JPH04297134A - Pulse noise detection circuit in am receiver - Google Patents

Abstract

PURPOSE:To improve waveform of the pulse noise detection circuit in the AM receiver detecting the pulse noise to be mixed in the AM receiver. CONSTITUTION:A pulse noise elimination part 2 eliminating the pulse noise signals included in the output signal of AM tuners 1 and 100 and pulse noise detection parts 3 and 40 provided with a high-pass filter 31, 43 and a level detecting part 33, 44 to output a gate signal for removing a pulse noise signal to the elimination part 2 after detection of the pulse noise signal are provided. The level detection means 33 and 44 change the gate signal width in accordance with the pitch of the input pulse height of high-pass filters 31 and 43.

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 into the AM receiver. In particular, the present invention refers to improvements in pulsed noise detection circuits in AM receivers that can improve waveform distortion.

0002

2. Description of the Related Art FIG. 16 is a diagram showing a conventional pulse noise detection circuit in an AM receiver. Note that similar components are represented by the same reference numbers or symbols throughout the drawings. The configuration in this figure includes the tuner 10 of the AM receiver.
0, a pulse noise removing section 2 for removing pulse noise from the output signal of the tuner 100, and a pulse noise removing section 2 for detecting the pulse noise and sending it to the pulse noise removing section 2 for removing the pulse noise signal. A pulse noise detection section 40 that outputs a gate signal is included.

The tuner 100 includes an antenna 101.
and a high frequency amplifier 10 connected to the antenna 101.
2 and a mixer 1 connected to the high frequency amplifier 102
03, a local oscillator 104 that supplies a mixed wave to the mixer 103, a broadband filter 105 connected to the mixer 103, an intermediate frequency amplifier 106 connected to the band filter 105, and the intermediate frequency amplifier It includes a narrowband bandpass filter 107 connected to the bandpass filter 106 and, for example, an envelope detector 108 connected to the bandpass filter 108. Furthermore, the detector 108
Automatic gain control is performed to control the amplification gain of the intermediate frequency amplifier 106 using the output of the wave detector 108 to keep the output of the detector 108 constant.

The pulse noise removing section 2 includes a gate circuit 2.
1 and a hold capacitor 22. Figure 1
7 is a diagram illustrating the state of noise removal by the pulse noise removal section of FIG. 16. As shown in this figure (a), pulse noise is superimposed on the detected signal in the input signal to the pulse noise removal section 2. This pulsed noise is noise mixed in from ignition noise, power transmission lines, etc. in a car-mounted receiver. As shown in FIG. 3B, a gate signal is detected by the pulse noise detection section 40 and is synchronized with the pulse noise. As shown in this figure (c),
The gate circuit 21 is opened by the gate signal, and the pulse noise is removed. At this time, the capacitor 22 holds the detection signal at the level before removal. When the gate circuit 21 is closed, the holding of the detection signal is released. As shown in the figure (d), the removed shape wave shown in the figure (c) is corrected by a subsequent device (not shown).

The pulse noise detection section 40 in FIG. 16 includes an amplifier 41 connected to the output of the broadband filter 105, an envelope detector 42 connected to the amplifier 41, and an envelope detector 42 connected to the detector 42. a high-pass filter 43; and a level detection section 4 connected to the high-pass filter 43 and generating a gate signal for operating the gate circuit 21.
4 is included. The reason why the tuner 100 is provided with a broadband filter 105 is to increase the wave height of the noise in the pulse noise detector 40 when it is detected in a wide band, thereby making it easier to detect the pulse noise.

Furthermore, automatic gain control is performed to control the amplification gain of the amplifier 41 in order to keep the output of the detector 42 constant. Next, the operation will be explained. The received signal mixed with pulse noise is branched by a bandpass filter 105 and sent to an amplifier 41.
It becomes a demodulated wave from which the carrier wave is removed by the envelope detector 42 , filters other than high-frequency pulse noise are removed by the high-pass filter 43 , and is shaped into a gate signal by the level detector 44 and output to the gate circuit 21 . .

