JPH0771014B2 - Pulse noise detection circuit in AM receiver - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse noise detection circuit in an AM receiver for detecting pulse noise mixed in the AM receiver. In particular, the present invention refers to an improvement of the pulse noise detection circuit in the AM receiver, which improves the degree of freedom in the structure of the AM receiver and prevents malfunction.

[0002]

2. Description of the Related Art FIG. 16 is a diagram showing a conventional pulse noise detection circuit in an AM receiver. In addition, the same reference numerals or symbols are used to represent the same components throughout the drawings. The configuration of this figure includes the tuner 100 of the AM receiver.
A pulse noise removing unit 2 for removing pulse noise from the output signal of the tuner 100; and a gate for detecting the pulse noise and removing the pulse noise signal to the pulse noise removing unit 2. Pulse noise detector 4 that outputs a signal
0 and are included.

The tuner 100 includes an antenna 101, a high frequency amplifier 102 connected to the antenna 101, a mixer 103 connected to the high frequency amplifier 102, a local oscillator 104 for supplying a mixed wave to the mixer 103, A wide band filter 105 connected to the mixer 103, and the band filter 10
5, an intermediate frequency amplifier 106 connected to the intermediate frequency amplifier 106, a narrow band filter 107 connected to the intermediate frequency amplifier 106, and an envelope detector connected to the band filter 108, for example.
108 and are included. Further, the automatic gain control for controlling the amplification gain of the intermediate frequency amplifier 106 is performed by the output of the detector 108,
The output of the detector 108 is kept constant.

The pulse noise removing unit 2 includes a gate circuit 2
1 and a holding capacitor 22 are included. Figure 1
FIG. 7 is a diagram for explaining the situation of noise removal by the pulse noise removal unit of FIG. As shown in FIG. 4A, the pulse noise is superposed on the detection signal by the input signal to the pulse noise removing unit 2. This pulse noise is, for example, an ignition noise in a vehicle-mounted receiver and noise mixed from a power transmission line. As shown in FIG. 6B, the gate signal is detected by the pulse noise detector 40 and is synchronized with the pulse noise. As shown in FIG. 3C, the gate circuit 21 is opened by the gate signal to remove the pulse noise, and at this time, the detection signal level before removal is held by the capacitor 22, and when the gate circuit 21 is closed. , The hold of the detection signal is released. As shown in this figure (d),
The post-removal shape wave shown in FIG. 6C is corrected by a subsequent device (not shown).

The pulse noise detector 40 of FIG. 16 has an amplifier 4 connected to the output of the wide band filter 105.
1, an envelope detector 42 connected to the amplifier 41, a high frequency filter 43 connected to the detector 42, for example.
And the gate circuit 21 connected to the high frequency filter 43.
And a level detection unit 44 that generates a gate signal for operating.

The tuner 100 has a wide band filter 105.
The reason why the pulse noise is provided is that the pulse noise is easily detected by increasing the peak value of the noise in the pulse noise detector 40 when it is detected in a wide band. Further, automatic gain control for controlling the amplification gain of the amplifier 41 is performed for the purpose of keeping the output of the detector 42 constant.

Next, the operation will be described. The received signal mixed with pulse noise is divided by the band filter 105 and becomes a demodulated wave in which the carrier is removed by the envelope detector 42 via the amplifier 41, and the high frequency filter 43 removes components other than high frequency pulse noise. The level detector 44 shapes the gate signal and outputs the gate signal to the gate circuit 21.

[0008]

However, the conventional A
In the pulse noise detection circuit in the M receiver, it is necessary to further amplify the branch signal in the band filter 105 and perform detection. Therefore, the harmonic component of 910 KHz due to the detection distortion with respect to the intermediate frequency 455 KHz after the mixer 103 is detected. Sound, a beat (tweet), etc., a problem that requires special consideration in the component layout to prevent mixing due to the above-mentioned harmonics, and also a restriction on the configuration of the band filter 105. There was a problem that the degree of freedom in design was low.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a pulse noise detection circuit in an AM receiver which has a high degree of freedom in design in view of the above problems and is improved in terms of malfunction.

[0010]

FIG. 1 is a diagram showing the principle configuration of the present invention. In order to solve the above-mentioned problems, the present invention provides an intermediate frequency signal that passes through a bandpass filter.
Envelope detection section (10
8) to the AM receiver having the envelope detector (10
8) Remove the pulse noise signal included in the output signal
The pulse noise elimination unit (2) and the envelope detection unit (1
08) detects the pulse noise signal from the output signal of
The pulse noise signal is removed by the loose noise remover (2).
Therefore, a pulse noise detector (3) for outputting a gate signal is provided.

