JPH0330330B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pulse noise detection circuit for a receiver that removes local oscillation signals, detects pulse noise components, and controls the gate of the receiver.

[Summary of the Invention] The pulse noise detection circuit of the present invention is provided in a receiver with two holding means for holding pulse noise component detection signals, and the pulse noise detection circuit of the present invention includes two holding means for holding a pulse noise component detection signal, and detects the pulse noise component detection signal in the period of a beat signal that occurs when a radio wave other than the signal desired to be received is present. The pulse noise component is detected by switching the outputs of the holding means and comparing the output with a pulse noise component detection signal that does not pass through these holding means.

[Prior Art] Figure 5 is a block diagram showing the configuration of an AM receiver including a pulse noise detection circuit that has been commonly used in the past. In the figure, indicates the AM receiver section, and indicates the pulse noise detection section. . The AM receiver section consists of a high frequency amplifier 2 that amplifies the radio waves input from the antenna 1, a mixing circuit 3 that performs frequency conversion, an intermediate frequency amplifier 4 that amplifies the IF signal, and a detector 5, and a gate circuit 6 that removes noise. The audio signal is output through.

The pulse noise detection section uses the output signal of the mixing circuit 3 as an IF signal having a relatively wide band.
This signal is passed through an IF filter 7 for removing leakage of the local oscillation signal contained in the output of the mixing circuit 3;
A switching pulse is generated through an amplifier 8, a detector 9, a bandpass filter 10 for extracting pulse noise components, and a Schmitt trigger circuit 11 for generating a switching pulse, and the gate circuit 6 is controlled. The band of the band pass filter 10 is determined to remove audio signals and drop unnecessary high-frequency components, but since the IF signal used for noise detection has a wide band, it includes signals other than the desired received signal. A beat signal with a broadcast wave other than the desired received signal occurs at the output of the bandpass filter 10, which interferes with pulse noise detection.

Therefore, the conventional method shown in FIG. 5 has the disadvantage that pulse noise cannot be detected when radio waves other than the desired signal are present nearby.

FIG. 6 shows a noise detector considered to solve this problem. The channel space for AM broadcasting is 9 or 10kHz. Therefore, the beat frequency is an integral multiple of 9kHz. Therefore, 9k
A comb filter 13 using a delay element 12 is inserted to remove frequency components that are integral multiples of Hz.

[Problems to be Solved by the Invention] In the circuit shown in FIG. 6, the beat frequency component is removed, but the delay time of this delay element 12 is 100 μs.
However, it has the drawback of high price and has not been put into practical use.

The object of the invention is therefore to enable the circuit shown in FIG. 6 to achieve the same object without using delay elements. That is, it is an object of the present invention to provide a pulse noise detection circuit for a receiver that can reduce the influence of interference caused by beats between broadcast stations.

[Means for Solving the Problem] In order to achieve the above object, a pulse noise detection circuit for a receiver according to the present invention includes first and second holding means for holding a pulse noise component detected signal; and a switching means for alternately switching the input of the second holding means, and a determining means for detecting the pulse noise component detection signal from the alternately outputted output of the holding means and generating a pulse signal for controlling the gate. The gist is to include the following.

The switching means for switching the outputs of the first and second holding means, the switching signal generating means, and the determination pulse generating means can be replaced by means including a simple differentiating circuit.

[Function] The means for holding the pulse noise component detection signal is switched at the beat cycle between broadcasting stations, and its output is compared with the pulse noise component detection signal delayed by one cycle, and only the difference becomes a problem. The influence of interference caused by beats between stations can be reduced.

Hereinafter, the present invention will be explained in more detail using examples with reference to the drawings, but these are merely illustrative and it is understood that various modifications and improvements may be made without going beyond the scope of the present invention. Of course.

[Embodiment] FIG. 1 is a block diagram showing the configuration of an embodiment of a receiver including a pulse noise detection circuit according to the present invention.
In the figure, reference numbers common to those in FIG. 5 represent the same parts as in FIG. FIG. 2 shows signal waveforms at various points in the circuit shown in FIG.

