JPH0734598B2 - Cordless telephone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial Field B Outline of Invention C Conventional Technology D Problems to be Solved by the Invention E Means for Solving Problems F Action G Example G ₁ First Example (FIGS. 1 to 1) Fig. 7) G ₂ Second embodiment (Figs. 8 and 9) G ₃ Other embodiments H Effect of the invention A Industrial field of application This invention relates to a cordless telephone.

B Outline of the Invention The present invention is, for example, a cordless telephone base unit that checks the reception level of a signal from a handset and opens the telephone line when the reception level fluctuates in a predetermined pattern. is there.

C Conventional Technology In a general telephone, its telephone cord is connected to a rosette attached to a pillar or a wall. Therefore, the range in which the telephone can be moved is determined by the length of the telephone cord and is about several meters. However, if the phone cord is lengthened to increase the range of movement, the cord will become entangled or obstructed.

Therefore, in the United States and the like, a telephone system called a cordless telephone is considered.

As shown in FIG. 10, this is composed of a transceiver (1) called a handset and a transceiver (2) called a base unit, and a telephone line (3) is connected to the base unit (2). At the same time, the base unit (2) and the handset (1) are coupled by radio waves, and the telephone of the subscriber is answered by the handset (1) in the same manner as a general telephone.

Therefore, the subscriber can freely move the handset (1) when making a call, and can use the phone outdoors, for example. What's more, the phone cord doesn't get tangled or get in the way.

The distance (service area) where the handset (1) can be separated from the base unit (2) is about 300 m. The frequency of radio waves used between the handset (1) and the base unit (2) is 49 MHz band for the up channel and 46 MHz band for the down channel, and 10 duplex channels are approved by the FCC.

Thus, according to this cordless telephone, the telephone can be conveniently used.

By the way, in such a cordless telephone,
The handset (1) is provided with a mode switch called a talk switch, and when the mode switch is switched to the standby contact, only the receiving circuit operates and waits for a call from the base unit (2). When the talk switch is switched to the talk contact, the transmission circuit also works to call the base unit (2).

In addition, the base unit (2) does not have a mode switch such as a talk switch, and normally only the receiving circuit works to call from the handset (2) or there is an incoming call from the telephone line (3). Then, the transmission circuit also works to link the handset (1) and the base unit (2) through radio waves.

Then, when the call ends, in the handset (1), the talk switch may be switched to the standby contact.

However, since the base unit (2) does not have a mode switch like a talk switch, the base unit (2)
A method of using a guard tone signal or an end code is considered as a method of ending the call.

That is, the former is, during a call, from the handset (1) to the base unit (2) outside the voice band, for example in
A 4 kHz guard tone signal is continuously transmitted at the same time as a voice signal, and when the base unit (2) cannot obtain this guard tone signal, it is regarded as an end call and the end call processing is performed and the standby mode is entered. .

Also, the latter, when the talk switch of the handset (1) is switched to the standby contact, the handset (1)
When the base unit (2) receives the end code from the base unit (2) and the base unit (2) receives the end code, the base unit (2) performs a call termination process and enters the standby mode.

However, in either method, even if the other party hangs up before the talk switch of the handset (1) is switched to the standby contact, this cannot be detected by the base unit (2), so that the handset (1) eventually turns off the talk switch. When is switched to the standby contact, the call termination processing is performed as described above.

D Problem to be solved by the invention However, in the method using the guard tone signal, the oscillator circuit for forming the guard tone signal, the low pass filter and the band pass filter for separating the voice signal and the guard tone signal from each other. However, a guard tone signal detection circuit is required, resulting in an increase in cost.

Also, with the method of using the end code, when the handset (1) is used in a place where the radio wave condition deteriorates, such as near the limit of the service area, the base unit (2) cannot receive the end code correctly. As a result, the base unit (2) may not perform the call termination processing, and the telephone line (3) may remain unopened.

