JPS6248946B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image quality adjustment device for a television receiver.

Conventionally, the image quality adjustment device for television receivers is
The reproduction waveform is set to be optimal when a standard transmission signal is received. A in FIG. 1 is a video detection result of a standard received signal, and shows a state in which there is a slight pre-overshoot and overshoot due to the band limitation by the VIF filter. In order to optimally reproduce this signal on a CRT, the constants of the image quality circuit are determined so that the pre-overshoot and overshoot amounts are equal, as shown in B. However, in actual reception conditions, waveforms such as C and D are often reproduced as video detection waveforms due to antenna system mismatching, proximity ghosts, and the like. When this waveform is reproduced on a CRT through a circuit with preset image quality constants, the C and D states are extremely emphasized, and the pre-overshoot and overshoot become very noticeable, resulting in an unsightly image. .

The present invention provides means for correcting such drawbacks.

FIG. 2 shows a first embodiment of the present invention. FIG. 3 shows a standard detection signal, and FIG. 4 shows a detection signal distorted due to the causes mentioned above. An input video signal is supplied from A in FIG. 2 and split into two. Corresponding signal waveforms are a and e in FIG. 3 and a and e in FIG. 4. When one of these is passed through the second-order differentiator circuit 1, it becomes a waveform corresponding to b and f in FIGS. 3 and 4. Furthermore, when the signal is passed through the small time delay circuit 2, it becomes the waveforms c and g in FIGS. 3 and 4. This delay time is externally variable, and is optimally changed according to the distortion of the input signal. If the output signals of circuits 1 and 2 are combined in addition circuit 3, d and h in Figs. 3 and 4 are obtained.
As shown in the figure, it is possible to perform image quality correction in an optimal state regardless of the distortion of the input signal. 4 is a circuit for changing the frequency versus amplitude characteristic of the reproduced image, and its output is supplied from B to the subsequent circuit.

FIG. 5 shows a specific circuit example. The portions surrounded by broken lines and labeled with symbols correspond to the blocks in FIG. 1 connects the input signal to the impedances L ₂ and C ₃ of the inductor L ₂ and capacitor C ₃
The amount of delay is proportional to _√2 · ₃ , and in the present invention, both L ₂ and C ₃ are variable. In No. 2, second-order differentiation is performed by passing the signal through a series resonant circuit formed by impedances L _{1 and} C ₁ of an inductor L 1 and a capacitor C ₁ . 3 is a circuit that supplies one signal from the base of the transistor Q ₆ and the other signal from the emitter and synthesizes them at the collector. transistor Q ₆
The signal input from the base of is supplied to the base of transistor _Q7 through the emitter of transistor _Q6 . The collectors of transistors Q ₆ and Q ₇ are the ( _{Q 2 , Q 3 )} , (Q ₄ , Q ₅ ) of transistors Q 2 to Q 5.
The mixing ratio at the common collector of (Q ₃ , Q ₅ ) and (Q ₂ , Q ₄ ) can be changed by an external voltage using a double transformer circuit connected by a common emitter. Capacitors C ₁ and C ₂ and impedance C ₂ of inductor L ₁ (C ₁ , L ₁ ) are connected to the emitter of transistor Q ₆ between low impedances, so the gain of high frequency components is high. There is. The output signal of the resistor _R11 is a signal whose frequency and amplitude characteristics change depending on the voltage applied from the outside by the variable resistor _VR1 . Note that V ₁ and V ₂ are bias potentials.

FIG. 6 shows group delay characteristics and waveform changes.
The horizontal axis is the frequency, and the vertical axis is the delay time t. As shown in a, the waveform passed through a circuit with characteristics a' does not lose the balance between pre-overshoot and overshoot. When the delay in the high range becomes large, as shown in b', the waveform becomes overshooting, followed by linking, as shown in b. A waveform with a small amount of delay in the high range, such as c', has a pre-overshoot and a shoulder at the falling edge, as shown in c. If we take the sum of the respective characteristics of b' and c', , we can see that the amount of high-frequency delay is large, flat, or small, as in d'.
Characteristics can be created. Therefore, the waveforms have large overshoots as shown in d and , respectively.
Creates a waveform with equal amount and large pre-overshoot. No matter which input waveform A, C, or D of the waveform shown in Figure 1 is received, if it is reversely corrected through the characteristics of d and , it will be optimal regardless of the distortion of the input signal waveform. can provide a wide range of waveforms.