[0007]

[Problem to be solved by the invention] However, the conventional A
The pulse noise detection circuit in the M receiver has the following problems. FIG. 18 is a diagram showing the configuration of the level detection section of FIG. 16. This figure shows a comparator 441 which inputs the output signal of the high-pass filter 43 to the non-inverting terminal and inputs the reference voltage Vr to the inverting terminal, and a comparator 441 which inputs the output signal of the high-pass filter 43 to the inverting terminal and inputs the reference voltage Vr to the inverting terminal. A comparator 442 input to the non-inverting terminal, and the comparator
an OR circuit 443 connected to 441 and 442; and a pulse noise removal section 2 connected to the OR circuit 443.
Monostable multivibrator 44 that outputs a gate signal to
4 including.

Next, the operation of the level detection section will be explained. Figure 1
9 is a diagram showing a signal waveform in the level detection section of FIG. 18. This figure (a) shows the waveform of the output signal from the detector 42, and this figure (b) shows the waveform of the signal from the high-pass filter 43, which has extracted high-frequency noise components from the signal of the detector 42. The original waveform of the output signal of the device 42 is different from the original waveform. This figure (c
) is the output signal of comparators 441 and 442, which is equal to or higher than Vr in the case of a positive signal and -Vr in the case of a negative signal.
A positive rectangular pulse is shown below. This figure (d) shows the OR circuit 44 from the comparators 441 and 442.
3 is the output signal waveform generated by the monostable multivibrator.

This figure (a) shows cases where the pulse noise is large and small. Pulse noise has a larger wave height and a larger width, but it is also essentially an impulse of the tuner 100 intermediate frequency stage filter. It is determined by the response, and if the pulse noise added to it is large, various distortions will occur and the pulse width will widen. Places where the distortion occurs are the intermediate frequency amplification sections 106, 41, the detection sections 107, 42, etc. Therefore, when detecting the positive and negative pulses and creating the gate pulse width using the monostable multivibrator 444, the pulse width changes depending on the peak value of the pulse, so normally, as shown in the figure,
Optimize to the higher value of pulse height and calculate τB = τ1 +
I set it to α. Here, τ1 is the time interval between the positive side and the negative side, and α is the design margin. In this case, even if the pulse noise disappears, the gate will be opened by τB = τ1 + α, but compared to the case where the peak value of the pulse noise is small, the gate width is too wide, and in FIG. 17(c), Therefore, there is a problem in that unnecessary waveform distortion occurs. Furthermore, the installation of two comparators necessary to detect the positive side pulse and the negative side pulse poses a problem in order to simplify the structure.

[0010] Therefore, in view of the above problems, the present invention has the following features:
It is an object of the present invention to provide a pulse noise detection circuit in an AM receiver that makes the gate width variable depending on the input pulse peak value.

[0011]

[Means for Solving the Problems] FIG. 1 is a diagram showing the basic configuration of the present invention. In order to solve the above problems, the present invention provides an AM tuner 1,100 with an AM tuner 1,100.
A pulse noise removing unit 2 that removes a pulse noise signal included in the output signal of 00, and a gate that detects the pulse noise signal and causes the pulse noise removal unit 2 to remove the pulse noise signal. At least high-pass filters 31, 43 and level detectors 33, 4 are used to output signals.
A comprising a pulse noise detecting section 3, 40 having a
In the pulse noise detection circuit in the M receiver, the level detection sections 33 and 44 are connected to the high-pass filter 31.
, 43, the gate signal width is varied wide and narrow according to the height of the input wave.

The level detecting sections 33 and 44 have a positive/negative discriminating section 441, a holding attenuation section 442, a subtracting section 443, and a comparing section 444.

[0013]

[Operation] In FIG. 1, according to the pulse noise detection circuit in the AM receiver of the present invention, the pulse noise detection circuit 3
, 40 becomes a high frequency component through the high-pass filters 31 and 43, and is separated into positive or negative signals by a positive/negative discriminator 441, and the peak of the input signal is temporarily held by a holding attenuator 442. It is attenuated over a predetermined period of time. The signal processed in this way is sent to the subtraction unit 443.
Since the difference is taken, the rising and falling edges of the pulse noise are shaped into one pulse, and if the pulse height of the pulse noise is high, it takes time to attenuate. The comparator generates a gate signal from when the processed signal exceeds a predetermined reference voltage until it decreases below it, so the higher the pulse height of the pulse noise is, the wider the gate width becomes. The smaller the value, the narrower the gate width.

