JPS634971B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise blanker, and more particularly to a noise blanker that is connected to a transmission line of a receiver and is used to remove pulsed noise mixed together with a desired signal from an antenna.

In radio receivers for automobiles, pulsed noise with a relatively strong electric field strength, such as ignition noise when the engine is ignited or noise when the wiper motor is activated, mixes together with the desired signal from the receiving antenna. Therefore, in order to prevent the pulse noise from being reproduced, a noise blanker having a configuration as shown in FIG. 1 has conventionally been used. The receiver includes an antenna 1, a high frequency amplification circuit 2,
A frequency conversion circuit 5, a band filter 6, an intermediate frequency amplification circuit 7, a detection circuit 8, a low frequency amplification circuit 9, and a speaker 10 are connected by a transmission line. The noise blanker 11 includes a noise amplification circuit 12, a noise detection circuit 13, and a switch circuit 14 that shuts off when noise is detected, and is connected, for example, between the frequency conversion circuit 5 and the band filter 6 via transmission lines 15 and 16.

According to such conventional technology, when connecting a noise blanker to the receiver's transmission line later, it is necessary to disconnect a part of the receiving circuit.
Moreover, a power source is required, connection work at at least three locations is essential, and the connection circuit is complicated.

The present invention is a noise blanker that solves the above technical problems, eliminates the need to disconnect the internal connections of the receiver circuit, allows the connection points to be connected as a single unit, and does not require separate power wiring. The purpose is to provide

The present invention provides a noise blanker that is connected to a transmission line of a receiver on which a modulated wave and a power supply voltage are superimposed, and that detects pulse noise mixed in from an antenna and removes the pulse noise. a single input/output line connected to the input/output line, a noise amplification circuit connected to the input/output line to amplify pulsed noise, a noise detection circuit connected to the noise amplification circuit to detect pulsed noise, and the noise detection circuit. a switch circuit connected to the input/output line and conductive for a period exceeding the pulse width of the pulse noise to ground the input/output line in an alternating current manner; and a switch circuit connected to the input/output line for blocking only the modulated wave; This is a noise blanker characterized by including an amplifier and a power supply line that supplies power to a switch circuit.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a simplified electrical circuit diagram of one embodiment of the present invention, in which parts corresponding to the prior art shown in FIG. 1 are given the same reference numerals. Desired modulated wave S
The pulse noise N is guided to the high frequency amplification circuit 2 via the antenna 1, and the high frequency amplification circuit 2
is tuned and amplified. Frequency conversion circuit 5
includes a mixing circuit 3 and a local oscillation circuit 4, and includes a signal from the high frequency amplification circuit 2 and the local oscillation circuit 4.
The oscillation signals from the oscillation signal are mixed in the mixing circuit 3 and frequency-converted. In the bandpass filter 6, the signal from the frequency conversion circuit 5 is converted into an intermediate frequency signal, and the intermediate frequency signal is further amplified in the intermediate frequency amplification circuit 7. In the detection circuit 8, the signal from the intermediate frequency amplification circuit 7 is detected and becomes a desired low frequency signal, which is amplified in the low frequency amplification circuit 9 and then reproduced in the speaker 10.

A noise blanker 18 is connected to the transmission line 17 of the receiver as described above, for example, between the mixing circuit 3 of the frequency conversion circuit 5 and the bandpass filter 6 via a single input/output line 19. Ru. This noise blanker 18 is the noise amplifier circuit 2
0, a noise detection circuit 21 and a switch circuit 22.

The mixing circuit 3 of the frequency conversion circuit 4 is, for example, 2
An input field effect transistor 61, a resistor 62 and a capacitor 63 which are a bias circuit and are connected to the source of the field effect transistor 61.
and a coil 64, a capacitor 65, and a resistor 66, which are intermediate frequency transformers and are connected to the drain of the field effect transistor 61 via the transmission line 17. Field effect transistor 61
A signal from the high frequency amplifier circuit 2 is applied to one input of the field effect transistor 61, and a signal from the local oscillation circuit 4 is applied to the other input of the field effect transistor 61 via a capacitor 67. A DC voltage V _cc is applied to the coil 64 , capacitor 65 , and resistor 66 via a resistor 68 . Therefore, transmission line 1
A DC voltage and a signal obtained by combining the modulated wave and local oscillation are applied in a superimposed manner to 7.

In the noise blanker 18 , the DC voltage from the transmission line 17 via the input/output line 19 is applied to the power supply line 23 via the coil 100 . The signal component is transmitted through the coil 100 and the power line 23.
and is smoothed by capacitors 56 and 57 connected between the ground line 24. Therefore, only the DC voltage is transmitted from the power supply line 23 to the noise amplification circuit 2.
0 and the switch circuit 22.

In the noise amplification circuit 20, the power supply line 23,
A series circuit consisting of a resistor 25, a transistor 26 and a resistor 27, and a series circuit consisting of a resistor 28 and a transistor 29 are connected between the ground line 24 and the ground line 24. A capacitor 30 is connected in parallel to the resistor 27. A resistor 31 is connected between the collector of the transistor 26 and the ground line 24.
A series circuit consisting of 32 and a bypass capacitor 33 for preventing high frequency oscillation are connected in parallel. A connection point between the resistors 31 and 32 is connected to the base of the transistor 26. A resistor 34 is connected between the collector and base of the transistor 29, and a bypass capacitor 35 for preventing high frequency oscillation is connected between the collector and emitter of the transistor 29.

