JP2000101458A - Noise canceller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly eliminate a pulse noise, even if electric field strength fluctuates. SOLUTION: A noise AMP 30 of the noise canceller 21, that eliminates a pulse noise intruded in a receiver 22 amplifies an output of a mixer 26, while a voltage controlled amplifier circuit 31 and a gain control circuit 32 control the gain. A comparator 33 detects the pulse noise from an output of the voltage- controlled amplifier circuit 31. A control circuit 37c selects a capacitor 37a or 37b, in response to an output from an S meter circuit 40, generates a gate signal from an output of the comparator 33 so as to decrease correction quantity, when the electric field strength is high and a switch circuit 34 eliminates pulsating noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise canceller for removing a pulse noise mixed in a radio signal when receiving the signal.

[0002]

2. Description of the Related Art Conventionally, a vehicle body receiver or the like is provided with a noise canceller for removing pulse noise. For example, Japanese Patent Application Laid-Open No. Sho 60-79830 discloses that when pulse noise is removed from FM detection output, the noise removal period is made variable according to the electric field intensity, and the period is reduced at a strong electric field intensity with a good S / N ratio. Prior art has been disclosed that shortens the period for long, weak electric field strengths. JP-A-6
No. 21836 discloses a prior art in which noise components included in an audio signal obtained by detecting an FM signal are classified by a filter having a plurality of frequency characteristics, and noise is removed with a pulse width corresponding to the frequency component. JP-A-6-314980 discloses that a timer is used to set a gate time when noise is detected from an output of a detected FM signal and is removed by a gate circuit, and the count-up value of the timer is changed according to the electric field strength of the received signal. There is disclosed a concept of setting so as to be large when the intensity is strong and to be small when the electric field intensity is weak.

In these prior arts, in order to remove pulse noise contained in a detection output, a pulse to be removed is detected, and removal is performed based on a detection signal. For this reason, in order to adjust a time delay caused by pulse detection or the like, an equivalent delay is given to a signal to be subjected to noise removal.

FIG. 7 shows a schematic electrical configuration of a receiver 2 including a noise canceller 1 on which the present invention is based.
The receiver 2 receives the radio wave by the antenna 3 and amplifies it by a high frequency (hereinafter sometimes abbreviated as “RF”) amplifier circuit 4.
A local oscillation signal from the local oscillation circuit 5 and a mixer (hereinafter referred to as “M
IX) 6 and converted into an intermediate frequency (hereinafter sometimes abbreviated as “IF”) signal. The IF signal is amplified by an IF amplifier circuit 7 and a detection circuit 8
And demodulates a low-frequency output such as an audio signal.
An IF filter 9 having a steep selectivity characteristic is provided at a stage preceding the IF amplifying circuit 7. The signal passing through the IF filter 9 is delayed. The pulsed noise is delayed and widened as it is delayed, resulting in a so-called “rounding” state.

The noise canceller 1 inputs a signal for noise detection from a stage preceding the IF filter 9 in order to avoid the influence of delay and rounding of pulse noise.
The input destination signal is amplified by a fixed gain by a noise AMP 10 which is an amplifier circuit for noise (hereinafter, may be abbreviated as “AMP”), and further amplified by a voltage control amplifier circuit (hereinafter, abbreviated as “VCA”). A) is amplified at 11.
The voltage control amplifier circuit 11 includes a gain control circuit (hereinafter referred to as “AG”).
C) (which may be abbreviated as “C”), and the gain is controlled when the input signal level is low.
As the input signal level increases, the gain is automatically adjusted so that the gain decreases. Since the signal level of the pulse noise in the input signal changes rapidly, the gain control by the gain control circuit 12 cannot follow. Comparator 1
Reference numeral 3 detects pulse noise as a sudden change in the output of the voltage control amplifier circuit 11.

