JP3512263B2 - Noise canceller for in-vehicle TV receiver - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an on-vehicle television (T
V) A noise canceller for a receiver, and more particularly, a noise canceller for a vehicle-mounted TV receiver that can reduce demodulation distortion when receiving a stereo broadcast.

[0002]

2. Description of the Related Art As an on-vehicle TV noise canceller, there is one disclosed in JP-A-6-292103. Here, as a method of reducing the noise for switching the versatility antenna of the sub (LR) component at the time of receiving the audio multiplex broadcast, the noise of the independent two-gate method for the main (L + R) and the sub (LR) is used.・ A canceller is provided. The optimum gate widths of these main and sub gates are set so that main gate width <sub gate width, but they are different. For this reason, it is difficult to adjust and set the timing of the control signal of each gate independently, and when these gates are integrated circuits, adjustment,
The setting itself becomes impossible. This was resolved as follows.

FIG. 3 is a block diagram of a conventional receiver for audio signals in television broadcasting. This receiver shown in this figure is used for vehicle installation, and so-called diversity reception is performed in order to obtain a good received image. A plurality of antennas 71 are provided, and the antenna with the best reception state is selectively connected to the tuning / detection circuit 72 by a configuration not shown. F received by antenna 71
The received signal of the M broadcast is selected by the tuning / detection circuit 72 from the desired received signal of the broadcasting station and is FM detected. The received signal from the tuning / detection circuit 72 has only a lower sideband component filtered by a low pass filter (LPF) 73, and is provided from a buffer 74 to a demodulation circuit 76 via a first switch 75.

Further, the received signal from the tuning / detection circuit 72 is given to the noise detection circuit 77. The noise detection circuit 77 is realized by a high-pass filter (HFP) that filters noise components, a one-shot multivibrator, and the like. The noise detection circuit 77 detects a noise component superimposed on a received signal, and the first OR gate 78 is used to detect the noise component. The switch 75 controls conduction / cutoff of the second switch 81 connected to the sub-OR gate 79 via the delay circuit 80. At the time of diversity reception, a cut pulse of several tens to several hundreds of microseconds is superimposed on the received signal of the received television broadcast in order to specify the switching timing of the antenna (normal retrace line period). Therefore, in order to prevent the cut pulse from being mixed with the audio signal and reproduced, when the cut pulse is input to the external gate terminal 82, the control generator 83 generates an appropriate switching timing signal. Thus, the first switch 75 is controlled by the main OR gate 78, and the second switch 81 is controlled by the sub OR gate 79.
That is, when the noise or the switching pulse is detected, the first switch 75 and the second switch 81 are cut off, and the first switch 75 and the second switch 81 are kept conductive during the period when they are not detected. However, the first switch 7
5. The optimum timing for shutting off the second switch 81 is slightly different depending on the signal characteristics passing through it. Therefore, the control signal generator 83
Control signals of different timings are generated to control the first switch 75 and the second switch 81 at different timings.

Furthermore, in connection with the first switch 75, a first hold circuit 8 realized by an RC time constant circuit or the like.
4 is provided, and the time constant of the first hold circuit 84 is the first switch 7 based on the noise and the cut pulse.
It is set to be longer than the interruption time of 5. Therefore, the received signal is input to the demodulation circuit 76 during the period in which the noise and the cut pulse are not detected, and when the noise and the cut pulse are detected, the level immediately before the detection is input to the demodulation circuit 76. Further, in addition to the first hold circuit 84, a tank circuit 85 realized by an LC resonance circuit or the like is provided. The resonance frequency of the tank circuit 85 is set to 31.5 KHz, which is twice the frequency of 15.75 KHz which is the horizontal scanning frequency, and the sub audio signal component (audio signal component of the L-R channel or foreign language). This is compensated when the subcarrier for demodulating the audio signal component) is blocked by the blocking of the first switch 75.

The received signal from the tuning / detection circuit 72 is directly applied to the demodulation circuit 76. The received signal input to the demodulation circuit 76 via the first switch 75 is input from the LPF 87 to the de-emphasis circuit 88 via the buffer 86. The LPF 87 filters a main audio signal component (a stereo L + R audio signal component or a bilingual main audio signal component). The de-emphasis circuit 88, the characteristics of the audio signal is enhanced as Oite advance the frequency increases to the transmitting side in order to improve the transmission efficiency, is provided to flat restored, for example, RC integrating circuit, The time constant is 75 μsec. In this way, the de-emphasis circuit 8
From 8, the main audio signal is demodulated and input to the matrix circuit 89.

