JPH06284350A - Non-signal detection circuit - Google Patents

Abstract

PURPOSE:To secure highly accurate discrimination performance and to accurately discriminate input signals. CONSTITUTION:This circuit is provided with a pulse width detection part 10 for outputting a first detection pulse in a state where it is detected that the pulse width of the input signals is within the range of a first threshold value and a second threshold level and outputting a second detection pulse in the state where it is detected that the pulse width of the input signals is equal to or more than the second threshold level, non-signal is discriminated in the state where the first detection pulse detected in the pulse width detection part 10 is equal to or more than a threshold level A and the other second detection pulse is equal to or more than the threshold level B and equal to or less than the threshold level C and an initial purpose is accomplished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a no-signal detection circuit used for determining whether or not an input signal such as a video signal is input.

[0002]

2. Description of the Related Art Generally, a no-signal detection circuit measures the number of pulses of a horizontal / vertical synchronizing signal within a fixed time of an input signal and determines whether or not the measured number falls within a predetermined range. A method for discriminating no signal is known.

FIG. 2 shows such a conventional no-signal detecting circuit. The pulse width detecting section 1 detects the pulse width of an input signal based on a reference clock, and a predetermined threshold value (eg, When it exceeds 3 μSec), a detection pulse is output to the up counter 2. The up counter 2 measures the input detection pulse and is reset based on the reference signal, and the measurement result is output to the range detection unit 3.
The range detection unit 3 sets the threshold value X (for example, -10% of the standard setting value) at the time immediately before the up counter 2 is reset.
When the threshold value Y (+ 10% of the standard setting value) is not exceeded, that is, within a range of ± 10% of the standard setting value, H
The output is output to the knot (NOT) circuit 4, and the inverted signal of the knot circuit 4 is output as no-signal detection.

However, in the above no-signal detection circuit,
3μSe when there is no signal such as when receiving an empty channel
If the number of noises with a pulse width of c or more accidentally falls within a predetermined range (± 10% of the standard setting value), it will malfunction and determine that there is an input signal, even though there is no input signal. Have.

[0005]

As described above, in the conventional no-signal detection circuit, even though there is no input signal,
There is a problem that it malfunctions due to noise and is discriminated as a signal present.

The present invention has been made in view of the above circumstances, and provides a no-signal detection circuit capable of realizing accurate discrimination of an input signal while ensuring highly accurate no-signal discrimination performance. The purpose is to

[0007]

The present invention detects that the pulse width of an input signal is between a first threshold value and a second threshold value and outputs a first detection pulse. Of the first and second threshold values, a pulse width detecting means for detecting that the second threshold value is larger than the second threshold value and outputting a second detection pulse; and a pulse width detecting means for outputting the pulse width detecting means. And a first counter means for measuring the number of pulses of the first detection pulse for a certain period, and a first counter means for detecting whether or not the measurement result of the first counter means is within a predetermined range of a standard set value or more. Range detection means, second counter means for measuring the number of second detection pulses output from the pulse width detection means for a certain period, and the measurement result of the second counter means is centered on the standard set value. 2nd range to detect whether or not it is within a certain range A no-signal detection circuit is constituted by the output means and the no-signal detection means for detecting whether or not the input signal is no-signal based on the outputs of the first and second range detection means. .

[0008]

According to the above structure, the first detection pulse is set to the standard set value based on the measurement results of the first and second counters for measuring the first and second detection pulses from the pulse width detection means, respectively. Within the above predetermined range, the non-signal detection result is output in a state where it is detected that the other second detection pulse is within the predetermined range centered on the standard set value. As a result, in the absence of an input signal, if the number of noises having a pulse width equal to or greater than the second threshold value happens to fall within a predetermined range centered on the standard setting value, the first range detection unit detects the first value. When the number of the detection pulses is larger than the predetermined range of the standard set value or more, the no-signal detecting means determines that there is no input signal.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a no-signal detecting circuit according to an embodiment of the present invention. First and second up counters 11 and 12 are connected to the output terminal of a pulse width detecting section 10, respectively. It Then, the pulse width detection unit 10 determines that the pulse width of the input signal is the first threshold value (for example, 2 μSec) based on the reference clock and the second threshold value that is larger than the first threshold value. When it is detected that it is between (for example, 3 μSec), the first detection pulse is output to the first up counter 11. This first up counter 11
Measures the input first detection pulse, is reset by the reference signal, and outputs the measurement result to the first range detection unit 1
Output to 3. The first range detection unit 13 is connected to one input terminal of a NAND circuit 14, and when the input measurement result is within the threshold value A (+ 20% of the standard set value), the H output is output to the NAND circuit. It outputs to one input terminal of 14.

