JPS6238367Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a pulse noise suppression device that removes ignition noise and pulse noise of an FM receiver.

FM receivers are extremely susceptible to impulse noise, and therefore have the problem that ignition noise is received as pulse noise. For this purpose, conventionally commonly used
The FM receiver is provided with a pulse noise suppression device to remove pulse noise.

FIG. 1 is a circuit diagram showing an embodiment of a pulse noise suppression device commonly used in the past.
A low-pass filter 1 and a high-pass filter 2 are connected in parallel to the output side of an FM detection circuit (not shown), and a pilot cancel circuit 3 is connected to the output side of the low-pass filter 1, so that the pilot signal necessary for stereo demodulation is transmitted through the low-pass filter. Filter 1
It is bypassed from the output side. A pilot cancel signal is generated by a voltage controlled oscillator provided in a stereo demodulator (not shown) in a generally known manner and is supplied to the pilot cancel circuit 3. Further, a gate circuit 4 is connected to the output side of this pilot cancel circuit 3.
is provided to gate the output of the pilot cancel circuit 3, and the gate output is supplied to a demodulation circuit (not shown) via a level hold circuit 5. On the other hand, an automatic noise gain control circuit 6 is provided on the output side of the high-pass filter 2.
The monostable multi-circuit 7 is configured to be triggered by the output thereof. The output signal of the monostable multi-circuit 7 is supplied to the gate circuit 4 to control opening and closing of the gate.

In the circuit configured in this manner, the path passing through the low-pass filter 1 is a signal path, and the path passing through the high-pass filter 2 is a noise path. The low-pass filter 1 is provided for delay, and synchronizes the pulse noise with the operation timing of the gate circuit 4. The pilot cancel circuit 3 prevents noise generated when the pilot signal is cut off in the gate circuit 4 by removing the pilot signal immediately before the gate circuit 4, and also removes the pilot signal just before the gate circuit 4. Cancellation processing is performed using the pilot cancel signal C supplied from the. A pilot signal necessary for stereo demodulation is bypassed from the front side of the pilot cancel circuit to a stereo demodulation circuit (not shown). On the other hand, since the high-pass filter 2 is set to a cutoff frequency of about 100 KHz, if a noise component is included in the signal output from the detection circuit (not shown), only this noise component is extracted. There is. The noise component extracted by the high-pass filter 2 is amplified in an automatic noise gain control circuit 6, and a monostable multivibrator 7 is triggered by the output thereof. In this case, the monostable multicircuit 7 is provided to prevent the gate circuit 4 from operating frequently due to noise. Therefore, in such a configuration, when noise of a predetermined level or higher arrives, the monostable multicircuit 7 is activated to close the gate circuit 4, thereby preventing pulsed noise from entering the signal system. Pulse noise is suppressed by preventing it from occurring.

However, in the circuit with the above configuration, three signal lines consisting of a normal signal line, a pilot signal bypass line, and a pilot cancel signal line are required between the stereo demodulation circuit and each signal line. A coupling capacitor is also required for each. Furthermore, since these circuits are integrated circuits, they have problems such as an increase in the number of input/output pins as the number of signal lines increases.

The purpose of this invention is to provide a pulse noise suppression circuit with a reduced number of signal lines.

In order to achieve this purpose, this idea
By adding a pilot adder circuit to the output side of the level hold circuit, a pilot signal bypass line between the level hold circuit and the stereo demodulator circuit is omitted.

Hereinafter, the pulse noise suppressing device according to this invention will be explained in detail with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the pulse noise suppression circuit according to this invention, and the same parts as in FIG. 1 are indicated using the same symbols. In the figure, 8 is a pilot adder circuit provided on the output side of the level hold circuit 5, which adds the pilot cancel signal supplied from the demodulation circuit to the output of the level hold circuit 5 and outputs the result. The difference from FIG. 1 lies in the addition of the pilot adder circuit 8 and the removal of the pilot signal bypass line.

In a circuit configured in this way, the pilot signal necessary for stereo demodulation is added in the pilot adder circuit 8 by the amount canceled in the pilot cancel circuit 3, so that the waveform becomes the same as the waveform before pilot canceling. . That is, when the signal shown in FIG. 3a is supplied as signal A from the detection circuit, this signal A is delayed by a predetermined time in the low-pass filter 1 and then supplied to the pilot cancel circuit 3. In the pilot cancel circuit 3, the triangular wave pilot cancel signal C supplied from the demodulation circuit is supplied and subtraction processing is performed, resulting in the pilot cancel signal output shown in FIG. 3b, and the output signal is sent to the level hold circuit. 5, the signal is supplied to the pilot adder circuit 8 in the form of a waveform shown in FIG. 3c. Then, in the pilot adder circuit 8, a pilot cancel signal, which is the same as the signal when pilot cancel is performed, is added to the output of the level hold circuit 5, and the signal is demodulated into the waveform shown in FIG. 3d. In this case, as shown in FIG. 3a, if the input signal A contains pulse noise shown as P, then during the time t in FIG. 3d when the gate circuit 4 is closed by this noise, In this case, the signal is replaced with the pilot cancel signal.

As explained above, according to the pulse noise suppression device of this invention, since the pilot addition circuit is provided on the output side of the level hold circuit, the signal line between the pulse noise suppression device and the stereo demodulation circuit is The number of pins has been reduced from the conventional three to two, and accordingly the number of pins in the case of integration can be reduced, resulting in various excellent effects such as space advantages.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional pulse noise suppressing device, Fig. 2 is a circuit diagram showing an example of a pulse noise suppressing device according to this invention, and Fig. 3 a to d are as shown in Fig. 2. FIG. 3 is a waveform chart showing the operation of each part of the circuit shown in FIG. 1...Low pass filter, 2...High pie filter, 3...Pilot cancel circuit, 4...
Gate circuit, 5...Level hold circuit, 6...
Noise automatic gain amplification circuit, 7... monostable multi circuit, 8... pilot addition circuit.

Claims (1)

[Scope of utility model registration request] A low-pass filter delays the output signal of the detection circuit for a predetermined period of time to perform time alignment, and a pilot signal cancel signal supplied from a stereo demodulation circuit is supplied to the output of this low-pass filter to perform subtraction processing to cancel the pilot signal. a pilot cancel circuit, a high-pass filter that detects noise contained in the output of the detection circuit, a noise automatic gain control amplifier that amplifies the output of the high-pass filter and applies automatic gain control when the output rises above a predetermined level; A monostable multi-circuit that is triggered by the output of the amplifier, a gate circuit that blocks the output of the pilot cancel circuit only when the monostable multi-circuit is output, and a level that maintains the DC level when the gate circuit is closed. A pulse noise suppression device comprising: a hold circuit; and a pilot addition circuit that adds a pilot cancel signal supplied from the stereo demodulation circuit to the output of the level hold circuit to reproduce a pilot signal for stereo demodulation.