A gate signal is generated in accordance with the detection output from the comparator 13, and the switch circuit 14 is controlled to remove pulse noise from the audio signal output from the detection circuit 28. The switch circuit 14 shuts off the detection output when a gate signal for removing the pulse noise is given. The level immediately before the interruption is supplied from the capacitor 16 of the sample and hold circuit 15 to the audio output terminal. A gate signal is generated based on the output of the comparator 13 by a charging / discharging circuit that combines a capacitor 17 and a constant current source 18, and switching between charging and discharging is performed by a switching transistor 19. When the comparator 13 detects the pulse noise and turns on the transistor 19, the charge in the capacitor 17 is rapidly discharged. When the comparator 13 does not detect pulse noise, the transistor 19 is turned off.
In this state, the capacitor 17 is charged with a constant current from the constant current source 18, and the terminal voltage continuously rises. The rising speed of the terminal voltage of the capacitor 17 is determined by the capacitance ratio of the capacitor 17 and the output current value of the constant current source 18.
The switch 14 cuts off the audio signal while the terminal voltage of the capacitor 17 is lower than the fixed voltage value.

FIG. 8 shows waveforms at various parts when the noise canceller 1 shown in FIG. 7 removes pulse noise contained in a signal received by the receiver 2. FIG. 8A shows an input signal to the noise AMP 10 of the noise canceller 1. The input signal shown in FIG.
It is also provided to the F amplifier circuit 7. Although the IF filter 9 is configured to obtain a steep selectivity, it gives a somewhat large delay and a rounded waveform to a passing signal. Therefore, the detection output from the detection circuit 8 shown in FIG. 8B has a pulse width of the pulse noise of FIG.
The time delay from t1 to t2 shown in FIG. Even within the noise canceller 1, the signal shown in FIG.
As shown in (3), there is a time delay. However, the input signal of the noise canceller 1 shown in FIG. 8A is input from the output of the mixer 6 so that the gate signal precedes the detection output even if it is delayed. The gate signal is preferably generated temporally earlier than the palace noise included in the detection output, and preferably lasts for a period during which the intensity of the pulse noise included in the detection output can be removed.
If the timing between the detection output and the gate signal is adjusted,
As shown in FIG. 8D, the audio output can be removed so as not to include pulse noise.

[0008]

As shown in FIG. 8, the pulse width of the pulse noise is the time width of t1 at the output stage of the mixer 6 as shown in FIG. When the signal passes through the IF filter 9 or the like, the signal is delayed by t2, and the time width t3 is also increased. Under such conditions, the noise canceller 1 normally operates the comparator 13 with a time width of t3, but the comparator 13 actually operates only with a time width of t1. In order to compensate for this shortage of time width, the time constant of the charging circuit including the constant current source 18 and the capacitor 17 is increased, so that a gate width of about t3 is maintained as a result. In other words, the gate width is constant current source 1
8, which is determined by the output current value and the capacitance value of the capacitor 17, and is constant with respect to any noise, which means that it is impossible to cope with a change in the width of the pulse noise.

FIG. 9 shows a comparison of the states up to the state of creating a gate signal when the pulse noise width is different between (a) and (b). The output signal from the mixer 6 in FIG. 9A includes pulse noise with a time width of t11.
The time width of this detection output expands to t12. The charging time based on the time constant of the capacitor 17 and the constant current source 18 is t
Assuming that 10, the gate signal is generated by adding t10 to t11. As shown in FIG. 9B, the pulse noise existing in the output of the mixer 6 with the time width of t13 spreads in the detection output and spreads in the time width of t14. The gate signal at this time is a time obtained by adding the pulse width of t13 and the charging time t10 corresponding to the charging time constant. (T1
(T11 + t10) ≒ (t12 + t10) despite the fact that (t3−t11) << (t14−t12).