FIG. 7 shows a first means for realizing this. 1a is a group delay characteristic correction circuit having the characteristic c' in FIG. 6, which is capable of changing only the group delay circuit without changing the amplitude characteristic. The output of the circuit 1a is supplied via a signal delay circuit 2a and an image quality adjustment circuit 3a to a circuit for varying frequency versus amplitude characteristics, and the output signal is supplied from B to a subsequent stage. An example of a circuit with the characteristics shown in FIG. 6 is shown in FIG. Blocks surrounded by broken lines and labeled with symbols correspond to those in FIG. The circuit 1a is constituted by a lattice circuit, and the inductors L ₁ and L ₂ are wound with a coupling coefficient of 1. By changing the impedance of inductor L ₃ or capacitor C ₃ in this circuit, it is possible to obtain changes as shown in c' and , in FIG. 6. The circuit 2a is a signal delay line, and the circuit 3a is an image quality correction circuit using the emitter peaking method, and by changing the variable resistor _VR1 , the frequency versus amplitude characteristic can also be made variable. However, the emitter peaking circuit has a delay characteristic like b' in FIG. Therefore, this comprehensive characteristic is shown in Figure 6.
It is possible to obtain both properties of d′. Note that it is also possible to use the circuit shown in FIG. 5 as the circuit 3a. In this case, circuit 1
It is sufficient that a has a total coefficient m<1.

Note that if the color demodulation signal is supplied from the output of the circuit 1a, precise adjustment of the color signal and the luminance signal is possible.

FIG. 8 shows a second means. Reference numeral 1b designates a circuit for switching signal delay lines, each having a different group delay characteristic, whose delay characteristic changes as shown in c' in FIG. 6, and having the same amplitude characteristic. 2b is a circuit for varying frequency versus amplitude characteristics. FIG. 10 shows an example of the circuit shown in FIG. 8. The broken line portion corresponds to the block in FIG. 1b is externally connected to the delay line DL.
The configuration is such that it can be switched. Both switches _SW1 and _SW1 are interlocked. Note that this switch may be mechanical or electronic. Since 2b is the same emitter peaking circuit as 3a in FIG. 9, its explanation will be omitted. As in the case of FIG. 9, the circuit of FIG. 5 can also be used for 2b, but it goes without saying that in this case, it is necessary to change the group delay characteristics of each delay line DL. In short, if the input signals are A, C,
When D is received, the correction characteristic is d in Figure 6.
This is to make it look like this.

As described above, if the present invention is used,
Since input waveform distortion caused by antenna mismatching, proximity ghost, etc. can be corrected, optimal reproduced image quality can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram showing distortion of an input signal, FIG. 2 is a block circuit diagram of the first embodiment of the present invention, and FIG.
The figure and Figure 4 are waveform diagrams of the signals at each part in Figure 2,
5 is a diagram showing an example of the circuit shown in FIG. 2, FIG. 6 is a diagram showing the relationship between group delay characteristics and waveforms, and FIG.
8 is a block circuit diagram of the third embodiment of the present invention, FIG. 9 is a diagram showing a specific example of FIG. 7, and FIG. 10 is a diagram showing a specific example of FIG. 8. FIG. 1...Second-order differentiator circuit, 2...Delay circuit, 3...Addition circuit, 4...Circuit that can change frequency versus amplitude characteristics, 1a
...Group delay characteristic correction circuit, 2a...Signal delay circuit, 3
a... Image quality adjustment circuit, 1b... Delay line switching circuit, 2b
...A circuit that can change the frequency versus amplitude characteristics.

Claims (1)

[Claims] 1. An input signal is divided into two signals, a first signal and a second signal.
A signal is added to a delay circuit that can change the delay time, and a second signal is added to a second-order differentiator circuit, and the first signal delayed by the delay circuit and the second signal subjected to second-order differentiation processing are obtained. An image quality adjustment device characterized in that a synthesis circuit synthesizes the signals and supplies the synthesized signal to a circuit that can change frequency versus amplitude characteristics. 2. Adding the input signal to a group delay characteristic correction circuit that can change group delay characteristics, adding the output of this group delay characteristic correction circuit to a signal delay circuit, and supplying the output of the signal delay circuit to a circuit that can change frequency versus amplitude characteristics. An image quality adjustment device characterized by: