KR200241480Y1 - Noise eliminating circuit of video signal - Google Patents

Abstract

The present invention relates to a video signal noise canceling circuit, and particularly a circuit for removing noise by varying filtering characteristics of a low pass filter that performs a noise canceling operation according to the electric field strength of a received signal and whether the received signal is an external signal. .

In the prior art, the black noise signal is removed from the low pass filter by detecting only black noise in the image noise detector. The low pass filter removes noise because the time constant is always fixed to a constant value regardless of the electric field strength of the input video signal. In addition, unnecessary filtering is also applied to the strong electric field input signal, which is not necessary, so that the frequency characteristic of the input video signal is deteriorated.

The present invention is configured to detect the input field detection means for determining the electric field strength of the received signal from the result of comparing the automatic gain control (AGC) detection voltage to the reference voltage to solve the above problems The low pass filter variably controls the filter time constant according to the electric field strength, and also configures an external signal detection means for detecting whether the received signal is an external signal, and controls the low pass filter not to be performed in the case of external input. The purpose is to remove the noise of the video signal by making the most of the frequency characteristics of the input signal.

Description

Video signal noise reduction circuit {NOISE ELIMINATING CIRCUIT OF VIDEO SIGNAL}

The present invention relates to a video signal noise canceling circuit, and more particularly, an input field sensing means for judging the electric field strength of a received signal and variably controlling the noise canceling filtering characteristic according to the electric field strength, and whether the received signal is an external signal. It is a circuit for removing video noise by making the maximum frequency characteristics of the input video signal by configuring an external signal detection means for sensing and selectively controlling the noise removing filtering characteristics in case of external input.

At this time, the input field detection means determines the electric field strength of the received signal from the result of comparing the AGC detection voltage with the reference voltage. The greater the field strength, the lower the AGC detection voltage is, and the smaller the field strength, the greater the AGC detection voltage. Is given.

As shown in FIG. 1, the conventional video signal noise canceling circuit using a video detection signal includes a high pass filter 1 for passing only a high frequency component of an image signal, and a high frequency signal output from the high pass filter 1. What is more than a predetermined level is a coring unit (2) for recognizing and removing as a noise signal and passing only below a predetermined level, an amplitude adjusting unit (3) for adjusting the amplitude of the signal output from the coring unit (2) and A low pass filter (4) for passing only low frequency components of the video signal, an adder (5) for synthesizing the video signals output from the amplitude adjusting section (3) and the low pass filter (4), and Controls the driving of the amplitude adjusting unit 3 and the low pass filter 4 by switching on or off according to an output signal of the image noise detector 6 and an image noise detector 6 for detecting a noise component. Is composed of a transistor Q1.

In this case, the image noise detection unit 6 compares the image detection signal and the reference voltage V1 to detect a noise component of the image detection signal and includes a differential amplifier composed of resistors R1 and R2 and transistors Q2 and Q3. 6a) and a constant current source 6b composed of a transistor Q4 and a resistor R3 which are driven by a reference voltage V2 and always supply a constant current to the differential amplifier 6.

Referring to the accompanying drawings, the operation of the video signal noise cancellation circuit using the conventional video detection signal configured as described above is as follows.

First, the image detection signal inputted to the base of the transistor Q2 in the differential amplifier 6a is the reference voltage V1 of the transistor Q3, which is black noise below the synchronous peak value, as shown in Fig. 2A. Or less), the transistor Q2 is turned off, the transistors Q3 and Q4 are turned on, and the transistor Q1 is turned on so that the amplitude adjusting section 3 and the low pass filter 4 are driven. At this time, when the transistor Q1 is turned on, a video signal containing noise (b of FIG. 2) is input. The video signal passes through a low pass filter 4 and a low frequency component passes and a high frequency component is blocked. As shown in 2, the signal from which the noise is removed is output.

In addition, the high frequency component is passed through the high pass filter 1 composed of the second derivative circuit, and the low frequency component is blocked, so that the video signal containing noise (b) of FIG. 2 is outputted. do.

