JPS60167582A - Video detection device - Google Patents

Abstract

PURPOSE:To discriminate a white directional standard of a video signal by making detection phases different at the first signal arrival period and the second signal arrival period which is the other period, except a synchronizing signal pulse arrival period within a horizontal flyback period, in detecting amplitude modulated television signal. CONSTITUTION:When assuming a phase transition amount as DELTAtheta for a luminance signal level x% and assuming an amplitude VY between video signal reference black level and maximum white peak signals as 100 in a standard television system, a synchronizing signal pulse amplitude VS is specified as 40, thus representing by an equation I , where said amplitude VS is specified as 87.8% at the maximum modulation factor of m=video signal. Therefore it can be simplified as an equation II. For example, if said transition DELTAtheta is zero, x=0 can be obtained from theta=180 deg.. When assuming that a phase shifter 6 gives a phase transition of DELTAtheta=90 deg., x=120% can be obtained from the equation II, and an output level of a multiplier 2 with respect to the first signal arrival period is increased with respect to the luminance level 0% in the case of the output level being DELTAtheta=zero, thereby transmitting signals which exceed 100% white peak levels.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video detection device that reproduces an amplitude modulated signal by synchronous detection, and in particular relates to the configuration of a detection circuit for telepijo/intermediate frequency signals. It is something.

Conventional configuration and its problems As is well known, television signals are transmitted using residual sidebands, so an example of a video detection circuit for receiving the signal and reproducing the video signal is shown in FIG. A synchronous detection circuit is used.

2! - In the figure, intermediate frequency signal components of a composite video signal including a luminance signal, a synchronization signal used for synchronizing the carrier color signal and the scanning circuit, a burst signal as a color synchronization signal, etc. are supplied to the signal input terminal T1, If necessary, audio intermediate frequency signal components are also synthesized and supplied. The intermediate frequency carrier wave signal generator 1 generates a carrier wave signal that maintains a substantially constant phase and frequency relationship with respect to the carrier component of a video intermediate frequency signal, which is an incoming input signal, and signal frequency components in the vicinity thereof. For example, it is constructed by using a filter using a known phase-locked loop (PLL) or a crystal oscillator. The conductors 10 and 11 supply the output signal components of the carrier wave signal generator to the first phase comparator 2 and the second phase comparator 3, respectively, and have a relative phase difference of approximately 90 degrees between 1o and 11. , the first phase comparator 2 constitutes an in-phase synchronous detector, and the second phase comparator 3 constitutes a quadrature synchronous detector, and when the PLL 1 is used to reproduce the carrier signal, the second phase comparator 3 is It can also be used in common with the phase comparator that constitutes the PLL. From the above explanation, the composite video signal is output to the signal output terminal T2, and the high-frequency components of the video signal are output from the terminal T3 as orthogonal components, that is, the high-frequency component of the luminance signal, the carrier color signal component, and the two of the second phase comparator 3. The relative phase difference between the input signals also provides a direct current signal component, and when an audio intermediate frequency signal is synthesized at terminal T1, the intercarrier audio signal becomes T2. The signal is sent out in a superimposed form to each signal output terminal of T3.

The above-mentioned known configurations are the most basic, but in order to put these circuits into practical use, it is difficult to detect them due to the generation of interference signal components associated with detection or the generation of distortion that is likely to occur during large-level amplification of intermediate frequency signals. It is known that it is effective to perform the operation at a low level and amplify the low-level composite video signal that is the output thereof. Therefore, an amplifier is connected between the output terminal of the first phase detector 2 and the signal output terminal T2. (not shown) It is common to have all of them arranged. The purpose of the signal output from the signal output terminal T3 is appropriately selected depending on the need, but the terminal T3 is not essential for transmitting a detected signal of a television signal.