As a result, while the time width of the pulse noise in the detection output greatly changes, the time width of the gate signal can be regarded as substantially constant, and when the actual time width of the pulse noise is narrow, If the time width of the actual pulse noise is wide, an uncut portion from which the entire noise cannot be removed occurs. Such a situation is particularly noticeable with a change in the electric field situation even if the pulse noise is the same. The pulse noise mixed into the antenna 3 is, for example, an ignition noise generated from an engine of an automobile having the receiver 2 mounted thereon.
The gain in the AGC control decreases, and the pulse noise is relatively reduced by being suppressed by the signal component.

FIG. 10 shows the relationship between the level fluctuation of the electric field strength and the removal state of the pulse noise when the same pulse noise is mixed. When the electric field level is small, the pulse noise becomes relatively large, so that the time width of the pulse noise also becomes large and uncut portions occur.
When the electric field level increases, the pulse noise decreases relatively, so that the time width of the pulse noise also decreases, and overcut occurs at a substantially constant gate signal time width. If excessive noise occurs in the noise canceller, the audio signal included in the received signal is also removed, and the sound quality deteriorates. Also, when the uncut portion occurs, pulse noise is mixed into the audio signal, thereby deteriorating the sound quality.

An object of the present invention is to provide a noise canceller capable of appropriately removing pulse noise and improving sound quality.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a noise canceller for removing a pulse noise by a switch circuit from a reception signal of a receiver detected after passing through a band selection filter. A noise detection circuit that detects pulse noise from the side and derives a detection signal corresponding to the pulse width of the noise, and responds to the detection signal from the noise detection circuit, cuts off the switch circuit and removes noise from the reception signal A gate signal generation circuit that generates a gate signal to be generated, and a correction circuit that corrects the width of the gate signal in the gate signal generation circuit so as to decrease as the electric field intensity increases in response to the electric field intensity of the received radio wave. It is a noise canceller characterized by the following.

According to the present invention, since the noise detection circuit detects the pulse noise from the preceding stage of the band selection filter, the pulse noise in the reception signal of the receiver detected after passing through the band selection filter is detected. The pulse noise is detected in a short time width earlier in time. The gate signal generation circuit generates a gate signal in response to a detection signal from the noise detection circuit. The pulse noise in the received signal is removed by controlling the switch circuit with the gate signal from the gate signal generation circuit. The correction circuit responds to the electric field strength of the received radio wave and controls the width of the gate signal in the gate signal generation circuit to decrease as the electric field strength increases. As the electric field strength increases, the pulse noise in the received signal decreases relatively and the time width also decreases,
By reducing the width of the gate signal, overcut can be prevented. When the electric field strength is small, the width of the gate signal is corrected so as to be large.Therefore, it is possible to remove the relatively large pulse noise based on the gate signal having a large time width and avoid uncut portions. it can.

Further, in the present invention, the gate signal generation circuit includes:
The gate value is created by a charge / discharge circuit including a capacitor whose capacitance value can be switched in a plurality of stages, and the correction circuit includes:
The correction is performed by switching the capacitance value of the capacitor.

According to the present invention, since the width of the gate signal is corrected by a charge / discharge circuit including a capacitor that can be switched in a plurality of stages, the capacitance value is increased to increase the correction amount, and the capacitance value is reduced. Thus, the correction amount can be reduced.

Further, in the present invention, the gate signal generation circuit includes:
The gate signal is created by a charge / discharge circuit capable of switching the output current value of a current source for charging a capacitor in a plurality of stages, and the correction circuit switches and corrects the output current value of the current source. .

According to the present invention, in the gate signal generation circuit, the gate signal is generated by the charge / discharge circuit capable of switching the output current value of the current source for charging the capacitor in a plurality of stages. The charging time is shortened to reduce the width of the gate signal. If the output current value is reduced, the correction can be performed so that the charging time is extended and the width of the gate signal is increased.

Further, in the present invention, the receiver includes a signal meter circuit for deriving a signal meter output corresponding to the signal strength of a received signal, and the correction circuit corrects in response to the signal meter output from the signal meter circuit. It is characterized by doing.

