JPS59149466A - Measuring device for video signal - Google Patents

Abstract

PURPOSE:To obtain an accurate, high-precision measuring device of simple constitution by sampling and holding a signal generated by clipping the peak of a luminance signal of video at a constant voltage, and measuring a frequency after frequency modulation by said output through a counter. CONSTITUTION:The peak of the horizontal synchronizing signal of an input video luminance signal 18 is clamped by a clamping circuit 11 to the constant voltage, and the clamped luminance signal is processed by high-frequency emphasis 12. A spike pulse generated at this time is suppressed by a white clip/ dark clip circuit 13 and inpt the resulting signal 22 to a sample holding circuit 14. When a switch 20 is placed on the side of measurement of a sink chip level SCL, a sampling pulse SP generating circuit 17 outputs an SP signal 24A which synchronizes the horizontal synchronizing signal of the signal 18 except in a vertical blanking period to a circuit 14, which holds the SL of the signal 22. The SCL is converted 15 into a frequency, which is measured 16. Then, the switch 20 is placed at the side of measurement of a white peak level and an SP signal 25B is outputted from the circuit 17 to take a measurement 16 of a white peak carrier frequency.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention is applicable to the measurement of the synchronous leading carrier frequency (hereinafter referred to as synctenop frequency) of the luminance signal of a home video tape recorder, and the measurement of the synchronous leading carrier frequency and the white peak carrier frequency. This invention relates to a device that measures the difference between

Conventional Structure and Problems Conventionally, an apparatus having the structure shown in FIG. 1 has been generally used to measure the sync frequency and deviation of the video luminance signal of a home video tape recorder. This will be explained in detail below with reference to the signal waveform diagram of the main part in FIG. This consists of a clamp circuit 1 that clamps the leading end of the horizontal synchronizing signal 8 of the input video luminance signal 7 to a constant voltage VC shown in FIG. 2(a), and a pre-emphasis circuit that emphasizes the output of the clamp circuit 1 in high frequencies. 2. White clip/dark clip circuit 3 for suppressing the snow-like pulses occurring at the rising and falling portions of the output signal of the pre-emphasis circuit 2;
In a video tape recorder equipped with an FM modulation circuit 4 that frequency modulates the signal 9 shown in FIG. The output signal was demodulated by an FM demodulation circuit 5, the output signal of the FM modulation circuit 6 was input to an oscilloscope 6, and the display on the oscilloscope 6 was read to measure the frequency.

Therefore, reading errors on the oscilloscope tube surface and FM
The disadvantages were that there were calibration errors in the demodulation circuit, it was not possible to make accurate measurements, and the accuracy was not high.

OBJECTS OF THE INVENTION The present invention aims to eliminate such conventional drawbacks, and to provide a video signal measuring device that has a simple configuration and can perform accurate and highly accurate measurements.

Structure of the Invention The video signal measuring device of the present invention includes a clamp circuit that clamps the leading edge of the horizontal synchronizing signal of the input video signal to a constant voltage, and a clamp circuit that clamps the leading edge of the horizontal synchronizing signal of the input video signal to a fixed voltage, and a clamp circuit that clamps the leading edge of the horizontal synchronizing signal of the input video signal to sampling pulse generation means for generating a pulse signal; sample and hold means connected to sample and hold the output signal of the clamp circuit using the pulse signal and input the sampled and held signal to the FM modulation circuit; and the FM modulation circuit. It is equipped with a counter circuit that measures the sync step frequency and deviation of the output of the circuit.

DESCRIPTION OF EMBODIMENTS As an embodiment of the present invention, an NTSC video signal measuring device for an H8 home video tape recorder will be described below with reference to the drawings.

Figure 3 is a block diagram of the main parts showing the configuration of this embodiment, and Figures 4 (a), (b), (C), and (d) are each main part of Figure 3.
Part f7) is a signal waveform diagram. In those drawings,
11 is a counter circuit that clamps the tip of the horizontal synchronizing signal 19 of the input video signal 18 to a constant voltage 1 (hereinafter referred to as a sync step level); 12 is the clamp circuit 1;
1, a pre-f7 assist circuit for emphasizing the high frequency range of the output signal of the pre-emphasis circuit 12; 13, a white clip/dark clip 21 circuit for suppressing spikes in the rising and falling portions of the output signal of the pre-emphasis circuit 12; 14iIl;
l: The signal 22 clipped by the white clip/dark clip circuit 13 is converted into a sampling pulse 2
6A and 25B are sample hold circuits that sample and hold only during the H level period, and 17 is a sync step level sample pulse 25A and a white peak level sample pulse 25B in synchronization with the horizontal synchronization signal other than the vertical blanking period of the input video signal 18. This is a sampling pulse generation circuit that generates a 2mtAo pulse of Σ.