The present invention is intended to solve such a problem.

E Means for solving the problem In the cordless telephone, since the FM wave is used between the handset (1) and the base unit (2), the squelch signal NSQL is obtained in the base unit (2). This changes, for example, as shown in FIG.

That is, when the base unit (2) can sufficiently receive the FM wave from the handset (1), the signal NS
Signal QL when QL becomes "L" level and reception is not possible
Is at "H" level. Then, as shown in the period T ₁ , the FM wave from the handset (1) can be stably received,
Therefore, when you can make a stable call (for example, when the handset (1) is in the service area)
NSQL is always "L" level. However, as shown in the period T ₂ , the reception of the FM wave from the handset (1) becomes unstable, so that when some noise is mixed in the call (for example, the handset (2) is near the limit of the service area). Signal NSQL is often at "L" level, but occasionally becomes "H" level in response to noise. The period τ ₂ for which NSQL = “L” is 200 ms or more, depending on the time constant of the squelch detection circuit.

Further, as shown in the period T _3, when the FM wave from the handset (1) is hardly received, and therefore the call is hardly available (for example, when the handset (1) stops transmitting or when the handset (1) is in service. When outside the area), the signal NSQL remains almost at the “H” level, and occasionally becomes the “L” level.

This invention focuses on the fact that the squelch signal NSQL changes in this way, and basically uses the end code to perform the end processing of the base unit (2), but also uses the squelch signal NSQL in combination. The end call processing is also performed based on the change pattern of NSQL.

Even if the termination code cannot be received by the F-action base unit (2), the termination processing of the base unit (2) is performed.

G Embodiment G ₁ First Embodiment FIG. 1 shows an example of a handset (1), in which (110) is a transmitting circuit and (120) is a receiving circuit. Further, FIG. 2 shows an example of the base unit (2), in which (210) is a transmitting circuit and (220) is a receiving circuit.

Then, at the time of transmission, in the handset (1), the audio signal St from the transmitter (111) is changed to the low frequency amplifier (112).
Is supplied to the VCO (not shown) of the PLL (113) through and is converted to the FM signal Su of the upstream channel, and this FM signal Su is
It is supplied to the antenna (100) through a high frequency power amplifier (114) and a band pass filter (115) whose pass band is all upstream channels, and is supplied to the base unit (2).
Sent to.

Then, in the base unit (2), the signal (radio wave) Su from the handset (1) is received by the antenna (200), and the received signal Su is a bandpass filter (221) having all upstream channels as pass bands. ) And the high frequency amplifier (222) to the mixer circuit (223), and the local oscillation signal of a predetermined frequency from the PLL (224) is supplied to the mixer circuit (223) to convert the signal Su into an intermediate frequency signal. The intermediate frequency signal is supplied to the FM demodulation circuit (226) through the intermediate frequency amplifier (225) to demodulate the audio signal St, and this signal St is converted to the low frequency amplifier (22
7) → 2 wire to 4 wire conversion circuit (231) → relay circuit (232)
Is sent out to the telephone line (3) through the signal line.

In this case, the relay circuit (232) is a line relay for turning on / off the connection between the base unit (2) and the telephone line (3), and a call is made after the base unit (2) and the line (3) are connected. When suspending, the line (3)
It has a hold relay and so on for holding.

In addition, when receiving a voice signal Sr from the telephone line (3)
Is supplied to the handset (128) of the handset (1) by the same processing as when transmitting. That is, the voice signal Sr from the line (3) is converted into the relay line (232) → the conversion circuit (231).
→ The PLL (21
3) It is supplied to the VCO (not shown) and is converted to the FM signal Sd of the downlink channel that is paired with the FM signal Su of the uplink.
Sd is a high frequency power amplifier (214) and a band pass filter (215) whose pass band is all downlink channels.
Through the antenna (200) and transmitted to the handset (1).

