JPH0332148Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a differential phase correction circuit suitable for application to a television receiver.

[Conventional technology]

As is well known, the video detector of a television receiver has non-linear phase characteristics, and the phase of the color subcarrier of the video signal supplied to it varies according to the amplitude of the luminance signal. The hue changes depending on the phase.

In order to correct this differential phase, it is conceivable to use a correction circuit 10 as shown in FIG. 6.

In the same figure, terminal 1 is connected to the seventh
A video signal shown in the figure is supplied, which is supplied to a chroma phase shifter 2, and also to a Y/C separator 3, where a luminance signal is separated, and the separated luminance signal is supplied to an amplitude detector 4. The amplitude level of the input video signal is detected, and the chroma phase shifter 2 is controlled according to this amplitude level, thereby correcting the phase of the color subcarrier included in the input video signal. terminal 5
The phase-corrected video signal obtained is supplied to a video output circuit and a chroma separation circuit (both not shown).

The differential phase generally tends to change in a fixed direction depending on the amplitude level of the luminance signal Y. Therefore, if the differential phase is controlled so that the phase delay amount or phase advance amount has an opposite tendency depending on the amplitude level, the differential phase Phase can be corrected.

[Problem that the invention attempts to solve]

By the way, as mentioned above, the differential phase correction circuit 10
In addition to the chroma phase shifter 2, Y/
Since the C separator 3 and the amplitude detector 4 are required, there is a drawback that the circuit configuration becomes complicated.

Therefore, this invention solves these problems and proposes a differential phase correction circuit that has a simple configuration and can achieve the same differential phase correction as described above.

[Means for solving problems]

In this idea to solve the above problems,
As shown in FIG. 1, a phase compensation circuit 20 constituted by a series circuit of a resistor 21, an inductance element 22, and a variable capacitance element 23 is provided on a transmission path for a video signal subjected to image detection.

[Effect]

Since a video signal of opposite polarity having a DC level as shown in FIG. 2 is applied to both ends of the variable capacitance element 23, the capacitance of the variable capacitance element 23 is varied according to this DC level, and thus the phase compensation circuit 20
The amount of phase shift changes. Therefore, when the differential phase characteristic of the video detection stage is a delayed phase characteristic, the variable capacitance element 23 has a capacitance characteristic as shown in curve 1 of FIG.
By using this phase compensation circuit 20, differential phase distortion received at the video detection stage can be corrected.

〔Example〕

FIG. 1 shows a differential phase correction circuit 10 according to this invention.
This is a system diagram showing an example, and the video signal S _io after image detection supplied to the input terminal 1 is connected to the resistor 11.
through the transistor, in this example PNP type transistor _Q1 . A pedestal clamp circuit 12 is connected to the base of the transistor _Q1 , and its predetermined pedestal level is clamped to a predetermined level determined by the volume 13, so that the base of the transistor _Q1 has this pedestal clamped video signal. Signal S _io (Figure 2)
is supplied. The sink tip level may be clamped instead of the pedestal level.

The emitter of transistor Q ₁ is connected via a resistor 15 to the power supply V _CE , and its collector is connected via a resistor 16 to a reference potential point, in this example a zero potential point. The resistance values of the resistors 15 and 16 are made equal. Therefore, when a video signal having the same phase as the video signal _Sio shown in FIG.
Reverse polarity video signal _io (second
) is output.

A phase compensation circuit 20 is connected between the emitter and collector of the transistor _Q1 . Phase compensation circuit 2
0 consists of a series circuit of a resistor 21, an inductance element 22, and a variable capacitance element 23. In this example, the resistor 21 is connected to the emitter side, the inductance element 22 is connected to the collector side, and there is a The variable capacitance element 23 is connected so that its cathode is on the resistor 21 side, and the output terminal 5 is led out from the cathode side.

As a result, the DC level of the video signal S _io obtained on the cathode side of the variable capacitance element 23 is applied to the cathode side, and the DC level of the video signal _io obtained on the collector side of the transistor Q ₁ is applied to the anode side. . As the variable capacitance element 23, a nonlinear capacitance characteristic element such as a Zener diode or a varicap is used.

The output video signal S _put is supplied via the buffer amplifier 26 to the above-mentioned video output circuit and chroma separation circuit.

Now, the elements 21 constituting the phase compensation circuit 20,
If the values of 22 and 23 are R, L, and C, then the transfer function G of this phase compensation circuit 20 is G=V _put /V _io =1−ω ² LC−jωCR/1−ω ² LC+jωCR …… (1) However, ω is given by the angular frequency.

Here, since the resistance values of resistors 15 and 16 are equal, |V _put /V _io |=1, so the amplitude characteristic of equation (1) is constant at any amplitude level, and the phase φ
changes based on equation (2).

φ=tan ^-1 [2ωCR(1-ω ² LC)/(ωCR) ^2- (1-
ω ² LC) ² ]...(2) In equation (2), the capacitance C changes depending on the magnitude of the voltage V _D applied to both ends of the variable capacitance element 23.

