JP2002280914A - Disturbance wave detecting squelch circuit and method for detecting the disturbance waves - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and circuit that can detect the disturbing wave signal of a channel close to that of a desired wave signal or of the same channel as the desired wave signal with high accuracy for a noise squelch circuit of a radio receiver, and to realize the radio receiver having stable noise-squelch function. SOLUTION: In the squelch circuit of the radio receiver, an intermediate frequency signal 32, resulting from down-converting a received signal 300 of the radio receiver, is distributed into two. A multiplier 100 multiplies the two branched signals in1, in2. A low-pass filter 110 separates and extracts a low frequency beat component in an output 102 of the multiplier, and a comparison discriminator 120 amplifies and detects the extracted low frequency beat component to obtain an output 122 proportional to the beat component. A control section 80 discriminates whether the detection output 122 exceeds a predetermined reference threshold, discriminates the presence of a disturbing wave in the input signal, when the threshold is exceeded and activates a switch 60 to shut off transmission of an output 51 of a demodulator 50 to the outside of the receiver.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a squelch circuit mainly used for a radio system such as an analog FM radio receiver.

[0002]

2. Description of the Related Art In a radio receiving apparatus, if a received signal is lost or a received signal is disturbed by an interfering wave or the like, a large noise may be generated. To suppress. As the squelch method, there are a carrier squelch method and a noise squelch method, which are generally widely used.

In the carrier squelch method, a received high-frequency signal is mixed with a local oscillation signal, a frequency-converted (down-converted) intermediate frequency signal is limited-amplified by a limiting amplifier placed before the demodulator, and its output is output. Is determined by a comparator to detect the presence or absence of a carrier from the transmitter, and when there is no carrier, the output of the demodulator is suppressed by a squelch circuit to suppress the noise output from the demodulator.

In the noise squelch method, a specific component included in an output signal from a demodulator, for example, a band component of 100 KHz to 120 KHz is regarded as an interference wave and a band-pass filter (Band-Pass Filt) is used.
er; BPF), amplify and detect, and determine the magnitude with a comparator. When an interference wave level exceeding a reference voltage is detected, the demodulator output is suppressed.

[0005] The original purpose of squelch is, as mentioned above,
An object of the present invention is to prevent noise from appearing on the output side when there is no signal component or when the interference component becomes dominant. For that purpose, a problem is how to measure and detect the amount of the interference component included in the received signal. The farther the disturbing component is from the signal band, the easier this separation can be made by a filter. However, as the interference component approaches the signal band, this separation and detection becomes difficult.

Japanese Patent Application Laid-Open No. 10-336050 discloses a switch for switching a cutoff frequency of a noise filter according to an occupied bandwidth of a selected channel when receiving two kinds of frequency band signals of a wide band and a narrow band. A method is shown in which a circuit is provided to obtain good and stable noise squelch characteristics.

In the above publication, the cutoff frequency of the noise filter is switched to a higher value in a wide band and a lower value in a narrow band. As a result, a stable noise squelch that can receive a wideband signal and a narrowband signal with one device and selectively prevent interference from an adjacent channel by selectively using a noise cutoff filter corresponding to the occupied bandwidth of the selected channel. A wireless device having characteristics can be realized.
Here, the cutoff frequency of the noise filter is controlled by channel information from an external channel setting unit. The noise filter is an active filter including an operational amplifier, a resistor, and a capacitor. The cut-off frequency is selected so as to be a cut-off frequency determined by the values of the resistor and the capacitor. However, in the wide band and the narrow band, the value of the resistor is switched by a switch.

[0008]

However, in the above method, a noise component is detected based on a cutoff filter characteristic determined by a resistance value and a capacitance of a capacitor. Therefore, only a noise component included in a specific frequency component can be detected. Also, a filter with a steep cutoff frequency is required to increase the detection accuracy of the noise component near the desired signal. It was virtually difficult. For example, when using a bandpass filter having a demodulation frequency of 100 KHz to 120 KHz, 10
At frequencies below 0 KHz, there is a modulated signal component near the transmission carrier, and it is difficult to distinguish it from noise components with achievable filter characteristics.