Then, in the handset (1), the signal Sd from the base unit (2) is received by the antenna (100), and the received signal Sd has a band pass filter (121) having a pass band in all downlink channels and a high frequency wave. The local oscillation signal of a predetermined frequency is supplied to the mixer circuit (123) from the PLL (124) through the amplifier (122) to the mixer circuit (123), and the signal Sd becomes an intermediate frequency signal. The signal is supplied to the FM demodulation circuit (126) through the intermediate frequency amplifier (125) to demodulate the audio signal Sr, and the signal Sr is supplied to the receiver (128) through the low frequency amplifier (127).

Further, in the handset (1), reference numeral (140) represents a control circuit for controlling a communication channel and the like. The control circuit (140) is composed of a one-chip type microcomputer. For example, (141) is a CPU for 4-bit parallel processing, (142) is a ROM in which a program is written, and (143) is RAM for work area, (144) is an input / output port. The ROM (142) is also provided with a routine (300) shown in FIG. 3, for example.

Furthermore, the microcomputer (140) has a dial key (151),
The talk switch (152) and the ROM (153) are connected.
In this case, the dial key (151) is a non-lock type push switch for inputting the other party's telephone number,
The talk switch (152) is a three-position selector switch for selecting the operation mode of the handset (1), and when the switch (152) is at the contact O, the power of the circuits other than the microcomputer (140) is turned off. When the contact S is turned off (off mode), the signal Sd from the base unit (2) is in a standby state (standby mode),
At the contact point T, the handset (1) and the base unit (2) are in a call state (talk mode), and are normally connected to the standby contact point S.

The ROM (153) is for giving an identification code ID, and these keys and the outputs of the ROMs (151) to (153) are supplied to the microcomputer (140).

Further, (161) shows an MSK modulation circuit which, when supplied with a code signal such as an identification code ID and a dial signal DS from a microcomputer (140), shows this code signal from a binary signal in FIG. As described above, the MSK signal Sm in the audio band is converted, and the signal Sm is supplied to the amplifier (112).

Further, (162) represents a squelch detection circuit, which is connected to the demodulation circuit (126), and the frequency component of the output of the demodulation circuit (126) differs depending on the presence or absence of the signal Sd from the base unit (2). Signal Sd as shown in FIG.
Is detected, and the squelch signal NSQL is supplied to the microcomputer (140).

Further, (163) indicates an MSK demodulation circuit, which is connected to the demodulation circuit (126) and demodulates a code signal from the MSK signal Sm sent from the base unit (2). Supplied to the microcomputer (140).

Further, (164) represents a ring tone signal forming circuit, which is controlled by the microcomputer (140) and forms a bell sound signal (ring tone signal) when a call is received. Supplied to the Ringer (165).

Further, a signal CH designating a channel is supplied from the microcomputer (140) to the PLLs (113) and (124), and a signal TXEN for controlling whether or not the FM signal Su is sent is PL.
Supplied to L (113). The muting signal MUTE is supplied from the microcomputer (140) to the amplifier (127).

Further, in the base unit (2), (240) indicates a control circuit. The control circuit (240) is configured similarly to the control circuit (140) of the handset (1) and has the same function, and the circuit (141) of the control circuit (140).
For the circuits corresponding to (144), replace the numbers in the 100s
Numbers in the 200s are attached and explanations are omitted. However, ROM
For example, the routine (400) shown in FIG. 4 is provided in (242).

The ROM (253) and the circuits (261) to (264) are also the same as the ROM (153) and the circuits (161) to (164) of the handset (1), and the same applies to each signal. The description is also omitted. However, the forming circuit (264) forms the tone encode signal (DTMF signal) TE corresponding to the telephone number when making a call to the other party.

Furthermore, (265) shows a ring tone signal detection circuit,
This is for detecting a bell sound signal (ring tone signal) when a call is received by being connected to the telephone line (3), and the detection signal BL is supplied to the microcomputer (240).