According to the present invention, since the width of the gate signal is corrected by the signal meter output corresponding to the signal strength of the received signal from the signal meter circuit provided in the receiver, the electric field strength is high and the signal strength of the received signal is high. When it is high, the width of the gate signal is small, and when the strength of the received signal is low and the electric field strength is weak, the width of the gate signal can be increased.

In the present invention, the receiver includes an automatic gain control circuit for controlling a reception gain so that a signal strength of a received signal falls within a predetermined range, and the correction circuit responds to a control output of the automatic gain control circuit. It is characterized in that the correction is made by performing

According to the present invention, in the automatic gain control circuit,
The receiving gain is controlled so that the signal strength of the received signal falls within a predetermined range. When the electric field strength is high, the signal strength of the received signal also increases, and the gain is greatly reduced. When the electric field strength is weak, the signal strength of the received signal is also reduced and the reception gain is controlled to be large. Since the correction circuit corrects the width of the gate signal in response to the control output of the automatic gain control circuit, the correction to the appropriate gate signal width according to the electric field strength can be easily performed.

[0023]

FIG. 1 shows a noise canceller 21 according to an embodiment of the present invention, and a receiver 2 having the same.
2 shows a schematic electrical configuration. The receiver 22 high-frequency-amplifies the radio signal input to the antenna 23 by the RF amplification circuit 24, and outputs the IF signal by the local oscillation circuit 25 and the mixer 26.
Convert to a signal. The IF signal is further amplified by an IF amplification circuit 27, detected by a detection circuit 28, and a sound signal is demodulated. An IF filter 29 such as a ceramic filter is inserted in a stage preceding the IF amplifying circuit 27 to ensure necessary selectivity.

The noise canceller 21 has a noise AMP3
0, a voltage control amplifier circuit 31, a gain control circuit 32, a comparator 33, a switch circuit 34, a sample and hold circuit 35, a capacitor 36, capacitors 37a and 37b, a control circuit 37c, a constant current source 38, and a transistor 39. The receiver 22 further includes an S-meter circuit 40 for deriving a signal meter output indicating the signal strength of the received signal.

In the noise canceller 21, the noise AMP
The gain of 30 is amplified by a constant gain, and the combination of the voltage control amplifier circuit 31 and the gain control circuit 32 controls the gain so that the gain is large when the input signal level is small and small when the input signal level is large. hand,
Compresses the level difference of the input signal. Comparator 33
Detects pulse noise from the output of the voltage control amplifier circuit 31. The gain control circuit 32 does not follow an abrupt level change such as pulse noise. The comparator 33 derives a logical output corresponding to the pulse width of the pulse noise, and based on the logical output, opens and closes the switch circuit 34 to remove the pulse noise from the audio signal. When the switch circuit 34 is shut off, the capacitor 36 of the sample and hold circuit 35
A DC voltage corresponding to the electric charge stored in is output as a sound output.

In the noise canceller 21 of the present embodiment,
A charging circuit is formed by a capacitor composed of a plurality of capacitors 37a and 37b and a control circuit 37c, the capacitance of which can be switched between Ca and Cb, and a constant current source 38 for supplying a constant output current I0. At both ends of the capacitor 17,
The collector and emitter of NPN transistor 39 are connected in parallel. The output of the comparator 33 is provided to the base of the transistor 39. Comparator 33
Detects the pulse noise and derives a high-level output, the transistor 39 is turned on, and the charges in the capacitors 37a and 37b are rapidly discharged. When the pulse noise detection by the comparator 33 is completed, the transistor 39 is also turned off. In the OFF state, the impedance between the collector and the emitter of the transistor 39 increases, so that the capacitors 37a and 37b are charged by the output current I0 from the constant current source 18. In response to the output from the S-meter circuit 40, the control circuit 37c selects the capacitor 37a when the S-meter output is in the range from 0 to Vth which is the threshold, and the S-meter output is set to Vth
In the case described above, switching is performed so as to select the capacitor 37b. In response to the switching by the control circuit 37c, the charging time is switched as shown in Table 1 below.

