JPH03238929A - Noise canceller - Google Patents

Abstract

PURPOSE:To obtain a voice output with high quality by combining a couple of comparators and an analog switch circuit so as to apply interpolation for the generating period of pulse noise and eliminating the pulse noise. CONSTITUTION:A voice signal including a pulse noise is inputted to an input terminal 21 and the voice signal is fed to an analog switch circuit 22 and a high pass filter (HPF) 23. The high pass filter 23 extracts only pulse noise component and it is fed to noise detection comparators 24a, 24b. The comparator 24a detects positive noise and the comparator 24b detects negative noise. The noise detection signal is fed to a control terminal of the analog switch circuit 22 through an OR circuit 25 and the switch circuit 22 is turned off for the period of the detection signal, the pulse noise does not pass the switch circuit 22 and the interpolation for the period is implemented by a voltage latch circuit 26. Thus, the voice signal with high quality from which the pulse noise is eliminated is outputted from the output signal 27.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a noise canceler for removing pulse noise, for example, for use in an audio circuit of a vehicle-mounted television receiver or an FM receiver. .

<Conventional technology> Conventionally, in the audio circuits of in-vehicle television receivers and M receivers, pulse noise is mixed into the audio signal due to ignition system noise, motor system noise, and noise generated by switch operations. do.

FIG. 5 is a block diagram showing a conventional noise canceller used in the audio circuit. Here, we will explain what is used in a vehicle-mounted television receiver.

In FIG. 5, an audio signal subjected to audio detection is input to an input terminal 1, and a low pass filter (LPF) 2. It is supplied to the input terminal of an operational amplifier 4 through a low-pass amplifier (LPA) 3. Also, the audio signal input to the input terminal 1 is passed through a high-pass filter (mouth PF) 5. Bypass amplifier (
The signal is supplied to the noise detector 7 through the port PA) 6, and when noise is detected here, a noise detection signal of a certain period T1 is generated and is supplied to the control terminal of the analog switch circuit 8 as a switch control signal. An integrating circuit consisting of a resistor RO and a capacitor CO that determines the pulse width T1 of the detection signal is connected to the PW terminal of the noise detector 7. One terminal of the analog switch circuit 8 is supplied with a signal (actually unmanned power) from the PC terminal through the inverting amplifier 9, and the other terminal of the switch circuit 8 is supplied with one input terminal of the operational amplifier 4. A voltage holding circuit 10 is connected between the 10th input terminal and the 1st input terminal of the operational amplifier 4 to hold the output of the low-pass amplifier 3 and supply it to the 1st input terminal of the operational amplifier 4.
is connected. Then, an audio signal from which pulse noise has been removed is output from the output terminal 11. The dashed line frame 12 is “
It is used as an IC for receiving M signals, and the PC terminal is designed to receive the pilot signal of M stereo broadcasting, but when used in a television receiver, there is no pilot signal, so the PC terminal The terminal is left unattended.

Next, the operation shown in FIG. 5 will be explained with reference to FIG. 6. When an audio signal containing pulse noise (spark plug noise, DC motor noise, etc.) as shown in FIG. 6(a) is applied to the input terminal 1, the signal is passed through the LPF 2. It passes through LPA3 and is supplied to the ten input terminal of operational amplifier 4. At this time, if one input terminal of the operational amplifier 4 is grounded in an alternating current manner, the audio signal at the tenth input terminal is output as is. Note that during normal operation periods when noise is not detected, there is no switch control signal from the noise detector 7, the switch circuit 8 is on, and the output of the inverting amplifier 9 is applied to one input terminal of the operational amplifier 4, but the PC Since the terminal is unmanned and the output impedance of the amplifier 8 is low, the - input terminal is equivalent to being grounded in an alternating current manner, and the audio signal input to the - input terminal is output as is. However, during a period when there is a pulsed noise component, only the pulsed noise component is extracted by the HPF 5 and amplified by the HPA 6, and then the noise component of a certain level or higher is detected as noise by the noise detector 7.

This noise detection 2I! 7 consists of a comparator, a monostable multivibrator, etc., and R attached to the PW terminal.
A switch control signal (see FIG. 6(b)) that becomes low level is output during a constant period of vIIIi1 determined by O and Go. This switch control signal turns off the analog switch circuit 81 for a certain period of time 111flT1. At this time, a voltage holding circuit 10 is connected to one input terminal of the operational amplifier 4.
Due to the action of PF2. LPA3
Since the audio signal that has passed through the
is equivalent to unmanned force, and as shown in Figure 6 (C), 11
As for the period, the DC voltage immediately before the switch circuit 8 is turned off is output. In this way, after noise is detected, the noise component is removed by an interpolation operation according to the constant rule 111TI.

As a result of the above operations, the audio signal containing pulse noise as shown in FIG. 6(a) becomes one in which the pulse noise has been interpolated and removed as shown in FIG. 6(C). Figure 6 (C)
In this case, interpolation causes a step difference in the output signal, but this can be reduced by passing it through the LPF. however,
The size of the step is proportional to the signal amplitude, and this step occurs in a constant time width T1 regardless of the duration of the noise, so there is a problem in that there is a limit to the improvement in the quality of the final audio output.