Further, when an interference wave having a reception carrier frequency within ± 100 KHz is present, it is within the band of the desired wave and cannot be distinguished from the signal of the desired wave, so that there is a problem that the interference wave cannot be detected. Especially foreign wave interference and sporadic E
In fixed radio lines where interference is often caused by abnormal propagation of ionospheric layers, stable detection of interference is not possible.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a noise detection type squelch circuit and an interference wave detecting method capable of accurately detecting even an interference wave close to a desired wave. I do.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a squelch circuit for detecting an interference wave in a signal received by a radio receiver and turning on and off the output of the device. Means for splitting the signal into two, analog multiplying means for multiplying the split signal by two, low-pass filtering means for extracting a predetermined low-frequency beat component from the multiplied signal, It includes a means for detecting the level, a means for determining whether the detected level exceeds a predetermined threshold, and outputting a result of the determination, and a means for turning on and off the output of the radio receiving apparatus based on the result of the determination.

Further, the radio receiving apparatus according to the present invention has control means for controlling a changeover switch for switching whether or not to output a signal obtained by demodulating the intermediate frequency signal to the outside, based on the result of the determination. .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a squelch circuit of a radio receiving apparatus according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 is a functional block diagram of an embodiment of the squelch circuit according to the present invention, and FIG. 3 conceptually shows a spectrum of an output signal of a multiplier described later in connection with the operation of the squelch circuit of FIG. .

In FIG. 2, a signal generator (Signal Gener
ator; SG) 202, for example, mixes a reception signal of a wireless reception device with a local oscillation signal and outputs an intermediate frequency signal (for example, 10.7 MHz).
Down-converted band-pass filter (Band-Pass Filte)
r; BPF) A pseudo wave signal D corresponding to the output signal wave is generated in a pseudo manner. In this description the frequency of the desired signal D and f _d. The signal generator 206 generates a signal U corresponding to an interference wave signal in a pseudo manner. The frequency of the disturbing wave signal U and f _u.
The combiner 210 combines the desired signal D from the signal generator 202 and the interference signal U from the signal generator 206 to form a combined signal 212. That is, the output 212 of the synthesizer 210 can be regarded as a pseudo received intermediate frequency signal including the actual interference signal.

The next-stage multiplier (Multiplier; MP)
Y) 214 are inputs in1 and in2 from which the synthesized signal 212 is branched.
Are multiplied by each other. The multiplication process utilizes the nonlinearity of the multiplier. FIG. 3 shows the frequency spectrum of the output signal of the multiplier 214 multiplied.

If the multiplier 214 is constituted by a balanced type multiplier, the output signal 216 of the multiplier 214
As shown in FIG. 3, in addition to the desired signal D and the disturbing signal U indicated by reference numeral 404, the frequency distribution of kf _d ± mf _u (where k and m are integers) indicated by reference numeral 406 The generation of waves is a well-known fact in the relevant technical field. When the interference signal U is close to the desired signal D,
The spectrum is near the desired wave D as indicated by reference numerals 404 and 406 in FIG. 3, and in this example, is distributed near 10.7 MHz and near an integral multiple of the frequency.

For example, the input signals in1 (frequency f _d ) and i
Let n2 (frequency f _u ) be A · sin (2πf _d t) and B · s
When in (2πf _u t), the output 216 of the multiplier 214 is as follows.

[0018]

[Number 1] _{A · sin (2πf d t)} × B · sin (2πf u t) = A · B · sin
_{(2πf d t) · sin (} 2πf u t) = (A · B / 2) [cos {2π (f d + f u)
_{t} -cos {2π (f d} -f u) t}] Therefore, if when you enter the same signal as the input signal in1, in2 becomes the double frequency is caused.