[0011]

According to the pulse noise detecting circuit in the AM receiver of the present invention shown in FIG.
When pulse noise is input to, a harmonic is generated due to the asymmetry of the pulse noise, and this harmonic is detected by the high frequency filter 31 to form a gate signal for operating the pulse noise remover 2. Therefore, it is no longer necessary to have a detection unit inside as in the prior art, and it is no longer necessary to consider the influence of detection distortion.

Further, since the adjacent interference is dealt with and the asymmetry of the band filter in the intermediate frequency stage of the tuner is taken into consideration, the reliability is improved without malfunction due to these factors. Further, the signal delay circuit 201 adjusts the timings of the pulse noise detection circuit and the tuner 1 so that the pulse noise remover 2 can be synchronized.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram showing a pulse noise detection circuit in the AM receiver according to the embodiment of the present invention. The configuration of this figure will be described. The pulse noise detection circuit 3 in the AM receiver shown in the figure includes a high frequency filter 31 connected to the output of the envelope detection unit 108 of the tuner 1, and the high frequency filter 3
1, an amplifier 41 connected to 1, a level detector 33 connected to the amplifier 41 and connected to the gate circuit 21 of the pulse noise canceller 2, and a band filter 34 connected to the output of the envelope detector 108. , The band filter 34
And a level detection unit 35 connected to the
And a low pass filter 36 for controlling the amplification gain of the amplifier 41.

Comparing FIG. 16 with the tuner 200,
The band filter 105 is removed, and the envelope detector 108, which is premised on envelope detection, is used as the detector.
In order to synchronize with the pulse noise detection circuit 3, a signal delay circuit 201 is newly included between the envelope detector 108 and the pulse noise remover 2. Next, the envelope detector
108 will be described.

FIG. 3 is a diagram showing the configuration of the envelope detector of FIG. This figure includes a diode 1081 that inputs to the anode and outputs an output signal from the cathode, a resistor 1082, one of which is connected to the cathode of the die auto 1081 and the other of which is grounded, and a capacitor 1083. Next, the operation of the envelope detector 108 will be described. Assuming that the modulated signal has a frequency bandwidth, the modulated signal v _m (t) is

[0016]

[Equation 1]

Where A _{m is} the amplitude of the modulation signal, P is the angular frequency of the modulation signal φ _{n is} the initial phase of the modulation signal A is the amplitude of the carrier wave ω is the angular frequency of the carrier φ ₀ is the initial phase of the carrier wave, and FIG. It is a figure which shows the spectrum of the modulation signal when there is no pulse noise. This figure illustrates Equation 1.

FIG. 5 is a diagram showing a spectrum of a demodulated signal when there is no pulse noise. This figure demodulates the spectrum of the modulated signal and corresponds to the equation v _m (t) of the equation 1. FIG. 6 is a diagram showing a spectrum of a modulated signal when there is pulse noise. As shown in this figure, the upper sideband,
The lower sideband is located symmetrically with respect to the carrier, but the pulse noise is usually located asymmetrically with respect to the carrier and rarely comes to the symmetrical position.

Now, the pulse noise signal v _E (t) is

[0020]

[Equation 2]

[0021] Where the pulse noise modulated wave Δv _E
As follows,

[0022]

[Equation 3]

It becomes FIG. 7 shows a modulation / demodulation signal portion which is not affected by the pulse noise of the equation (2). This figure (a) is composed of the carrier signal, the upper sideband and the lower sideband of the equation (2). b) shows the signal demodulated by the envelope detector 108. These demodulated signals are used in the high frequency filter 31.
Entered in.

FIG. 8 is a diagram showing the modulated and demodulated signal portion (Δv _E ) affected by the pulse noise of the equation 2, and FIG. 8A shows the pulse noise modulated wave Δv _E of the equation 2. The figure (b) shows the rectification by the diode 1081 of the envelope detector 108, and the figure (c) shows the resistor 1082 and the capacitor 10.
Shows envelope extraction by 83. These demodulated signals are input to the high frequency filter 31.

Comparing the demodulated signals subjected to the envelope detection shown in FIGS. 7B and 8C, FIG.
The waveform of FIG. 8 changes continuously, but the waveform of FIG. 8C changes discontinuously at the point where it changes from falling to rising. This difference is that in FIG. 7B, a sideband that is symmetrical with respect to the frequency of the carrier wave is generated by the modulation signal, whereas in FIG. 8B.
In (1), the pulse noise is caused asymmetrically with respect to the frequency of the carrier.