It is known that identifying the specified amplitude range of a composite video signal is effective, for example, when reproducing it after removing the DC component, or when performing automatic gain control. Only the peak value and pedestal level can be used as the reference, which has the disadvantage that the reference in the white direction of the video signal cannot be identified. Furthermore, as mentioned above, when a DC-coupled video amplifier is placed after the first phase detector, the pedestal level on which the color burst signal is superimposed and the luminance level on which the skin color signal is superimposed, which is the reference for the visual color phase, are specified. Approximately 7o% within the amplitude range
Since there is also a difference between the two, it has drawbacks such as being susceptible to the differential phase stability of the video amplifier.

OBJECTS OF THE INVENTION The present invention provides a peak value of a synchronization signal indicating a negative amplitude reference;
A first object of the present invention is to provide a video detection circuit capable of transmitting a video signal having a single peak signal representing a positive amplitude reference.

A second object of the present invention is to completely prevent the color burst signal forming a part of the composite video signal from being affected by the differential phase and differential gain of the video amplifier that is DC-coupled to the video detector. .

A third object of the present invention is that when the circuit that performs predetermined processing using all the quasi-white peak signals representing the amplitude reference in the positive direction is of a known peak detection type, the video modulation level significantly exceeds the predetermined level. The purpose of the present invention is to send out a video signal having a quasi-peak signal that allows all of the processing circuits to operate satisfactorily.

Structure of the Invention The video detection circuit according to the present invention has multiplication means for regenerating the carrier wave signal component of a video intermediate frequency signal, which is an incoming input signal, using a predetermined filter means, and performing total multiplication detection of the reproduced carrier wave signal and the video intermediate frequency signal. The above-mentioned filter means is basically configured to reproduce a carrier wave signal having a substantially constant phase using a crystal filter or a phase-locked loop, but it is also possible to use a device such as an LC tuning circuit.

The video intermediate frequency signal is detected by the multiplication means, and the horizontal synchronizing signal pulse reaches 6 during the horizontal retrace period.

Either or both of the video intermediate frequency signal and the reproduced carrier signal are controlled to a predetermined phase so that the multiplicative detection phase is different between the first signal arrival period that does not include the next period and the second signal arrival period that is another period. be done.

During the second signal arrival period, the multiplication means detects the video intermediate frequency signal using the same mechanism as a known video detection circuit and sends out a video signal including the horizontal synchronization signal to its output terminal, but during the first signal arrival period, Since the detection phase is changed, a single peak signal whose level is changed in the white direction compared to the pedestal level of the video signal is sent out, and these horizontal synchronization signals and single peak signals are used to set the reference levels in the black and white directions. expressed. The detection phase during the arrival period of the third signal is changed so that the single peak signal sent out from the multiplier has the desired luminance signal level, but the detection phase is set at 2 with the pedestal level of the video signal as a reference.
It has the feature that it is possible to output any luminance level up to the 40% white peak level.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be briefly described below with reference to the drawings, and the same reference numerals will be used for parts having the same functions as those in FIG. 1 which shows a conventional configuration example.

In FIG. 2, the video intermediate frequency signal supplied to the first signal input terminal T1 is supplied to the signal removal circuit 4, the signal sampling circuit 6, and the second phase comparator 3, respectively. A signal pulse having a horizontal scanning period is supplied to the second signal input terminal T4, but this signal is located in the horizontal retrace period, and its width and phase are set so as not to include the horizontal synchronizing signal pulse, but the color burst signal The arrival period can be selected as appropriate. The signal removal circuit 4 and the signal extraction circuit 6 each perform a predetermined operation in response to a signal pulse from the terminal T4, and the conductor 4o removes the video intermediate frequency signal during the signal pulse arrival period (hereinafter referred to as the first signal arrival period). The output signals are transmitted to one conductor 60 via a phase shifter 6 and outputted from the signal sampling circuit 6, respectively, and are combined by an adder 7. is the above-mentioned signal) Since a video intermediate frequency signal whose carrier wave signal has a different phase between the pulse arrival period and another period (hereinafter referred to as the second signal arrival period) is sent out, the multiplier 2 is supplied via the conductor 10. The reproduced carrier wave signal is approximately constant.