[0019] ± delta] f of FIG. 3, the spread of the desired signal component of the distribution of the interference wave signal component when ± 2.DELTA.f such that the difference frequency between the interference wave signal frequency f _u and the desired signal frequency f _d and Δf It is shown as a reference. If a balanced type multiplier is used as the multiplier 214, the desired wave signal D is canceled out, so that the output 216 of the multiplier 214 (FIG. 2)
Does not appear in. Since the interference wave signal U is canceled by the multiplier 214 similarly to the desired wave D, it does not appear in the output 216 in principle. Actually, there are some components due to the imbalance of the circuit and the like, but they are greatly attenuated compared to the input level. Although components of the n-fold of the desired wave and interference wave (n is an integer of 2 or more) is output by the nonlinearity of the multiplier, the original signal frequency f _d or disturbance signal frequency f _u
Since they are sufficiently far apart from each other, they can be easily separated by a filter.

In this embodiment, a balanced type multiplier is used, but a non-balanced type multiplier can also be used. In this case, even frequency components of the fundamental wave are not cancelled, but can be separated by a filter. The equilibrium type is more effective because this component is canceled.

On the other hand, the difference frequency between the desired wave D and the interference wave U
The so-called beat frequency f which is a number_d-f _u(F_d≤f_uF
_u-f_d) Is generated in the low frequency band as indicated by reference numeral 402 in FIG.
Is done. Therefore, this low frequency beat signal is shown in FIG.
The low pass filter 218 allows for separation. Low-pass filter 2
18 is, for example, FFT (Fast Fourier Transformation;
A fast Fourier transform) analyzer may be used. Reference numeral 40 in FIG.
0 is the low-pass filter 218 for separating low-frequency beat components.
It is a diagram schematically showing pass characteristics. Low-pass filter power
The cutoff frequency is the desired wave frequency f_dLow enough compared to
Value, for example, if the desired signal frequency is 10.7 MHz,
Set to 1MHz or less.

Beat frequency component f _d -f _u (when f _d ≤ f _u , f
The output of _u -f _d ) is obtained in proportion to the interference signal strength which is separated from other components by the low-pass filter 218. The extracted beat component compares the magnitude of the extracted component with a predetermined reference voltage threshold, as described in an embodiment described later, and determines that there is interference if the extracted threshold component exceeds the threshold voltage. Is operated to suppress the output of the noise signal.

FIG. 1 is a block diagram showing a configuration of an embodiment of an FM radio receiving apparatus using the present invention, and particularly shows a detailed configuration example of a noise squelch circuit of the present invention. Here, the reference numerals of the signals are represented by the reference numbers of the connecting lines in which they appear. The wireless receiving apparatus according to the present embodiment includes a down-converter unit 2 that converts a received high-frequency signal into an intermediate frequency signal.
A demodulation unit 4 for demodulating the intermediate frequency signal to a baseband signal; and a squelch unit 6 for detecting an interference wave signal of the received signal and shutting down the output of the receiver when there is an interference wave of a certain value or more.
Is provided.

The down-converter unit 2 includes a high-frequency amplifier (described as HA in the figure) 10 and a mixer (described as MIX in the figure) 2
0, a local oscillator (described as LOCAL in the figure) 70, and a bandpass filter (described as BPF in the figure) 30. The demodulation unit 4 includes a limiting amplifier (described as LIM in the figure) 40 and a demodulator (described as DEM in the figure) 50. The squelch unit 6 includes a multiplier (described as MPY in the figure) 100, a low-pass filter (described as LPF in the figure) 110, a determiner (described as DET in the figure) 120, and a controller (see FIG. Is indicated as CONT) 80 and a changeover switch (SW in the figure)
60). These components will be described in detail below.

The high-frequency amplifier 10 of the down converter unit 2
It has a function of receiving the received high-frequency signal 300 of the FM radio receiver and amplifying the received high-frequency signal to a certain level required for the mixer 20 at the next stage. The output 12 of the high-frequency amplifier 10 is a mixer
The mixer 20 has a terminal for inputting a local oscillation signal 72 from a local oscillator 70. The mixer 20 includes a non-linear circuit that mixes the received high-frequency signal 12 from the high-frequency amplifier 10 and the local oscillation signal 72 from the local oscillator 70, and has a function of generating a non-linear mixed output 24 of both signals.