Furthermore, compared to the conventional method, which required two comparators, only one comparator is required, which simplifies the configuration.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a diagram showing a level detection section related to a pulse noise detection circuit in an AM receiver according to an embodiment of the present invention. The configuration of the level detection section 33 (44) in this figure will be explained. The level detection section 33 (44) in this figure has a resistor 501, one of which is connected to the output of the high-pass filter 31 (43) and the other connected to the voltage power supply VCC, and one of which is connected to the output of the high-pass filter 31 (43). A resistor 502 is connected to the output and the other side is grounded, and a pnp transistor 503 whose base is connected to the output of the high-pass filter 31 (43) and whose collector is grounded.
and a resistor 50, one of which is connected to the emitter of the transistor 503 and the other to the voltage power supply VCC.
4, an npn transistor 505 whose base is connected to the emitter of the transistor 503 and whose collector is connected to the voltage power supply VCC, and whose base is connected to the output of the high-pass filter 31 (43) and whose collector is connected to the voltage power supply VCC. npn transistor 506 connected to
and one of them is connected to the emitter of the transistor,
a resistor 507 whose other end is grounded; a pnp transistor 508 whose base is connected to the emitter of the transistor 506 and whose collector is grounded; and a capacitor 509 whose one end is connected to the emitter of the transistor 505 and whose other end is grounded. and capacitor 50
A resistor 510 is connected in parallel to the transistor 508, one of which is connected to the emitter of the transistor 508, and the other is connected to the voltage power supply VCC, one of which is connected to the emitter of the transistor 508, and the other is grounded. a resistor 515, one of which is connected to the emitter of the transistor 505, a resistor 516, one of which is connected to the emitter of the transistor 508, one of which is connected to the other of the resistor 515, and the other is connected to the power supply. A resistor 517 connected to the voltage VBB, a differential amplifier 518 whose non-inverting terminal is connected to the other of the resistor 515, and whose inverting terminal is connected to the resistor 516, and one of which is connected to the output of the differential amplifier 518. A resistor 519 whose non-inverting terminal is connected to the output of the differential amplifier and whose inverting terminal is supplied with a reference voltage, the other of which is connected to feed back to its input, is gated to the pulse noise removing section 2. Comparator 52 outputting a signal
Contains 0.

Here, the resistors 501 to 510 constitute a positive/negative discriminator 441, the capacitors 509 to 512 constitute a holding and attenuating part 442, and the resistors 515
~The resistor 519 constitutes the subtraction unit 443, and the comparator 5
20 etc. constitute a comparison section 444. FIG. 3 is a diagram illustrating the gate width that is variable with respect to the pulse height. This figure (a) is a partial diagram of FIG. 2, in which the transistor 505
When a signal with a wave height VM is input to the capacitor 510, the capacitor 510 having a capacitance C is temporarily charged to the wave height VM, and when the input is removed, it is discharged via a resistor 509 having a resistance value R with a time constant RC. This figure (b) shows the change in the voltage V0 across the capacitor 510, and this V0 is the reference voltage Vr of the comparator 520.
The time t until the gate width becomes equal to the gate width.

Next, a series of operations of this embodiment will be explained. FIG. 4 is a diagram showing signal waveforms for explaining the operation of the embodiment of the present invention. Figures (a) and (b) are shown in Figure 19 (a) (
In order to correspond to the signal waveform V of the emitter of the transistor 505, this figure (c) shows the signal waveform V of the emitter of the transistor 505.
p, and this figure (d) is the signal waveform Vn of the emitter of the transistor 508, this figure (e) is the output signal waveform of the differential amplifier 518, and this figure (f) is the signal waveform of the emitter of the comparator 5.
20 is the output signal waveform.

In forming the signal waveforms Vp and Vn, a pnp transistor 503, an npn transistor 505, and an npn transistor 506 are used.
and pnp type transistors 511 are connected in two stages, so that the DC bias is the same and no deviation occurs when no input is applied. The output signal waveform Vs in FIG. 5(e) is expressed as Vs = Vp - Vn, and the width becomes wider depending on the waveform of the pulse noise, and the width of the gate pulse VG passing through the comparator 520 also becomes wider.

With the above configuration, it is possible to reduce the number of comparators or amplifiers to one compared to the conventional one. Next, a modification of the embodiment of the present invention will be explained. FIG. 5 is a diagram showing a level detection section according to an embodiment of the present invention used in a pulse noise detection circuit in another AM receiver.