Note that since the video signal S _io is pedestally clamped, the amount of phase shift of the burst signal S _B inserted at the pedestal level is fixed, and therefore,
The phase φ of the carrier chrominance signal with respect to the burst signal weighted into the luminance signal Y varies depending on the amplitude level of the video signal S _io , _io available at the emitter and collector of the transistor Q ₁ .

The emitter potential V _E of the transistor Q ₁ changes around the pedestal potential V _EP according to the input video signal S _io as shown in FIG. 2, and the collector potential V _c is a potential V _CP lower than V _EP by a predetermined level. Therefore, voltages (V _A , V B , V _B ,
V _C …) is applied.

Therefore, as the variable capacitance element 23, the curve l in FIG.
If we use voltage-capacitance characteristics as shown in , the capacitance C will be inversely proportional to the amplitude level, as shown in C _A , C _B , C _C , etc., that is, when the amplitude level is small, the capacitance will be large. Because it changes like this,
(2) When using such a variable capacitance element 23
The amount of delay of the phase φ shown in the equation becomes smaller as the amplitude level becomes larger.

From this, the burst signal S _B obtained at the output terminal 5 is delayed by a predetermined phase by passing through the phase compensation circuit 20, and this burst signal S _B
The delay phase of the carrier color signal S _C relative to the carrier color signal S C decreases as the amplitude level of the luminance signal Y increases.

On the other hand, since the phase characteristics of the video detection stage are delayed as the amplitude level of the luminance signal Y increases as described above, the phase characteristics of the video detection stage are inversely corrected by the phase compensation circuit 20 and output to the output terminal 5. The phase relationship of the carrier color signal S _C with respect to the obtained burst signal S _B is:
This almost matches the positional relationship of the carrier color signal S _C with respect to the burst signal S _B before image detection. As a result, the differential phase distortion is corrected, and variations in hue due to changes in the amplitude level of the luminance signal Y are prevented.

Note that the burst signal is
Although the phase of S _B itself is delayed by a predetermined amount, this amount of delay can be compensated by adjusting the delay time of a delay circuit provided in the luminance signal system.

The change in capacitance C with respect to the applied voltage V _D of the variable capacitance element 23 is as shown in curve l in Figure 3.
It differs depending on the value of V _D , and which region of the voltage-capacitance characteristic is used can be adjusted by the pedestal clamp level V _EP , so that the phase characteristic of the video detection stage is reversely corrected. The pedestal clamp level is set so that the voltage-capacitance characteristics are
V _EP is set.

Note that when sufficient capacitance cannot be obtained with only the capacitance C of the variable capacitance element 23, this variable capacitance element 23
A fixed capacitor can be connected in parallel with .

If the phase characteristic of the video detection stage is a leading phase characteristic opposite to the above, either invert the polarity of the video signal _Sio applied to input terminal 1, or use an NPN type transistor _Q2 as shown in Figure 4. You can use .

In these cases, the relationship between the emitter output S _io and the collector output _io of the transistors Q ₁ and Q ₂ is as shown in FIG. 5, so the relationship between the voltage V _D applied to the variable capacitance element 23 and the variable capacitance C is is reversed, and the differential phase distortion caused by the video detection stage can be corrected.

Note that the compensation characteristic of the phase compensation circuit 20 does not need to be selected to have a completely opposite phase characteristic to the phase characteristic of the video detection stage, and it is sufficient to correct the hue change to the extent that it is not visually noticeable. Therefore, a linear variable capacitance characteristic can be used in this case.

[Effect of idea]

As explained above, according to this invention, by simply providing the simple phase compensation circuit 20, the differential phase generated in the video detection stage can be almost reliably corrected.
For this reason, the variation in hue due to changes in the amplitude level of the luminance signal Y is reduced, or becomes almost stepless,
The hue becomes more stable.

Since the phase compensation circuit 20 in this invention is simply a series circuit of L, C, and R, the circuit configuration is extremely simple. Moreover, since the differential phase can be corrected only by this phase compensation circuit 20, the circuit configuration can be significantly simplified compared to the case described above, and therefore, this invention is extremely useful in practical use.

[Brief explanation of the drawing]

1 and 4 are connection diagrams showing an example of the differential phase correction circuit according to this invention, FIGS. 2, 3, and 5 are diagrams for explaining the operation, respectively, and FIG. 6 is a diagram showing an example of the differential phase correction circuit according to this invention. FIG. 7 is a system diagram showing an example of a differential phase correction circuit for explanation, and is a waveform diagram of a video signal. 10 is a differential phase correction circuit, 20 is a phase compensation circuit, 21 is a resistor, 22 is an inductance element,
23 is a variable capacitance element.

Claims (1)

[Scope of utility model registration request] The detected video signal is supplied to a transistor, and a phase compensation circuit configured as a series circuit of a resistor, an inductance element, and a variable capacitance element is connected between the emitter and collector of the transistor, and the video signal is output from one end of the variable capacitance element. A differential phase correction circuit from which an output terminal is derived, and the differential phase generated in the video detection stage is compensated by the phase compensation circuit.