When the pulse width detecting section 10 detects that the pulse width of the input signal exceeds the second threshold value based on the reference clock, the pulse width detecting section 10 outputs the second detection pulse to the second up counter 12 Output to. Second up counter 1
2 measures the input second detection pulse, is reset by the reference signal, and outputs the measurement result to the second range detection unit 15. The second range detector 15 is connected to the other input terminal of the NAND circuit 14,
The input measurement result is the threshold value B (standard setting value -10
%), And outputs the H output to the other input terminal of the NAND circuit 14 within the threshold value C (+ 10% of the standard setting value). The NAND circuit 14 includes the first and second range detectors 1.
The negative logical product of the outputs from 3 and 15 is taken and output as a no-signal detection result.

The threshold value A is, for example, in consideration of noise having a width of 3 μSec or more, and when the noise falls within the detection range, the number of noise having a width of 2 μSec or more becomes larger than the number of noise having a width of 3 μSec or more. Therefore, it is necessary to set the threshold value A small so that the number of the noises exceeds the threshold value A. On the other hand, when receiving in the weak electric field region, the threshold value A is such that the number of the second detection pulses exceeds the threshold value A while the number of the detection pulses having a width of 3 μSec or more is within a predetermined range. It is necessary to set the threshold value A as large as possible so as not to exist. Therefore, the threshold value A is set from the viewpoint of both prevention of erroneous determination when there is no signal (determining no signal as a signal) and erroneous determination in a weak electric field area (determining no signal as a signal).

As described above, the no-signal detection circuit detects that the pulse width of the input signal is within the range between the first threshold value and the second threshold value, and then the first detection pulse is detected. And a pulse width detection unit 10 that outputs a second detection pulse in a state where the pulse width of the input signal is detected to be equal to or larger than the second threshold value. In the state where the detected first detection pulse is equal to or higher than the threshold value A and the other second detection pulse is equal to or higher than the threshold value B and equal to or lower than the threshold value C, no signal is determined.
According to this, for example, when the number of noises having a pulse width equal to or larger than the second threshold value happens to fall within the range between the threshold values B and C, only the second detection pulse is output from the pulse width detection unit. Then, there is an H output from the second range detector 15,
Since the first range detection unit 13 outputs L, the NAND operation output from the NAND circuit 14 outputs L, which determines no signal, so that erroneous detection due to noise is prevented.

In the above embodiment, one pulse width detecting section 10 is used to detect different pulse widths of the input signal and generate the first and second detection pulses. However, without being limited to this, for example, the first and second pulse width detection units for detecting the pulse width of the input signal are separately provided, and the first and second pulse width detection units respectively have the first and second pulse width detection units. And a second detection pulse.

Further, in the above embodiment, the pulse width of the input signal is detected between the first and second threshold values and at two points equal to or larger than the second threshold value. However, the present invention is not limited to this, and the detection may be performed at two points, for example, a first threshold value or more and a second threshold value or more. Therefore, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

[0016]

As described above in detail, according to the present invention, there is provided a no-signal detection circuit capable of accurately discriminating an input signal while ensuring highly accurate no-signal discrimination performance. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a no-signal detection circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional no-signal detection circuit.

[Explanation of symbols]

Reference numeral 10 ... Pulse width detection unit, 11, 12 ... First and second up counters, 13, 14 ... First and second range detection unit, 14 ... NAND circuit.

Claims (2)

[Claims] 1. A first detection pulse is output by detecting that the pulse width of an input signal is between a first threshold value and a second threshold value, and the first and second threshold values are output. A pulse width detecting means for detecting that the threshold value is equal to or larger than a second threshold value having a large value and outputting a second detection pulse, and a first detection pulse of the first detection pulse output from the pulse width detecting means. First counter means for measuring the number of pulses for a certain period of time; first range detecting means for detecting whether or not the measurement result of the first counter means is within a predetermined range of a standard set value or more; Second counter means for measuring the number of second detection pulses output from the width detection means for a certain period, and the measurement result of the second counter means is within a certain range centered on the standard set value. Second range detecting means for detecting whether or not the first range No signal detecting circuit and a no-signal detection means for the input signal based on the output of the second range detection means for detecting whether a no signal. 2. A first detection pulse is output by detecting that the pulse width of the input signal is equal to or larger than a first threshold value, and the first detection pulse is output.
The pulse width detection means for detecting the second threshold value having a value larger than the threshold value and outputting the second detection pulse, and the pulse number of the first detection pulse output from the pulse width detection means First counter means for measuring for a fixed period, first range detecting means for detecting whether or not the measurement result of the first counter means is within a predetermined range of a standard set value or more, and the pulse width detecting means Second counter means for measuring the number of pulses of the second detection pulse output from the second counter means for a certain period, and whether the measurement result of the second counter means is within a certain range centered on the standard set value. No signal detection including a second range detecting unit for detecting a signal and a no signal detecting unit for detecting whether or not the input signal is a no signal based on the outputs of the first and second range detecting units. circuit.