JPS63138823A - Cordless telephone - Google Patents

Abstract

PURPOSE:To detect the operation of a channel even at the time of muting by applying low frequency modulation to a local oscillation frequency of a direct conversion system reception circuit. CONSTITUTION:The direct conversion reception system is adopted for a main set A connected to a telephone line and a portable sub set B and they are interlinked in radio by using an idle channel. A radio wave received by an antenna Aa of the set A or B (hereinafter the set A is used for the explanation) is amplified by an amplifier circuit A2 and demodulated via a low frequency filter A5. The frequency of the local oscillation circuit A4 is varied sequentially by a PLLA9 in a CPUA1 and the oscillation frequency of the local oscillator circuit A4 is subject to low frequency modulation at the channel scan. Then even with the reception frequency at the time of muting, whether or not the channel is in use is detected, nearly 1ms.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cordless telephone that allows communication between a main set and a subset over a plurality of communication channels.

[Prior Art] So-called cordless telephones, which allow calls to existing telephones wirelessly, are now indispensable for people who frequently go out because they are portable and allow calls to be made from anywhere when needed. It is becoming.

This cordless telephone basically consists of a main set connected to a telephone line and a subset wirelessly connected to the main set, and calls between the subset and an outside line and calls between the main set and the subset are made via the main set.
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Current cordless telephones automatically detect an unused channel (empty channel) from among multiple communication channels when communicating between two sectors, and communicate on that channel, thereby preventing interference with neighboring stations. It is now possible to avoid this.

In addition, various technical improvements have been made in the wireless communication system between both sets in order to achieve appropriate and good call quality, but in recent years, attempts have been made to apply a direct conversion reception system that has excellent communication performance. ing.

In this direct conversion method, as shown in Fig. 6, the output from a local oscillation circuit 1 consisting of a synthesizer, etc. is input to a synchronous detector 2, and the audio signal is directly demodulated via a low-pass filter 3 at the subsequent stage. Its advantages are (a) there is no need to worry about image reception, and (i) the low frequency band can be narrowed easily, so the selectivity can be easily increased. , (8) Since the signal level entering the detector is small and the necessary gain can be obtained at a low frequency, there are cases such as 0 in which the generation of spurious is extremely small even if a nearby large signal is entered.

As described above, since this direct conversion reception method has various excellent advantages, it is widely desired to apply it to the reception circuit of a cordless telephone.

[Problems to be Solved by the Invention] However, when the above-mentioned direct conversion reception method is applied, a problem arises in that the above-mentioned empty channel cannot be detected properly. In other words, to detect an empty channel, it is possible to determine whether the channel is being used by sequentially shifting the receiving channels and detecting whether or not an audio signal (low frequency signal) is output from the receiving circuit for each channel. Therefore, if the direct conversion reception method described above is applied to the receiving circuit, the presence or absence of an audio signal output from this circuit does not necessarily correspond to whether the channel is empty; A problem arises in that a communication channel cannot be set for a channel.

For example, if the conversation is temporarily interrupted and the high frequency signal is not modulated by the audio signal, there will be no output from the detector 2, and if a channel search is performed at this time, the Despite this, this channel is determined to be an empty channel and is set as a communication channel.

The present invention was made in view of the above-mentioned problems, and an object of the present invention is to provide a cordless telephone that can reliably detect an empty channel from among a plurality of channels.

[Means for Solving the Problems] The present invention includes a main set and a subset receiving circuit that includes a detection circuit to which a high frequency signal received by an antenna is input, and a signal having the same frequency as the high frequency signal to the detection circuit. and a low-pass filter for extracting a necessary low-frequency signal from the output signal of the detection circuit, and a low-pass filter for outputting the output signal from the local oscillation circuit to at least one receiving circuit. A modulation means for modulating a frequency signal is provided.

[Operation] In this invention, even if a channel in use where no audio is being transmitted or received is scanned, a signal having the same frequency as the received signal is modulated by a low frequency signal and input to the detection circuit. Therefore, the low frequency signal is input to the reception signal detection circuit via a low pass filter, and it is determined that the channel is in use.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on FIG. 1 to tJSS diagram.

FIG. 1 is a perspective view of the appearance of the cordless telephone according to this embodiment. As shown in FIG. 1, this cordless telephone consists of a main set A and a subset B, each of which has a built-in transmitter/receiver circuit, which will be described later. In addition, main set A is connected to the telephone line, and is responsible for answering calls from subscribers.
Subset B is carried out in the same manner as a general TL telephone set. In sets A and B, Ak and Bk are keyboards, Am and Bm are microphones, Ar and Br are receivers, and Aa and Ba are antennas.

FIG. 2 is a block diagram showing the overall circuit configuration of subset B.

