JPS6253536A - Noise preventing circuit - Google Patents

Abstract

PURPOSE:To prevent a noise at the input point of time of a transmission line alarm signal by providing a delay circuit between a decoder of a reception section and a switch and inputting a voice output of a decoder to a D/A converter while being retarded for a prescribed time. CONSTITUTION:When a fault takes place in a transmission line, no transmission alarm signal ALARM is inputted to a switch 3, which is closed and a signal outputted from a decoder 1 is inputted to the D/A converter 2 via a delay circuit 4 and the switch 3 and converted into an analog signal. If a fault takes place on a transmission line, noise is inputted to a delay circuit via the decoder 1, the transmission line alarm signal ALARM is inputted to the switch 3, which is opened and the input to the D/A converter is '0'. Thus, the noise when the transmission line alarm signal is inputted is prevented.

Description

[Detailed Description of the Invention] [Summary] This is a noise prevention circuit that attempts to effectively prevent noise at the moment when a transmission alarm signal is generated.

[Industrial application field]

The present invention relates to a noise prevention circuit.

If a failure occurs in the transmission path between the transmitter, which encodes the audio signal, converts it into a digital signal, and sends it out, and the receiver, which decodes it and converts it into analog, this system prevents noise from entering the receiver. There is a need to.

For this reason, a switch is installed just before the D/A converter on the receiving side, so that when a failure occurs, the input to the D/A converter is cut off by a transmission line alarm signal.

[Conventional technology]

The conventional noise prevention circuit has a decoder 1 as shown in FIG.
' and the D/A converter 2', a switch 3' is connected between the transmission line alarm signal ALARM and the D/A converter 2'.
′ is input to decoder 1 by switching switch 3′.
' is disconnected and "0" is output from the D/A converter 2'.

[Problem that the invention seeks to solve]

However, the conventional technology has a problem in that noise cannot be prevented at the moment when a transmission line alarm occurs.

That is, in FIG. 4, even if a transmission failure occurs when 1=10 (FIG. 4(A)), the transmission line alarm signal ALARM is not immediately input to the switch 3', and when 1=1. (Fig. 4(B)).

Therefore 1=1. From to t, the switch 3' remains closed and noise is input from the decoder 1' to the D/A converter 2'.

Therefore, noise is output from the D/A converter 2' as shown by diagonal lines (FIG. 4(C)), and there is a problem that the noise cannot be prevented at the moment when the transmission line alarm signal is generated.

[Means for solving problems]

An object of the present invention is to solve the above-mentioned problems and to prevent noise at the moment when a transmission line alarm signal is input.

As a means for this purpose, the present invention provides a delay circuit 4 between the decoder 1 of the receiving section and the switch 3 as shown in FIG. That's how it is.

[For production]

According to the present invention, since a delay circuit is provided between the decoder and the switch, if the delay time by this delay circuit is set to be longer than the time from when a fault occurs to when a transmission line alarm signal is input, it is possible to Since this noise will not be input to the D/A converter, it is possible to prevent noise at the time when the transmission line alarm signal is input.

〔Example〕

The present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a principle diagram of the present invention, and FIG. 2 is an explanatory diagram of the operation of FIG. 1.

The noise prevention circuit shown in FIG. 1 is composed of a decoder 1, a delay circuit 4, a switch 3, and a D/A converter 2.

A decoder 1 receives an audio signal from a transmission path, such as a PC.
This is a device that converts M codes into digital audio signals.

The delay circuit 4 is a circuit that delays the output of the decoder 1 by a certain period of time.

Switch 3 is switched by the transmission line alarm signal ALARM which is input when a failure occurs in the transmission line.
/ Set the input of A converter 2 to "0".

The D/A converter 2 is a device that converts a digital audio signal into an analog signal.

Hereinafter, the operation of the circuit shown in FIG. 1 having the above configuration will be explained based on FIG. 2.

If no fault has occurred in the transmission line, the transmission line alarm signal ALARM is not input to the switch 3 and the switch 3 is closed. Therefore, the signal output from the decoder 1 is input to the D/A converter 2 via the delay circuit 4 and the switch 3, and is converted into an analog signal.

However, if a failure occurs in the transmission path when 1=10 (FIG. 2(A)), the noise shown in the figure is input to the delay circuit via the decoder l.

1=1. At this point, the transmission line alarm signal ALARM is input to the switch 3.

This causes switch 3 to open and the input to the D/A converter to become 0''.

Therefore, the time from 1=18 when a failure occurs in the transmission line to wj+ when the alarm signal ALARM is input to switch 3 is 1. If the delay time T by the delay circuit 4 is set to -10 or more, after the switch 3 is turned off (t=
The signal decoded at tl) is input to switch 3 (
Figure 2 (B)).

Therefore, the D/A converter 2 has 1=1. After that, no signal is input and "O" is output (Figure 1, Figure 2 (D)
).

On the other hand, if there is no failure in the transmission path when 1=12, then 1=
1. At this point, the alarm signal ALARM is no longer input, and the switch 3 is closed.

〔Effect of the invention〕

As described above, according to the present invention, since the delay circuit is provided between the decoder and the swift, if the delay time by this delay circuit is set to be longer than the time from the occurrence of a fault to the time when the transmission line alarm signal is input, Since the noise generated on the transmission path is not input to the D/A converter, it is possible to prevent noise at the time when the transmission path alarm signal is input.

[Brief explanation of drawings]

FIG. 1 is a diagram of the principle of the present invention, FIG. 2 is an explanatory diagram of the operation of the present invention, FIG. 3 is a configuration diagram of the prior art, and FIG. 4 is an explanatory diagram of the operation of the prior art. I...Decoder, 2...D/A converter, 3...Switch, 4...Delay circuit. Figure 1: Principle diagram of the present invention Figure 2: Explanation diagram of the operation of the present invention

Claims (1)

[Scope of Claims] In a circuit for preventing noise input to the receiving section when a failure occurs in the transmission path connecting the transmitting section and the receiving section, between a decoder and a D/A converter constituting the receiving section. In addition, a switch is provided to cut off the input to the D/A converter in response to a transmission line alarm signal, and a delay circuit is provided on the input side of the switch, and the delay time of the delay circuit is set so that the delay time of the delay circuit is determined by the time when a failure occurs on the transmission line. The noise prevention circuit is configured to be set for a period longer than the time from when the transmission line alarm signal is input to the switch.