And the handset (1) and the base unit (2)
In accordance with routines (300) and (400), CP
The following processes are performed by U (141) and (241).

That is, in the handset (1), in the standby (standby mode), in the step (301), the signal CH
Controls the PLLs (113) and (124) to set the upstream and downstream channels corresponding to the value of the signal CH, and then checks the switching position of the talk switch (152) in step (302). Since it is connected to the contact S in standby mode,
Proceed from step 2) to step (303). Then, in this step (303), it is checked by the signal NSQL whether or not the carrier signal such as the FM signal Sd is received by the downlink channel set in the step (301). If the signal is not received, the process is performed in step. The process proceeds from step (303) to step (304), the signal CH is set to the value of the next channel (adjacent channel) in step (304), and then the process returns to step (301).

When the signal is received in step (303), the process proceeds from step (303) to step (305), in which the identification code ID from the demodulation circuit (163) and the ROM (153) are read. It is checked whether the identification code ID and the identification code ID match, and if they do not match (from the base unit (2) of another subscriber), the process proceeds from step (305) to step (304).

Therefore, in the handset (1), when waiting,
Steps (301) to (305) are repeated, and as shown in FIG. 6A, all downlink channels are sequentially and repeatedly scanned.

In FIG. 6, the left side shows the channels managed by the handset (1), and the right side shows the channels managed by the base unit (2). Also, [1] to [10]
The numbers in () indicate the channel numbers, the ○ mark indicates an empty channel, the ● mark indicates the channel used by oneself, and the X mark indicates the channel used by another station.

In the base unit (2), steps (401) to (405) and (441) of the routine (400) are executed during standby. In this case, steps (401) to (405) perform the same processing as steps (301) to (305), and a description thereof will be omitted, but in step (402),
The presence or absence of an incoming call from the outside line (3) is detected by the detection signal BL, and when there is no incoming call, the process proceeds from step (402) to step (403). In step (403), the presence / absence of a carrier signal such as FM signal Su is checked instead of the presence / absence of a carrier signal such as FM signal Sd in step (303).

Therefore, in the base unit (2), steps (401) to (405) are repeated in the standby state, and all the upstream channels are repeatedly and sequentially scanned as shown in FIG.

When the handset (1) makes a call, the talk switch (152) is switched to the talk mode contact T. Then, this is determined in step (302), the process proceeds from step (302) to step (311), and in this step (311), the uplink and downlink channels set by step (301) are used by another station. If it is not used, the process proceeds from step (311) to step (312). Then, in this step (312), the sending of the FM signal Su is permitted by the signal TXEN, and then in the step (313), the identification code ID of the ROM (153) is converted into the MSK signal Sm by the modulation circuit (161) and the amplifier ( 112)
6 and thus the identification code ID is transmitted to the base unit (2) by the FM signal Su of the upstream channel set in step (301).

In this case, if the identification code ID is not returned from the base unit (2), the transmission of the identification code ID in the step (313) is performed for at least one round of scanning the channel in the base unit (2). It is repeated.

Then, in the base unit (2), while waiting, all the upstream channels are sequentially scanned by repeating steps (401) to (405), but the handset (1) transmits the identification code ID. When the number of the upstream channel is reached, the process is step (403).
To step (405), the scan is stopped, and it is determined that the identification code ID has been sent.

Then, the process proceeds from step (405) to step (421), and in this step (421), the signal TXEN causes FM.
Transmission of the signal Sd is permitted, and then in step (422), the identification code ID of the ROM (253) is set to M by the modulation circuit (261).
The SK signal Sm is supplied to the amplifier (212). Therefore, as shown in FIG. 9B, the identification code ID is determined by the FM signal Sd of the downlink channel paired with the uplink channel set in step (301). Returned to handset (1).