In addition, the (C) signal of FIG. 2 passes through the coring unit 3, and noise is removed as shown in FIG. 2 (D). The edge signal output from the coring unit 3 receives the amplitude control unit 3. The amplitude a is amplified and input to the adder 5 as shown in the waveform (e) of FIG.

At this time, the adder 5 synthesizes the output waveform of the amplitude adjusting unit 3 (e.g., FIG. 2) and the output waveform of the low pass filter 4 (bar of FIG. 2). Outputs the video signal without noise.

On the other hand, if noise is not included in the image signal, the image detection signal input to the base of the transistor Q2 in the differential amplifier 6a becomes larger than the reference voltage V1 of the transistor Q3, so that the transistor Q2 is turned on. Transistors Q1 and 13 are turned off.

Therefore, since the amplitude adjusting unit 3 and the low pass filter 4 do not operate, the input video signal is output as it is.

In the prior art, only the black noise is detected by the image noise detector, and the black noise signal is removed from the low pass filter. Since the low pass filter is always fixed at a constant value regardless of the electric field strength of the input video signal, the noise is reduced. Unnecessary filtering is also applied to the strong electric field input signal that does not need to be removed, and thus the frequency characteristic of the input video signal is deteriorated.

In order to solve the above problems, the present invention is to determine the electric field strength of the received signal from the result obtained by comparing the automatic gain control (AGC) detection voltage with the reference voltage to configure the input signal field detection means The filter time constant of the low pass filter is variably controlled according to the detected electric field strength, and the external signal sensing means for detecting whether the received signal is an external signal is configured so that the filtering of the low pass filter is not performed in the case of external input. The purpose of the control is to remove noise of the video signal by making the most of the frequency characteristic of the input signal.

1 is a block diagram of a video signal noise removing circuit using a conventional video detection signal

2 is an output waveform diagram of each part of a conventional video signal noise canceling circuit

3 is a block diagram showing a first embodiment of the image signal noise canceling circuit of the present invention

Figure 4 is a block diagram showing a second embodiment of the video signal noise cancellation circuit of the present invention

5 is a block diagram showing a third embodiment of the image signal noise canceling circuit of the present invention

6 is a graph showing the relationship between the AGC detection voltage and the electric field strength in the present invention

A first embodiment of the inventive image signal noise reduction circuit for achieving the above purpose is shown in FIG. 3 and its configuration is as follows.

A high pass filter 1 for passing only a high frequency component of an image signal, and a coring unit for recognizing and removing a noise level above a predetermined level among signals output from the high pass filter 1 and passing only a predetermined level or less. (2), an amplitude adjusting unit 3 for adjusting the amplitude of the signal output from the coring unit 2, a low pass filter 4 for passing only low frequency components of the video signal, and the amplitude adjusting unit 3 And an adder (5) for synthesizing the video signal output from the low pass filter (4), an image noise detector (6) for detecting a noise component of the input image detection signal, and an image noise detector (6). A transistor Q1 for controlling the driving of the amplitude adjusting section 3 and the low pass filter 4 by switching on or off in accordance with the output signal, and a signal received from the result of comparing the AGC detection voltage with a reference voltage. Input field detecting means (7) for determining the electric field strength, and Consists of a filter characteristic changing means (8) under the control of the input electric field detection means (7) variably controlling the filter characteristics for noise reduction.

Reference numerals C1 and C2 are capacitors, R2 to R15 are resistors, Q2 to Q9 are transistors, and D1 and D2 are diodes.

The operation of the inventive image signal noise canceling circuit configured as described above will be described with reference to FIG. 3.

First, since the high pass filter 1, the coring unit 2, the amplitude adjusting unit 3, the low pass filter 4, and the adder 5 perform the same operations as in the prior art, redundant description thereof will be omitted.

6 is a graph showing the relationship between the automatic gain control (AGC) detection voltage and the electric field strength. The larger the field strength, the smaller the AGC detection voltage is, and the smaller the field strength, the larger the AGC detection voltage is.

That is, if the AGC detection voltage is between 0 and V1 (TI section), the received signal is no noise with a strong electric field. If the AGC detection voltage is between V1 and V2 (T2 section), the received signal contains some noise with a heavy electric field. the state is a state where the detection voltage of the AGC signal that is received is between V2~V _max (T3 zone) with a lot of noise to step arrangements.

