JP3157629B2 - Modem for wireless communication device and control method therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a radio communication device such as a cordless telephone or a transceiver for transmitting and receiving a voice signal and a digital signal for controlling a switching of a communication channel, and modulating and demodulating a digital signal. The present invention relates to a modem for a communication device and a control method thereof.

[0002]

2. Description of the Related Art This type of radio communication device employs a multi-channel access method in which an unused channel is determined and used. This method requires transmitting and receiving digital control signals such as channel numbers between the transceivers.
It has a modem that performs MSK modulation and demodulation. This modem uses MS at frequencies in the voice band due to frequency band limitations.
Since K modulation and demodulation are performed, the audio signal and the control signal cannot be transmitted and received simultaneously, and the audio signal and the control signal are transmitted and received by time division multiplexing. In the case of the time-division multiplexing method, if a control signal is transmitted / received to change the channel during a call to prevent eavesdropping, the call is interrupted.

[0003] In some cases, a method has been proposed in which the modulation signal frequency of the control signal is set to a frequency lower than the voice band, and the voice signal and the control signal are frequency-division multiplexed without expanding the frequency band (Japanese Patent Application Laid-Open No. H11-157572). 1963-2473
No. 1).

[0004]

However, before demodulation, it is necessary to pass the received control signal through a different band-pass filter depending on whether the frequency band of the modulated signal is within the voice band. When the pass filter is a component of the modem integrated circuit, the circuit configuration of the modem becomes complicated.

An object of the present invention is to provide a modem for a wireless communication device having a simple configuration and a control method therefor in view of such problems.

[0006]

A description will be given of a modem for a radio communication apparatus and a control method therefor according to the present invention with reference to the reference numerals of corresponding components in the embodiment.

The modem for a radio communication apparatus according to the first invention generates a subcarrier proportional to the frequency of an input clock φ and converts the subcarrier into an input digital signal as shown in FIGS. Modulator 12 for frequency shift keying with DT
And the frequency-shift-modulated signal is input and the clock φ
A band-pass filter 24 having switched capacitors 51 to 54 that are controlled to be switched by the band-pass filter 24 in which the pass frequency band shifts in proportion to the frequency of the clock φ.
And a demodulator 25 for performing frequency shift demodulation of the output signal of No. 4 at a speed proportional to the clock φ frequency.

Since the modulator 12, the band-pass filter 24, and the demodulator 25 operate with a common clock φ, it is preferable that these are formed as a single integrated circuit as the modem 30. According to the first aspect of the present invention, since the pass frequency band of the band-pass filter 24 shifts in proportion to the frequency of the clock φ, there is no need to provide a different band-pass filter 24 for each pass frequency band. 30
Is simpler than before.

In the first aspect of the first invention, the band-pass filter 24 is constituted by cascading a plurality of secondary filters 24a.

In this case, since a plurality of secondary filters 24a may be simply connected in cascade according to the required order of the band-pass filter 24, the design and configuration are simplified.

According to a second aspect of the present invention, there is provided a method for controlling a modem for a wireless communication device, wherein the modem for a wireless communication device having the above-described configuration is used for a cordless telephone to limit a frequency band and set a communication channel at a high speed before a call is started. The frequency of the clock φ is set to a predetermined value such that the frequency of the subcarrier is within the audio frequency band, and after setting the communication channel, the frequency band is restricted and the communication channel can be changed without interrupting the communication after the start of the communication. The frequency of the clock φ is switched to a predetermined value at which the frequency of the subcarrier is lower than the audio frequency band.

According to the second aspect of the present invention, by simply switching the frequency of the clock φ, it is possible to use subcarriers having different frequencies before and after the start of a call, and to switch the communication channel without interrupting the call during the call. Automatic switching or manual switching becomes possible.

[0013]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a main part of a wireless communication device to which a modem for a wireless communication device according to the present invention is applied.

The wireless communication device includes a transmission circuit 10, a reception circuit 20, and components 31 to 35 common to transmission and reception. The transmission circuit 10 includes a band-pass filter 11
And a minimum shift keying (MSK) modulator 12, which is a type of frequency shift modulator (FSK modulator), an adder 13, an FM modulator 14, and a power amplifier circuit 15. , A high-frequency amplifier 21, an FM demodulator 22, band-pass filters 23 and 24, an MSK demodulator 25, and an S / P converter 26.