The received signal from the buffer 86 is input to the BPF 90. BPF90 is 31.5
The sub-carrier signal of KHz is used to filter the FM-modulated sub-audio signal component (stereo LR audio signal component or bilingual sub-audio signal component) and output to the FM detection circuit 91. The FM detection circuit 91 demodulates the FM-modulated sub-audio signal component based on the sub-carrier, and the de-emphasis circuit 92 having the same configuration as the de-emphasis circuit 88 and the second switch 8 are provided.
1 is input to the matrix circuit 89.

The received signal directly input to the demodulation circuit 76 is also input to the control signal detection circuit 94 via the BPF 93. The BPF 93 filters a band near 55 KHz in which a control signal for audio multiplex broadcasting is included, and outputs it to the control signal detection circuit 94. Control signal detection circuit 94
Identifies the type of audio multiplex signal, which is a monaural broadcast, a stereo broadcast, or a bilingual broadcast, from the amplitude-modulated sine wave signals of two different frequencies. The identification result is output to the matrix circuit 89.

The delay time of the second switch 81 is set by the delay circuit 80, and the sub-OR
It is turned on / off according to the noise detection result from the gate 79. Furthermore, in connection with the second switch 81, RC
A second hold circuit 95 realized by a time constant circuit or the like is provided, and the time constant of the second hold circuit 95 is set in the second switch 81 due to the noise and the cut pulse longer than the cutoff time. Therefore, the noise,
When the cut pulse is not detected, the received signal is input to the de-emphasis circuit 92. When the noise or cut pulse is detected, the level immediately before the detection is input to the de-emphasis circuit 92.

In response to the identification result, the matrix circuit 89 outputs a monaural audio signal composed of a main audio signal to the power amplification circuits 96L and 96R, for example, in the case of monaural broadcasting. Also, in the case of stereo broadcasting, the audio signals of the left and right channels (L, R) are output, and in the case of bilingual broadcasting, the main sound such as Japanese sound or foreign language sound selected by the selecting means (not shown). One of the sub-voices such as is selectively output and converted into an acoustic signal from the speakers 97L and 97R,
Is output.

FIG. 4 shows the control signal generator 8 of FIG.
It is a figure which shows 3. This control signal generator 83
Are resistors R1 and R2, a capacitor C, a transistor T
r, a switching circuit S, a first comparator 11, a second comparator 12, a first reference power supply 13, a second reference power supply 14, and a time constant switching circuit 15, and is an integrated circuit section 16 which is an integrated circuit. And an external circuit 17 connected to a terminal 18 of the integrated circuit 16. The input terminal T1 is connected to the base terminal of the transistor Tr, and the collector terminal of the transistor Tr is connected to the power supply Vcc. The emitter terminal of the transistor Tr has a capacitor C and a resistor R.
1. Connected to one end of switching circuit S, and terminal T
It is connected to the non-inverting input terminals of the first comparator 11 and the second comparator 12 via Nos. 2 and 18. The first reference power supply 13 is connected to the inverting input terminal of the first comparator 11, and the second reference power supply 14 is connected to the inverting input terminal of the second comparator 12. The other end of the switching circuit S is connected to one end of the resistor R2,
The other ends of the capacitor C and the resistors R1 and R2 are grounded. The time constant switching circuit 15 monitors the voltage of the terminal T2, and when the voltage becomes equal to or lower than a predetermined value, the switching circuit S is turned off. The first comparator 11, the second comparator 12, the first reference power supply 13, and the second reference power supply 14 are configured in the integrated circuit section 16, and the first comparator 11, the second comparator 12 are not connected to each other. The inverting input terminals are grouped together at terminal 18. The external circuit 17 including the charge / discharge circuit and the time constant switching circuit 15 is connected to terminals T2 and T18. The operation of this device will be described below.