[0027]

[Table 1]

FIG. 2 shows the relationship between the electric field level representing the electric field strength and the S-meter output voltage VS, which is the output of the S-meter circuit 40. By setting the threshold voltage Vth so as to correspond to an appropriate electric field strength, the capacitors 37a, 37
If the capacitance values Ca and Cb of b are Ca> Cb, it is possible to make a correction to increase the time width of the gate signal when the electric field strength is weak and to reduce the time width of the gate signal when the electric field strength is strong. .

FIG. 3 shows a partial configuration of a noise canceller 41 as another embodiment of the present invention. In the noise canceller 41 of the present embodiment, portions corresponding to the noise canceller 21 of the embodiment of FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. In the present embodiment, the capacitance of the capacitor 41 of the gate signal generation circuit is not switched by setting the capacitance value to C0, and the constant current sources 48a and 48b are switched by the control circuit 48c in a plurality of stages. The control circuit 48c switches between the two constant current sources 48a and 48b to output the output currents Ia and Ia.
If it is switched to b, the charging time can be switched as shown in Table 2 below. The threshold value Vth for switching the S-meter output is the same as in FIG.

[0030]

[Table 2]

In FIG. 3, the relationship between the output current values Ia and Ib of the constant current sources 48a and 48b is defined as Ia <Ib.

FIG. 4 shows a partial electrical configuration of a noise canceller 51 as still another embodiment of the present invention. Parts corresponding to the embodiment of FIG. 1 or FIG. 3 are denoted by the same reference numerals, and redundant description will be omitted. The control circuit 37c of the present embodiment switches the capacitors 37a and 37b according to a control signal from the gain control circuit 32 that adjusts the gain of the voltage control amplifier circuit 31.

FIG. 5 shows the electric field level, which is the electric field strength of the received signal, and the control signal voltage _VAGC from the gain control circuit 32.
The relationship is shown below. In this case, V _AGC electric field level is increased is changed to decrease. The control circuit 37c
Switching of the capacitors 37a and 37b is performed according to this change. In FIG. 5, contrary to the S-meter output shown in FIG. 2, although the control voltage V _AGC decreases according to the electric field level, depending on the circuit configuration, the V _AGC may increase according to the electric field level. . In some cases, a current value instead of a voltage is derived as a signal for AGC control. According to the configuration of the AGC control, the control circuit 37c can be configured to switch to a capacitor having a small capacitance value when the electric field level increases.

FIG. 6 shows a partial configuration of a noise canceller 61 as still another embodiment of the present invention. In this embodiment, the constant current sources 48a and 48b shown in FIG.
The switching by the control circuit 48c is performed according to the control voltage from the gain control circuit 32 as shown in FIG. Also in the present embodiment, switching is performed so that the output current value is increased when the electric field level is large, and the output current value is decreased when the electric field level is small.

In each of the embodiments described above, the control circuit 3
7c and the switching of the constant current sources 48a and 48b by the control circuit 48c.
Although the control is performed in stages, it is also possible to perform fine control in three or more stages. In particular, the constant current source can be changed continuously according to the S meter output and the AGC voltage. Further, a resistor can be used instead of the constant current source. Furthermore, the correction amount of the gate signal can be adjusted by digital signal processing using a counter or a timer.

[0036]

As described above, according to the present invention, even when the pulse width of the same pulse noise is changed according to the electric field intensity, the time width of the gate signal for noise removal is reduced. Can also be corrected to properly remove the pulse noise.

Further, according to the present invention, the time width for removing the pulse noise can be corrected by switching the capacitance value of the capacitor of the charge / discharge circuit in the gate signal generation circuit.

