JP2638900B2 - Cordless telephone - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital data transmission circuit.

[Summary of the Invention]

According to the present invention, for example, in a case where digital data is converted into an FM signal and transmitted, during a non-data period, an average DC level of “0” and “1” is set so that reliable conversion can be performed. It was done.

[Conventional technology]

In Japan and the United States, a telephone system called a cordless telephone has been considered.

As shown in FIG. 2, 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 connected by radio waves, and the telephone of the subscriber is handled in the same manner as a general telephone.

The distance that the handset (1) can be separated from the base unit (2), that is, the service area is about 300 m. The frequency of the radio wave used between the handset (1) and the base unit (2) is
In the United States, the up channel is in the 49 MHz band, the down channel is in the 46 MHz band, and 10 duplex channels are allowed.

Therefore, the subscriber is a telephone, a handset (1)
Can be moved freely, for example, a telephone can be used outdoors. Moreover, the phone cord is not tangled or obstructed.

FIG. 3 shows an example of such a handset (1) and a base unit (2).

That is, at the time of speech transmission, the audio signal St from the transmitter (111) is transmitted to the handset (1) by the amplifier (112).
And supplied to a VCO (not shown) of a PLL (115) through an adder circuit (114) to become an upstream channel FM signal Su. This signal Su is supplied to an antenna (110) through a high frequency power amplifier (117). And transmitted to the base unit (200).

Then, in the base unit (2), the signal (radio wave) Su is received by the antenna (200), and this signal Su is received.
Is supplied to a tuner circuit (226) having from the antenna input circuit to the FM demodulation circuit, and the FM signal Su converts the audio signal St
Is demodulated, and this signal St is sent out to the telephone line (3) through the signal line of the amplifier (227) → the 4-wire / 2-wire conversion circuit (231) → the relay circuit (232).

At the time of reception, the voice signal Sr from the telephone line (3) is received.
However, the relay circuit (232) → conversion circuit (231) → amplifier (21
2) → PLL (215) through the signal line of the adder circuit (214)
Is supplied to a VCO (not shown) as a down channel FM signal Sd.
It is supplied to the antenna (200) through 7) and transmitted to the handset (1).

Then, in the handset (1), the signal Sd is received by the antenna (100), and this signal Sd is supplied to a tuner circuit (126) having from the antenna input circuit to the FM demodulation circuit, and the audio signal is converted from the FM signal Sd. Sr is demodulated and this signal Sr is passed through the amplifier (127) to the receiver (128).
Supplied to

Further, (140) and (240) show microcomputers for system control.
At the time of calling and receiving according to (0) and (240), the following processing is performed.

That is, at the time of calling, when the talk key (152) is changed from the standby mode to the talk mode in the handset (1), the PLL (115) is controlled by the signal TXEN from the microcomputer (140) and the sending of the FM signal Su is permitted. Is done. Subsequently, the microcomputer (140) outputs a command signal CMND (to be described in detail later) for instructing a call, and this signal CMND is transmitted through the correction circuit (161) and the addition circuit (114).
PLL (115) and therefore the command signal CMND
Is transmitted from the antenna (100).

Accordingly, the command signal CMND is taken out from the tuner circuit (226), and this command signal is sent to the shaping circuit (26).
It is supplied to the microcomputer (240) through 3), and it is determined that the call has been made. Then, the microcomputer (240) controls the relay circuit (232) to the off-hook state, connects the modulation circuit (231) to the line (3) through the relay circuit (232), and sends out the FM signal Sd by the signal TXEN. Is allowed.

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

Therefore, when the telephone number of the other party is input from the dial key (151), a command signal CMND including the transmission of the telephone number and the data of the input telephone number is output from the microcomputer (140), and is transmitted by the FM signal Su. Sent.

When the FM signal Su is received by the base unit (2), the command signal CMND is transmitted to the microcomputer (24).
0) and the microcomputer (240) controls the dial signal forming circuit (265) to form a tone encode signal (DTMF signal) TENC corresponding to the telephone number sent by the command signal CMND. signal
TENC is supplied to the amplifier (227) and sent out to the line (3).

Therefore, when the signal TENC is sent out, the other party is called, and once the other party answers the telephone, the call can be made thereafter as described above.