Next, the operation of the pulse noise detector 3 will be described. FIG. 9 is a diagram showing a high-pass filter of the pulse noise detector of FIG. 2, and the high-pass filter 31 includes a capacitor 311 and a coil 312 as shown in the figure. FIG. 10 is a diagram showing the relationship between the tuner band filter and the cutoff frequency characteristic of the pulse noise detector. As shown in the figure, the cut-off frequency f _b of the high band filter 31 is the band filter 107.
Of the capacitor 311 of the high frequency filter 31 and the coil 31 so that the frequency becomes higher than the upper limit cut-off frequency f _{b of}
The inductance of is determined.

FIG. 11 is a diagram showing an output waveform of the pulse noise detector when the pulse noise is generated. First, the envelope detection signal when there is no pulse noise, or the portion of the envelope detection signal that is not affected by the pulse noise even if there is pulse noise is blocked by the high frequency filter 31, and the output of the pulse noise detector does not occur. On the other hand, of the envelope detection signals affected by the pulse noise as shown in FIG. 4A, the harmonic signal includes the harmonic signal with respect to the pulse noise at the discontinuity point. It passes through, is amplified by the amplifier 32, is shaped by the level detection unit 33, and is formed into a gate signal as shown in FIG.

The harmonic signal will be described. 12
FIG. 4 is a diagram showing spectra of a demodulated signal and a pulse noise signal. As shown in the figure, the envelope detector 10 of the demodulated signal and pulse noise that have passed through the band filter 107
The harmonics of the pulsed noise formed by 8 are high frequency filters 3
It will pass 1. According to the present embodiment, the envelope detection unit in the tuner is shared without including the envelope detection unit as in the conventional case, so that detection distortion does not occur in the pulse noise detection circuit, and the design arrangement is free. It will increase the frequency.

Next, the deformation of the high frequency filter 31 will be described. When the frequency of the adjacent broadcasting station is mixed, it is judged as a pulse noise signal, and the pulse noise detector 3 detects this and tries not to remove it, but the original purpose is the pulse noise caused by the ignition noise of the automobile. Since it is for noise removal, it is not preferable. The frequency interval between such adjacent broadcasting stations is 9 KHz in Japan and 10 KHz in the United States, and when the level of the adjacent frequency is considerably large, the cutoff characteristic of the band filter 107 of the intermediate frequency amplification stage of the tuner is finite. It is mixed because of it.

FIG. 13 illustrates trapping of adjacent interfering frequencies. As shown in this figure, the distance between adjacent frequencies is 9KH.
If a frequency trap (Δf) for adjacent interference is provided at z (10 KHz), the above problem can be solved. FIG. 14 is a diagram showing a high band / band elimination filter for trapping an adjacent interference frequency.

As shown in FIG. 3A, the high band / band elimination flag is set.
The ilter 52 is a coil of inductance L connected in series.
521 and capacity C₁Capacitor 522 and parallel connection
Capacity to be continued C₂Capacitor 522 and the output side
A resistor 524 having a resistance of R. This high band / band eraser
The characteristics of the output filter 52 are as shown in FIG.
Number f ₁To form a trap with

[0032]

[Equation 4]

It is Therefore, a high band / band filter 52 is used in place of the high band filter 31, and its coil 521,
Capacitors 522 and 523 inductance L, capacitance C ₁ ,
It is possible to adjust C ₂ to form the trap of FIG. Next, the operation of the system such as the band filter 34 will be described. First, as described above, the basic principle is that no distortion occurs even if the broadcast wave is envelope-detected.
There are many cases in which detection distortion occurs due to the characteristics of the receiver.
The main cause is that asymmetry of the upper and lower frequency characteristics of the band filter 107 in the intermediate frequency stage causes a level inbalun in the upper sideband and the lower sideband. Output distortion occurs. This phenomenon tends to occur as the modulation frequency increases.
Therefore, the pulse noise detection circuit 3 can easily detect the high modulation degree.

FIG. 15 is a diagram showing the characteristics of the band filter of the pulse noise detection circuit. As shown in the figure, the band filter 34 has the same frequency range as the detected broadcast wave, but its relative gain is asymmetric in the high and low frequency ranges, and as shown in the figure, it is inclined in the low frequency part. Have.
Therefore, in the level detector 35, even if signals of the same level are input to the band filter 34, a signal having a high level when the frequency is high and a signal having a low level when the frequency is low is formed. Averaging is performed to adjust the amplification gain of the amplifier 32. This is because the low-pass filter 36 removes a frequency of about pulse noise so that the system such as the band filter 34 does not operate due to pulse noise, and when it operates, the achievement of the original purpose is hindered. This is because.