The bandpass filter 30 is connected to the output 24 of the mixer 20, and has a function of filtering out and extracting a desired intermediate frequency signal from the output signal 24 of the mixer 20. The output 32 of the bandpass filter 30 is branched, one of which is connected to the limiting amplifier 40 of the demodulation unit 4. The limiting amplifier 40 includes a limiting amplification (limiter) circuit, and has a function of amplifying the intermediate frequency signal output from the bandpass filter 30 to an amplitude level necessary for FM demodulation, which will be described later, and limiting the amplitude. Demodulator 50 is connected to output 41 of limiting amplifier 40 and demodulates signal 41 to a baseband signal.

The other of the output 32 of the bandpass filter 30 is divided into two and supplied to the input terminals in1 and in2 of the multiplier 100 of the squelch unit 6. The multiplier 100 is a balanced type multiplier, and the multiplier shown in FIG.
Same as 214. That is, each input terminal in1,
An output 102 is obtained by multiplying the signals supplied to in2 with each other.
As described above, the output 102 of the multiplier 100 includes, as nonlinear outputs of the two signals in1 and in2 applied to the balanced-type multiplier, a signal having a frequency that is a difference or a sum of integer multiples of the respective input signal frequencies. Output components are included. In the balanced multiplier, a signal component that is an integral multiple of the input signal frequency is also output, but even-numbered frequency components are balanced and canceled, so that they do not appear on the output side. In practice, it is not completely canceled out due to the slight imbalance of the circuit, but its level is greatly attenuated.

The output 102 of the multiplier 100 is connected to a low pass filter (LPF) 110. The low-pass filter 110 may be the same as the low-pass filter 218 described in FIG. That is, the low-pass filtered by a cut-off frequency for passing only the beat frequency component between the desired signal and the interference wave signal (difference frequency f _d and f _u). Therefore, the output 112 is obtained from the low-pass filter 110 only when the interference signal exists.
An interference wave signal component that is very close to the desired signal frequency or on the same channel is also output as the beat frequency.

The output 112 of the low pass filter 110 is connected to a decision unit 120. The determiner 120 has a function of determining the level of the beat component signal 112 and detecting a beat component exceeding a specific threshold. The determiner 120 includes an amplification and detection circuit, and has a function of detecting the minute output beat signal 112 of the low-pass filter 110 after amplifying it to a level at which the determination of the interference signal is easy. The detected output voltage becomes an output voltage proportional to the beat component 112 of the output of the low-pass filter 110. This voltage is determined by Judgment 1
The detection voltage is compared with a predetermined reference threshold voltage inside 20, and when the detected voltage exceeds the threshold voltage, the determination output 122 is output to the control unit 80. The reference threshold voltage is separately set to a value suitable for the squelch operation due to the nature of the interference wave and the like.

The control unit 80 has a function of receiving a determination result 122 of the determination unit 120 and outputting a control signal for performing on / off control of the switch 60. On the other hand, the control unit 80 includes the demodulation unit 4
Has a terminal for receiving a carrier squelch signal 42 which is a detection result of a carrier for carrier squelch from the limiting amplifier 40 of FIG. That is, the control unit 80 has a function of receiving the output from the determiner 120 and the carrier squelch signal 42 from the limiting amplifier 40, outputs a squelch control signal 82, and supplies the squelch control signal 82 to the control terminal of the switch 60.

The switch 60 includes an on / off switch, and has an input terminal connected to the FM demodulation output 51 of the demodulator 50.
According to a control signal 82 from the control unit 80, connection or disconnection of the demodulated output to the external output 302 is performed. When the output of the beat component due to the interference signal exceeds a predetermined threshold, the control unit 80 sends a cutoff control signal 82 to the switch 60, and the noise due to the interference is output from the receiver to an external speaker (not shown). The switch 60 is shut off so as not to be output to the switch.