At this time, V _max >V2> V1, and V _max is the maximum AGC detection voltage.

On the other hand, to determine the electric field strength of the received signal, the differential amplifiers 7a and 7b output the AGC detection voltages to the base reference voltages of the transistors Q5 and Q7.

At this time, if the input AGC detection voltage is in the range of 0 to V1, in the differential amplifier 7a, since the AGC detection voltage input to the base of the transistor Q4 is smaller than the base reference voltage V1 of the transistor Q5, the transistor Q4. ) Is turned off and transistor Q5 is turned on so that a low potential is input to the base of transistor Q2 connected to the collector terminal of transistor Q5.

In the differential amplifier 7b, since the AGC detection voltage (section 0 to V1) input to the base of the transistor Q6 is smaller than the base reference voltage V2 of the transistor Q7, the transistor Q6 is turned off and the transistor ( Q7) is turned on and a low potential is input to the base of transistor Q3 connected to the collector terminal of transistor Q7.

Accordingly, the transistors Q2 and Q3 are turned off, and the current of the constant current source composed of the transistors Q8 and the resistors R9 and R10 flows through the transistor Q5 to the transistor Q8 and the transistor Q9 and the resistor ( The current of the constant current source consisting of R11 and R12 flows through transistor Q7 to transistor Q9.

At this time, the reference bias source consisting of the resistors R1, R2 and the diode D2 supplies the reference bias to the bases of the transistors Q8, Q9, and the reference consisting of the resistors R13, R14, R15 and the diode D1_. The bias source supplies a reference bias to the bases of the transistors Q5 and Q7.

On the other hand, when the transistors Q2 and Q3 are turned off, the capacitors C1 and C2 that determine the cutoff frequency of the low pass filter 4 do not operate.

Therefore, when the received signal is a strong electric field (no noise is included in the video signal), the low pass filter 4 does not perform the noise removing filtering and the video signal is output as it is.

Next, when the AGC detection voltage input to the bases of the transistors Q4 and Q6 in the differential amplifiers 7a and 7b is V1 to V2, the AGC detection voltage is the base reference of the transistor Q5 in the differential amplifier 7a. Since the voltage V1 is greater than the voltage V1, the transistor Q4 is turned on and the transistor Q5 is turned off so that a high potential is input to the base of the transistor Q2 connected to the collector terminal of the transistor Q5.

In the differential amplifier 7b, since the AGC detection voltages (V1 to V2) are smaller than the base reference voltage V2 of the transistor Q7, the transistor Q6 is turned off and the transistor Q7 is turned on so that the transistor Q7. The low potential is input to the base of the transistor Q3 connected to the collector terminal of.

Accordingly, the transistor Q2 is turned on and the transistor Q3 is turned off, and the current of the constant current source flows through the transistor Q4 to the transistor Q8 and through the transistor Q7 to the transistor Q9. .

On the other hand, when the transistor Q2 is turned on and the transistor Q3 is turned off, the capacitor C1 operates and the capacitor C2 does not operate.

Therefore, if the received signal is a heavy electric field (the image signal contains a little noise), the low pass filter 4 performs filtering at the cutoff frequency determined by the condenser C1 to remove some noise signal included in the image signal. Remove

To the next, in the transistor when this V2~V _max interval AGC detection voltage input to the base of (Q4, A6), said differential amplifier (7a) in the differential amplifiers (7a, 7b) of the AGC voltage detection transistor (Q5) Since it is greater than the base reference voltage V1, the transistor Q4 is turned on and the transistor Q5 is turned off so that the high potential is input to the base of the transistor Q2 connected to the collector terminal of the transistor Q5.

Further, in the differential amplifier 7b, since the AGC detection voltage (V2 to V _max interval) is greater than the base reference voltage V1 of the transistor Q7, the transistor Q6 is turned on and the transistor Q7 is turned off so that the transistor ( The high potential is input to the base of the transistor Q3 connected to the collector terminal of Q7).