The audio signal ST is supplied to a band-pass filter 11.
And its frequency band is f1 to f2, e.g.
The frequency is limited to 3 to 3 kHz and becomes an audio signal ST1. The audio signals ST and ST1 are shown in FIGS. A two-dot chain line in the figure indicates a pass frequency characteristic of the band pass filter 11.

On the other hand, the control signal DT is modulated by the MSK modulator 12 based on the operation clock φ, and becomes an MSK modulated signal DTM. The MSK modulator 12 also generates a clock C having a frequency equal to the transfer rate based on the clock φ.
The microcomputer 31 supplies a control signal DT to the MSK modulator 12 in synchronization with the clock CK. The control signal DT, the clock CK, and the MSK modulation signal DTM are as shown in FIGS. 4A, 4B, and 4C, for example. That is, if the control signal DT is “0” at the rising edge of the clock CK, the frequency of the MSK modulation signal DTM becomes fL during one cycle of the clock CK, and the control signal DTM becomes at the rising edge of the clock CK.
If T is '1', MSK for one cycle of clock CK
The frequency of the modulation signal DTM becomes fH. Also, fL / f
The phase is made continuous by setting H = 3/2 and setting the wave height to 0 at the rise of the clock CK.

In FIG. 1, a clock φ includes a clock φ1 output from a clock generator 33 and a clock φ1.
Is passed through a 1 / N divider 34 and a clock φ2 obtained by a selector 35 by a control signal from the microcomputer 31. The frequencies fL and fH of the subcarriers are proportional to the frequency of the clock φ, and when φ = φ1,
As shown in FIG. 5D, fL = fSL, fH = fSH, and when φ = φ2, fL = fD as shown in FIG.
L, fH = fDH.

Voice signal ST1 and MSK modulated signal DTM
Are supplied to the adder 13 and added, then supplied to the FM modulator 14 and subjected to FM modulation, and then supplied to the power amplifier circuit 15 to be amplified and transmitted from the antenna 32.

The signal received by the antenna 32 is amplified by a high-frequency amplifier 21 in a predetermined frequency band, FM-demodulated by an FM demodulator 22, and supplied to band-pass filters 23 and 24. The band-pass filter 23 is for passing the audio signal SR, and the passing frequency band is f1 to f2 like the band-pass filter 11. On the other hand, the band-pass filter 24 is for passing the control signal, and its passing frequency band is proportional to the frequency of the clock φ, and when φ = φ1, FIG.
F3 to f4 as shown in FIG.
F5 to f6 as shown in FIG.

The output of the band-pass filter 24 is supplied to an MSK demodulator 25, which performs MSK demodulation on the basis of an operation clock φ, and outputs a control signal DR and a control signal DR as shown in FIGS. Generate a clock CKR.
The S / P converter 26 converts the control signal DR into a clock CKR.
Is converted into parallel data on the basis of and supplied to the microcomputer 31.

MSK modulator 12 and band pass filter 2
4 and the MSK demodulator 25 operate with a common clock φ, and therefore, it is preferable that these are configured as a modem 30 by one IC. In this case, since the pass band of the band-pass filter 24 shifts in proportion to the frequency of the clock φ, it is not necessary to provide a different band-pass filter 24 for each of the two pass frequency bands.
The configuration of the modem 30 is simpler than before.

FIG. 2 shows a configuration example of the MSK modulator 12.
The clock φ is supplied to a 1 / N1 frequency divider 40 and a 1 / N2 frequency divider 41, and is divided by 1 / N1 and 1 / N2 to become clocks φ3 and φ4, respectively. Selector 42
Selects the clock φ3 when the control signal DT is “0”, selects the clock φ4 when the control signal DT is “1”, and supplies the clock φ4 to the clock input terminal of the counter 43. The sine wave ROM 44 is addressed by the count value of the counter 43, and the data of the sine wave as the subcarrier is read from the sine wave ROM 44. This data is converted into an analog voltage by the D / A converter 45, and then the waveform thereof is smoothed through a low-pass filter 46 and output as an MSK modulated signal DTM. The polarity of the output voltage of the D / A converter 45 is switched by a control circuit (not shown) so that the phase continuously changes as shown in FIG. Also,
The clock φ4 is divided by 1 / N3 by the 1 / N3 divider 47 to generate the clock CK.

