JPH0136143Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency measuring device that can be used for adjusting a video signal recording/reproducing device, and more specifically, to a frequency measuring device that measures frequencies in a predetermined range on the time axis.

(Prior Art) In a video signal recording and reproducing apparatus, a luminance signal separated from a composite color television signal is converted into a low carrier wave FM signal and recorded on a magnetic tape. However, in a video signal recording and reproducing device, the difference between the frequencies corresponding to the white signal in the luminance signal and the sync chip, that is, the frequency shift, has a large effect on image quality. The frequency of the frequency modulated signal corresponding to the frequency is measured.

Conventionally, this frequency measurement involves supplying a frequency-modulated signal frequency-modulated with a luminance signal to a spectrum analyzer, observing the spectrum group, and increasing the accuracy of the spectrum analyzer to find the position corresponding to the sync chip or white level signal. They were able to determine the frequency by reading the frequency on the screen.

However, the above-mentioned measurement method is an extremely inaccurate measurement method, and has the disadvantage that there are many individual differences in measurement and that measurement requires a long time to obtain accurate measurement values.

In addition, the output signal of the high-frequency signal generator is supplied to the spectrum analyzer, superimposed on the frequency-modulated spectrum group on the spectrum analyzer screen, and placed at the sync chip or white level signal position. Measurements have also been made by reading the output signal frequency.

However, even when using this method, it is necessary to increase the measurement accuracy of the spectrum analyzer and to make the superimposed high-frequency signal spectrum as needle-like as possible. It is necessary to converge as much as possible to form a dot, which has the disadvantage that measurement takes a long time and accurate measurement results cannot always be obtained.

(Purpose of the invention) The present invention has been made in view of the above, and it is an object of the present invention to eliminate the above-mentioned drawbacks and provide a frequency measuring device that can accurately and quickly measure frequencies in a predetermined range on the time axis with a simple configuration. The purpose is to

The present invention will be explained below with reference to examples.

(Structure of the invention) FIG. 1 is a block diagram showing the structure of an embodiment of the invention.

In the following description, a signal frequency-modulated with a luminance signal separated from a composite color television signal will be described as a signal to be measured.

IN ₁ is an input terminal to which a composite color television signal is supplied, and IN ₂ is an input terminal to which a luminance signal separated from the composite color television signal supplied to input terminal IN ₁ is supplied via frequency modulator 1. The input terminal IN 2 is an input terminal, and a frequency-modulated signal frequency-modulated with a luminance signal is supplied to the input terminal IN ₂ .

2 is a pulse generator, which outputs an output pulse A at a partial range position where the frequency of the frequency modulated signal is to be measured, an output pulse B which is an inversion of the output pulse A, and an output pulse A located within the pulse width of the output pulse A.
An output pulse C having a width shorter than the pulse width of the output pulse B and an output pulse D positioned within the pulse width of the output pulse B are output, respectively. If we were to measure the frequency of a frequency-modulated signal corresponding to a sync chip in a luminance signal, output pulse A is an output pulse obtained by separating and regenerating the sync chip in a luminance signal, and its pulse width is equal to the pulse of the sync chip. It is a pulse whose width is equal to or narrower and whose position on the time axis is also equal to the position of the sync chip on the time axis.

On the other hand, the frequency modulated wave supplied to the input terminal IN ₂ is supplied to the limiter 3 to limit the amplitude and then supplied to the mixer 4, where it is mixed with the oscillation output of the oscillator 5, converted to a high frequency, and then sent to the tuned amplifier 6. supply to. The output signal from the mixer 4 amplified by the tuned amplifier 6 is supplied to a sampling circuit 7 and sampled using the output pulse A output from the pulse generator 2. On the other hand, 8 is a reference frequency oscillator (hereinafter referred to as
The oscillation output of the REF OSC 8 is supplied to a sampling circuit 9 and sampled with the output pulse B output from the pulse generator 2.