Input to the pulse noise detection section shown in Figure 1
The IF signal includes, in addition to the desired signal, an IF signal of an adjacent broadcast wave, a local oscillation signal of the receiver, and the like. Therefore, when the local oscillation signal is removed by the IF filter 7, the desired signal and the IF signals of a plurality of broadcast waves adjacent thereto are obtained. When this is passed through an amplifier 8 and detected, a beat signal of the channel space 9 of the broadcast wave or an integral multiple of 10 kHz is generated at the output of the detector 9. This beat signal is generated when two or more broadcast waves fall within the IF signal bandwidth input to the pulse noise detector, and if each of those broadcast waves is unmodulated, the level and frequency of the beat signal are constant. becomes. However, if the broadcast wave has amplitude modulation, the level of the beat signal changes depending on the modulation level of the broadcast wave. However, since the modulation frequency of the broadcast wave is kept below channel space 9 or 10 kHz, the frequency of the level change of the beat signal is lower than the beat frequency.

Therefore, it can be considered that the frequency of the beat signal is constant and the amplitude change is a slow fluctuation with respect to the beat frequency. When there are two or more beat signals, the composite signal has periodicity as shown in Figure 2a, and the period is 1/9kHz or 1/10kHz depending on the channel space.
The longest period T is equal to . Therefore, the beat composite signal will be 1/9kHz or 1/10kHz, although there will be some amplitude deviation due to the amplitude modulation of the broadcast wave.
Repeats equal amplitude with a period of Hz.

The present invention focuses on this, and compares the amplitudes for each of the longest beat periods T, and when this level difference exceeds the change due to amplitude modulation, it is detected as pulse noise.

The pulse noise detection section shown in FIG. 1 will be explained in more detail. The signal input from mixing circuit 3 is IF
The filter 7 extracts the IF signal.
When this is amplified by the amplifier 8 and detected by the detector 9, the amplitude component of the IF signal is obtained as its output. This detected signal contains the audio component of the desired received signal, but since the pulse noise detection signal output from the mixer 3 has a wide frequency band, it also contains higher frequency components than the audio frequency component. Therefore, when this detected signal is passed through a band pass filter 10 to remove unnecessary high frequency components such as audio signal components and IF carrier wave components, pulse noise is obtained in the output of this filter. However, if there is an adjacent broadcast wave, the beat frequency component within the band of the filter 10 cannot be removed. FIG. 2a shows the output signal of the bandpass filter 10 in the presence of pulse noise and a plurality of beat signals. If the longest period due to a beat is T, then for each period of amplitude T, P ₁ ,
The level is the same as P ₂ , P ₃ , P ₄ , etc. At this time, if the noise shown by diagonal lines is mixed in at time T ₂ , P ₂ becomes
The level becomes P′ ₂ . Whether P′ ₂ is noise or not is determined by P ₁
Judgment is made in comparison with

The clock generator 14 outputs a signal _S2 having a period of T and a pulse width of ΔT, as shown in FIG. 2b. This is divided by flip-flop 15,
Obtain the pulse _S5 shown in Fig. 2e and control the switch _SW2 . Furthermore, the signal of _S5 is inverted by the inverter 16 to obtain the signal of _S3 . S ₃ signal is switch SW ₁
When _S3 is "H", it controls switch _SW1 , and when _S3 is "H", switch _SW1 is set to the a side, and when _S3 is "L", switch _SW1 is set to the b side. Make it.

When switch _SW1 moves from side A to side B, capacitor _C1 holds the level of _S1 immediately before moving to side B in capacitor _C2 , and when switching from side B to side A, the level of S1 immediately before moving to side A is held in capacitor C2. Maintain the level of S ₁ .

The control signal _S3 of switch _SW1 is “H” with a period of T.
and “L” repeatedly, “H” at T ₁ , “L” at T ₂ , and “L” at T ₃
Then, it changes to "H"... Therefore, the switch
The output on the a side of SW ₁ , that is, the signal S ₄ obtained from the capacitor C ₁ becomes the signal shown in FIG. 2d. That is, at time T ₂ , the signal S ₁ shown in FIG.
The level of P′ ₂ is maintained at v ₂ and is maintained on capacitor C ₁ until time T ₃ . On the other hand, switch SW ₂ is controlled by S ₅ , but when S ₅ is “H”, switch SW ₂
is set on the b' side, and when it is "L", it is set on the a' side. As shown in Fig. 2e, _S5 becomes "L" at time _T1 , "H" at time _T2 , "L" at time _T3 , etc., and at time _T1
On the a′ side, switch the voltage level of capacitor C ₂ .
Output from SW ₂ . The voltage level of capacitor C ₂ is set by switch SW ₁ to the level just before time T ₁ .
The voltage of _P1 is held at _v1 , and this voltage is output by switch _SW2 .