FIG. 5 is a waveform diagram showing the states of signals at the terminals of the control signal generator 83. The pulse a shown in the figure is input to the input terminal T1 (H level)
Then, the transistor Tr is turned on, the capacitor C is charged, and the voltage output to the terminal T2 rises according to the charging time constant (instantaneously rises because the charging resistance is 0),
When charging is completed, the power supply voltage becomes Vcc. When the pulse a is not input (L level), the transistor Tr is turned off.
Next, the capacitor C starts discharging. The discharge time constant τ at this time is τ = C (R1 · R2 / (R1 + R2)) (1), and the voltage output to the terminal T2 decreases according to this discharge time constant, and the discharge voltage is a constant value (V ), The time constant switching circuit 15 shuts off the switching circuit S and the resistor R2 is not energized. Discharge time constant at this time τ
Becomes τ = CR1 (2), and the voltage output to the terminal T2 is the discharge time constant τ.
According to. As a result, the voltage output to the terminal T2 becomes a signal as shown in b of FIG. Then, this signal b is input to the non-inverting input terminals of the first comparator 11 and the second comparator 12.
The signal b is compared with the first reference voltage V1 by the first comparator 11 and the second reference voltage V2 by the second comparator 12, and the first comparator 1
1 outputs the first control signal as shown in FIG. 5c, and the second comparator 12 outputs the second control signal as shown in FIG. 5d at different timings (rising edges).

In this way, since the discharge time constant can be changed by the values of the resistors R1 and R2, the resistors R1 and R2 can be changed.
It is possible to obtain a control signal at an appropriate timing by setting the value of and the operating voltage of the time constant switching circuit 15 (voltage V for switching the switching circuit S). Further, even when the plurality of comparison circuits 11 and 12 are integrated circuits and the input terminals are the same terminal, by connecting the external circuit 17 to the terminals, it is possible to obtain a plurality of control signals at optimum timings. .

[0014]

By the way, the matrix section 83 performs the following demodulation. L = {(L + R) + (LR)} / 2 R = {(L + R)-(LR)} / 2 However, the control signal generator 83 has the following problems when receiving a stereo broadcast. There is.

FIG. 6 is a diagram for explaining demodulation distortion in the matrix section 89 when receiving a stereo broadcast. There is no problem when receiving bilingual broadcasting, but as shown in this figure (for example, R
= 0. ), When the stereo broadcast is received, the matrix unit 89 performs the operation (demodulation) after the gate processing, which causes a problem that the demodulated signal is distorted in the main gate period and the sub period. That is, (L + R), (L-
If both R) are sine waves, it works well,
This is because the music source does not work well.

Therefore, in view of the above problems, it is an object of the present invention to provide a noise canceller for an in-vehicle TV receiver which can prevent distortion of matrix demodulation even during stereo broadcasting.

[0017]

In order to solve the above problems, the present invention provides a noise canceller for an on-vehicle TV receiver having the following configuration. A noise canceller for an in-vehicle TV receiver that cancels pulse noise in the in-vehicle TV receiver's received signal has a cut-out pattern superimposed on the received signal.
It is generated at the timing of the loose and the trailing edge changes gently.
A first comparator for forming a main gate signal for canceling noise by comparing the pulse signal to be converted with a first reference voltage, and the pulse signal with a second reference voltage different in magnitude from the first reference voltage. A second comparator is provided for forming a sub-gate signal for comparing and canceling noise. The reference voltage control unit equalizes the first reference voltage and the second reference voltage during stereo detection.

Furthermore, the gate width control unit the pulse signal and the second reference voltage is compared with and prior <br/> Symbol of the first comparator instead of the output signal to the pulse signal first during stereo detection It may be supplied to two comparators. The reference voltage control unit may make the first reference voltage and the second reference voltage equal or different with a constant time constant when detecting the presence or absence of stereo broadcasting.

The gate width control unit compares the pulse signal with a second reference voltage with a constant time constant when detecting the presence or absence of stereo broadcasting, and outputs the output signal from the first comparator and the second comparator. it is supplied to, or these comparison may be stopped.