The outputs of the sampling circuits 7 and 9 are supplied to a synthesis circuit 10 for synthesis. The output signal of the synthesis circuit 10 is supplied to a frequency-voltage converter (hereinafter referred to as an F-V converter) 11 for frequency-voltage conversion.

The output of the F-V converter 11 is supplied to sample and hold circuits 12 and 13, and sampled and held using output pulses C and D output from the pulse generator 2, respectively. The output signals of sample and hold circuits 12 and 13 are supplied to voltage comparison circuit 14, and their levels are compared. The output of the voltage comparator circuit 14 is supplied to an instruction circuit 15 for instruction.

(Operation of the invention) In one embodiment of the invention constructed as described above, the operation will be explained by taking as an example the case where the frequency of a frequency modulated signal corresponding to a sync chip is measured.

The composite color television signal supplied to the input terminal IN ₁ is supplied to a pulse generator 2 which outputs the output pulses A to D as shown in FIGS. 2A to D.
Output D. Here, FIG. _2A0 shows the luminance signal waveform separated from the composite color television signal. Output pulse A is a pulse produced by separating and reproducing the sync chip from the composite color television signal, and is a pulse of the same pulse width generated at the same position on the time axis as the sync chip, as shown in Figure 2A. . The output pulse B is an output pulse obtained by inverting the output pulse A shown in FIG. 2A, and is as shown in FIG. 2B. The output pulse C has a narrower pulse width than the output pulse width of the output pulse A shown in FIG. 2A and is located within the pulse width of the output pulse A, as shown in FIG. 2C. The output pulse D is a pulse output at an arbitrary position within the output pulse B, as shown in FIG. 2D.
Here, the pulse width of the output pulse A may be set narrower than the pulse width of the output pulse shown in FIG. 2A.

On the other hand, the frequency modulated wave frequency-modulated by the frequency modulator 1 with the luminance signal having the waveform shown in FIG. _2A0 is supplied to the limiter ₃ via the input terminal IN2 and is amplitude limited. In the frequency modulated signal, let _H be the frequency corresponding to the sync chip in the luminance signal. The amplitude-limited frequency modulated signal is mixed with the oscillation output of the oscillator 5 in the mixer 4 . Now, if the oscillation frequency of the oscillator 5 is _p , then if we pay attention to the frequency _H corresponding to the sync chip, the frequency _H will be converted to _HD (= _p + _H ). The mixed output of the mixer 4 is selectively amplified in a tuned amplifier 6,
The spurious generated by mixer 4 is removed. Therefore, a bandpass filter may be used in place of the tuned amplifier 6.

The output signal of the tuned amplifier 6 is transmitted to the sampling circuit 7
and sampled by output pulse A. Therefore, the frequency of the output signal of the sampling circuit 7 is _HD . On the other hand, the oscillation output of the REF OSC 8 is supplied to the sampling circuit 9 and sampled by the output pulse B. Therefore, the frequency of the output signal of the sampling circuit 9 is REF
This is the oscillation frequency _REF of OSC8.

The output signals of sampling circuits 7 and 9 are combined in a combining circuit 10. Therefore, the output of the combining circuit 10 is the output pulse A as shown in FIG.
During the period of occurrence, the output is of frequency _HD ,
In other periods, the oscillation frequency of REF OSC8
This is the output of _REF .

The output of the combining circuit 10 is supplied to the F-V converter 11 and converted into a voltage signal, and the F-V converter 11 generates an output as shown in FIG. 2F. In FIG. 2F, V _fHD is the output voltage for the output signal of the frequency _HD output from the sampling circuit 7, and V _fREF is the output voltage for the output signal of the frequency _REF output from the sampling circuit 9.

