice input signal Ain of the confidential circuit, and FIG. 10 is a spectrum diagram of the output signal OUT of the confidential circuit. The vertical axis represents power density and the horizontal axis represents frequency. . Comparing FIG. 9 and FIG. 10, 0.3 kHz is converted to 3 kHz as shown at point A, 1 kHz is converted to 2.3 kHz as shown at point B, and 3 kHz is 0. 3 as shown at point C. It can be seen that the confidential circuit has a confidential function because it is converted to 3 kHz.
As described above, in the second embodiment, the frequency band used as the modem is set to a frequency lower than the lower limit of 300 Hz of the voice band, so that the time when the secret circuit 41 is passed and the time when it is bypassed are compared. There is an advantage that the sound quality does not differ. Further, by utilizing the feature of simultaneously transmitting a voice signal and a data signal, the switch 42, 44 is switched at the same time as another opposing baseband device by using the timing of the received data, thereby improving the confidentiality level.

The present invention is not limited to the above embodiment, but various modifications can be made. Examples of modifications thereof include the following (1) to (4). (1) Although FIGS. 1 and 4 show only the components that are closely related to the simultaneous transmission of voice and data,
There is no problem in using the additional components included in the general baseband device. (2) The LPF 29 in FIGS. 1 and 4 may be replaced with a BPF. This improves the bit error rate of the modem 6A. (3) A compander or emphasis may be added to improve the SN ratio of voice, and a limiter or splatter filter may be added to prevent interference with adjacent channels. (4) Regarding the confidential talk circuit 41 in FIG. 4, the frequency reversal confidential talk system has been described, but the effects of the present invention can be similarly expected in other secret talk systems. For example, it is possible to further improve the degree of confidential talk by changing the secret talk system to band division replacement and changing the replacement method with time. Since the replacement timing can be made at the same time as the opposing baseband device by using the timing of the received data, it is possible to realize a baseband device with little deterioration in sound quality and a high degree of confidentiality.

[0022]

As described in detail above, according to the first invention, the frequency band of the output signal of the first HPF is the first.
Since it overlaps with the frequency band of the output signal of the LPF, the speed of data communication by the modulator and demodulator can be made faster than before. According to the second invention, since the frequency band of the output signal of the first HPF does not overlap with the frequency band of the output signal of the first LPF, the voice signal and the data communication by the modulator and the demodulator are simultaneously performed. . Therefore, for example, a mobile phone or the like can send a control signal during a call. Third
According to the invention, since the frequency of the clock of the first or second invention is varied by the variable clock generation unit, the frequency band of the output signal of the first HPF and the first baseband device can be varied in the same baseband device. It is set when the frequency band of the output signal of the LPF overlaps and when it does not overlap. Therefore, both the high speed modem circuit and the low speed modem circuit can be used,
The device can be downsized. According to the fourth invention, the baseband device of the first, second, or third invention is provided with a confidential circuit and a restoration circuit, and the frequency band of the data communication by the modulator and the demodulator is set to the frequency of the voice signal. Since the frequency is lower than the lower limit frequency of the band, it is possible to prevent the sound quality from being different when the secret circuit is passed and when it is bypassed.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a baseband device showing a first embodiment of the present invention.

FIG. 2 is a configuration block diagram of a conventional baseband device.

FIG. 3 is a spectrum diagram of FIG. 1.

FIG. 4 is a configuration block diagram of a baseband device showing a second embodiment of the present invention.

5 is a circuit diagram of a confidential circuit in FIG.

FIG. 6 is a time chart of FIG.

FIG. 7 is a spectrum diagram of the audio input signal Ain in FIG.

FIG. 8 is a spectrum diagram of the output signal Rev in FIG.

FIG. 9 is a spectrum diagram of a voice input signal of the confidential circuit.

FIG. 10 is a spectrum diagram of an output signal of the confidential circuit.

[Explanation of symbols]

3A adder (selection means, addition means) 6A modem (modulation section, demodulation section) 22,30 HPF 27,29 LPF 32 frequency divider (variable clock generation section) 33 changeover switch (variable clock generation section) 41 confidential circuit 43 Restoration circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04L 27/10 Z 9297-5K

Claims (4)

[Claims] 1. A baseband device for transmitting and receiving a voice signal and a data signal, comprising: a first high-pass filter for removing a frequency component lower than a predetermined cutoff frequency from a voice input signal for transmission; A modulator for modulating a data signal at a frequency based on a clock to convert it into a modulated signal, and a cutoff frequency higher than the cutoff frequency of the first high pass filter is determined based on the clock, and the cutoff is performed from the modulated signal. A first low-pass filter that removes a frequency component higher than the frequency, and an external control of either the output signal of the first high-pass filter or the output signal of the first low-pass filter. Selecting means for selecting based on a signal and outputting as a transmission output signal; an output signal of the first high-pass filter and an output signal of the first low-pass filter. A second input for removing a frequency component lower than the cut-off frequency same as the cut-off frequency of the first high-pass filter from the received input signal composed of signals in the same frequency band as A cutoff frequency that is the same as the cutoff frequency of the first lowpass filter that is higher than the cutoff frequencies of the highpass filter and the second highpass filter is determined based on the clock, and the cutoff frequency is determined from the received input signal. A second low-pass filter that removes frequency components higher than the cut-off frequency; and a demodulation unit that demodulates the output signal of the second low-pass filter at a frequency based on the clock and converts it into received data, A baseband device characterized by being provided. 2. A first high pass filter according to claim 1, a modulation section according to claim 1, and a cutoff frequency lower than a cutoff frequency of the first high pass filter is determined based on the clock. And a first low-pass filter for removing frequency components higher than the cut-off frequency from the modulated signal, an output signal of the first high-pass filter, and an output signal of the first low-pass filter. And a second high-pass filter according to claim 1, and a cut-off frequency equal to the cut-off frequency of the first low-pass filter lower than the cut-off frequency of the second high-pass filter. A second low-pass filter, a frequency of which is determined based on the clock, for removing a frequency component higher than the cut-off frequency from the received input signal; and an output signal of the second low-pass filter, which is the clock. A baseband device, comprising: a demodulation unit that demodulates to a received data by demodulating at a frequency based on. 3. The baseband device according to claim 1, further comprising a variable clock generator that varies the frequency of the clock. 4. A secret-talk circuit for performing a predetermined secret-talk process on the voice input signal and inputting it to the first high-pass filter, and the second high-pass filter subjected to the predetermined secret-talk process. 5. A baseband device according to claim 1, further comprising a restoration circuit that performs a predetermined restoration process on the output signal of.