In the figure, Bl includes a CPU that controls various parts described later, ROMBla and RAMBlb that store operating programs, etc., and a timer Blc. B2 is a reception amplifier circuit that amplifies the high frequency signal received by antenna Ba, and B3 is an output signal fR from this high frequency amplifier circuit B2 and an output signal f from reception local oscillation circuit B4.
The reception detection circuit to which L is input, BS is this detection circuit B3
Low frequency signal (audio signal) required from the output signal fA of
The output of the low-pass filter that extracts fAl is amplified by a low-frequency amplifier circuit B6 and a receiver amplifier circuit B7, and is output as voice from the reception receiver Br.

As described above, the reception circuit BR of the direct conversion reception system is configured by B1 to B6. Also, B8 is PLL
@ Quasi-oscillation circuit B9 is a PLL control circuit, which controls the frequency of the output signal from the local oscillation circuit B4 to be the same frequency as the reception frequency according to the channel data from the CPUB1. Furthermore, the local oscillation circuit B4 is inputted with a low frequency signal fs output from the CPUBI at the time of channel detection, and the high frequency signal fL output from the local oscillation circuit B4 is modulated with this low frequency signal fs. It is output to the detection circuit via the receiving local amplification circuit 810. Note that this local oscillation circuit B4 and CPUB1 constitute a modulation means. B
11 is an incoming signal detection circuit as an empty channel detection means, and when the low frequency signal fA1 outputted from the low-pass filter B5 is outputted via the low-frequency amplifier circuit B6, the received signal fA1 is sent to the CPUB 1 for predetermined detection. Output a signal.

In addition, B12 is a reception power supply control circuit, and
The supply of power to the reception amplifier circuit B2 and the reception local amplifier circuit BIO is controlled in accordance with the control signal from the reception amplifier circuit BIO.

B14 is a microphone amplifier circuit that amplifies the signal output from the microphone Bm, and B15 is a voice signal detection circuit that receives the voice signal from the microphone amplifier circuit B14 and outputs a detection signal to the CPUB1.

B16 is an analog delay element that delays the output signal from the microphone amplifier circuit B14, B17 is a clock oscillation circuit that generates an operating clock for the analog delay element 16 according to a control signal from CPUB1, and 18 is an output signal from the analog delay element 16. This is an analog switch that selectively switches and outputs the signal directly output from the microphone amplifier circuit 14 according to the switching signal from CPUB1. B19
The FSX circuit converts the low frequency analog signal sent from the receiving circuit BR into a digital signal and outputs it to CPUBI, and also converts the digital data signal from CPUB 1 into a low frequency analog signal and sends it to the transmitting circuit BO, which will be described later. At the same time, the audio signal output from the microphone Bm during a call is output to the transmitting circuit BO. B21
is the signal sent out from the local oscillation circuit B4 via the transmission local amplifier circuit B22 and the transmission modulation circuit B20.
The output is transmitted from the antenna Ba to the main set A via the transmission amplifier circuit 823.

B24 is a transmission power supply control circuit, which operates the transmission modulation circuit B20, the transmission section mixing circuit B21 . It controls the supply of power to the transmission local amplifier circuit B22 and the transmission amplifier circuit B23. In addition, the above B4, B8, B9, BIO and B
19 to B23 constitute a transmitting circuit BO. Further, B25 is a battery, and B26 is a charging circuit that charges this battery B25, and has a charging terminal B26a.

B27 is a power supply circuit that supplies power supplied from the battery B25 to the reception power supply control circuit B12, the transmission power supply control circuit 824, and the like. In addition,
B28 generates a buzzer B29 in response to a control signal from CPUB1.
This is the buzzer circuit that activates the.

FIG. 3 is a block diagram showing the overall circuit configuration of the main set A. Note that this main set A has almost the same configuration as the subset B above, and both sets A,
B is connected to each other through multiple channels. Hereinafter, the differences from the subset B in the main set A will be explained.

In the figure, A30 is a line relay that cuts off the connection between the telephone line and the transmitting/receiving circuits AO and AR.

Reference numeral A31 is a speech network circuit, which sends a reception signal sent from the telephone line to the transmission circuit AO, and also sends a transmission signal sent from the reception circuit AR to the telephone line. A32 is a dialer circuit as a dialing means for sending a dialing signal to a telephone line, and is controlled by CPUAl. A33
is a ringer circuit that activates the buzzer A33a in response to an incoming call from the outside and outputs an incoming call detection signal to CPUAl; A35 is a power supply circuit that supplies commercial power to the power supply circuit A27; A36 is an auxiliary battery; is a charging circuit that charges this auxiliary battery A36 and has a charging terminal A37a.

Note that the other configurations are the same as the subset B described above.

Next, Figure 4 and wSl! The operation of the cordless telephone having the above configuration together with I will be explained.