[0020]

According to the noise canceller for a vehicle-mounted TV receiver of the present invention, the reference voltage control section equalizes the first reference voltage and the second reference voltage during stereo detection, thereby making the width of the main gate signal Since the sub-gate signals have the same width, distortion that occurs during demodulation can be reduced. The gate width control unit by Rukoto to the supply first comparator and said second comparator pulse signal compared to the output signal and a second reference voltage during a stereo detection, the width of the main gate signals, sub-gate signal Have the same width, and distortion that occurs during demodulation can be reduced. By providing the reference voltage control unit with a constant time constant when detecting the presence or absence of stereo broadcasting, frequent switching in a weak electric field can be prevented when stereo broadcasting is detected.
Similarly, by providing the gate width control unit with a constant time constant when detecting the presence or absence of stereo broadcasting, it is possible to prevent frequent switching in a weak electric field when stereo broadcasting is detected.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vehicle-mounted TV according to a first embodiment of the present invention.
A noise canceller for a receiver, which is an integrated circuit unit 16
It is a figure which shows the structure of. In noise canceller for vehicle TV receiver shown in the figure, the integrated circuit portion 16 of the control signal generator 83 of FIG. 3, the reference voltage control unit 20 for controlling the first reference voltage V1 at the time the stereo detection is provided. The reference voltage control unit 20 is provided as an external component of the integrated circuit unit 16. The reference voltage controller 20 connects a resistor R11 that is connected in parallel to a resistor that divides the voltage to the first reference voltage V1 to reduce the first reference voltage V1 to V2, and connects and disconnects the resistor R11 in parallel based on the stereo detection signal. The switching transistor Tr1 to be selected, a resistor R12 connected to the base of the switching transistor Tr1 and inputting "H (high)" or the like at the time of stereo detection, and the resistor 1
A resistor R10 and a capacitor C10 that are grounded between 2 and the base of the switching transistor Tr1 are provided.

The reference voltage control section 20 makes the first reference voltage and the second reference voltage to the inverting input terminals of the comparison circuits 11 and 12 equal by the stereo detection time signal, and the outputs of the comparison circuits 11 and 12 become equal. It is possible to make the width of a certain first control signal and the width of a second control signal, that is, the main gate width and the sub-gate width the same. As a result, it is possible to prevent demodulation distortion from occurring when receiving a stereo broadcast. During stereo detection, this stereo detection signal is "L
(Low) changes to “H (high)”, but this change changes gently due to the charging time constant τ1 of the resistor R12 and the capacitor 10. Further, when stereo detection is stopped, the stereo detection signal changes from “H” to “L”, but this change changes gently due to the discharge time constant τ2 of the resistor R10 and the capacitor C10. In this way
Frequent switching in a weak electric field can be prevented when stereo broadcasting is detected. Since the reference voltage control unit 20 is externally attached, it is possible to prevent demodulation distortion at the time of receiving a stereo broadcast with a simple configuration without changing the integrated circuit unit 16. In other words, it is possible to deal with peripheral applications. The integrated circuit unit 16
It can be easily built in.

FIG. 2 is a vehicle-mounted T according to a second embodiment of the present invention.
A noise canceller for a V receiver, which is an integrated circuit unit 1
It is a figure which shows the structure of 6. The noise canceller for a vehicle-mounted TV receiver shown in this figure has a gate width control unit 19 for matching the main gate width and the sub gate width at the time of stereo detection at the input stage of the integrated circuit unit 16 of the control signal generator 83 of FIG. It is equipped with. The gate width control unit 19 uses the terminal T
2 and a diode D1 connected between the terminal 18 and a switching transistor Tr connected to the terminal T2 side.
2, a resistor R12 connected to this and grounded, a resistor R22 connected to the base of the switching transistor Tr2 to input a stereo detection signal, and a resistor R22 connected to the base of the switching transistor Tr2 and grounded. Resistor R20 and capacitor C20
And a non-inverting input terminal to which the emitter of the switching transistor is connected and an inverting input terminal to which the second reference voltage of the comparator 12 is input, and a connection between the output of the comparator 13 and the terminal 18. And a diode D2 that is operated. The stereo detection signal "H" causes the switching transistor Tr2 to conduct, and the comparator 13 receives the gate control signal from the terminal T2. The output signal of the comparator 13 has the same width as the sub-gate signal, and this is input to the comparators 11 and 12. Therefore, as described above, the main gate signal width and the sub gate signal width of the comparators 11 and 12 match. As a result, it is possible to prevent demodulation distortion from occurring when receiving a stereo broadcast. In addition, as described above,
At the time of stereo detection, this stereo detection signal changes gently according to the charging time constant τ1 and the discharging time constant τ2. In this way, frequent switching in a weak electric field can be prevented when stereo broadcasting is detected. Since the gate width control unit 19 is externally attached, it is possible to prevent demodulation distortion at the time of receiving a stereo broadcast with a simple configuration without changing the integrated circuit unit 16. In other words, it is possible to deal with peripheral applications. It should be noted that it can be easily incorporated in the integrated circuit unit 16.