In this way, the detection sensitivity of the pulse noise detection circuit 3 can be lowered when the modulation frequency is high on average. The same effect can be obtained by providing the band filter 34 on the higher side and reversing the amplifying function of the amplifier 32. Finally, the signal delay circuit 201 in FIG. 2 uses a high-order low-pass filter or the like, adjusts the signal timing between the tuner 200 and the pulse noise detection circuit 3 described above, and the pulse noise remover 2 Synchronize with.

[0036]

As described above, according to the present invention, the pulse noise is detected by using the envelope detection of the tuner, and the interference by the adjacent broadcasting station and the asymmetry of the band filter in the intermediate frequency stage of the tuner are caused. Since the detection distortion is taken into consideration, the degree of freedom in designing the AM receiver is improved and the operation preventing function is also improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention.

FIG. 2 is a diagram showing a pulse noise detection circuit in the AM receiver according to the embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of an envelope detection unit in FIG.

FIG. 4 is a diagram showing a spectrum of a modulated signal when there is no pulse noise.

FIG. 5 is a diagram showing a spectrum of a demodulated signal when there is no pulse noise.

FIG. 6 is a diagram showing a spectrum of a modulated signal in the presence of pulse noise.

FIG. 7 is a diagram showing a modulated and demodulated signal portion that is not affected by the pulse noise of Equation 2.

FIG. 8 is a diagram showing a modulation / demodulation signal unit (Δv _E ) which is affected by the pulse noise of Expression 2.

FIG. 9 is a diagram showing a high frequency filter of the pulse noise detection unit of FIG. 2;

FIG. 10 is a diagram showing a relationship between a band filter of a tuner and a cutoff frequency of a high band filter of a pulse noise detector.

FIG. 11 is a diagram showing an output waveform of a pulse noise detection unit when pulse noise is generated.

FIG. 12 is a diagram showing spectra of a demodulated signal and a pulse noise signal.

FIG. 13 is a diagram illustrating trapping of adjacent interference frequencies.

FIG. 14 illustrates a high band / band stop filter for adjacent jamming frequency traps.

FIG. 15 is a diagram showing characteristics of a bandpass filter of the pulse noise detection circuit.

FIG. 16 is a diagram showing a conventional pulse noise detection circuit in an AM receiver.

FIG. 17 is a diagram illustrating a situation of noise removal by the pulse noise removal unit of FIG. 16;

[Explanation of Codes] 1 ... Tuner 2 ... Pulse noise removal unit 3 ... Pulse noise detection unit 31 ... High band filter 52 ... High band / band elimination filter 108 ... Envelope detection unit 201 ... Signal delay circuit

Claims (5)

[Claims] 1. An intermediate frequency signal passing through a bandpass filter
Envelope that detects the envelope and outputs an audio signal
In an AM receiver having a detection unit (108), the envelope
Pulse noise included in the output signal of the rope detector (108)
A pulse noise removal unit (2) that removes the signal and a pulse noise from the output signal of the envelope detection unit (108).
The noise signal is detected and pulsed to the pulse noise elimination section (2).
Output the gate signal to remove the noise signal.
An AM including a loose noise detector (3)
Pulse noise detection circuit in receiver. 2. The AM according to claim 1, wherein the pulse noise detector (3) includes a high-pass filter (31) having a cutoff frequency higher than an upper limit cutoff frequency of a bandpass filter through which the intermediate frequency signal passes. Pulse noise detection circuit in receiver. 3. The high / low band having a cut-off frequency higher than the upper cut-off frequency of a bandpass filter through which the intermediate frequency signal passes and erasing a frequency band of an adjacent broadcast. The pulse noise detection circuit in the AM receiver according to claim 1, further comprising an erasing filter (52). 4. The output of a gate signal for removing a pulse noise signal to the pulse noise elimination unit (2) is blocked when the modulation frequency of the envelope detection unit (108) is high. 3. A pulse noise detection circuit in the AM receiver according to 3. 5. A pulse noise detection circuit in an AM receiver according to claim 2, 3 or 4, further comprising a signal delay circuit (201) connected to the envelope detection section (108) and adjusting the timing of the gate signal. .