Then, the process proceeds from step (422) to step (431), in which the base unit (2) and the telephone line (3) are connected, that is, the signal
Muting of the amplifier (227) is released by MUTE, and the conversion circuit (23
1) and the line (3) are connected.

In the handset (1), step (31
At the same time as transmitting the identification code ID in 3), it is checked by the output signal of the demodulation circuit (163) whether or not the identification code ID is returned in step (314) (actually, in step (313) (314) and (314) are alternated in a time-division manner, and are performed until the channel is scanned once in the base unit (2) or until the return of the identification code ID is confirmed).

Then, in this case, since the base unit (2) has returned the identification code ID, the process proceeds from step (314) to step (331), and in this step (331), the handset (1) and the base unit (2). ) Is connected, that is, in the handset (1), the muting of the amplifier (127) is released by the signal MUTE.

Therefore, the handset (1) is connected to the telephone line (3) through the base unit (2).

Therefore, in the handset (1), dial key (15
When 1) is operated according to the telephone number of the other party, the corresponding dial signal DS is formed by the microcomputer (140) and is converted into the MSK signal Sm by the modulation circuit (161).
Similarly, it is returned to the base unit (2).

Then, in the base unit (2), the dial signal DS is taken out from the demodulation circuit (263), and this signal DS
Based on, the formation circuit (264) is controlled by the microcomputer (240) to form a tone encode signal TE corresponding to the telephone number of the other party, and this signal TE is passed through the amplifier (227),
Further, it is sent to the telephone line (3) through the conversion circuit (231) and the relay circuit (232). Therefore, this signal
When the other party is called by the TE and the other party answers the call, the call becomes possible as described above.

In step (311), if the channel set in step (301) is already used by another station, the process proceeds from step (311) to step (304), and the signal is transmitted by this step (304). CH is set to the value of the next channel, and the process returns to step (301).
Therefore, steps (312) to (314), (421), (4
The processing of 22) will be performed on an empty channel, and subsequent calls will be made on that empty channel.

If the correct identification code ID is not returned from the base unit (2) in step (314), the process proceeds from step (314) to step (315).
Then, in this step (315), the transmission of the signal Su is stopped by the signal TXEN, and then the process proceeds to the step (30
Go to 4). Therefore, when the identification code ID is not returned from the base unit (2), the base unit (2) is similarly called in the next vacant channel.

Thus, when the handset (1) makes a call, when the talk switch (152) is set to the talk contact T, an empty channel is searched for, the base unit (2) is called by the empty channel, and a response is sent from the base unit (2). If there is, a channel is opened between the handset (1) and the base unit (2), and it becomes possible to call and talk with the other party.

When an incoming call is received from the telephone line (3), steps (411) to (415) of the routine (400) and steps (321) and (322) of the routine (300) are executed.
In this case, these steps (411) to (415) and (32
1) and (322) are steps (311) to (315) and (42).
1) and (422), the signal BL is discriminated in step (402) when there is an incoming call, so the process proceeds from step (402) to step (411), and thereafter. As shown in FIG. 6C, the telephone line (3) is connected to the handset (1) through the base unit (2) in the same manner as when making a call.

Then, when the handset (1) and the base unit (2) are connected to each other by a call from the handset (1) or an incoming call from the telephone line (3) to make a call, the handset (1) In, the processing proceeds from step (331) to step (351). In this step (351), the contact position of the talk switch (152) is checked, and when it is connected to the talk contact T,
Return to processing (351). Therefore, the contact position of the talk switch (152) is always monitored during a call.

Then, when the call ends, the talk switch (152)
When the switch is switched to the standby contact S, this is discriminated by the step (351), and the processing advances from the step (351) to the step (352). By this step (352), an end code indicating the end of the call in the microcomputer (140). Is formed, and this end code is converted into an MSK signal Sm by the modulation circuit (161) and transmitted to the base unit (2) by the FM signal Su.