Reference numeral 20 indicates an output pulse switching switch for the sampling pulse generation circuit 17 to switch between the sync step level sample pulse 25A and the white peak level sample level 25B. F for converting to FM modulation signal
The M modulation circuit 16 is a counter circuit that measures the sync tip frequency and white peak carrier frequency of the output of the FM modulation circuit 15.

Next, the operation of each block when measuring the sync step frequency in this embodiment will be explained along the flow of signals.

The leading end of the horizontal synchronizing signal 19 of the video luminance signal 18 input to the clamp circuit 11 is clamped to a constant voltage v1 preset within the clamp circuit 11. The clamped video luminance signal is generally high-frequency emphasized by a pre-amplifier circuit 12, and the rising edge of the signal 9. A spike-like pulse 21 is generated at the 9th falling edge. This spike-like pulse 21 is generated by the white clip/dark clip circuit 13.
This is suppressed by clipping the white clip level v'w7 to the dark chrysop level VD.

The sampling pulse 25A for sampling the sync step level S of the signal 22 in which the spike-like pulse has been clipped can be obtained by turning the switch note 20 connected to the sampling pulse generation circuit 17 to the sync step level measurement side. The 0 sampling pulse 25A output from a sampling pulse generation circuit composed of a circuit that generates sampling pulses in synchronization with a horizontal synchronization signal other than the vertical blanking period of the video luminance signal 18, such as a mono multi-circuit, is H. Only during this period, the sample and hold circuit 14 samples and holds the sync step level, and
The M modulation circuit 15 can measure the sync step frequency by performing frequency eK conversion on the sync step level and inputting the converted signal to the counter circuit 16 .

Next, when measuring deviation, in the configuration in which the sync step frequency was measured, turn the switch 20 connected to the sampling pulse generation circuit 17 to the white peak level measurement side, and remove the vertical blanking period of the input video luminance signal 18. A sampling pulse 26B, which is a pulse signal synchronized with the horizontal synchronization signal of do.

The frequency of the sampled and held white peak carrier level vP is measured by the FM modulation circuit 15 and the counter circuit 16 to obtain the white peak carrier frequency. Deviation can be measured by subtracting the white peak carrier frequency measured here from the sync tip frequency measured in the operation description of the above embodiment.

Effects of the Invention As described above, the present invention is applicable to a general home video tape recorder equipped with a clamp circuit, a pre-emphasis circuit, and a white clip/dark clip circuit for the purpose of converting an input video signal into a recording signal. It has a simple configuration that only includes a sample hold circuit, a sampling pulse generation circuit, and a counter circuit, and the pre-emphasis circuit emphasizes the high frequencies and contains spike-like pulses at the rise and fall portions of the signal.It is accurate and precise. It is capable of measuring high sync step frequencies and deviations.

Further, by controlling the switch for switching between the sampling pulses of the sync step level and the white peak carrier level using a computer, and also inputting the counter circuit output to the computer, automation of this measuring device can be easily realized.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the main parts during conventional video signal frequency measurement, Figs. 2 (a) and (b) are signal waveform diagrams of the main parts of Fig. 1, and Fig. 3 is a diagram of the main parts according to the embodiment of the present invention. Main part block diagram of video signal measurement device, Figure 4 (&) ', (b)
. (C) and (d) are signal waveform diagrams of the main parts of FIG. 3. 11... Clamp circuit, 14... Sample hold circuit, 15... FM modulation circuit, 16
... Counter circuit, 17 ... Sampling pulse generation circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person36

Claims (1)

[Claims] a clamp circuit that clamps the leading end of a luminance signal of a video signal to a constant voltage; a sampling pulse generator that generates a pulse signal in synchronization with a horizontal synchronization signal excluding a vertical blanking period of the video signal; Sample and hold the output signal of the clamp circuit by 5,
A video signal measuring device comprising a sample and hold means connected to input the sampled and held signal into a frequency modulation circuit, and a counter circuit for measuring the frequency of the output of the frequency modulation circuit. .