JPH06164442A - Radio communication equipment modem and its control method - Google Patents

Abstract

PURPOSE:To simplify the constitution of a radio communication equipment MODEM by constructing a modulator, a BPF and a demodulator in a single integrated circuit. CONSTITUTION:An MSK modulator 12 works with a clock phi, a BPF 24 contains a switched capacitor which receives an MSK modulated signal and undergoes the switch control by the clock phi and deviates its pass frequency band in proportion to the frequency of the clock phi. Then an MSK demodulator 25 actuates the output signal of the BPF 24 with the clock phi. These modulator 12, BPF 25 and demodulator 25 are constructed in a single integrated circuit. This constitution is applied to a cordless telephone set. The frequency of the clock phiis set at a prescribed level where the subcarrier frequency is set within a voice frequency band before the talking is started so that the frequency band is limited and at the same time a message channel is set at a high speed. Then the frequency of the clock phi is switched to another prescribed level where the subcarrier frequency is reduced less than the voice frequency band after the message channel is set so that the frequency band is limited and also the message channel is changed without interrupting the talking after its start.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a wireless communication device for transmitting and receiving a voice signal and a digital signal for controlling a communication channel such as a cordless telephone and a transceiver, and performs modulation and demodulation of the digital signal. The present invention relates to a communication device modem and a control method thereof.

[0002]

2. Description of the Related Art A wireless communication device of this type employs a multi-channel access method in which an empty channel is discriminated and used. In this method, it is necessary to send and receive digital control signals such as channel numbers between transceivers,
It has a modem for performing MSK modulation / demodulation. Due to frequency band limitation, this modem uses MS at frequencies within the voice band.
Since the K modulation / demodulation is performed, the voice signal and the control signal cannot be transmitted / received at the same time, and the voice signal and the control signal are transmitted / received by time division multiplexing. In the case of the time division multiplex system, the call is interrupted when a control signal is transmitted and received while trying to change the channel to prevent eavesdropping during the call.

Therefore, 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. Sho 63-2473
No. 1).

[0004]

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

In view of the above problems, an object of the present invention is to provide a wireless communication device modem having a simple structure and a control method thereof.

[0006]

A wireless communication device modem and a control method therefor according to the present invention will be described with reference to the reference numerals of corresponding components in the drawings.

A radio communication device modem according to the first aspect of the present invention, for example, as shown in FIGS. 1 to 3, generates a subcarrier that is proportional to the frequency of an input clock φ, and outputs the subcarrier to the input digital signal. Modulator 12 for frequency shift keying with DT
And the frequency shift keyed signal is input, and the clock φ
The bandpass filter 24, which includes the switched capacitors 51 to 54 whose switching is controlled by, and whose pass frequency band shifts in proportion to the frequency of the clock φ, and the bandpass filter 2.
A demodulator 25 that frequency-shift-demodulates the output signal of No. 4 at a rate proportional to the clock φ frequency is configured by one semiconductor integrated circuit.

Since the modulator 12, the bandpass filter 24, and the demodulator 25 operate with the common clock φ, it is preferable to construct them as a modem 30 in one integrated circuit. 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, it is not necessary to provide a different band pass filter 24 for each pass frequency band, and therefore the modem Thirty
The configuration of is simpler than in the past.

In the first aspect of the first aspect of the present invention, the bandpass filter 24 is constructed by connecting a plurality of secondary filters 24a in cascade.

In this case, since a plurality of secondary filters 24a may be simply cascaded in accordance with the required order of the bandpass filter 24, the design and configuration are simplified.

In the method for controlling a modem for a wireless communication device according to the second aspect of the present invention, the modem for wireless communication device having the above-mentioned configuration is used for a cordless telephone, and the frequency band is limited and the communication channel is set at high speed before starting a communication. In order to set the frequency of the clock φ to a predetermined value such that the frequency of the subcarrier is within the voice frequency band, limit the frequency band after setting the call channel, and enable the call channel to be changed without interrupting the call after the call starts. The frequency of the clock φ is switched to a predetermined value such that the frequency of the subcarrier is lower than the voice frequency band.

According to the second aspect of the present invention, the subcarriers of different frequencies can be used before and after the start of the call only by switching the frequency of the clock φ, and the call channel can be changed without interruption during the call. It is possible to switch automatically or manually.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 wireless communication device modem according to the present invention is applied.