Note that 4th Ug shows the receiving circuits AR and BR in both sets A and B, and FIG. 5 shows the empty channel detection operation flow.

When a call start operation is performed, CPUAl.

Bl is the local oscillation circuit A4. While outputting the low frequency signal fs to B4, the PLL control circuit A9. Send channel scan data to B9.

Local oscillation circuit A4. The output frequency of B4, i.e.
The receiving frequency is sequentially tuned to each channel (steps 1 and 2).

At this time, local oscillation circuit A4. The high frequency signal fL output from B4 is the low frequency signal fs from CPUAl and Bl.
The signal is modulated by

The reception detection circuit A3, 83 receives this modulated signal and the antenna Aa.
, the sum ° and the difference (
A signal fA of fFt-fLE and fR+fL) is output.

Therefore, now, as described above, local oscillator circuit A4. B4
Considering the case where the output signal fL from is not modulated by the signal fs, if the received signal fR is not modulated by an audio signal, that is, if a channel is scanned that is in use but no audio is being exchanged. in case of.

Since fr=fL, the detection circuit A3. The signal fA output from B3 is only fR+fL. This signal is passed through a low-pass filter A5. Since it is removed by the BS, there is no input to the received signal detection circuits All and Bll in the subsequent stage, and it is determined that the channel is an empty channel.

However, in this embodiment, local oscillator circuit A4. B4
Since the output signal fL from the detection circuit A3.B3 is modulated by the low frequency signal fs, the detection circuit A3.B3 outputs the low frequency signal fs (=fR-fL) in addition to fR+fL, and the low-pass filter A5.B3 outputs the low frequency signal fs (=fR-fL). fs is output from the BS. Therefore, the reception signal detection circuits All and Bll make a proper judgment that the channel currently being scanned is in use, and the result is input to the CPUAl and Bl.

Note that if the received high frequency signal fR is modulated by an audio signal, this audio signal is transmitted to the detection circuit A3. It is output from B3. This is the low pass filter A5. The reception signal detection circuit A3. B
3, so it is determined that the channel is in use. Furthermore, when an empty channel is scanned, it goes without saying that it is determined to be an empty channel since there is no output to the reception signal detection circuits All and Bll.

As described above, when an empty channel is detected during channel scanning, the data representing that channel is
In step 4), the local oscillation circuit A4. After stopping the output of the signal fs to B4 (step 5), communication channels for both sets A and B are set based on the data stored in RAM Alb and Bib, and one conversation is performed.

In the above embodiment, either the empty channel detection operation is performed in both sets A and B, or one of the sets is provided with this empty channel detection function, and data communication is performed between both sets when setting a communication channel. The empty channel detected in one set may be matched with the other channel, and the present invention is not particularly limited to the above embodiment.

[Effects of the Invention] As explained above, according to the present invention, even if no audio is being exchanged, if that channel is in use, it is possible to avoid that channel and reliably detect an empty channel. This has the effect that good call quality can always be obtained.

[Brief explanation of the drawing]

FIG. 1 is an external perspective view of an embodiment according to the present invention, FIG. 2 is a block diagram showing the overall circuit configuration of a subset in this embodiment, and FIG. 3 is a block diagram showing the entire circuit configuration of a main set in this embodiment. 4 is a block diagram showing a schematic configuration of the receiving circuit in both sets, FIG. 5 is a flowchart showing the empty channel detection operation of this embodiment, and FIG. 6 is a direct conversion reception method in a conventional wireless communication device. FIG. L: Telephone line AR: Receiving circuit AO: Transmitting circuit BR: Receiving circuit BO: Transmitting circuit A1: CPU) Modulation means A3: Local oscillation circuit (signal generation means) Alb: RAM (storage means) A8: PLL reference oscillation circuit A9 : PLL control circuit All: Received signal detection circuit (empty channel detection means) Bl: CPU) Modulation means B3: Local oscillation circuit (signal generation means) Bib: RAM (storage means) B8: PLL reference oscillation circuit B9: PLL control circuit Bll: Receiving signal detection circuit (empty channel detection means)

Claims (1)

[Claims] It consists of a main set connected to a telephone line and a portable subset, both of which are equipped with a radio transmitting/receiving circuit that can change the communication channel and detecting an empty channel by detecting the presence or absence of an output from the receiving circuit. A cordless telephone is provided with an empty channel detecting means, in which both sets of receiving circuits include a detection circuit to which a high frequency signal received by the antenna is input, and a signal having the same frequency as the high frequency signal to the detection circuit. and a low-pass filter for extracting a necessary low-frequency signal from the output signal of the detection circuit, and transmitting the output signal from the local oscillation circuit to at least one of the receiving circuits as a low-frequency signal. A cordless telephone characterized in that it is provided with a modulation means for modulating.