Further, according to the present invention, the correction amount of the gate signal for determining the time width for removing the pulse noise can be appropriately corrected by switching the constant current source for charging the capacitor in the charge / discharge circuit.

Further, according to the present invention, the time width for removing the pulse noise can be appropriately corrected based on the output from the signal meter circuit.

Further, according to the present invention, the time width for removing the pulse noise can be properly corrected based on the control power of the automatic gain control.

[Brief description of the drawings]

FIG. 1 shows a noise canceller 21 according to an embodiment of the present invention.
FIG. 3 is a block diagram showing a schematic electrical configuration of the first embodiment.

FIG. 2 is a graph showing a relationship between an electric field level used by the noise canceller 21 of FIG. 1 for correcting a gate signal and an S-meter output.

FIG. 3 shows a noise canceller 4 according to another embodiment of the present invention.
FIG. 2 is a block diagram showing a partial electrical configuration of FIG.

FIG. 4 is a block diagram showing a partial electrical configuration of a noise canceller 51 according to still another embodiment of the present invention.

FIG. 5 is a graph showing a relationship between an electric field level and a control output voltage V _AGC of the gain control circuit 32 in the embodiment of FIG.

FIG. 6 is a block diagram showing a partial electrical configuration of a noise canceller 61 according to still another embodiment of the present invention.

FIG. 7 is a block diagram showing a schematic electrical configuration of a noise canceller 1 which is a basis of the present invention.

8 is a signal waveform diagram of a main part of the noise canceller 1 of FIG.

9 is a waveform diagram showing a relationship with a gate signal generated when noise having different pulse widths is input to the noise canceller 1 of FIG.

10 is a graph showing a state in which uncut and excessive cuts of pulse noise occur in the noise canceller 1 of FIG. 7 according to the electric field level.

[Explanation of symbols]

 21, 41, 51, 61 Noise canceller 22 Receiver 26 Mixer 27 IF circuit 28 Detection circuit 29 IF filter 30 Noise AMP 31 Voltage control amplifier circuit 32 Gain control circuit 33 Comparator 34 Switch circuit 35 Sample hold circuit 37a, 37b, 47 Capacitor 37c , 48c control circuit 40 S meter circuit

Claims (5)

[Claims] 1. A noise canceller for removing a pulse noise by a switch circuit from a reception signal of a receiver detected after passing through a band selection filter, wherein the pulse noise is detected from a preceding stage of the band selection filter. A noise detection circuit that derives a detection signal corresponding to the pulse width of the noise; and a gate signal that responds to the detection signal from the noise detection circuit and creates a gate signal that cuts off the switch circuit and removes noise from the reception signal. A noise canceller comprising: a generation circuit; and a correction circuit that responds to the electric field strength of a received radio wave and corrects the width of a gate signal in the gate signal generation circuit so that the width decreases as the electric field strength increases. 2. The gate signal creation circuit creates the gate signal with a charge / discharge circuit including a capacitor whose capacitance value can be switched in a plurality of stages, and the correction circuit switches and corrects the capacitance value of the capacitor. The noise canceller according to claim 1, wherein: 3. The gate signal creation circuit creates the gate signal with a charge / discharge circuit capable of switching an output current value of a current source for charging a capacitor in a plurality of stages, and the correction circuit outputs an output of the current source. The noise canceller according to claim 1, wherein the correction is performed by switching a current value. 4. The receiver includes a signal meter circuit for deriving a signal meter output corresponding to a signal strength of a received signal, and the correction amount control circuit corrects in response to the signal meter output from the signal meter circuit. The noise canceller according to any one of claims 1 to 3, wherein: 5. An automatic gain control circuit for controlling a reception gain so that a signal strength of a reception signal is within a predetermined range, wherein the correction circuit is responsive to a control output of the automatic gain control circuit. The noise canceller according to claim 1, wherein the noise canceler corrects the noise.