JPS6347297B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an interference detection circuit that detects interference between radio waves in a radio frequency band by detecting beats in a demodulated signal of a radio receiver.

Some cordless telephone systems use a connection system called a multi-channel access system. This method allows connection between a connecting device and a wireless telephone using multiple wireless channels,
The connection device monitors the channel usage status of other adjacent sets, and when making a call, selects an empty channel from among the wireless channels. Therefore, in this system, sets that are separated by a material through which radio waves do not easily pass, such as a reinforced wall or a shielded room, may select the same channel when making a call.

However, while two sets are talking on the same channel, opening a door such as a reinforced wall or a shield room, or opening a door and causing one set A to
When Set A moves into an area within the radio range of Set B, such as when a wireless telephone in Set B approaches the other Set B, the connection device in Set B will receive the radio waves from both Set A and Set B's radio telephones. As a result, interference may occur and communication may become impossible.

Therefore, it is necessary to detect the occurrence of this interference in some way and deal with it, but conventionally, speakers have to listen to the beats caused by the interference and deal with it. Ta. For this reason,
This is extremely undesirable as it causes various inconveniences such as the call being interrupted or the call being terminated without knowing how to deal with it.

The present invention has been made in view of the above circumstances, and its purpose is to automatically detect interference between radio waves in a radio frequency band by detecting a beat signal, and to promptly deal with the interference. An object of the present invention is to provide an interference detection circuit that provides an improved interference detection circuit.

In the present invention, a demodulated signal of a radio receiver or a signal obtained by converting the frequency of this demodulated signal is introduced into a phase lock loop circuit, and when a beat due to radio wave interference in the radio frequency band occurs in the demodulated signal, this beat is Using the fact that the loop is locked to the frequency, a lock detection signal is generated at the time of this lock, and the continuous generation time or generation time rate of this lock detection signal is detected, and when these detection results exceed a predetermined value The above object is achieved by determining that interference between radio waves has occurred in the radio frequency band and outputting a signal to that effect.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. The figure is a block configuration diagram of a wireless transmitter/receiver using the interference detection circuit in the same embodiment.
is the interference detection circuit. This interference detection circuit 1 is
A phase lock loop circuit main body 14 including a phase comparator 11, a loop filter 12, and a voltage controlled oscillator (VCO) 13, and a frequency conversion circuit 15 that shifts up the demodulated signal obtained by the receiver 2.
A high-pass filter (HPF) 16 that supplies only the shifted up high frequency component of the demodulated signal from the output of the frequency conversion circuit 15 to the phase lock loop circuit main body 14; It is composed of a sweep circuit 17 that sweeps the free run frequency of the voltage controlled oscillator 13, and a control circuit 18. Control circuit 18
has a gate circuit 19 that is opened by the lock detection signal generated from the phase comparator 11 of the phase lock loop circuit 14, and the number of clock signals fed back via this gate circuit 19 is calculated by the control circuit main body 20. I am counting. When this counting operation continues for a predetermined time or longer, it is assumed that a beat has occurred in the demodulated signal, or in other words, that interference between radio waves has occurred in the radio frequency band, and the frequency synthesizer 3 is A channel change signal is being generated. In the figure, 15a represents an oscillator that generates a shift-up signal, 15b represents a mixer, and 4 represents a transmitter.

Next, the operation of the circuit configured as above will be explained. First, when no radio wave interference occurs, the demodulated signal is a signal such as an audio signal whose frequency changes greatly, and does not include a constant frequency such as a beat. Therefore, the phase lock loop circuit main body 14 does not become locked, and even if it does, it is only temporary and immediately returns to the unlocked state. Therefore, during this time, continuous lock detection signals are not sent from the phase comparator 11, and the count value of the lock signal in the control circuit main body 20 does not reach the value set for detecting a beat, so a beat is detected. No signal is generated to that effect. Therefore, the transmitter 4 and the receiver 2 maintain the channel according to the oscillation frequency set by the synthesizer 3.

Now, in this state, if radio wave interference occurs due to movement of the speaker, etc., the frequencies of the radio waves are generally slightly different even if they are on the same channel, so a beat will occur in the demodulated signal. Then, the phase lock loop circuit main body 14 searches for the beat by moving the lock range using the sweep circuit 17, and when it finds the beat, it locks the loop at that frequency. At this time, the demodulated signal (for example, 0.3 to 3KHz) is shifted up in the frequency conversion circuit 15 to reduce the frequency change rate (if shifted up by fKHz, the frequency change rate is (f+3)/(f+
0.3)), the shift-up frequency (oscillation signal of the oscillation circuit 10) and the lower sideband are removed by the high-pass filter 16, and the resulting signal is supplied to the phase lock loop circuit main body 14. Therefore, even if the voltage controlled oscillator 13 cannot follow a large change in frequency change rate like the demodulated signal, the phase lock loop circuit main body 14 can adjust the lock range to the entire band of the shifted up demodulated signal. Correspondingly, sufficient scanning can be performed, and as a result, the beat frequency can be reliably detected in any band of the demodulated signal. However, depending on the degree of interference, the beat frequency component contained in the demodulated signal is not so large, and the phase lock loop circuit is not necessarily locked to this beat frequency. For this reason, a sweep circuit is used to change the oscillation frequency of the VCO, giving a chance for the frequency to match the beat frequency and making it easier to lock.