(Am to be Solved by the Invention) In this way, in the conventional circuit, when pulse noise is detected, an interpolation operation is performed for a certain period of time regardless of the duration of the noise, so unnecessary steps are created in the interpolation output. There was a problem in that there was a limit to the improvement of the quality of the final audio output.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a noise canceller that performs interpolation operation only during noise generation periods, minimizes the level difference after interpolation, and obtains higher quality audio output. The purpose is to

[Structure of the Invention] (Means for Solving Problem 1) The noise canceller of the present invention includes an analog switch circuit that receives pulse noise and turns off during the period of the noise to remove the noise, and this analog switch. During the off period of the circuit, the voltage just before turning off is held as an interpolation voltage,
a voltage holding circuit that performs noise interpolation on the audio signal from the analog switch circuit; and a voltage holding circuit that is supplied with the input audio signal;
It consists of a high-pass filter that passes the pulse noise contained in the audio signal, and a pair of comparators in the oven collector output format, the output ends of both comparators are OR-connected, and the signal passed through the high-pass filter is input as an One comparator detects pulse noise of positive polarity, while the other comparator detects pulse noise of negative polarity, so that the output terminal receives noise corresponding to the noise period of both positive and negative polarities The noise detecting means outputs a detection signal, and uses the detection output to turn off the analog switch circuit for noise interpolation.

(Function) In the present invention, since pulse noise is detected using a comparator, the noise detection signal becomes a digital signal whose waveform is shaped in synchronization with the noise period. Then, since the interpolation operation is performed by directly turning on and off the analog switch circuit using this digital signal, interpolation is performed only during the period of the pulse width of the detected noise, and the minimum necessary interpolation is performed.

Therefore, there is little deterioration of the audio signal due to the interpolation operation, and it is possible to obtain higher quality audio output than before.

(Example) Examples will be described with reference to the drawings.

FIG. 1 is a block diagram showing a noise canceller according to an embodiment of the present invention.

In FIG. 1, an audio signal containing pulse noise is input to an input terminal 21. As shown in FIG. This audio signal is supplied to an analog switch circuit 22 and a high pass filter (HPF) 23. The high-pass filter 23 extracts only pulse noise components, and the noise detection comparator 24a
, 24b. The comparator 24a detects positive polarity noise, and the comparator 24b detects negative polarity noise. These noise detection signals are applied to the control terminal of the analog switch circuit 22 through the OR circuit 25, and the switch circuit 22 is turned off during the period of this detection signal, so that the pulse noise does not pass through the switch circuit 22 and the interpolation during that period is This is performed in the holding circuit 26, and an audio signal from which pulse noise has been removed is output from the output terminal 27.

FIG. 2 is a circuit diagram showing a specific circuit configuration of the noise canceller shown in FIG. 1, and FIG. 3 is a waveform diagram showing signal waveforms of each part (1) to (2) in FIG. 2.

In FIG. 2, the audio signal input terminal 21 is connected to an analog switch Q3, while a bypass capacitor C1,
It is connected to the ten input terminals of the comparator Q1 and one input terminal of the comparator Q2 via R3. Comparator Q
1 and Q2 are oven collector output type comparators. One input terminal of comparator Q1 is capacitor C
2 to the reference potential point. Further, the input terminal of the comparator Q2 is connected to the reference potential point via the capacitor C4. Resistors R1, R2, and R3 are connected in series between the DC power supply +VCC and the reference potential point, and R
The connection point between R2 and R2 is connected to the ten input terminal of the comparator Q1, and the connection point between R2 and R3 is connected to one input terminal of the comparator Q1.

In addition, a resistor R4 is connected between the DC power supply element Vcc and the reference potential point.
, R5, and R6 are connected in series, and the connection point of R4 and R5 is connected to the input terminal of comparator Q2, and R5 and R5 are connected in series.
The connection point 6 is connected to the - input terminal of the comparator Q2. Furthermore, the output terminals of oven collector output type comparators Ql and Q2 are commonly connected, and the connection point is connected to a resistor R.
7 to the DC power supply Vcc (referred to as a wired-OR connection), and to the control end of the analog switch Q3. The output end of the analog switch Q3 is connected to the audio signal output terminal 27 via a resistor R8 and a voltage holding capacitor C5.

Next, the operation of the circuit shown in FIG. 2 will be explained with reference to FIG. 3.

