KR910005808Y1 - Amplification and separating circuit of color difference signal - Google Patents

Abstract

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Description

Amplification and Separation Circuit of Color Difference Signal

1 is a conventional circuit diagram.

2 is a circuit diagram of the present invention.

* Explanation of symbols for main parts of the drawings

10: differential amplifier circuit 20: control unit

30: load detector 40: low pass filter

P1-P3: Input terminal P4: Output terminal

R1-R21: Resistance VR1: Variable resistor

Q1-Q15: Transistor C1-C4: Capacitor

TC1: Trimmer Capacitor + Vcc: Power

LPF: Low Pass Filter

In the video camera of the present invention, the present invention relates to an amplification and separation circuit of a chrominance signal capable of amplifying and separating a color signal at an accurate reference signal level without affecting noise.

The color signal of the video camera is obtained by amplifying and separating the color difference signal obtained through the PREAMP and MATRIX circuits. Conventionally, the color difference applied to the input terminals P1 and P2 as shown in FIG. The signals 1 and 2 are differentially amplified and amplified in the differential amplification circuit 10 including the amplifying transistors Q1 to Q4 through a low pass filter LPF composed of a buffer transistor Q5 and a passive element. After passing only the color signal band, the color signal is output to the output terminal P4 through the buffer transistor Q6. However, since the output resistors R1 and R2 connected to the transistors Q1 and Q2 are fixed, the reference signal is fixed. Not only the level is incomplete, but also the blanking signal is also amplified in the pickup device such as the solid state image pickup device, which causes unnecessary noise in the output color signal.

In addition, the passive element includes a low pass filter (LPF) for removing the high frequency part from the color signal differentially amplified in the differential amplifier circuit 10 and passing through the buffer transistor Q5 and passing only the frequency of the color signal band of 0.7 MHz or less. Therefore, there is a disadvantage that the noise is generated in the peripheral circuit because the bulky and unnecessary magnetic field is formed by the use of passive elements, and the circuit configuration is complicated.

The object of the present invention is to stabilize the reference signal level by replacing the fixed load of the differential amplifier circuit that amplifies the color difference signal with the active load in amplifying and separating the color signal in the video camera. Differential amplification circuit that differentially amplifies the chrominance signal input by eliminating the signal amplification during the blanking period, eliminating unnecessary noise in composing the color signal and replacing the low pass filter separating the color signal with an active element to eliminate the influence of the magnetic field. The control unit is configured to be inoperative during the blanking period, and a load detection unit configured to detect an output of the differential amplifier circuit as an active element, and the output of the load detection unit is configured to output a color signal through a low pass filter unit configured as an active element.

Hereinafter, the present invention will be described in detail by the accompanying drawings, the configuration and operation effects as follows.

2 is a circuit diagram of the present invention, a vehicle amplifier circuit 10 for differentially amplifying an input color wave signal, a control unit 20 for stopping the operation of the differential amplifier circuit 10 during a blanking period, and the differential amplifier circuit ( 10) and a load detection circuit 30 for detecting the differential amplification output as an active load, and a low pass filter unit 40 for passing only the color signal band through the detection signal of the load detection unit 30 to the active element.

That is, according to the present invention, a differential amplifier circuit is applied such that the color difference signal applied to the input terminals P1 and P2 is differentially amplified by the differential amplifier transistors Q11 to Q14 to which the bias resistors R16 and R17 and the variable resistor VR1 are connected. And the control unit 20 drives the transistors Q7 and Q8 connected to the bias resistors R11-R13 and the noise canceling capacitor C2 by the blanking signal applied to the input terminal P3. It is configured to control the driving of the differential amplifier circuit 10.

The load detector 30 detects the output of the differential amplifier circuit 10 output from the collector side of the transistor Q12 through the PNP transistors Q9 and Q10 connected to the load resistors R14 and R15. The low pass filter unit 40 is configured such that the output of the differential amplifier circuit 10 is blocked by the time constants of the resistor R20, the capacitors C3, C4, and the trimmer capacitor TC1. Vcc drives the buffer transistor Q15 through the bias resistors R18-R21 to apply a color signal to the rear end of the output terminal P4.

Here, the values of the resistors R14 and R15 are set equal.

In the present invention configured as described above, the color difference signal obtained through the preamplifier and the matrix circuit is applied to the input terminals P1 and P2 of the differential amplification 10, and a negative blanking pulse is applied to the input terminal P3 of the controller 20. Apply.

First, when the negative blanking signal is applied to the input terminal P3 and applied to the base of the transistor Q7, the transistors Q7 and Q8 constituted by the differential amplifier are operated, and accordingly, the emitters of the transistors Q7 and Q8 are operated. The rotor potential is lowered.

In other words, when a negative blanking signal is applied to the input terminal P3, the transistors Q7 and Q8, which are differential amplifiers, operate to reduce the emitter potential of the transistors Q7 and Q8.