The process then proceeds to step (353), where F is generated by the signal TXEN.
While the transmission of the M signal Su is stopped, the signal MUTE mutes the amplifier (127) to close the channel, and then the process returns to step (301).

Therefore, in the handset (1), the call is ended. Therefore, when the talk switch (152) is connected to the standby contact S, the end code is transmitted to enter the standby mode, and the channel next to the one used for the call up to now is transmitted. The scanning of the channel is started from the channel of as shown in FIG. 6A.

In the base unit (2), the process proceeds from step (431) to step (451) during a call. This step (451) and subsequent steps (452) to (456)
Is for detecting that the state is in the period T ₃ , and the details thereof will be described later.

Then, in the present case, if the base unit (2) is in the state of the period T ₁ , the process proceeds to step (455) or (45).
Proceed from step 8) to step (461) and proceed to this step (461).
At, it is checked whether the end code from the handset (1) is obtained as the demodulation output of the demodulation circuit (263). If the end code is not obtained, the process returns to step (452). Therefore, the reception of the end code is always monitored during the call.

Then, when the call ends and the end code is sent in step (352), this is discriminated in step (461), and the process proceeds from step (461) to step (462).
To F by the signal TXEN in this step (462).
The transmission of the M signal Sd is stopped, and the amplifier (22
Muting is applied to 7), and the connection between the conversion circuit (231) and the telephone line (3) is turned off by the relay circuit (232), and the base unit (2) is connected to the line (3).
Is released from.

Therefore, when the end code is received in the base unit (2), the base unit (2) enters the standby mode and starts scanning the channel from the channel next to the channel used for the communication as shown in FIG. .

Even if the other party hangs up before switching the talk switch (152) to the standby point S, this cannot be detected by the base unit (2), so the talk switch (15
When 2) is switched to the standby contact S, the above-mentioned processing for ending the call is performed.

On the other hand, if the base unit (2) is in the state of the period T ₂ or T ₃ , in steps (451) to (456),
The period when the signal NSQL does not become "L" level for the period τ ₂ or more,
Predetermined period of time tau _{3 (which} is the user of the handset (1) is, in the time required to return to normal service area from the vicinity of the limit of the service area, for example, tau _{3 =} 10 seconds) when over the period T ₃ It is considered that the state is, and the end call processing is performed.

That is, the timer TMR2 for measuring the period τ ₂ and the period τ
A timer TMR3 for counting ₃ is prepared by software, for example, and these timers TMR2,
TMR3 is cleared, then in step (452) signal N
When the SQL level is checked and NSQL = "L" (mainly in the periods T ₁ and T ₂ ), the process proceeds from step (452) to step (453) in which the timer TMR2 Is incremented by a predetermined amount. Then, in the next step (454), the timer TMR2 sets the period τ
_It is checked whether or not it becomes ₂ or more, and when TMR2 ≥ τ ₂ , the processing is from step (454) to step (455).
To step (461) after the timer TMR3 is cleared in this step (455), and it is checked in this step (461) whether an end code has been received. If not, the process proceeds to step (461). Return to step (452) from.

Further, when the NSQL = "H" in step (452) (mainly when the period T _3), the process proceeds from step (452) to the step (456), the timer TMR2 is cleared in step (456) , then in step (457) the timer TMR3 is incremented by a predetermined amount, followed by whether the timer TMR3 is time tau ₃ or more in the step (458) is checked, TMR3 <processing at the time of the tau ₃ steps (458 ) To step (461), TM
When R3 ≧ τ ₃ , the process proceeds from step (458) to step (462). In addition, in step (454)
Process when TMR2 <tau ₂ proceeds from step (454) to the step (457).

Therefore, step (454) checks whether the period of NSQL = "L" is longer than the period τ ₂ , and when the period of NSQL = "L" does not reach the period τ ₂ , NS
Since it is checked whether the period of QL = “H” is longer than the period τ ₃ , the period of NSQL = “L” is longer than the period τ ₂ (in the state of the period T ₁ ), or NSQL ＝
When the "H" period is shorter than the period τ ₃ (when the period is T ₂ )
, The process proceeds to step (461), and therefore steps (452) to (458) and (461) are repeated in the periods T ₁ and T ₂ , and the end code and the level of the signal NSQL are monitored. It will be.