The wireless communication device includes a transmission circuit 10, a reception circuit 20, and constituent elements 31 to 35 common to transmission and reception. The transmission circuit 10 includes a bandpass 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, and the receiving circuit 20 includes The high frequency amplifier circuit 21, the FM demodulator 22, the band pass filters 23 and 24, the MSK demodulator 25, and the S / P converter 26 are provided.

The audio signal ST is a bandpass filter 11
To the frequency band f1 to f2, for example, 0.
The audio signal ST1 is limited to 3 to 3 kHz. The audio signals ST and ST1 are shown in FIGS. 5 (A) and 5 (B). The chain double-dashed line in the figure shows the 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 to become the MSK modulation signal DTM. The MSK modulator 12 also uses a clock C having a frequency equal to the transfer rate based on the clock φ.
K is generated, and the microcomputer 31 supplies the control signal DT to the MSK modulator 12 in synchronization with this 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 time of the clock CK, the frequency of the MSK modulation signal DTM becomes fL for one cycle of the clock CK, and the control signal D at the rising time of the clock CK.
If T is '1', then MSK for one cycle of clock CK
The frequency of the modulation signal DTM becomes fH. Also, fL / f
The phase is continuous by setting the wave height to 0 at H = 3/2 and the rising edge of the clock CK.

In FIG. 1, a clock φ is a clock φ1 output from the clock generator 33 and a clock φ1.
The clock φ2 obtained by passing the clock signal through the 1 / N frequency divider 34 is selected by the selector 35 by the control signal from the microcomputer 31. The subcarrier frequencies fL and fH are proportional to the frequency of the clock φ, and when φ = φ1,
As shown in FIG. 5D, fL = fSL and fH = fSH. When φ = φ2, as shown in FIG. 6B, fL = fD.
L, fH = fDH.

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

The signal received by the antenna 32 is amplified by the high frequency amplifier circuit 21 to have a high frequency within a predetermined frequency band, FM demodulated by the FM demodulator 22, and supplied to the band pass filters 23 and 24. The band pass filter 23 is for passing the audio signal SR, and its pass frequency band is f1 to f2 as in the band pass filter 11. On the other hand, the bandpass filter 24 is for passing the control signal, and its pass frequency band is proportional to the frequency of the clock φ, and when φ = φ1, FIG.
F3 to f4 as shown in Fig. 6, and when φ = φ2,
As shown in (A), f5 to f6.

The output of the bandpass filter 24 is supplied to the MSK demodulator 25, which MSK demodulates based on the operating clock φ and outputs the control signals DR and DR as shown in FIGS. 4D and 4E. Generates clock CKR.
The S / P converter 26 sends this control signal DR to the clock CKR.
Is converted into parallel data based on the above, and is supplied to the microcomputer 31.

MSK modulator 12 and bandpass filter 2
Since the 4 and the MSK demodulator 25 operate with a common clock φ, it is preferable to configure them as a modem 30 with one IC. In this case, since the bandpass filter 24 shifts its pass frequency band in proportion to the frequency of the clock φ, it is not necessary to provide a different bandpass filter 24 for each of the two pass frequency bands.
The configuration of the modem 30 becomes simpler than the conventional one.

An example of the structure of the MSK modulator 12 is shown in FIG.
The clock φ is supplied to the 1 / N1 frequency divider 40 and the 1 / N2 frequency divider 41, and is divided into 1 / N1 frequency and 1 / N2 frequency 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 sine wave data that is 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 the low-pass filter 46 and output as the MSK modulation 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 constructed so as to perform an operation reverse to that of the MSK modulator 12 based on the clock φ, and its detailed description will be omitted.

The bandpass filter 24 is constructed by cascade-connecting five secondary bandpass filters 24a as shown in FIG. 3, for example. Second-order bandpass filter 24
In a, one end of the switched capacitors 51, 52 and 53 is 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 has an operational amplifier 5
5, 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 output terminals of the operational amplifiers 50 and 55, respectively. Further, a voltage that is half the power supply voltage VDD is applied to both the non-inverting input terminals of the operational amplifiers 50 and 55.
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 an analog changeover switch 58 is connected to one end of the capacitor 57 and an analog changeover switch 59 is connected to the other end of the capacitor 57. Analog changeover switches 58 and 5 of the switched capacitors 51 to 53
9 is switched and controlled by the clock φ. For example, when the clock φ is at the low level, the state shown in the figure is obtained, and when the clock φ is at the high level, the potentials across 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 second-order bandpass filter 24a is equivalently an RC active filter, and as the frequency of the clock φ increases, the capacitance of the switched capacitor 51 decreases and the pass frequency band shifts to the high 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, and in the case of 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 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, on the basis of FIG. 7, a call channel switching control between wireless communication devices, for example, a call channel switching control between the base unit and the handset when a call is made from the handset through the base unit to the other party in a cordless telephone. Will be explained. Hereinafter, the numerical value in the parenthesis represents the step identification number in the figure.