At the time of an incoming call, a ring tone signal when a call is received is detected by a detection circuit (268), and a command signal CMND indicating an incoming call is output from the microcomputer (240) according to the detection signal. CMND is supplied to the PLL (215) through the correction circuit (261) and the addition circuit (214), and is transmitted by the FM signal Sd.

Then, in the handset (1), the command CMND is supplied to the microcomputer (140) through the shaping circuit (163). Then, the linger (1
66) is informed that a call has been received.

Therefore, when the talk switch (152) is switched from the standby mode to the talk mode, the same processing as that performed when making a call is performed, and the handset (1) is connected to the line (3) through the base unit (2). You can talk with the other party.

When the call ends, the talk switch (15
When 2) is changed from the talk mode to the standby mode, the microcomputer (140) forms a command signal CMND indicating the end of the call, which is transmitted by the FM signal Su, and
Thereafter, the transmission of the FM signal Su is stopped by the signal TXEN.

In the base unit (2), when the command signal CMND indicating the end of the call is sent, the microcomputer (240)
Controls the relay circuit (232) to the on-hook state, and the transmission of the FM signal Sd is stopped by the signal TXEN.

Therefore, thereafter, the handset (1) and the base unit (2) wait for a call or an incoming call.

FIG. 4 shows an example of the signal format of the command signal CMND. At the beginning, 12 bits or more, in this example,
It has a 16-bit bit synchronization signal BSYN, followed by a 16-bit frame synchronization signal FSYN. In this case, these signals BSYN and FSYN have a specific bit pattern represented by, for example, BSYN = “0101010101010101” FSYN = “1100010011010110”... For upstream channel FSYN = “1001001100110110”.

In addition, the command signal CMND follows the signal FSYN, followed by the paired handset (1) and base unit (2).
And a 12-bit error correction code ECC for the identification code ID in order, and an 88-bit control code CTRL following the code ECC.

In this case, the identification code ID is checked on the receiving side every time the command signal CMND is accessed between the handset (1) and the base unit (2), and the paired handset (1) and base unit (2) are checked. ), The command signal CMND is made valid.
The control code CTRL is a code for controlling the opening and closing of the channel between the handset (1) and the base unit (2) as described above, and indicates that the transmission of the telephone number of the other party is the telephone number. Code, etc.
For example, when a channel is opened, it has data of a first bit pattern and dummy data, and when it is a partner's telephone number, it has data of a second bit pattern and data of the telephone number. , Data indicating the type of control (operation code), and data (operand) required for the control.

In this command signal CMND, the synchronization signal BSY
N and FSYN are RNZ signals, but identification code ID to control code C
TRL is a split phase signal (Manchester code) converted from the NRZ signal. The transmission speed of the signal CMND is, for example, 1200 bps.

Therefore, when the command signal CMND is transmitted, the signals Su and Sd are FSK signals (MSK signals).

Also, since the signal CMND is in the format described above,
The correction circuit (161) (and (216)) has resistors R ₁ and R ₂ for level adjustment and a capacitor C ₁ for DC cut.

Reference: Specification and drawings of Japanese Patent Application No. 61-1774397 [Problem to be Solved by the Invention] However, the command signal CMND is temporarily formed at the time of outgoing call, incoming call, end of call, etc. The remaining period is, for example, “0” level.

Therefore, when such a command signal CMND is supplied to the VCO of the PLL (115) through the correction circuit (161), the DC level of the signal CMND fluctuates at the start and end of the command signal CMND. The frequency of Su also fluctuates, and when the command signal CMND is extracted from the FM signal Su in the base unit (2), an error occurs in the signal CMND.

The present invention is intended to solve such a problem.

[Means for solving the problem]

In order to solve the above problems, a cordless telephone according to the present invention includes the following means. That is, in a cordless telephone in which a carrier signal is analog-modulated by a binary signal obtained intermittently and the modulated signal is transmitted as a command signal, a first and a second output port for supplying the binary signal A first and a second input terminals respectively connected to outputs of the first and second output ports, and a first and a second terminals connected in series between the first and second input terminals. Two resistors, third and fourth resistors connected in series between a connection midpoint between the first and second resistors and ground, and a connection midpoint between the third and fourth resistors. A level adjustment circuit having an output terminal connected to the level adjustment circuit; and a modulation circuit connected to the output terminal of the level adjustment circuit for performing the analog modulation. The signal in the intermittently obtained binary signal is transmitted. Not during the period above To "0" and "1" to output complementary signals consisting of the level of the first and second output ports.