The level detecting section 33 in this figure has the same structure as described above and has the same functions and effects. however,
The tuner 1 and the pulse noise detection circuit in this figure are different from the conventional technology, and will therefore be explained. The configuration of this figure will be explained. The pulse noise detection circuit 3 in the AM receiver shown in this figure is the envelope detection section 10 of the tuner 1.
8, an amplifier 41 connected to the high-pass filter 31, and a level detection section 33 connected to the amplifier 41 and connected to the gate circuit 21 of the pulse noise removal section 2. and the envelope detection section 1
08, a level detection unit 35 connected to the bandpass filter 34, and a low-pass filter 36 connected to the level detection unit 35 and controlling the amplification gain of the amplifier 41. .

In comparison with FIG. 16, the tuner 1 has the bandpass filter 105 removed, and the detector is an envelope detection section 108 that assumes envelope detection.
In order to synchronize with the pulse noise detection circuit 3, an envelope detection section 108 and a pulse noise removal section 2 are installed.
A signal delay circuit 201 is newly included between the two. Next, the envelope detection section 108 will be explained.

FIG. 6 is a diagram showing the configuration of the envelope detection section of FIG. 5. This figure includes a diode 1081 whose anode is input and an output signal is taken out from its cathode, a resistor 1082 whose one side is connected to the cathode of the diode 1081 and whose other side is grounded, and a capacitor 1083. Next, the operation of the envelope detection section 108 will be explained. Assuming that the modulated signal has a frequency bandwidth,
The modulation signal Um (t) is

[0023]

[Math 1]

FIG. 7 is a diagram showing the spectrum of a modulated signal in the absence of pulse noise. This figure illustrates Equation 1. FIG. 8 is a diagram showing the spectrum of the demodulated signal when there is no pulse noise. This figure shows the demodulated spectrum of the modulated signal, and corresponds to the equation Um (t) of Equation 1.

FIG. 9 is a diagram showing the spectrum of a modulated signal in the presence of pulse noise. As shown in this figure, the upper sideband and lower sideband waves are located symmetrically with respect to the carrier wave, but pulse noise is usually located asymmetrically with respect to the carrier wave.
They are rarely in symmetrical positions. Now let us consider the pulse noise signal UE (t) as

[0026]

[Math 2]

[0027] Here, pulse noise modulated wave ΔUE
If you do as below,

[0028]

[Math 3]

becomes 0029. FIG. 10 shows the modulation and demodulation signal part that is not affected by the pulse noise of Equation 2, and this figure (a)
consists of a modulated signal of several carrier waves, an upper side band wave, and a lower side band wave, and FIG. These demodulated signals are input to a high-pass filter 31.

FIG. 11 is a diagram showing the modulation and demodulation signal portion (ΔUE) affected by pulse noise as shown in equation 2.
This figure (a) shows the pulse noise modulated wave ΔUE of the number 2, this figure (b) shows the rectification by the diode 1081 of the envelope detection section 108, and this figure (c) shows the rectification by the resistor 108
2 and capacitor 1083 are shown. These demodulated signals are input to a high-pass filter 31.

Comparing the envelope-detected demodulated signals in FIGS. 10(b) and 11(c), FIG.
The waveform in FIG. 11(b) changes continuously, but the waveform in FIG. 11(c) changes discontinuously at the point where it changes from falling to rising. This difference is because in Fig. 10(b), the modulated signal produces double-side band waves that are symmetrical with respect to the carrier frequency, whereas in Fig. 11(c), the pulse noise is asymmetrical with respect to the carrier frequency. Attributable to what happens.

Next, the operation of the pulse noise detector 3 will be explained. FIG. 12 is a diagram showing a high-pass filter of the pulse noise detection section of FIG. 5, and the high-pass filter 31 includes a capacitor 311 and a coil 312 as shown in the figure. FIG. 13 is a diagram showing the relationship between the bandpass filter of the tuner and the cutoff frequency characteristics of the pulse noise detector. As shown in the figure, the capacitance of the capacitor 311 and the inductance of the coil 31 of the high-pass filter 31 are determined so that the cutoff frequency fb of the high-pass filter 31 is greater than the upper limit cutoff frequency fb of the bandpass filter 107.