The MSK demodulator 25 is configured to perform the reverse operation of the MSK modulator 12 based on the clock φ, and a detailed description thereof will be omitted.

The bandpass filter 24 is composed of, for example, five cascade-connected secondary bandpass filters 24a as shown in FIG. Secondary bandpass filter 24
In a, one ends of the switched capacitors 51, 52 and 53 are connected to the inverting input terminal of the operational amplifier 50. The output terminal of the operational amplifier 50 is connected to the other end of the switched capacitor 52 and one end of the switched capacitor 54. The other end of the switched capacitor 54 is connected to the operational amplifier 5
5, and the output terminal of the operational amplifier 55 is connected to the other end of the switched capacitor 53. Capacitors 60 and 56 are connected between the inverting input terminals and the output terminals of the operational amplifiers 50 and 55, respectively. Further, a voltage that is half of the power supply voltage VDD is applied to the non-inverting input terminals of the operational amplifiers 50 and 55.
Note that the bandpass filter 24 can also be configured by cascading a secondary lowpass filter and a secondary highpass filter (not shown).

The switched capacitors 51 to 53 have the same configuration, and one end of the capacitor 57 is connected to the analog changeover switch 58, and the other end of the capacitor 57 is connected to the analog changeover switch 59. Analog changeover switches 58 and 5 of switched capacitors 51 to 53
9 is controlled by a clock φ. For example, when the clock φ is at a low level, the state shown in the drawing is reached. When the clock φ is at a high level, the potentials at both ends of the capacitor 57 are both VDD / 2.
To be. The switched capacitor 54 is the same as the switched capacitors 51 to 53 except that the switching control phases of the analog changeover switch 58 and the analog changeover switch 59 are opposite to each other.

The secondary band-pass filter 24a is equivalently an RC active filter. When the frequency of the clock φ increases, the capacitance of the switched capacitor 51 decreases and the pass frequency band shifts to the higher frequency side.

For example, f1 = 0.3 kHz f2 = 3 kHz Frequency of clock φ1: 115.2 kHz N = 8 Frequency of clock φ2: 14.4 kHz N1 = 2 N2 = 3 N3 = 32 When φ = φ1, Frequency of clock φ3: 57.6 kHz Frequency of clock φ4: 38.4 kHz Frequency of clock φ5: 1.2 kHz fSL = 1.2 kHz fSH = 1.8 kHz, and when φ = φ2, frequency of clock φ3: 7.2 kHz Frequency of clock φ4: 4.8 kHz Frequency of clock φ5: 150 Hz fDL = 150 Hz fDH = 225 Hz.

Next, based on FIG. 7, control for switching a communication channel between wireless communication devices, for example, control for switching a communication channel between the parent device and the child device when a call is made from the child device to the other party through the parent device by a cordless telephone. Will be described. Hereinafter, numerical values in parentheses indicate step identification numbers in the figure.

(70) When the talk switch SW1 of the slave unit is set to the talk position, φ = φ1 and a talk channel is set between the slave unit and the master unit by a control signal. At this time, an analog switch (not shown) is turned off to prohibit the audio signal ST from being supplied to the bandpass filter 11. MSK
The frequency spectrum of the MSK modulated signal DTM output from the modulator 12 is as shown in FIG. 5D, and the frequency spectrum of the control signal input to the band-pass filter 24 and the pass frequency characteristic of the band-pass filter 24 are shown in FIG. (C). In this case, the transfer rate of the control signal is relatively high at 1200 bps, and the time required to enter the talking state is reduced.

(71) When transmission / reception of the control signal is completed, φ
= Φ2, the prohibition is released, and a call is made. Thus, the audio signal ST and the control signal DT can be transmitted and received by frequency division multiplexing. That is, the control signal can be transmitted and received without interrupting the call.

The frequency spectrum of the audio signal ST and the MSK modulated signal DTM and the pass frequency characteristic of the band pass filter 24 are as shown in FIG.
The frequency spectrum of the output signal is as shown in FIG. In this case, the transfer rate of the control signal is 150 bp.
s, which is lower than in step 70 above,
There is no problem because the call is not interrupted.

