KR910003473Y1 - Automatic gain control pulse generating circuit - Google Patents

Abstract

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Description

Automatic Gain Control Pulse Generator Circuit

1 is a block diagram of an automatic gain control pulse generation circuit of the present invention.

2 is a circuit diagram of an automatic gain control pulse generation circuit as one embodiment of the invention.

3 is an output waveform diagram of each part of the automatic gain control pulse generating circuit of the present invention.

* Explanation of symbols for main parts of the drawings

A: Clamping circuit B: Low pass filter

C: amplification and phase inversion roller: unstable multivibrator

E: Amplification and phase inversion circuit R _{1 ~} R ₁₄ : Resistance

C _{1 to} C ₈ : capacitors TR _{1 to} TR ₃ : transistors

D _1, D ₂ : Diode IC: Integrated Circuit

The present invention relates to an automatic gain control pulse generation circuit required for a positive modulation method in TVs. In particular, the input signal is inputted through a clamping circuit, a low pass filter, an amplification and phase inversion circuit, and an unstable multivibrator. The present invention relates to an automatic gain control pulse generating circuit that makes a kid automatic gain control operation accurate by generating a pulse).

In general, in case of a broadcasting system in which image modulation is positive modulation, keyed automatic gain control is used. In this automatic gain control method, an external keying pulse must be made.

In other words, the positive modulation method needs to make accurate keying pulses by using the kid automatic gain control unlike the submodulation method.

Therefore, the conventional automatic KID control circuit has a complicated circuit configuration and cannot produce accurate keying pulses, and therefore, the automatic KID control circuit cannot operate correctly and the circuit configuration is inefficient and inefficient due to the increase in the number of components due to complexity. Had The present invention amplifies and inverts an input video signal through an amplification and phase inversion circuit through a clamping circuit and a low pass filter, and applies the inverted signal to the reset terminal of an unstable multivibrator. In addition, the signal output through the unstable multivibrator is a keying pulse through the amplification and phase inverting circuit to generate the key automatic gain control operation can be made accurately. As follows.

As shown in FIGS. 1 and 2, the video signal input from the video signal input terminal V-IN includes a clamping circuit composed of a resistor R ₁ , a diode D ₁ , and a resistor R ₂ . Is applied to a low pass filter (LPF) consisting of a condenser (C ₁ ), a mixing resistor (R ₃ ) (R ₄ ), and a condenser (C ₂ ). ) Output signal is amplified and phase inverted consisting of transistor (TR ₁ ), resistor (R ₅ ), capacitor (C ₃ ) (C ₄ ) and resistor (R ₆ ), transistor (TR ₂ ), and resistor (R ₇ ) Connect to the reset terminal R of the unstable multivibrator circuit (D) consisting of resistors (R ₈ to R ₁₀ ) capacitors (C _{5 to} C ₇ ) and integrated circuits (IC) through the circuit (C). The output terminal OUT of the stable multivibrator circuit D includes an amplification and phase inversion circuit composed of a capacitor C ₈ , a resistor R ₁₁ to R ₁₄ , a transistor TR ₃ , and a diode D ₂ . Connected as above Referring to the effect of this invention is configured as follows.

First, when an image signal as shown in FIG. 3A is input from the image signal input terminal V-IN, the image signal is converted into a resistor R ₁ diode D ₁ and a resistor R ₂ of the clamping circuit. Pass the positive potential only through OV and fix the negative potential and clamp the negative potential to output a waveform as shown in FIG. 3b.The capacitor C ₁ and the resistance of the low pass filter This input signal is passed through (R ₃ ) (R ₄ ) and condenser (C ₂ ), and the high frequency is cut off, and the high frequency is blocked to accumulate the output waveform as shown in FIG.

The waveform signal output as described above is amplified by the transistors TR ₁ , capacitors C ₃ , C ₄ , and resistors R ₅ to R ₇ transistors TR ₂ of the amplification and phase half-circuit c. And an output waveform as shown in FIG. 3D reversed in phase and input to the reset terminal R of the unstable multivibrator (d).

At this time, the charge / discharge time constant of the unstable multivibrator (D) can be set to exactly match the input pulse. Therefore, since one cycle comes from the input signal at intervals of 63.51 μsec, it is set to one cycle of the unstable multivibrator (C).

Therefore, the unstable vibrator (D) is charged by resistance (R ₁₀ + R ₈ ) × capacitor (C ₆ ) and discharge by resistance by time constants by capacitor (C ₆ ), resistor (R ₈ ), (R ₁₀ ). (R _10), is according to occur by a capacitor (C ₆₎ slightly shorter than the charging time is give by the input signal a discharge time was set so that the number of charge-discharge time constant slightly longer than the incoming signal.

The reason for this is to ensure that the input signal is completely within the required output signal.

Accordingly, the signal passing through the unstable multivibrator C is discharged time (t ₂ ) = R ₁₀ × C ₆ and the time to be charged (t ₁ ) = (R ₁₀ compared with the waveform shown in FIG. 3d. + R ₅ ) × C ₆ , the discharge time t ₂ is long, the charging time t ₁ is short, and the waveform as shown in FIG. 3e is output through the output terminal of the unstable multivibrator (c). Output the waveform.

The waveform thus output is amplified by the capacitors C ₈ , resistors R ₁₁ , R ₁₂ , and transistor TR ₃ of the amplification and phase inversion circuit D, and at the same time the collector terminal of the transistor TR ₃ Through the phase inversion through the resistor R ₁₄ and the diode D ₂ , the phase inverted high signal as shown in FIG. 3f is output. This signal is a keying signal.

As described above, the present invention is a pulse generation circuit composed of a clamping circuit low pass filter amplification and phase inversion circuit unstable multivibrator amplification and phase inversion circuit to generate an accurate keying pulse. The keying pulse can operate the kid automatic gain control circuit accurately and can provide an advantage that can completely solve the inefficiency caused by the increase in the number of parts resulting from the complicated circuit configuration.

Claims (1)

A clamp circuit consisting of resistors R ₁ , R ₂ , and diodes D ₁ clamping the input image signal to a predetermined level, and a predetermined width with respect to the signal input from the clamp circuit A low pass filter (B) consisting of resistors (R ₃ ), (R ₄ ) and capacitors (C ₁ ), (C ₂ ) for outputting only the signal of, and amplifying the signal input from the low pass filter (B) Amplification and phase inversion circuits consisting of transistors TR ₁ , TR ₂ , resistors R ₅ to R ₇ , capacitors C ₃ , and C _{4 that} reverse the phase while It consists of the time constant element of the integrated circuit (IC), the resistors (R ₈ to R ₁₀ ) and the capacitors (C ₆ to C ₇ ) to which the input from the circuit (C) is inputted so as to change the same pulse as the above image signal. Unstable multivibrator circuit (D), capacitor (C ₈ ) for reversing the phase input from the unstable multivibrator (D), resistors (R ₁₁ to R ₁₄ ), and An automatic gain control pulse generation circuit comprising an amplification and phase inversion circuit (e) consisting of a transistor (TR ₃ ).