Further, at this time, the output signal of the sweep circuit 17 is amplitude-limited to a level corresponding to the shift-up oscillation frequency of the frequency conversion circuit 15, so that the lock range of the phase lock loop circuit main body 14 is limited to the shift-up oscillation frequency. It does not enter the oscillation frequency range, and as a result, the loop of the phase lock loop circuit body 14 is prevented from being locked to the shift-up oscillation frequency.

When the loop of the phase lock loop circuit main body 14 is locked to the beat frequency, a lock detection signal is continuously output from the phase comparator 11, so that the gate circuit 19 of the control circuit 18 is continuously gated. As a result, the control circuit main body 2
The clock signal is counted at zero. Note that when the lock detection signal is introduced, the control circuit 18 issues a command to the sweep circuit 17 to control the voltage controlled oscillator 1.
3. Stop the free run frequency sweep and fix it to the beat frequency. When the count value of the clock signal reaches a preset value, the control circuit main body 2
0 determines that a beat has occurred and outputs a signal for causing the synthesizer 3 to change the frequency division number, for example. As a result, a new oscillation frequency is supplied from the synthesizer 3 to the transmitter 4 and receiver 2, and the transmitter 4 and receiver 2 exchange communication signals and the like through the channel corresponding to the new oscillation frequency.

As described above, according to this embodiment, the demodulated signal is introduced into the phase lock loop circuit 14, and the loop of the phase lock loop circuit 14 is locked to the beat frequency generated in the demodulated signal, thereby locking the loop generated at that time. Since the length of the detection signal is measured, it is possible to automatically detect the beats that occur in the demodulated signal, and as a result, the desired countermeasures can be quickly taken to prevent interference of radio waves occurring in the radio frequency band. can be resolved reliably and quickly without bothering the speaker. Furthermore, in this embodiment, the lock range of the phase lock loop circuit main body 14 is swept by the sweep circuit 17 to scan the entire frequency range of the demodulated signal, so that beat generation can be performed reliably and quickly regardless of the frequency. can be detected. Furthermore, at this time, since the level of the output signal of the sweep circuit 17 is appropriately amplitude-limited, the characteristics of the high-pass filter 16 for removing the shift-up frequency can be relaxed, and the circuit can be simplified. be able to.

Note that the present invention is not limited to the above embodiments. For example, in the embodiment described above, the occurrence of a beat is determined by counting the number of clock signals that are continuously input. The occurrence of a beat may be determined based on the following. Further, if the beat generation frequency is substantially uniform, the lock range of the phase lock loop circuit main body 14 may be fixed. In this case, the sweep circuit 17 can be omitted. Further, if the voltage controlled oscillator 13 has a wide frequency range and can follow the entire frequency range of the demodulated signal, it is not necessary to shift up the demodulated signal. If the phase comparator 11 itself does not have the function of generating a block detection signal, it may be constructed by adding a separate circuit for generating a lock detection signal. In addition, various modifications may be made to the means for determining the occurrence of a beat from the length of the lock detection signal, the configuration of the phase lock loop circuit, and the application of the interference detection circuit, etc., without departing from the gist of the present invention. Can be implemented.

As described in detail above, the loop of the phase lock loop circuit is locked by a beat, a lock detection signal is generated at the time of locking, the continuous generation time or generation time rate is detected, and when this detection value is equal to or greater than a predetermined value, the lock detection signal is generated. According to the present invention, it is possible to automatically detect radio wave interference occurring in the radio frequency band and quickly deal with it. The circuit can be provided.

[Brief explanation of drawings]

The figure is a block diagram of a wireless transmitter/receiver using an interference detection circuit according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Interference detection circuit, 14... Phase lock loop circuit main body, 15... Frequency conversion circuit, 16... High pass filter (HPF), 18... Control circuit, 19...
Gate circuit, 20...control circuit main body.

Claims (1)

[Claims] 1. Introduce a demodulated signal from a radio receiver or a frequency-converted signal from this demodulated signal as an input signal, and when a beat occurs in this input signal due to radio wave interference in the radio frequency band, the loop is locked to the frequency of this beat. The phase lock loop circuit that generates the lock detection signal in this lock state and the continuous generation time or generation time rate of the lock detection signal generated from this phase lock loop circuit are detected and the continuous generation time or generation time of these is detected. 1. An interference detection circuit comprising: a determination circuit that assumes that radio wave interference has occurred in a radio frequency band when the ratio exceeds a predetermined value, and outputs a signal to that effect.