Therefore, during the second signal arrival period, it essentially operates as multiplication detection of the same phase axis, and sends out the synchronizing signal pulse and the video signal component within the scanning period to the signal output terminal T2, and during the first signal arrival period, the phase shifter 60 phase Since the multiplicative detection phase shifted from the in-phase axis is given by the amount of shift, the luminance signal level X□ during this period
For □□), if the amount of phase shift is Δθ, then in the standard television system, if the reference black level of the video signal - maximum white peak signal amount amplitude vY is 100, then the synchronizing signal pulse amplitude V5 is 4.
0, where m is the maximum modulation degree of the video signal, which is 87.
It is specified as 6%.

Therefore, X (support)) = 1201 cos (θ - Δθ) + 11...
It is simplified as (2). Assume that the first phase comparator 2 constituting the multiplicative detection means is substantially a negative polarity detection9! 〉゛Then, the second signal arrival period is set to θ=180, and during this period, the video and image intermediate layer wave signals from the signal input terminal T are not given any phase shift, so the above-mentioned It operates on substantially in-phase axes such as On the other hand, during the first signal arrival period, the detection phase changes by the amount of phase change Δθ of the phase shifter 6.

For example, if the phase shift (Δθ) is zero, then θ=180
yoF) becomes x-0. This is the output reference level of the multiplier 2 with respect to the pedestal level (reference black signal level) like the burst signal arrival period in the video signal, and x =
0 indicates that the luminance signal level is 0%.

Assuming that the phase shifter 6 gives a phase shift of Δθ - 90, x = 120% from the above @) formula, and the brightness level is 0% when the output level of the multiplier 2 for the first signal arrival period is Δθ = 0. , and sends out a signal that exceeds the 100% white peak level. Furthermore, Δθ=1
Assuming that a phase shift of 80 is given, the above (2
) formula is: 240 (%), which indicates that the luminance signal level is transmitted when the detection phase in the first signal arrival period is inverted.

According to the present invention, as described above, the detection phase during the first signal arrival period is instantaneously changed, and the output level of the multiplier 2 during this period is set to a luminance signal level of 0 to 24%. It is possible to transmit at any level within the range of . Therefore, the first objective of the present invention, which is to send out a video signal having a unidirectional peak signal representing the amplitude reference in the positive direction, can be achieved by making the transition more than the single beacon. Depending on the form of use, the transition of the detection phase may be
Effects can be obtained even if the value is within 0. For example, the position of the unidirectional peak signal added according to the present invention is calculated using the phase of the synchronization signal pulse as a reference.

When used with known gate processing, the brightness level of the unidirectional peak signal at any level from 0 to 240% is effective as a reference signal for the white direction; If this is the case, the detection phase should be set to be close to or exceed the 100% white peak level (11).

good.

Next, an example of the form of use related to the second object of the present invention will be described. As is known, in a signal processing circuit such as a video detection circuit, it is practical to use it in the form of an integrated circuit together with other intermediate frequency amplification circuits or automatic gain control circuits, and this has not only economic advantages but also It is currently widely used due to its stability and performance advantages. In the video detection circuit, it is effective to operate the multiplier 2 at a low signal level in the configuration shown in FIG. It is known. In such a configuration, the video signal has the disadvantage that it is susceptible to distortion due to the differential phase and differential gain of the video amplifier. In particular, differential phase distortion causes hue distortion of the image, so it is desirable to remove it. requires a measure to increase the bias current of the video amplifier. The effect of differential phase distortion in a video amplifier is well known as the fact that differences in luminance signal levels give different phase shifts to the phase of the superimposed carrier color signal, but the same holds true for the phase of the color burst signal that serves as the reference phase. . In many cases, differential phase distortion for the carrier color signal component, which is one of the video signal components, distorts the phase relationship defined between the skin color signal component, which is the reference phase of vision, and other hue components. be. The phase of the skin color signal component has a predetermined phase difference from the phase of the burst signal in the color demodulator, and since these two signals differ in luminance signal level by 70% as is known, the image in the receiver is particularly Signal processing circuits such as amplifiers are susceptible to distortion. According to one application of the present invention described above, the first signal arrival period is set to include the color burst signal arrival period,
The brightness signal level sent by multiplier 2 during this period is 70%.
By setting the detection phase so that at least the color burst signal and the skin color signal and the carrier color signal component of the phase near it can be eliminated, the difference in the luminance signal level can be eliminated, and therefore the influence of differential phase distortion can be eliminated. In order to effectively remove the distortion related to the color burst signal, the transition of the detection phase required to satisfy this requirement of 13° is approximately 66.

