JP3218803B2 - Cordless telephone - Google Patents

Abstract

PURPOSE:To avoid interference by comparing received electric field intensity with the phase error output of a bit cycle circuit, detecting the presence/absence of an interferred signal and sending a channel revision signal to a channel control circuit when the interference is generated. CONSTITUTION:When the data converting point of a detecting signal from a detection circuit 11 is fluctuated by interference, the phase of a converting point signal detected by a converting point detection circuit 13 is fluctuated as well, and the output of a phase comparator 14 inputting a regenerative clock 17 is considerably fluctuated. Then, a phase error voltage 30 exceeds a reference voltage 29, and the output voltage of a voltage comparator 32 is made positive. Since the data converting point is fluctuated when the received electric field intensity is weak in addition to when there is interference, the voltage 30 turns high. Therefore, a voltage 29 is set to an electric field intensity voltage 27 and when the received electric field intensity exceeds the set value, the output of a voltage comparator 31 is made positive. Thus, only when outputs from both the comparators 31 and 32 are made positive, the interference is judged. At such a time, an AND circuit 35 is also made positive, and the revised signal is outputted to a channel control circuit 34.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cordless telephone.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of a receiving section of a conventional cordless telephone. In FIG. 2 (a), 1 is an antenna (ANT), 2 is a high frequency circuit for amplifying and converting received radio waves, 3 is a detection circuit for detecting a signal from the high frequency circuit 2, and 4 is a detection circuit for a detection circuit 3. A bit synchronizing circuit for performing resampling to remove the influence of the transmission path after shaping the signal into a digital waveform, and a data / speech converter for converting demodulated data demodulated by the bit synchronizing circuit 4 into a received voice. The circuit outputs a received voice 6. FIG.
In (b), 7 is a channel change switch for manually changing a channel. When this switch is pressed,
A channel change signal is output to the channel control circuit 8 to change the transmission / reception channel.

[0003] A transmission signal from a fixed device or a mobile device enters the antenna 1, and passes through a high frequency circuit 2, a detection circuit 3, a bit synchronization circuit 4, and a data / voice conversion circuit 5 to become a received voice 6. Here, if there is interference at the same frequency as the received signal, the interference signal is demodulated in the same manner, so that noise due to the interference is mixed into the received voice 6.

[0004]

In such a conventional cordless telephone, when noise due to interference occurs, a user of the cordless telephone manually operates a channel change switch every time interference occurs. A channel change must be made. Also, some cordless telephones have a function to automatically select a channel that is not being used when the call channel is first determined, but it is determined that it is not used once and selected and used. If interference occurs later in the channel being used, interference cannot be avoided, so that a manual channel change is also required.

An object of the present invention is to provide a cordless telephone capable of detecting interference and changing the channel automatically to a channel free of interference with a simple configuration without changing the conventional data transmission format. With the goal.

[0006]

According to the present invention, an electric field intensity signal from a detection circuit of a receiving unit is provided.
The interference is automatically avoided by using the phase error signal of the bit synchronization circuit.

The electric field strength signal has a characteristic as shown in FIG. 3. When the distance between the fixed machine and the mobile machine of the cordless telephone increases and the received electric field strength decreases, the voltage decreases in proportion to the signal. In addition, since most current cordless telephones are already provided with a field strength detection circuit, a field strength signal can be obtained without adding a new circuit.

[0008] The bit synchronization circuit is a circuit for synchronizing the timing inside the receiving circuit with the change in data transmitted from the transmitting side. An operation of correctly determining data is performed excluding the influence of the data rate difference and noise occurring on the transmission path. This circuit can be constituted by a PLL circuit, and is realized by an operation of minimizing the phase of the data change point of the received data and the clock phase difference of the bit synchronization circuit. FIG. 4 shows the operation of the bit synchronization circuit. In FIG. 4, A is received data, and B, C and D are clock examples of the bit synchronization circuit. E and F are the changing points of the received data, and G, H, I, J and K are the phase differences between the received data and the clock. In this operation example, the bit synchronization circuit operates so as to synchronize the falling edge of the clock with the change point of the received data. The received data A is shown by superimposing both waveforms of data 0 and 1.

When the received data is received correctly without interference, the data change points C are at equal intervals, and the clock is shifted from the data change point to the phase difference as shown by B by the operation of the PLL circuit of the bit synchronization circuit. The waveform has no waveform. At this time, a phase difference may occur due to a delay of the PLL circuit or a fluctuation of the reception electric field, and the value may take a value of G or H.

[0010] On the other hand, when there is interference, the reception data often becomes such that data change points are not at equal intervals, such as a point F affected by the interference. At this time, the data change point and the clock phase difference are, as shown by I, J and K,
The phase difference is larger than when there is no interference. Therefore, a certain threshold value (L) is determined for the phase difference, and G, H <L <I, J, K The phase difference between the data change point and the clock <L...
When it becomes (1), interference can be determined.

However, the phase difference tends to increase even when the received electric field strength is low. Therefore, a certain threshold value (M) is also determined for the received electric field strength, and the received electric field strength is larger than M.
When both (1) and (2) are satisfied, it can be determined that there is interference. The values of L and M are determined according to the characteristics of the cordless telephone used and the degree of allowable interference.

[0012]

When the interference is detected by this means, a channel change signal is output to the channel control circuit to change the transmission / reception channel. In this way, a cordless telephone that automatically avoids interference can be provided.