From the above operation, switch SW ₁ is a capacitor.
_C1 and _C2 are made to hold the signal level of _S1 , and switch _SW2 takes out this held level. As a result, P ₁ at the time of T ₁ , T ₂ , T ₃ ... of S ₁ ,
Each level of P' ₂ , P _{3 .} . . is held for a time T and output from the switch SW ₂ . Comparator 17 compares the output of switch _SW2 and the signal of _S1 . If the pulse width of S ₂ is very small, the level of P ₁ at time T will be different from the signal S ₁ from T ₁ to T ₂ input after T 1, or _{T 2}
The level of P' ₂ at the time point can be compared by the comparator 17 with the signal S ₁ from T ₂ to T ₃ inputted after T ₂ . As a result, at the instant of time _T2 , the level of _P1 at the time of _T1 output from switch _SW2 and the level of _P'2 at the time of _T2 are equal to _T2 at the instant of _T3 .
It can be considered that the level of P' ₂ at time T ₃ and the level of P ₃ at time T 3 are compared by comparator 17 .

In FIG. 2, the level v ₁ of P ₁ at time T ₁ is applied to one input of comparator 17, which is held until T ₂ . At the same time, S ₁ is given as the other input of the comparator 17, and the level (v _{2 ) of P′ 2 of} S ₁ at v ₁ and time T ₂ can be known just before time T ₂ , and this v ₁
and the level of P′ _{2 (v 2 ) of S 1 at time T 2 are compared at the time ΔT immediately before time T 2} . If ΔT is very small, it is possible to compare v ₁ and P' ₂ (= v ₂ ) almost at time T ₂ , and at this time, when the level difference between v ₁ and P' ₂ (= v ₂ ) is large, , a determination pulse _S2 shown in FIG. 2g is generated. Note that the comparison between the output of switch SW ₂ and signal S ₁ shows that at time T ₂ , the output signal of switch SW ₂ is
Since v ₁ and the signal of S ₁ is V ₂ , it is equivalent to comparing v ₁ and v ₂ .

This operation is performed by comparator 17 and SW ₃ in FIG. In other words, the signal of S ₁ and the output signal from switch SW ₂ are compared by comparator 17, and the output is passed through switch SW ₃ , which is turned on only when the signal of S ₂ is "H", and the judgment output at the time of ΔT. S ₇ is obtained.
Therefore, when the level difference between two signals that are time-shifted by T is large, _S7 is determined to be pulse noise and becomes "H", and when the level difference is small, it is determined that there is no pulse noise mixed in. Pulse noise can be detected by setting the signal to L''.

Furthermore, as mentioned above, the output of switch SW ₂ and
Comparator 17 compares the signal of S ₁ with ΔT
Since the period of the beat signal is different at other times,
Signal levels at different periods will be compared. Therefore, the comparator outputs a large level difference between the output level of the switch SW ₂ and the signal S ₁ , making it inaccurate to determine whether the level difference is caused by noise.

However, the period synchronized with the period of the beat signal is
Comparing the output of switch SW ₂ and signal S ₁ , we get:
If there is no noise, both will be at almost the same level, but if noise is added to either of them, they will not be at the same level.

The reason why the comparator 17 is provided with SW ₃ and signal S ₂ to output this level difference is that at times other than ΔT, the signal levels with different periods of the beat signal are compared and output, so even if there is a level difference between the two, Even if the noise is caused by noise, it is not necessarily caused by noise, so it is inappropriate to drive the Schmitt trigger circuit 11 with the comparator output (causing malfunction). For this reason, SW ₃ and
It is necessary to provide S ₂ .

The purpose and function of ΔT are as follows.

In order to compare the levels before and after the beat in the longest period T of the beat, it is necessary to accurately handle the instantaneous level for each period T. If the signal levels shifted by the period T are compared and determined, the amplitude fluctuation of the beat signal will be included, and the noise determination accuracy will deteriorate. Therefore, ΔT is set in order to accurately determine the level difference before and after the period T. ΔT is Schmitt trigger circuit 1 including comparator
If the response speed up to 1 is fast, it can be shortened.

The smaller ΔT is, the more accurately the level difference before and after the period T can be compared.