Accordingly, the transistors Q2 and Q3 are turned on, and the current of the constant current source flows through the transistor Q4 to the transistor Q8 and through the transistor Q6 to the transistor Q9.

On the other hand, when the transistors Q2 and Q3 are turned on, both the capacitors C1 and C2 operate.

Therefore, when the received signal is a weak electric field (the image signal contains a lot of noise), the low pass filter 4 performs the filtering at the cutoff frequency determined by the capacitors C1 and C2, and thus contains a lot of noise signals included in the video signal. Remove it.

4 shows a second embodiment of a video signal noise canceling circuit of the present invention and its configuration is as follows.

A high pass filter 1 for passing only a high frequency component of an image signal, and a coring unit for recognizing and removing a noise level above a predetermined level among signals output from the high pass filter 1 and passing only a predetermined level or less. (2), an amplitude adjusting unit 3 for adjusting the amplitude of the signal output from the coring unit 2, a low pass filter 4 for passing only low frequency components of the video signal, and the amplitude adjusting unit 3 And an adder (5) for synthesizing the video signal output from the low pass filter (4), an image noise detector (6) for detecting a noise component of the input image detection signal, and an image noise detector (6). A transistor (Q1) for controlling the driving of the amplitude adjusting section (3) and the low pass filter (4) by switching on or off in accordance with the output signal, and an external signal detecting means (9) for detecting whether the received signal is an external signal; ) And noise control under the control of the external signal detecting means (9). For selectively controlling the filter characteristics for filtering it consists of a variable-characteristic means (10).

Reference numerals R16 to R24 denote resistors, Q10 to Q15 denote transistors, and D3 denotes diodes.

The operation of the inventive image signal noise canceling circuit configured as described above will be described with reference to FIG. 4.

First, since the high pass filter 1, the coring unit 2, the amplitude adjusting unit 3, the low pass filter 4, and the adder 5 operate in the same manner as in the prior art, redundant descriptions are omitted, and the reception is usually performed. As described in the first embodiment of the present invention, the electric field strength is determined, and the filtering characteristic of the low pass filter 4 is variably controlled according to the electric field strength to remove the noise signal.

On the other hand, if the received signal is an external input (Video / S-Video) irrespective of the electric field, the external signal detecting means 9 detects this and blocks the filtering operation of the low pass filter 4.

That is, when an external signal (Video / S-Video) is input, a high potential is input to the base of the transistor Q14 so that the transistor Q14 is turned on. When the transistor Q14 is turned on, the transistor in the differential amplifier 9a ( Q12 and Q13) are turned on.

When the transistors Q12 and Q13 are turned on, a low potential is input to the bases of the transistors Q10 and Q11 connected to the collector terminals of the transistors Q12 and Q13.

Accordingly, the transistors Q10 and Q11 are turned off, and the current of the constant current source composed of the transistors Q15 and the resistors R23 and R24 flows through the transistors Q12 and Q13 to the transistor Q15.

On the other hand, when the transistors Q10 and Q11 are turned off, the capacitors C3 and C4 which determine the cutoff frequency of the low pass filter 4 do not operate.

Therefore, when the external signal is input, the low pass filter 4 does not perform the noise elimination filtering so that the external image signal is output as it is.

FIG. 5 is a third embodiment of the inventive image signal noise canceling circuit, which incorporates a first embodiment and a second embodiment of the present invention into one configuration.

A high pass filter 1 for passing only the high frequency components of the video signal, and a coring unit for recognizing and removing a noise level higher than a predetermined level among signals output from the false pass filter 1 and passing only a predetermined level or less. (2), an amplitude adjusting unit 3 for adjusting the amplitude of the signal output from the coring unit 2, a low pass filter 4 for passing only low frequency components of the video signal, and the amplitude adjusting unit 3 And an adder (5) for synthesizing the video signal output from the low pass filter (4), an image noise detector (6) for detecting a noise component of the input image detection signal, and an image noise detector (6). A transistor Q1 for controlling the driving of the amplitude adjusting section 3 and the low pass filter 4 by switching on or off in accordance with the output signal, and a signal received from the result of comparing the AGC detection voltage with a reference voltage. Input field detecting means (7) for determining the electric field strength and the number Under the control of the external signal detection means (9) for detecting whether the signal is an external signal and the input field detection means (7) and the external signal detection means (9) to variably control the filtering characteristics for noise removal The filtering characteristic consists of a variable stage (8).