The above description is an example of the relationship between the skin color signal component and the color burst signal, and various selections can be made regarding the setting of the detection phase of the first signal arrival period that includes the color burst signal arrival period. Needless to say, the color burst signal component transmitted in the vestigial sideband only undergoes a phase shift and no amplitude change occurs.

Next, the mode of use related to the third object of the present invention will be explained below. The first signal arrival period for transmitting the single peak signal may not be modulated by the luminance signal component, but may only include a modulated component by the color burst signal, as explained in the above two usage forms. . The scanning period in the second signal arrival period is modulated by the luminance signal, and therefore, considering the occurrence of distortion in the amplitude or phase characteristics of the transmission system, it is easy to think that it will exceed the specified 100% white peak level. It is also necessary to consider the occurrence of signal components exceeding the zero carrier level of the amplitude modulated wave.As mentioned above, the modulation degree of the television signal is 87.5% including the synchronization signal pulse. It is specified as the maximum, and the zero carrier level is approximately 12 in luminance signal level.
It is 0%. According to the present invention, the single peak signal that can be sent out by the video detection circuit can be up to 240%1, so it can be selected and set within the range of 120% to 240%.

As mentioned above, in the video detection circuit of the present invention, the amplitude level of the single peak signal can be selected from a wide range of desired values in the range of 0 to 240% of the brightness signal level, and at the same time, the amplitude level of the single peak signal can be selected from a wide range of desired values in the range of 0 to 240%. It has the feature of being able to select signals that include both the peak value and the pedestal signal level. If this single peak signal is set to include the arrival period of the color burst signal, the phase of the color burst signal sent out superimposed on the single peak signal also changes, but it is static. In practical terms, there is no drawback whatsoever. It is also possible to use the color burst signal and carrier color signal component from the output of the second phase comparator 3.

16 ゛The present invention is not limited to the embodiments described above, but can also be realized by configuring the carrier wave regeneration circuit side to be compatible with the implementation of the present invention as shown in FIG. 3, but the operations etc. are the same. Since there is, detailed explanation will be omitted. Further, in the description of the embodiment, a detailed explanation of the second phase comparator 2 has been omitted, but it goes without saying that it can be used as a PLL phase comparator to obtain the control signal component of the intermediate frequency carrier signal generator 10. Not only that, but also other intercarrier audio signals etc. can be obtained from the output terminal T3 as needed.

Effects of the Invention In the video detection circuit according to the present invention, by shifting the detection phase during the first signal arrival period excluding the synchronization signal pulse arrival period during the horizontal retrace period, a white direction reference is created in the video signal to be sent out. A single peak signal is generated, and reference information regarding the amplitude of the video signal can be transmitted between the peak value or the pedestal level of the synchronizing signal pulse, which is the reference for the black direction. 1 peak signal to 0
The luminance signal level is configured such that it can be set to any level within the range of luminance signal levels of ~240%. Therefore, once the DC component is lost, it is regenerated.

It has great industrial value, as it can be used as a reference signal when applying automatic gain control to video signals.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the basic configuration of the video detection device.
FIGS. 2 and 3 are block diagrams of a video detection device according to an embodiment of the present invention. 4... Signal removal circuit, 6... Signal extraction circuit, 6... Phase shifter, 7... Adder,
2, 3... Multiplier. 1...Intermediate frequency carrier signal generator, T1...
...First signal input terminal, T4... terminal,
T2. T3...Output terminal.

Claims (1)

[Claims] When detecting amplitude modulated television signals,
A video detection device that reproduces a video signal by making the detection phase different between a first signal arrival period excluding a synchronization signal pulse arrival period within a horizontal retrace period and a second signal arrival period which is another period.