Then, when the end code is received, the process proceeds from step (461) to step (462), and thus the call termination process is performed as described above.

However, when the period during which the signal NSQL does not become the "L" level for the period τ ₂ or more extends for the period τ ₃ (in the state of the period T ₃ ), this is the step (452), (454), (458).
And the process proceeds to step (462).
In the state of the period T ₃ , the call ending process is performed in step (462), and the telephone line (3) is opened.

Therefore, even if the reception state of the FM signal Su from the handset (1) is bad in the base unit (2) and the end code cannot be received normally, the handset (1) switches the talk switch (152) to the standby contact S. As a result, when the transmission of the FM signal Su is stopped, the base unit (2) also ends the call after a period τ ₃ and enters the standby mode.

Thus, according to the invention, when communication between the handset (1) and the base unit (2) becomes difficult, or when the handset (1) enters standby mode, the base unit (2) enters standby mode and the telephone Open line (3).

Moreover, the structure for that purpose is simple and low cost because it is only necessary to add steps (451) to (458) to the routine (400), there is no need to provide a dedicated circuit as in the guard tone system.

G ₂ Second embodiment In this example, the call channel is changed when the period τ ₃ has passed after the period T ₃ , and the telephone line (3) is opened when the call is still not made. This is the case.

That is, as shown by the broken line on the handset (1),
A channel switch (154) is connected to the microcomputer (140). This switch (154) is a non-locking type push switch for changing the call channel to the next empty channel when the call channel with the base unit (2) becomes unstable while disturbing during the call. Is.

Further, steps (361) to (363) are added to the routine (300) of the ROM (142) as shown in FIG.
Steps (471) to (484) are added to the routine (400) of 2) as shown in FIG.

Then, the same processing as described above is performed at the time of waiting, making a call, and receiving a call, but the following processing is performed at the time of talking and ending the call.

That is, in the handset (1), the talk switch (152) is checked in step (351), and when it is switched to the talk contact T, the process proceeds from step (351) to step (361). If the channel switch (154) is checked at (361) and the switch (154) is not pressed, the process returns to step (351).

Therefore, the states of the switches (152) and (154) are monitored during the call.

Then, when the call is ended and the talk switch (152) is switched to the standby contact S, the process is step (351).
To (352) and (353), the call-end processing is performed as described above.

When the handset (1) is near the limit of the service area and noise is generated during a call, the channel switch (154) is pressed. Then, this is discriminated in the step (361), and the processing advances from the step (361) to the step (362).
In 2) the signal MUTE mutes the amplifier (127) and then in step (363) the signal TXE.
The process returns to step (304) after the transmission of the signal Su is stopped by N.

Therefore, in the handset (1), when the channel switch (154) is pressed, an empty channel is searched for as in the case of making a call, and when an empty channel is found, the identification code ID is transmitted again in that channel and the base unit ( It will wait for the response of 2).

On the other hand, in the base unit (2), steps (452) to (458) and (461) are repeated as described above during a call, and the end code and the level of the signal NSQL are monitored. Then, when the end code is sent, the process proceeds from step (461) to step (462), and the call end process is performed.

Furthermore, during a call, the handset (1) is in a state of time period T ₃ and the like going out of the service area, after the lapse of time tau _3, since the TMR3 ≦ tau _3, the process steps from step (458) ( 471), the amplifier (227) is muted by the signal MUTE in this step (471), and then the signal TXEN is set to F by the signal TXEN in step (472).
Transmission of the M signal Sd is prohibited, and then another timer TMR4 is cleared in step (473).