(70) When the call switch SW1 of the slave unit is set to the talk position, φ = φ1 is set and a call channel is set by a control signal between the slave unit and the master unit. 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 bandpass filter 24 and the pass frequency characteristic of the bandpass filter 24 are shown in FIG. As shown in (C). In this case, the transfer rate of the control signal is 1200 bps, which is relatively high, and the time until the call state is shortened.

(71) When transmission / reception of the control signal is completed, φ
= Φ2, the above prohibition is released, and the communication state is established. As a result, the voice 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 voice 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 of is as shown in FIG. 6 (B). In this case, the transfer rate of the control signal is 150 bp
s, which is lower than that in step 70,
There is no problem because the call is not interrupted.

(72, 73) Whether or not there is a channel change request, that is, the channel changeover switch SW2 of the own device (slave device) is operated, or the slave device or the master device is automatically operated for wiretapping prevention and noise reduction. Check if you are trying to change the call channel to. If the call switch is turned off, the process ends.

(74) When there is a request for changing the channel, a control signal is transmitted and received between the handset and the base unit to change the call channel without interrupting the call, and the process returns to step 72.

According to this embodiment, it is possible to use subcarriers of different frequencies before and after the start of a call only by switching the clock with the selector 35. In addition, the call channel can be automatically or manually switched without interrupting the call during the call.

[0036]

As described above, in the wireless communication device modem according to the first aspect of the present invention, the modulator, the bandpass filter, and the demodulator that operate with a common clock are formed by one integrated circuit, and the bandpass filter is used. Since the pass frequency band of the filter deviates in proportion to the frequency of the clock, it is not necessary to provide a different band pass filter for each pass frequency band, and therefore, the modem configuration can be simpler than the conventional one.

According to the first aspect of the first aspect of the present invention, a plurality of second-order filters are simply connected in cascade in accordance with the required order of the bandpass filter, which has the effect of simplifying the design and configuration.

According to the modem control method for a wireless communication device of the second invention, it is possible to use subcarriers of different frequencies before and after the start of a call only by switching the clock frequency, and the call is interrupted during the call. The effect that it becomes possible to automatically switch or manually switch the call channel without being required.

[Brief description of 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.

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

3 is a circuit diagram showing a configuration example of a secondary bandpass filter that is a component of the bandpass filter 24 of FIG.

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

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

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

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

[Explanation of symbols]

 10 transmitter circuit 11, 23, 24 band pass filter 12 MSK modulator 13 adder 20 receiver 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 changeover switch

Claims (3)

[Claims] 1. A modulator (1) for generating a subcarrier proportional to a frequency of an input clock (φ) and frequency-shift-modulating the subcarrier with an input digital signal (DT).
2) and a signal whose frequency shift keying has been input, and which is provided with a switched capacitor (51 to 54) which is switch-controlled by the clock, and a band pass filter whose pass frequency band shifts in proportion to the frequency of the clock. (24) and a demodulator (25) for performing frequency shift demodulation on the output signal of the bandpass filter at a rate proportional to the clock frequency.
And a single semiconductor integrated circuit, which is a modem for a wireless communication device. 2. The bandpass filter (24) comprises 2
2. The modem for a wireless communication device according to claim 1, wherein a plurality of the next filters (24a) are connected in cascade. 3. The frequency of the clock (φ) is used in order to limit the frequency band and set the call channel at high speed before the call is started by using the wireless communication device modem according to claim 1 or 2 in a cordless telephone. Is set to a predetermined value such that the frequency of the subcarrier is within the voice frequency band, and after the call channel is set, the frequency band is limited and the clock channel can be changed without interrupting the call after the call is started. A method of controlling a modem for a wireless communication device, wherein a frequency is switched to a predetermined value such that a frequency of the subcarrier is lower than a voice frequency band.