A coupling capacitor 36 is connected between the input/output line 19 and the base of the transistor 26. A series circuit consisting of a coupling capacitor 37 and a resistor 38 is connected between the collector of transistor 26 and the base of transistor 29. A series circuit consisting of a capacitor 39 and a coil 40 is connected between the input/output line 19 and the ground line 24, and a capacitor 41 is connected in parallel to the coil 40. Note that the capacitor 39, the coil 40, and the capacitor 41
need only be added when the input reactance component of the noise blanker 18 affects the tuning impedance to the receiver, and these capacitors 39, 41 and the coil 40 can prevent tuning deviation.

In the noise amplification circuit 20 configured in this way, the modulated wave S and the pulse noise N input from the transmission line 17 via the input/output line 19 are
The signal containing the signal is amplified by transistor 26 and then further amplified by transistor 29. This amplified modulated wave S or modulated wave containing pulsed noise N is given to a noise detection circuit 21.

In the noise detection circuit 21, the cathode of a diode 43 and the anode of a diode 44 are connected to the other end of a capacitor 42, one end of which is connected to the collector of the transistor 29 in the noise amplification circuit 20 described above. The anode of diode 43 is connected to ground line 24 . A capacitor 45 is connected between the cathode of the diode 44 and the ground line 24, and a resistor 46 is connected in parallel to the capacitor 45.

In such a noise detection circuit 21, the modulated wave amplified by the noise amplification circuit 20 is clamped by a capacitor 42 and a diode 43, and linearly detected by a diode 44 and a capacitor 45. Therefore, the DC voltage and the modulated wave S, or the voltage corresponding to the voltage variation of the modulated wave containing the pulse noise N, are applied to the resistor 46. Accordingly, pulse noise N having a large voltage variation is detected. This pulse noise N is given from the noise detection circuit 21 to the switch circuit 22.

In the switch circuit 22, a series circuit consisting of resistors 47 and 48 and a series circuit consisting of a transistor 49 and a resistor 50 are connected between the power supply line 23 and the ground line 24. resistance 50
A capacitor 51 is connected in parallel. Also, between the input/output line 19 and the ground line 24,
A series circuit consisting of capacitor 52 and transistor 53 is connected. A connection point between resistors 47 and 48 is connected to the base of transistor 49. A capacitor 54 is connected between the cathode of the diode 44 and the base of the transistor 49 in the noise detection circuit 21 . Also, transistor 49
A resistor 55 is connected between the emitter of the transistor 53 and the base of the transistor 53. Furthermore, power line 2
3 and the ground line 24, a low frequency bypass capacitor 56 and a high frequency bypass capacitor 57 are connected in parallel.

In the switch circuit 22 configured in this manner, the series voltage is interrupted by the capacitor 54. Further, the pulse noise N is applied to the base of the transistor 49 via the capacitor 54. Therefore, when the pulse noise N is input to the base of the transistor 49, the emitter voltage of the transistor 49 becomes high level. This high level period is selected by the resistor 50 and capacitor 51 to be a period exceeding the pulse width of the pulse noise N.

When the emitter voltage of the transistor 49 becomes high level, the transistor 53 becomes conductive, and the resistance value between the collector and emitter of the transistor 53 decreases accordingly, and the input/output line 19 is grounded via the capacitor 52 in an alternating current manner. .

When the modulated wave S flowing through the transmission line 17 contains pulse noise N in this way,
The input/output line 19 is AC-grounded only for a period exceeding the pulse width of the pulse noise N, and the transmission line 17 is also AC-grounded accordingly. Therefore, the pulse noise N is prevented from entering the bandpass filter 6.

Noise blanker 18 as another embodiment of the present invention
The connection point may be a transmission line on which other DC power supply voltages are superimposed, but preferably it is a transmission line on which DC power supply voltages are superimposed between the high frequency amplifier circuit 2 and the mixing circuit 3 before the bandpass filter 6. Good.

As described above, according to the present invention, it is possible to connect a noise blanker through a single input/output line without cutting the transmission line of the receiver, simplifying the connection circuit and reliably eliminating pulse noise. Can be removed. Further, there is no need to provide a special power source to energize the noise blanker.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of the prior art and FIG. 2 is a simplified electrical circuit diagram of the present invention. 17...Transmission line, 18...Noise blanker, 19...Input/output line, 20...Noise amplification circuit, 21...Detection circuit, 22...Switch circuit,
56, 57...capacitor, 100...coil.

Claims (1)

[Scope of Claims] 1. A noise blanker connected to a transmission line of a receiver in which a modulated wave and a power supply voltage are superimposed, detects pulse noise mixed from an antenna, and removes the pulse noise, comprising: a single input/output line connected to the input/output line; a noise amplification circuit connected to the input/output line to amplify pulsed noise; a noise detection circuit connected to the noise amplification circuit to detect pulsed noise; A switch circuit connected to the noise detection circuit and conductive for a period exceeding the pulse width of the pulse noise to ground the input/output line in an alternating current manner; and a means connected to the input/output line for blocking only the modulated wave. , and a power supply line that supplies power to the noise amplifier and the switch circuit.