[0024]

As described above, according to the present invention, the reference voltage controller controls the first reference voltage and the second reference voltage during stereo detection.
By making the reference voltage of the same, the width of the main gate signal becomes the same as the width of the sub-gate signal, and the distortion that occurs during demodulation can be reduced. The gate width control unit compares the received signal with the second reference voltage at the time of stereo detection, compares the output signal with the first reference voltage instead of the main component of the first comparator, and sub-component of the second comparator. By comparing with the second reference voltage instead of, the width of the main gate signal,
Since the sub-gate signals have the same width, distortion that occurs during demodulation can be reduced. By providing the reference voltage control unit with a constant time constant when detecting the presence or absence of stereo broadcasting, it is possible to prevent frequent switching in a weak electric field when stereo broadcasting is detected. Similarly, by providing the gate width control unit with a constant time constant when detecting the presence or absence of stereo broadcasting, frequent switching in a weak electric field can be prevented when stereo broadcasting is detected.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an integrated circuit unit 16 of a vehicle-mounted TV receiver noise canceller according to a first embodiment of the present invention.

FIG. 2 is a noise canceller for a vehicle-mounted TV receiver according to a second embodiment of the present invention, and is a diagram showing a configuration of an integrated circuit unit 16;

FIG. 3 is a block diagram of a conventional receiver for audio signals in television broadcasting.

4 is a diagram showing a control signal generator 83 of FIG.

FIG. 5 is a waveform diagram showing the states of signals at respective terminals in the control signal generator 83.

FIG. 6 is a diagram illustrating demodulation distortion in a matrix unit 89 when receiving a stereo broadcast.

[Explanation of symbols]

11 ... First comparator 12 ... Second comparator 18 ... Reference voltage control unit 19 ... Gate width control unit

Claims (4)

(57) [Claims] 1. A noise canceller for an on-vehicle TV receiver for canceling pulse noise of a received signal of an on-vehicle TV receiver, wherein a pulse is generated at a timing of a cut pulse superimposed on the received signal and a trailing edge of which gradually changes. A first comparator (11) forming a main gate signal for canceling noise by comparing the signal with a first reference voltage; and a second reference voltage having a magnitude different from the first reference voltage for the pulse signal. A second comparator (12) that forms a sub-gate signal for canceling noise by comparing with a reference voltage control unit (20) that equalizes the first reference voltage and the second reference voltage during stereo detection. A noise canceller for an in-vehicle TV receiver, which comprises: 2. A noise canceller for an in-vehicle TV receiver for canceling pulse noise of a received signal of an in-vehicle TV receiver, wherein a pulse is generated at a timing of a cut pulse superimposed on the received signal and a trailing edge of the pulse gradually changes. Signal
A first comparator (1 that forms a main gate signal for inputting and comparing with a first reference voltage to cancel noise
1) and a second comparator (12) for inputting the pulse signal and comparing it with a second reference voltage having a magnitude different from the first reference voltage to form a sub-gate signal for canceling noise.
When, the pulse signal at the time of the stereo detection is compared with the second reference voltage and the output signal, put into the first comparator (11)
Inputting the pulse signal and the second comparator (12)
A noise canceller for a vehicle-mounted TV receiver, comprising: 3. The reference voltage control unit (20) makes the first reference voltage and the second reference voltage equal or different at a constant time constant when detecting the presence or absence of stereo broadcasting. The noise canceller for a vehicle-mounted TV receiver according to claim 1. Wherein said gate width controller (19), the pulse signal at a predetermined time constant when the detection of the presence or absence of a stereo broadcast is compared with the second reference voltage and the output signal, the first comparator ( The noise canceller for an in-vehicle TV receiver according to claim 2, wherein the noise signal is supplied to the input of the pulse signal in 11) and the input of the pulse signal in the second comparator (12).