Then, in step (474), the signal CH is set to the value of the next channel used for communication until then, and in step (475), the signal CH sets the PLLs (213) and (224) to the next channel. Then, in step (476), it is checked by the signal NSQL whether or not a carrier signal can be obtained in the channel set in step (475), and when the carrier signal is not obtained, the process proceeds from step (476) to step (477). ), The timer TMR4 is incremented by a predetermined amount in this step (477). Then, in step (478), it is checked whether or not the timer TMR4 has exceeded a predetermined period τ ₄ (for example, τ ₄ = 10 seconds). If TMR4 ≦ τ ₄ , the process proceeds from step (478) to step (478). Return to (474).

Further, when the carrier signal is obtained in step (476), the process proceeds from step (476) to step (48).
Proceed to step 1), it is checked whether or not the correct identification code ID is obtained in this step (481), and if it is not obtained, the processing proceeds from step (481) to step (477).
Proceed to.

Therefore, when the period τ ₃ elapses in the state of the period T ₃ , steps (471) to (481) are repeated as in the case of making a call, and the base unit (2) calls the handset (1). You will be searching.

The search for this call is done over a period tau _4, when catching a call handset (1) within the period tau _4, this time, since the normal identification code ID is obtained, the process from step (481) Step (48
Proceeding to 2), the transmission of the FM signal Sd is permitted in this step (482), then the identification code ID is transmitted to the handset (1) in step (483), and then the amplifier (227) is transmitted in step (484). After muting is turned off, the process returns to step (451).

Therefore, when the call of the handset (1) is caught within the period τ ₄ , the call can be resumed on the new channel.

However, if the handset (1) call cannot be caught within the period τ ₄ , step (478)
Since TMR4 ≧ τ ₄ at
Go from step 8) to step (462) and proceed to this step (462)
After the end of call process is performed, the process returns to step (401).

Therefore, in this example, when the handset (1) goes out of the service area and enters the state of the period T ₃ , or even when the end code transmitted by the handset (1) cannot be correctly received due to the end of the call, the handset (1 )
, The channel scan is restarted after a period τ ₃ to form a communication channel with the handset (1), and if this fails, the end call processing is performed.

G ₃ Other Embodiments In the above description, the circuits (161) to (164), (261)
The operation of (264) can be realized by software. Further, the telephone number of the other party can be sent out by a dial pulse.

The identification code ID in steps (313) and (413)
And the presence or absence of FM signals Sd, Su from the other party, and if these signals Sd, Su are obtained, step (31
The identification code ID may be checked in 4) and (414). Furthermore, the handset (1) may also check the level change of the signal NSQL and perform the same processing as the base unit (2).

H Effect of the Invention According to the present invention, when the communication between the handset (1) and the base unit (2) becomes difficult, or when the handset (1) enters the standby mode, the base unit (2)
Enters standby mode and opens the telephone line (3).

Moreover, the structure for that purpose is simple and low cost because it is only necessary to add steps (451) to (458) to the routine (400), there is no need to provide a dedicated circuit as in the guard tone system.

[Brief description of drawings]

1 and 2 are system diagrams of one example of the present invention, and FIGS.
FIG. 10 is a diagram for explaining it. (1) is the handset, (2) is the base unit, (11
0) and (210) are transmission circuits, (120) and (220) are reception circuits, and (140) and (240) are control circuits.

Claims (1)

[Claims] 1. A base unit connected to a telephone line,
A cordless telephone that has a base unit and a handset that makes a pair, and the handset and the base unit are connected by a call channel by radio waves during a call. The reception level of the radio wave is detected, and by this detection output, when the reception level does not become a low level for a first predetermined period or more and a second predetermined period or more elapses, the telephone is set in the base unit. A cordless telephone that opens the line. However, the first predetermined period is the interval of noise generated in the detection output when the handset is near the limit of the service area. The second predetermined period is the time required for the user talking on the handset to return to the normal service area.