If the audio signal waveform at the input point ■ contains pulse noise as shown in Figure 3(a), the input terminal of the comparator Q1 and the input terminal of the comparator Q2 are As shown in FIG. 3(b), the 0-point waveform added to is one in which the audio signal component is attenuated and the pulse noise component is extracted. This signal is also applied to the other input terminals of comparators Ql and Q2 via resistors R2 and R5, but since high-cut capacitors C2 and C4 are connected to each terminal, the waveform at point C is shown in Figure 3. As shown in (C), the waveform has attenuated pulse noise. As a result, both comparators Q1 and Q2 perform comparison operations using the waveforms shown in FIGS. 3(b) and 3(c) as input signals. That is, the comparator Q1 works as a positive noise detector with one input terminal as a reference, while the comparator Q2 works as a negative noise detector with ten input terminals as a reference. By the way, when there is no pulse noise,
Both Ql and Q2 have resistances R1, R2, R3 and R4゜R5
, R6 applies a DC bias that turns the open collector output off, and this [IQl
, Q2, the output voltage at the 0 point becomes low level (+V CC) as shown in FIG. 3(d), and the analog switch Q3 is turned on. Therefore, a waveform equal to the input audio signal is obtained at the output point O of the analog switch Q3 as shown in FIG.
) The output waveform shown is obtained. Note that, in order to increase the noise detection sensitivity, the resistance value of R1-R6 is usually selected such that R1 or R3>)R2, R4 or R6>>R5.

Next, when positive or negative pulse noise is detected, if it is positive polarity noise, the open collector output of comparator Q1 will be in the on state, and if it is negative polarity noise, the open collector output of comparator Q2 will be in the on state. Therefore, the voltage at the 0 point is in the noise period f! as shown in Figure 3(d). IIL level (Ov). For this reason,
If there is pulse noise, the analog switch Q during that period
3 is turned off, and the voltage waveform at point 0 is changed to switch Q3 by the function of voltage holding capacitor C5, as shown in Fig. 3(e).
is maintained at the potential just before turning off, and when noise is no longer detected, the 0 point returns to low level as shown in Figure 3(d) and switch Q3 is turned on, so as shown in Figure 3(e). An output with noise removed is obtained. This output is waveform-shaped by the action of an LPF using a resistor R8 and a capacitor C5, and as a result, a noise-interpolated audio output as shown in FIG. 3(f) is obtained.

According to the embodiment described above, since the control pulse width of the analog switch for interpolation is not fixed as in the conventional case but is proportional to the noise generation period, it is possible to minimize the waveform deterioration of the audio signal due to the interpolation operation. You can

FIG. 4 is a waveform diagram illustrating another example of the noise removal effect according to FIG. 1 or 2. FIG.

FIG. 4 shows the effect of eliminating buzz components generated when the intercarrier system is adopted in a television receiving apparatus using a waveform of a vertical period (V period). Figure 4 (a
) shows the video detection output, and FIG. 4(b) shows the audio detection output detected by the intercarrier method. In this audio detection output, buzz is likely to occur in synchronization with the vertical synchronization signal part or the video part with a high degree of II due to the influence of the video signal when the signal deteriorates such as in the case of a weak electric field or a ghost. However, even with such an audio detection output, if the circuit of the above embodiment is used, the audio detection output (noise interpolation output) from which the buzz component has been removed without damaging the audio signal can be obtained as shown in FIG. 4(C). ) can be obtained.

Incidentally, in the above embodiment, the case where the noise canceller is used in the audio circuit of a television receiver was explained.
Of course, it may also be used in audio circuits such as radio receivers.

[Effects of the Invention] As described above, according to the present invention, with a relatively simple circuit configuration consisting of a combination of a pair of comparators and an analog switch circuit, it is possible to remove pulse noise by performing an interpolation operation only during the period in which it occurs. This is possible, the deterioration of the audio signal due to noise removal is extremely small, and it is possible to obtain higher quality audio output than before. In addition, when receiving television, it is also effective in reducing buzz during weak electric fields and ghosts.

[Brief explanation of drawings]

Fig. 1 is a 7099 diagram showing the configuration of a noise canceller according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing a specific example of the circuit shown in Fig. 1, and Fig. 3 is for explaining the operation of Fig. 2. FIG. 4 is a waveform diagram illustrating another noise removal effect obtained by the circuits in FIGS. 1 and 2.
FIG. 5 is a block diagram showing the configuration of a conventional noise canceller, and FIG. 6 is a signal waveform diagram of each part of the circuit for explaining the operation of FIG. 5. 21... Audio signal input terminal, 22... Analog switch circuit, 23... High pass filter, 24a, 24b... Comparator for noise detection, 25
...OR circuit, 26...voltage holding circuit, 27...
Audio signal output terminal.

Claims (1)

[Claims] An audio signal containing pulsed noise is supplied as an input,
an analog switch circuit that is controlled on and off by a control signal and turns off during the pulse noise period to output an audio signal in which the pulse noise is blocked; and an analog switch circuit that is connected to the analog switch circuit and turns off the analog switch circuit. a voltage holding circuit that holds the voltage immediately before turning off as an interpolation voltage during a period and performs noise interpolation on the audio signal from the analog switch circuit; It consists of a high-pass filter that passes noise, and a pair of comparators in the open collector output format.The output terminals of both comparators are connected to a common load to form an OR circuit at the output terminal, and the output terminal is passed through the high-pass filter as an input. The signal is supplied to both comparators, and one comparator detects pulse noise with positive polarity, while the other comparator detects pulse noise with negative polarity, so that pulses with both positive and negative polarities are output to the output terminal. a noise detection means for outputting a noise detection signal corresponding to a period of sexual noise, and turning off the analog switch circuit using this detection output.