The operation of this embodiment will be described below. The high frequency signal 300 including the received interference signal is
Is amplified to the required level with the high-frequency signal,
The mixer 20 mixes the signal with the local oscillation signal 72 of the local oscillator 70, performs frequency conversion to generate an intermediate frequency signal component, and the bandpass filter 30 selectively extracts only the intermediate frequency signal component 32 from the output 24. Output 32 of bandpass filter 30 is a limiting amplifier.
The signal is limited-amplified at 40 and demodulated to a baseband signal at a demodulator 50. The demodulation output 51 also includes an interference output when there is an input interference signal.

On the other hand, the output intermediate frequency signal 32 of the bandpass filter 30
Are branched to the input terminals in1 and in of the multiplier 100.
2 and multiplied by each other. As described above, an analog multiplied output of the two signals in1 and in2 is obtained from the multiplied output 102 of the multiplier 100. When the two signals in1 and in2 include the interference signal, the multiplication output 102 includes the low-frequency beat components of the desired signal and the interference signal,
The low-pass filter 110 filters only low-pass components and supplies the result to the decision unit 120. If there is no interfering wave signal, no low-frequency beat component is generated as described above.

The low-frequency beat component proportional to the intensity of the interference wave is amplified and detected by the determiner 120, and its level is compared with a reference threshold voltage. If the level exceeds the threshold value, it is determined that an excessive interference wave is present. The determination result 122 is supplied to the control unit 80, and the control unit 80 sends a noise squelch control signal 82 to the switch 60 according to the detection signal 122. When receiving the noise squelch signal 82, the switch 60 is turned off so that the noise signal due to the interference wave from the demodulator 50 is not output.

On the other hand, a carrier squelch signal 42 having detected the presence or absence of a received carrier signal is output from the limiting amplifier 40 to the control unit 80.
Signal in the case of carrier squelch
To close the switch 60 and send the demodulated output 51 from the demodulator 50 to the receiver output side. The priorities of the noise squelch signal 122 from the decision unit 120 and the carrier squelch signal 42 from the limiting amplifier 40 are determined separately. Even if it is determined that there is a carrier, in the case of an interference wave near a desired wave or in a channel, there is a possibility of erroneous detection as described above, so that it can be corrected by the noise squelch output of the present invention.

The present invention is not limited to the application as a noise squelch circuit, but can also be applied to detection of the same signal interference wave due to abnormal propagation of the ionosphere such as the sporadic E layer in addition to the proximity interference wave. is there. Abnormal propagation of signals due to ionospheric reflections, particularly E-layer reflections, often cause significant interference in wireless communication, and may cause variations in frequency and phase, and interfere with wireless received signals. Therefore, these E-layer abnormal propagation signals may be detected as interference signals for purposes such as wireless system control other than the squelch function of the wireless receiver.

Anomalous propagation due to E layer reflection is in the same frequency channel as the original signal, and conventionally, it has been impossible to detect them stably. According to the present invention, it is possible to stably detect these interference wave signals. Although the E-layer abnormal propagation signal is in the same frequency channel, the frequency and phase of the signal fluctuate with respect to the original signal.
Has a frequency corresponding to a frequency f _d as described in, the abnormal propagation signal can be considered as having a frequency corresponding to a frequency f _u.

Therefore, it is possible to generate those beat components by the multiplier in the configuration example of the present invention and extract them as the beat components by the low-pass filter. The basic configuration and operation may be the same as the operation of detecting a disturbance wave in the squelch circuit.

[0039]

As described above, according to the present invention, it is possible to detect an interfering wave having a frequency close to that of an input filter of a receiver, and the conventional noise squelch device cannot detect it. It is possible to detect even the same channel interference wave and the same frequency interference from foreign radio stations, which enables more accurate reception interference abnormality detection than before, so it is applied to highly reliable lines. Can be.

Further, by using the balanced type multiplier, the modulation content of the desired wave signal is completely canceled, so that the malfunction of the squelch circuit due to the modulation content is eliminated, and the stable operation of the squelch circuit becomes possible. .

By using the configuration according to the present invention, it is possible to realize a squelch circuit with a simple circuit configuration as compared with the case where a conventional complicated filter or the like is employed.