FIG. 14 is a diagram showing the output waveform of the pulse noise detector when pulse noise occurs. First, the envelope detection signal when there is no pulse noise or the portion of the envelope detection signal that is not affected by pulse noise even if there is pulse noise is blocked by the high-pass filter 31, and no output from the pulse noise detector is generated. On the other hand, as shown in this figure (a), among the envelope detection signals affected by pulse noise, the discontinuous points include harmonic signals relative to the pulse noise, so these harmonic signals pass through the high-pass filter 31. The signal passes through, is amplified by the amplifier 32, is shaped by the level detection section 33, and is formed into a gate signal as shown in FIG. 3(b).

The harmonic signal will be explained. Figure 15
is a diagram showing spectra of a demodulated signal and a pulsed noise signal. As shown in the figure, among the demodulated signal and pulsed noise that have passed through the bandpass filter 107 , the harmonics of the pulsed noise formed by the envelope detection 108 pass through the high-pass filter 31 .

[0035]

[Effects of the Invention] As explained above, according to the present invention, A
The level detection section of the pulse noise detection circuit in the M receiver changes the gate signal width widely and narrowly according to the input wave height of the high-pass filter, which suppresses waveform distortion and further simplifies the circuit. It can be expected that the effect of

[Brief explanation of drawings]

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

FIG. 2 is a diagram showing a level detection unit related to a pulse noise detection device in an AM receiver according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating possible gate widths with respect to pulse heights.

FIG. 4 is a diagram showing signal waveforms for explaining the operation of the embodiment of the present invention.

FIG. 5 is a diagram showing a level detection section according to an embodiment of the present invention used in a pulse noise detection circuit in another AM receiver.

FIG. 6 is a diagram showing the configuration of an envelope detection section in FIG. 5;

FIG. 7 is a diagram showing a spectrum of a modulated signal when there is no pulse noise.

FIG. 8 is a diagram showing a spectrum of a demodulated signal when there is no pulse noise.

FIG. 9 is a diagram showing a spectrum of a modulated signal when there is pulse noise.

FIG. 10: Modulation that is not affected by pulsed noise as shown in Equation 2.
FIG. 3 is a diagram showing a portion of a demodulated signal.

FIG. 11: Modulation affected by pulsed noise as shown in equation 2.
FIG. 3 is a diagram showing a demodulated signal section (ΔUE).

FIG. 12 is a diagram showing a high-pass filter of the pulsed noise detection section of FIG. 2;

FIG. 13 is a diagram showing the relationship between the cutoff frequencies of the bandpass filter of the tuner and the high-pass filter of the pulsed noise detection section.

FIG. 14 is a diagram showing an output waveform of a pulse noise detection section when pulse noise occurs.

FIG. 15 is a diagram showing spectra of a demodulated signal and a pulsed noise signal.

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

FIG. 17 is a diagram illustrating the state of noise removal by the pulse noise removal section of FIG. 16;

FIG. 18 is a diagram showing the configuration of the level detection section in FIG. 16.

FIG. 19 is a diagram showing signal waveforms in the level detection section of FIG. 18;

[Explanation of symbols]

1,100...AM tuner 2...Pulse noise removal section 3, 40...Pulse noise detection section 31, 43...High-pass filter 33, 44...Level detection section 441...Positive/negative identification section 442...Holding damping part 443...Subtraction part 444…Comparison section

Claims (2)

[Claims] [Claim 1] The AM tuner (1,100)
a pulse noise removing unit (2) that removes a pulse noise signal included in the output signal of the tuner (1, 100); and a pulse noise removal unit (2) that detects the pulse noise signal.
at least a high-pass filter (31, 43) to output a gate signal for removing the pulsed noise signal.
and a level detection section (33, 44).
33, 44) and the high-pass filter (31, 44).
43) A pulse noise detection circuit in an AM receiver, characterized in that the width of the gate signal is varied widely according to the height of the input wave. [Claim 2] The level detection section (33, 44)
includes a positive/negative identification unit (441) that identifies the output signal of the high-pass filter (31, 43) as positive or negative; and the high-pass filter (31, 43) identified by the positive/negative identification unit (441).
a holding attenuation section (442) that holds each output of the holding attenuation section (442) and attenuates it with a constant time constant; a subtraction section (443) that takes the difference between each output signal of the holding attenuation section (442);
a comparator (443) that outputs a gate signal to the pulse noise removing unit (2) when the output signal of the
444). The pulse noise detection circuit in an AM receiver according to claim 1.