[0013]

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

FIG. 1 is a block diagram of a receiving section of a cordless telephone according to an embodiment of the present invention. In FIG.
9 is an antenna, 10 is a high-frequency circuit that performs frequency conversion and amplification of a received signal, 11 is a detection circuit that detects received data,
A broken line 12 indicates a bit synchronization circuit for determining data in the middle of a data conversion point, a conversion point detection circuit 13 for detecting a data conversion point, a phase comparator 14, and a noise component 15 from a phase error signal. Loop filter (LP
F) and 16 are voltage controlled oscillators (VCOs), each of which is composed of a phase comparator 14 to a voltage controlled oscillator 16.
The L circuit outputs a reproduced clock 17 synchronized with the received data. Reference numeral 18 denotes a sampling circuit for sampling the detection output at the timing of the reproduction clock 17, and 19 denotes a conversion circuit for converting the received data into audio, and outputs a received audio 20.
The broken line 21 indicates an electric field strength detection circuit, 22 indicates a high frequency amplifier circuit (AMP), 23 and 24 indicate detection diodes,
5 is a resistor, 26 is a smoothing capacitor, 27 is an electric field strength voltage, 28 is a reference voltage for providing a reference for electric field strength, 29 is a reference voltage for providing a reference for phase error, 30 is a phase error voltage, and 31 and 32 are voltages. The comparator outputs a positive voltage when a voltage higher than the reference voltage input is input as a comparison voltage. Reference numeral 33 denotes a logical product circuit (AND circuit) whose output voltage becomes positive only when a positive voltage is input to both inputs. Reference numeral 34 denotes a channel control circuit, which changes transmission and reception.

The operation of the receiving section of the cordless telephone configured as described above will be described below. When there is no interference, the phase error voltage 30 of the bit synchronization circuit 12 becomes a voltage lower than the reference voltage 29.
When the data conversion point of the detection signal from the input terminal fluctuates, the phase of the conversion point signal detected by the conversion point detection circuit 13 also fluctuates, and the signal and the PLL circuit synchronize with the data conversion point at equal intervals without interference. The output of the phase comparator 14 to which the reproduced clock 17 is inputted fluctuates greatly, and the phase error voltage 3
0 is a voltage exceeding the reference voltage 29 and the voltage comparator 32
Becomes positive.

The received electric field intensity is amplified by a high-frequency amplifier circuit 22, half-wave rectified by diodes 23 and 24, and then converted into a DC voltage by a resistor 25 and a smoothing capacitor 26. Accordingly, the electric field intensity voltage 27 becomes higher as the reception electric field intensity becomes higher.

The phase error voltage 30 is a high voltage because the data conversion point fluctuates not only when there is interference but also when the received electric field strength is weak. Therefore, the electric field strength voltage 27
, A reference voltage 29 is set, and when the received electric field strength exceeds this set value, the output of the voltage comparator 31 becomes a positive voltage.

Therefore, the voltage comparator 32 and the voltage comparator 3
(1) Only when both output voltages become positive is determined to be interference.
At this time, the output of the AND circuit 33 also becomes positive, a channel change signal is output to the channel control circuit 34, and the transmission / reception channel is automatically changed.

[0019]

As described above, according to the present invention, the receiving unit is provided with the circuit for detecting the reception electric field intensity and the circuit for detecting the phase error voltage of the reception data, and the reference electric field intensity is set in advance. When the intensity exceeds and the phase error voltage of the received data exceeds a preset reference phase error voltage, it is determined that there is interference, and a channel change signal is output to the channel control circuit to change the transmission / reception channel. By doing so, it is possible to avoid interference.

Therefore, when interference occurs, the user does not need to manually change the transmission / reception channel and can automatically change the transmission / reception channel.
An extremely convenient cordless telephone can be realized.
Further, the electric field strength detection circuit and the bit synchronization circuit provided in the conventional cordless telephone can be effectively used, and there is no need to change a new transmission format or the like, and the number of parts can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a receiving unit of a cordless telephone according to an embodiment of the present invention.

FIG. 2 is a block diagram of a receiving unit of a conventional cordless telephone.

FIG. 3 is a diagram showing characteristics of an electric field intensity signal.

FIG. 4 is a diagram showing the operation of a bit synchronization circuit.

[Explanation of symbols]

 Reference Signs List 9 antenna 10 high frequency circuit 11 detection circuit 12 bit synchronization circuit 13 conversion point detection circuit 14 phase comparator 15 loop filter (LPF) 16 voltage controlled oscillator (VCO) 18 sample circuit 19 conversion circuit 21 electric field strength detection circuit 22 high frequency amplification circuit ( AMP) 23, 24 Diode 25 Resistor 26 Smoothing capacitor 27 Electric field strength voltage 28, 29 Reference voltage 30 Phase error voltage 31, 32 Voltage comparator 33 Logical product circuit (AND circuit) 34 Channel control circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 1/10-1/14 H04B 7/24-7/26 H04Q 7/06-7/38

Claims (1)

(57) [Claims] 1. A fixed machine connected to a telephone line and a mobile machine communicating wirelessly with the fixed machine. The fixed machine and the mobile machine convert voice and data into digital signals on a transmission side. And wirelessly transmitted, the receiving side has a function of inversely converting the digital signal into voice and data and transmitting the voice and data, the fixed machine and the mobile machine, a circuit for detecting the received electric field strength in the receiving circuit, A bit synchronization circuit composed of a PLL circuit for converting the detection signal into a digital signal, and detecting the presence or absence of an interference signal by comparing the received electric field strength with the transport error output of the bit synchronization circuit, A cordless telephone which automatically avoids interference by transmitting a channel change signal to a channel control circuit when an error occurs.