When the emitter potential of the transistors Q7 and Q8 is lowered, the base potential of the transistors Q13 and 14 directly connected thereto is also lowered, and the transistors Q13 and Q14 are 'turned off', so that the input terminal ( The operation of the transistors Q11 and Q12 for differentially amplifying the color difference signal input to P1) and P2 is stopped to stop the differential amplification of the color difference signal.

Therefore, when the negative blanking signal is applied, the differential amplification of the color difference signal is not performed, so that an unnecessary signal due to the signal amplification during the blanking period does not affect the color signal as noise.

However, when the blanking signal is not applied to the input terminal P3, the transistor B is provided by providing an existing bias to the base of the transistors Q13 and Q14 by a fixed bias by the resistors R12 and R13 of the controller 20. The color difference signals (+ R and -R applied to the input terminals P1 and P2 from the transistors Q11 and Q12 are turned on and the transistors Q13 and Q14 are 'turned on'). , + G and + B and -B) are differentially amplified.

The color difference signal differentially amplified by the transistors Q11 and Q12 is outputted to the load detector 30 including the transistors Q9 and Q10 and then passed through the resistor R20 to the low pass filter 40 as an active element. It is applied to the base of transistor Q15.

Since the bases of the transistors Q13 and Q14 are connected together and have the same bias, the sum of the emitter currents flowing through the transistors Q11 and Q12 is always constant, but the transistors Q11 and Q12 are inputted by the input color difference signal. Since the induced voltages are different from each other, the output current is changed by the difference of the voltages, and the difference is amplified.

In addition, in the load detector 30 composed of the transistors Q9 and Q10 and the resistors R14 and R15, the values of the resistors R14 and R15 are the same (R14 = R15) and the bases of the transistors Q9 and Q10 are the same. Since the collector currents of the transistors Q9 and Q10 are equal because they are connected together and act by a common bias, the differential amplification becomes more stable than the differential amplification operation due to the fixed load.

That is, the load detection unit 30 stabilizes the reference signal level by using an increase element, and adjusts the variable resistor VR1 connected between the emitters of the transistors Q11 and Q12 to adjust the gain ratio of the output color signal. do.

The color signal differentially amplified by the differential amplifier circuit 10 and detected by the load detector 30 is output to the output terminal P4 through the transistor Q15 to which the bias resistors R18 to R20 are connected. The unit 40 passes only a predetermined frequency and blocks other frequencies. The frequency is determined by the resistor R20, the capacitors C3, C4, and the trimmer capacitor TC1 connected to the transistor Q15.

That is, since the differentially amplified by the differential amplifier circuit 10 and the color signal detected by the load detector 30 is a high frequency including harmonic noise, the low pass filter unit 40 passes a frequency band (0.7 MHz or less) required for the color signal. The cutoff frequency of the low pass filter 40 is determined by the resistor R20, the capacitors C3, C4 and the trimmer capacitor TC1, and the low pass frequency can be adjusted by varying the trimmer capacitor TC1. .

Therefore, a stable color signal can be obtained on the output side of the low pass filter unit 40. By using an active element instead of a passive element to pass only the color signal band, the effect of the magnetic field can be eliminated. It can be.

As described above, the present invention eliminates unnecessary noise in constituting the color signal by disabling the differential amplifier circuit that differentially amplifies the color difference signal during the blanking period, and detects the output of the differential amplifier circuit as the active load to detect the reference signal of the differential amplifier circuit. By stabilizing the level and outputting the color signal through a low pass filter part composed of active elements, the amplification and separation of the color signal can be performed at a stable level.

Claims (4)

A video camera having a differential amplifier circuit 10 for differentially amplifying a color difference signal input through transistors Q11 to Q14, which are differential amplifiers, for controlling the operation of the differential amplifier circuit 10 to be stopped during a blanking period. The load detection unit 30 detects the output of the control unit 20 and the differential amplifier circuit 10 and stabilizes the reference signal level, and passes the detection signal of the load detection unit 30 only through a color signal band, and consists of active elements. Amplification and separation circuit of a color difference signal composed of a low pass filter unit (40). 2. The control circuit of claim 1, wherein the controller 20 is connected such that a blanking signal applied to the input terminal P3 is applied to the base of the transistor Q7, and the resistors R12 and R13 and the capacitors are connected to the base of the transistor Q8. And a common emitter contact of the transistors (Q7) and (Q8) connected to the base of the transistors (Q13) and (Q14) of the differential amplifier circuit (10). The collector side of the transistors of the differential amplification circuit 10 according to claim 1, wherein the collector side of the transistors Q9 and Q10 having the same value of the resistors R14 and R15 connected to the emitter side and the base of the load detection unit 30 coupled to the emitter side. (Q11) Amplification and separation circuit of a color difference signal configured to be connected to the collector side of (Q12). The low-pass filter unit 40 of claim 1, wherein the detection signal of the load detection unit 30 is connected to the base of the transistor Q15 through the resistors R18-R20, and the low pass of the base of the transistor Q15. A color difference configured to connect a resistor R20 for setting a frequency, a capacitor C3, a C4, and a trimmer capacitor TC1, and a load resistor R21 and an output terminal P4 connected to the Emmy side of the transistor Q15. Signal amplification and separation circuit.