The output voltage shown in FIG. 2F from the F-V converter 11 is supplied to sample and hold circuits 12 and 13, respectively.
The signal is sampled and held by the output pulse C in the sample and hold circuit 13, and sampled and held by the output pulse D in the sample and hold circuit 13. Therefore, the output signal of the sample and hold circuit 12 is a signal of the DC voltage V _fHD , and the output signal of the sample and hold circuit 13 is a signal of the DC voltage V _fREF .
Both signals are supplied to the voltage comparison circuit 14 and compared. Therefore, the output signal voltage of the voltage comparison circuit 14 corresponds to (V _fHD -V _fREF ), and this output signal is instructed by the instruction circuit 15 .

As a result, for example, if the indicating circuit 15 is configured with a center zero indicator, when the frequency to be measured is set to _M and _REF − _M = _O , the center zero indicator will give a center zero instruction. _REF or so that the center zero indicator indicates center zero.
( _{REF −
O} ) can measure the frequency _M to be measured.

Furthermore, the mixer 4 and the oscillator 5 may be omitted; in this case, the oscillation frequency of the REF OSC 8 when the output voltage of the voltage comparator 14 is zero will indicate the frequency _M to be measured.

In the above explanation, the operation was explained by taking as an example the case where the frequency of the part corresponding to the sync chip position in the frequency modulated signal frequency-modulated by the luminance signal is measured. The frequency of the part corresponding to can be measured in the same way. When measuring the frequency of the part corresponding to the white signal, it is sufficient to output the output pulse A (shown in FIG. 2 G) corresponding to the white signal position from the pulse generator 2, and this can be used for inspection of video signal recording and reproducing devices, etc. In this case, since a luminance signal with a specified white signal position is used, it is easy to generate the output pulse A shown in FIG. 2G based on the leading edge of the sync chip in the luminance signal. Furthermore, the output pulse A shown in FIG.
It is also easy to create output pulses B to D corresponding to It is also possible to know the frequency shift by calculating the difference.

For example, it is easy to measure the frequency of a modulated wave with a carrier frequency of about 3.5 MHz and a frequency deviation of about ±1 MHz with an error of within ±5 kHz.

Further, in the above explanation, the case where the frequency of the frequency modulated signal frequency-modulated by the luminance signal in the video signal recording and reproducing device is measured is exemplified, but there is no need to limit it to this, and the time axis of the signal under measurement is explained. It is clear that the frequency at a given position above can be measured.

(Effects of the Invention) As explained above, according to the present invention, the frequency of a signal under test in a predetermined range on the time axis can be measured accurately and in a short time with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a waveform diagram for explaining the operation of an embodiment of the present invention. 1... Frequency modulator, 2... Pulse generator, 7 and 9... Sampling circuit, 8... REF OSC, 10
...Synthesizing circuit, 11...F-V converter, 12 and 1
3...Sample hold circuit, 14...Voltage comparator,
15...Instruction circuit.

Claims (1)

[Claims for Utility Model Registration] A first output pulse having a predetermined range width on the time axis of the frequency measurement signal, a second output pulse obtained by inverting the first output pulse, and within the first output pulse width. a pulse generator that outputs a third output pulse located at and having a pulse width narrower than the first output pulse width and a fourth pulse located within the second output pulse width; and the frequency measured signal. or a first sampling circuit that samples the frequency-converted signal of the frequency-measured signal using the first output pulse; an oscillator; and a second sampling circuit that samples the oscillation output of the oscillator using the second output pulse. a circuit; an output of the first sampling circuit; and an output of the first sampling circuit;
a synthesis circuit that synthesizes the output of the sampling circuit; a frequency-voltage converter that converts the output of the synthesis circuit into frequency-voltage; and a frequency-voltage converter that converts the output of the frequency-voltage converter into the third output pulse and the fourth output pulse. first and second sample and hold circuits that separately sample and hold the output pulses of the circuit; and a voltage comparison circuit that compares the output level of the first sample and hold circuit with the output level of the second sample and hold circuit. A frequency measuring device comprising: , instruction means for instructing the output of the voltage comparison circuit.