Further, the present invention is not limited to application as a noise squelch circuit, but can be applied to detection of the same signal interference wave due to abnormal propagation of the ionosphere such as a sporadic E layer in addition to the proximity interference wave. is there.

[Brief description of the drawings]

FIG. 1 is a functional block diagram illustrating a configuration example of a wireless reception device to which an embodiment of a squelch circuit according to the present invention is applied.

FIG. 2 is a functional block diagram of an embodiment of a squelch circuit according to the present invention.

FIG. 3 is a conceptual diagram of an output frequency spectrum of the multiplier of FIG. 1;

[Explanation of symbols]

 2 Down converter section 4 Demodulation section 6 Squelch section 10 High frequency amplification section 20 Mixing section 30 Bandpass filter 40 Limiting amplifier 50 Demodulator 60 Switch 70 Local oscillator 80 Control section 100 Multiplier 110 Low-pass filter 120 Comparison / determination section 202 Desired wave Pseudo signal generator 206 Interference signal pseudo signal generator 210 Synthesizer 300 Receiver input signal 302 Receiver output

Claims (8)

[Claims] 1. An interference wave detection type squelch circuit for detecting an interference wave in a reception signal of a wireless reception device and turning on and off an output of the device, the circuit comprising: means for splitting an input signal into two branches; Analog multiplying means for multiplying the multiplied signals by each other; low-pass filtering means for extracting a predetermined low-frequency beat component from the multiplied signal; means for detecting the level of the extracted low-frequency beat component; Disturbance comprising: means for determining whether a detected level exceeds a predetermined threshold value and outputting a result of the determination; and means for turning on and off the output of the radio receiving apparatus based on the result of the determination. Wave detection type squelch circuit. 2. The circuit according to claim 1, wherein the bifurcated input signal to said analog multiplying means is an intermediate frequency signal obtained by down-converting a high-frequency signal received by said radio receiving apparatus. A squelch circuit that detects interference. 3. An interference wave detection method for detecting an interference wave in a reception signal of a wireless reception device and turning on and off an output of the device, the method comprising the steps of: bifurcating an input signal; An analog multiplying step of multiplying each other by a filter step; a step of filtering and extracting a predetermined low-frequency beat component in an output of the analog multiplying step; a step of detecting the level of the extracted low-frequency beat component; A method for detecting an interference wave, comprising: determining whether or not a level exceeds a predetermined threshold; and turning on and off an output of the wireless receiving apparatus based on a result of the determination. 4. The method according to claim 3, further comprising a step of inputting an intermediate frequency signal obtained by down-converting a high-frequency signal received by the radio receiving apparatus to the analog multiplying step. Interference detection method. 5. An ionospheric anomalous propagation identical interference wave detection circuit in an interference wave detection circuit of a wireless system, the circuit comprising: means for dividing an input signal into two; and analog multiplication means for multiplying the two branched signals by each other. Low-pass filtering means for extracting a predetermined low-frequency beat component from the multiplied signal; means for detecting the level of the extracted low-frequency beat component; and whether the detected level exceeds a predetermined threshold value. And a means for determining whether or not the ionospheric abnormal propagation same interference wave is detected. 6. The circuit according to claim 5, wherein the bifurcated input signal to said analog multiplying means is an intermediate frequency signal obtained by down-converting a high frequency signal received by said radio receiving apparatus. An ionospheric abnormal propagation same interference wave detection circuit. 7. A method for detecting anomalous propagation of ionosphere in an interference wave detection circuit of a wireless system, comprising: a step of dividing an input signal into two; an analog multiplication step of multiplying the two divided signals by each other; Filtering and extracting a predetermined low-pass beat component in the output of the process, detecting the level of the extracted low-pass beat component, and determining whether the detected level exceeds a predetermined threshold value And detecting the same interference wave in the ionospheric abnormal propagation. 8. The method according to claim 7, further comprising a step of inputting an intermediate frequency signal obtained by down-converting a high-frequency signal received by the radio receiving apparatus to the analog multiplying step. An ionospheric anomalous propagation identical coherent wave detection method.