[Action]

During non-data periods without the command signal CMND, the signal CMND
Is the average DC level in the data period.

〔Example〕

In FIG. 1, the microcomputer (140) (and (240))
Is a 4-bit parallel processing CPU (141), a ROM (142) in which a program is written, and a work area RAM (14).
3), an input port (144), and an output port (145), and these circuits (142) to (145) are connected to a CPU (141) through a system bus (149).

The ports (144) and (145) are representative of a plurality of ports, and these ports (144) and (145)
The above-mentioned signals (except the command signal CMND) are accessed.

Further, a 1-bit output port (1
46) and (147) are connected, and resistors R ₆ and R ₇ having the same value are connected in series between their output terminals.
Resistors R ₈ and R ₉ having a predetermined value are connected in series between the connection point of these resistors R ₆ and R ₇ and the ground, and these resistors R ₈ and R ₉
Is connected to the addition circuit (114).

The port (146), the output data (147) to (1-bit), if the D _6, D _7, according to the presence or absence and the level of the command signal CMND by a program of ROM (142), data D _6, D ₇ has the following levels:

_{CMND = "1" D 6 =} "1" _{when, D 7 = "1" CMND} = "0" D 6 = when _{"0", D 7 = "} 0" when there is no CMND D ₆ = "0" , D ₇ = “1” (or D ₆ = “1”,
D ₇ = “0” According to such a configuration, when the command signal CMND is output, the data D ₆ and D ₇ are added by the resistors R ₆ and R ₇ , and the added output D ₈ is the resistor R ₈ , It is supplied to the VCO of the PLL (115) through the adder circuit (114) after being level adjustment by R _9.

In this case, since the data D ₆ and D ₇ have the above-mentioned relationship with the signal CMND, when the command signal CMND is transmitted, D ₈ = CMND, and the data D ₈
Sent as CMND. That is, transmission of the command signal CMND is equivalent to the conventional one.

When the command signal CMND is not transmitted, D ₆ =
Since “0”, D ₇ = “1”, the data D ₈ is a DC level at the center between the levels “0” and “1” (generally, “0” =
0 [V], "1" = 5 since V, a D ₈ = 2.5 [V]) P is the center of the DC level through the addition circuit (114)
LL (115).

Therefore, the DC level supplied to the PLL (115) is the same regardless of whether the command signal CMND is transmitted or not, so that the frequency of the FM signal Su does not fluctuate. Can be demodulated correctly,
No errors occur.

Thus, according to the present invention, when the command signal CMND is not transmitted, the average DC level of the command signal CMND is output. No errors occur. Moreover, the configuration for this is simple, and there is almost no increase in cost.

In the above description, two ports (146), (14
Although 7) is used, when the output port has a 2-bit (or more) output terminal, the 2-bit data D ₈ and D ₉ may be used.

Further, the present invention is not limited to a cordless telephone, and the present invention can be applied to a case where analog modulation is performed using a binary signal obtained intermittently and the binary signal is transmitted.

〔The invention's effect〕

According to the present invention, when the command signal CMND is not transmitted, the average DC level of the command signal CMND is output.
When demodulating CMND, no error occurs due to fluctuations in the DC level. Moreover, the configuration for this is simple, and there is almost no increase in cost.

[Brief description of the drawings]

FIG. 1 is a connection diagram of an example of the present invention, and FIGS. 2 to 4 are diagrams for explaining the same. (115) and (125) are PLLs, and (140) and (240) are microcomputers.

Claims (1)

(57) [Claims] 1. A cordless telephone in which a carrier signal is analog-modulated by a binary signal obtained intermittently and the modulated signal is transmitted as a command signal. A microcomputer having an output port, and first and second input terminals connected to the outputs of the first and second output ports, respectively, and serially connected between the first and second input terminals. A third resistor connected in series between the first and second resistors and a connection midpoint between the first and second resistors and ground;
And a fourth resistor, a level adjusting circuit having an output terminal connected to a connection midpoint between the third and fourth resistors, and performing the analog modulation connected to an output terminal of the level adjusting circuit. And a modulation circuit, wherein during a period in which the signal of the intermittently obtained binary signal is not transmitted, “0” is supplied to the first and second output ports.
And a cordless telephone that outputs a complementary signal consisting of each level of "1".