As shown in FIG. 2, two determination pulses in which _S7 becomes "H" are generated due to the inclusion of one pulse noise, and the pulse interval is T. This time T
If the lowest frequency of the beat is 10kHz, then
0.1ms, and the gate circuit 6 of receiver 1 in Fig. 1
Switching time required to eliminate noise (approx.
0.3~0.5ms) shorter. Therefore, the signal of _S7 is expanded to about 0.3 to 0.5 ms by the switching pulse generating circuit consisting of the Schmitt trigger circuit 11. This state is shown in g and h of FIG.

As described above, even if a beat signal is mixed, pulse noise can be detected with high accuracy.

In the above embodiment, the comparator and switch _SW3 shown in FIG. 1 are used to obtain the pulse _S7 for determining pulse noise, but a method that does not use the comparator and switch is also conceivable.

S ₄ and S ₆ in Figure 2 d and f are capacitors C ₁ and C ₂
This is the terminal signal of If there is no noise, P ₁ , P ₂ , P ₃
At the same level, but with noise coming in, at time T ₃
At S ₄ , an abrupt signal change occurs from the level v ₂ to the level v ₁ of P ₃ , and at time T ₂ , at S ₆ , an abrupt signal change occurs from v ₁ to the level v ₂ of P′ ₂ . Such signal changes will not occur unless noise is input. Therefore, by taking out S ₄ and S ₆ through a differentiating circuit and combining their outputs, a noise judgment signal equivalent to the above-mentioned S ₇ corresponding to a sudden signal change caused by noise can be obtained.

FIG. 3 is a block diagram of a circuit that performs this operation. In the figure, 18 and 19 are differential circuits, and symbols common to those in FIG. 1 represent the same parts as in FIG. That is, the signal S ₆ shown in FIG. 2 f and d
and S ₄ are differentiated by differentiating circuits 19 and 18, respectively. Combining these outputs yields S' ₇ , and if the switching pulse generation circuit 11 generates a pulse wider than T when positive and negative signal changes are input, the result will be as shown in Figure 4 a and b. Thus, a switching pulse of S′ ₇ to S′ ₈ can be created.

[Effects of the Invention] As described above, according to the present invention, even small pulse noise can be detected even when a beat signal is mixed in, without using expensive elements such as delay elements.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a receiver including a pulse noise detection circuit according to the present invention, and FIG.
Figure 3 is a block diagram of a modification of the judgment pulse generation circuit; Figure 4 is a diagram showing signal waveforms at various points in the circuit shown in Figure 3; Figure 4 is a diagram showing signal waveforms at various points in the circuit shown in Figure 3; Diagram showing waveforms, 5th
This figure is a block diagram showing the configuration of an AM receiver including a conventional pulse noise detection circuit, and FIG. 6 is a block diagram of an improved conventional pulse noise detection section. 1...Antenna, 2...High frequency amplifier, 3...
Mixing circuit, 4... Intermediate frequency amplifier, 5... Detector, 6... Gate circuit, 7... IF filter, 8
...Amplifier, 9...Detector, 10...Band pass filter, 11...Schmitt trigger circuit, 12...
...Delay element, 13...Comb filter, 14...Clock generator, 15...Flip-flop, 16
...Inverter, 17... Comparator, 18, 19... Differentiating circuit.

Claims (1)

[Claims] 1. In a pulse noise detection circuit that removes the local oscillation signal from the IF signal in the receiver, detects the pulse noise component, and controls the gate of the receiver, a first and second holding means, a switching means for alternately switching the inputs of the first and second holding means, and a pulse noise component detection signal detected from the alternately outputted outputs of the holding means, and detecting a pulse noise component detection signal from the output of the holding means, and determining means for generating a pulse signal to control, the determining means comprising: switching means for switching the outputs of the first and second holding means; when the input of the first holding means is connected, the first holding means; switching signal generating means for alternately controlling the input and output so that the output of the second holding means is connected, and when the input of the second holding means is connected, the output of the first holding means is connected; , and a determination pulse generating means for generating the pulse signal by comparing the output signal of the holding means and the pulse noise component detection signal that are alternately output. . 2. In the pulse noise detection circuit that removes the local oscillation signal from the IF signal in the receiver, detects the pulse noise component, and controls the gate of the receiver, the first and second holding circuits hold the pulse noise component detected signal. means, switching means for alternately switching the inputs of the first and second holding means, and detecting a pulse noise component detection signal from the alternately outputted outputs of the holding means, and generating a pulse signal for controlling the gate. and a differentiating circuit for differentiating the alternately output outputs of the holding means, and generating the pulse signal by synthesizing the outputs of the differentiating circuits. A pulse noise detection circuit for a receiver.