(72, 73) Whether there is a channel change request, that is, the channel changeover switch SW2 of the own unit (slave unit) is operated, or the slave unit or the master unit is automatically set to prevent eavesdropping and noise reduction. Check if you are about to change the call channel. If the call switch is turned off, the process ends.

(74) If there is a channel change request, the control signal is transmitted and received between the slave unit and the master unit without interrupting the call to change the call channel, and the process returns to step 72.

According to the present embodiment, sub-carriers of different frequencies can be used before and after the start of a call only by switching the clock by the selector 35. In addition, a call channel can be automatically or manually switched without interrupting a call during a call.

[0036]

As described above, in the radio communication modem according to the first aspect of the present invention, the modulator, the band-pass filter, and the demodulator that operate on a common clock are formed by one integrated circuit. Since the pass frequency band of the filter shifts in proportion to the frequency of the clock, there is no need to provide a different band pass filter for each pass frequency band, so that the configuration of the modem is simpler than before.

According to the first aspect of the first invention, a plurality of secondary filters may be simply connected in cascade according to the required order of the bandpass filter, so that the design and configuration are simplified.

According to the second aspect of the present invention, a subcarrier having a different frequency can be used before and after the start of a call by simply switching the clock frequency, and the call is interrupted during the call. There is an effect that the communication channel can be automatically switched or manually switched without the need.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a wireless communication device to which a modem for a wireless communication device according to the present invention is applied.

FIG. 2 is a main block diagram showing a configuration example of an MSK modulator 12 in FIG. 1;

FIG. 3 is a circuit diagram showing a configuration example of a second-order bandpass filter which is a component of the bandpass filter 24 of FIG. 1;

FIG. 4 is a waveform diagram of a transmission / reception signal related to a control signal.

FIG. 5 is a frequency spectrum when an audio signal and a control signal are in the same band.

FIG. 6 is a frequency spectrum when an audio signal and a control signal are in different bands.

FIG. 7 is a flowchart showing a communication channel switching control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Transmission circuit 11, 23, 24 Band pass filter 12 MSK modulator 13 Adder 20 Receiving circuit 24a Secondary band pass filter 25 MSK demodulator 26 S / P converter 30 Modem 31 Microcomputer 33 Clock generator 34, 40, 41, 47 frequency divider 35, 42 selector 50, 55 operational amplifier 51-54 switched capacitor 58, 59 analog switch

──────────────────────────────────────────────────続 き Continued on the front page (56) References JP-A-63-24731 (JP, A) JP-A-56-131245 (JP, A) JP-A-53-148906 (JP, A) JP-A-56-148906 2756 (JP, A) JP-A-61-184935 (JP, A) JP-A-61-273099 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 1/38 H04B 7 / 26 H04J 1/00 H04L 27/12 H04L 27/14

Claims (3)

(57) [Claims] A modulator (1) that generates a subcarrier proportional to the frequency of an input clock (φ) and frequency-shift modulates the subcarrier with an input digital signal (DT).
2), a band-pass filter to which a frequency-shift-modulated signal is input and which is provided with switched capacitors (51 to 54) that are switched and controlled by the clock and whose pass frequency band is shifted in proportion to the frequency of the clock; (24) a demodulator for frequency-shift demodulating the output signal of the band-pass filter at a speed proportional to the clock frequency (25)
A modem for a wireless communication device, comprising: and a single semiconductor integrated circuit. 2. The apparatus according to claim 1, wherein said band-pass filter has a 2
2. The modem for a wireless communication device according to claim 1, wherein a plurality of next filters (24a) are connected in cascade. 3. The frequency of the clock (φ) for using a modem for a wireless communication device according to claim 1 or 2 for a cordless telephone, in order to limit a frequency band and set a communication channel at a high speed before a call is started. Is set to a predetermined value such that the frequency of the sub-carrier is within the audio frequency band. After the communication channel is set, the frequency band is limited and the communication channel can be changed without interrupting the communication after the start of the communication. A method for controlling a modem for a wireless communication device, wherein a frequency is switched to a predetermined value at which a frequency of the subcarrier is lower than a voice frequency band.