Reference numerals R1 to R19 denote resistors, Q2 to Q13 denote transistors, and D1 and D2 denote diodes.

The operation of the inventive image signal noise canceling circuit constructed as described above will be described with reference to FIG. 5.

First, since the high pass filter 1, the coring unit 2, the amplitude adjusting unit 3, the low pass filter 4, and the adder 5 perform the same operations as in the prior art, redundant description thereof will be omitted.

6 is a graph showing the relationship between the AGC detection voltage and the electric field strength as described in the first embodiment of the present invention, the greater the field strength, the lower the AGC detection voltage is, and the smaller the field strength, the larger the AGC detection voltage is.

That is, if the AGC detection voltage is between 0 and V1 (T1 section), the received signal is no noise with a strong electric field. If the AGC detection voltage is between V1 and V2 (T2 section), the received signal is weak with noise. the state is a state where the AGC voltage is detected the received signal is between V2~V _max (T3 zone) with a lot of noise to step arrangements.

At this time, the _{V max>V2> V1, V} max is the maximum value of the AGC voltage is detected.

On the other hand, to determine the electric field strength of the received signal, the differential amplifiers 7a and 7b output the AGC detection voltages to the base reference voltages of the transistors Q5 and Q7.

At this time, when the AGC detection voltage is in the range of 0 to V1, in the gain differential amplifier 7a, since the AGC detection voltage is smaller than the reference voltage V1, the transistor Q4 is turned off and the transistor Q5 is turned on, and the transistor Q5 is turned on. When turned on, the transistor Q2 connected to the collector terminal of the transistor Q5 is turned off.

Further, in the differential amplifier 7b, since the AGC detection voltage is smaller than the reference voltage V2, the transistor Q6 is turned off and the transistor Q7 is turned on. When the transistor Q7 is turned on, the collector of the transistor Q7 is turned on. Transistor Q3 connected to the terminal is turned off.

Since no external signal (Video / S-Video) is input to the base of the transistor Q11, the transistor Q11 is turned off, and the reference voltage V4 is input to the base of the transistors Q8 and Q9 so that the transistor is input. (Q8, Q9) is turned on.

Therefore, the current of the constant current source consisting of the transistor Q10 and the resistors R18 and R19 flows through the transistor Q5 to the transistors Q8 and Q10 and also through the transistor Q7 to the transistors Q9 and Q10. .

At this time, the reference bias supply source composed of the resistors R1 to R4 and the diode D2 supplies the reference bias consisting of the transistors Q8 to Q10, Q12, and Q13, and supplies the resistors R11 to R13 and the diode D1. The configured reference bias source supplies a reference bias to the bases of transistors Q5 and Q7.

On the other hand, when the transistors Q2 and Q3 are turned off, the capacitors C1 and C2 that determine the cutoff frequency of the low pass filter 4 do not operate. Therefore, the low pass filter 4 does not perform noise reduction filtering, thereby eliminating the input image. The signal (no noise is included in the strong field) is output as is.

Next, when the AGC detection voltage input to the bases of the transistors Q4 and Q6 in the differential amplifiers 7a and 7b is a V1 to V2 section, the transistors Q5 and Q6 are turned off and the transistors Q4 and Q7 are turned on. Transistor Q2 is thus turned on and transistor Q3 is turned off.

Since no external signal (Video / S-Video) is input to the base of the transistor Q11, the transistor Q11 is turned off, and the reference voltage V4 is input to the base of the transistors Q8 and Q9 so that the transistor is input. (Q8, Q9) is turned on.

Therefore, the current of the constant current source consisting of the transistor Q10 and the resistors R18 and R19 flows through the transistor Q4 to the transistors Q8 and Q10 and through the transistor Q7 to the transistors Q9 and Q10. .

On the other hand, when the transistor Q2 is turned on and the transistor Q3 is turned off, the capacitor C1 is operated and the capacitor C2 is not operated. Therefore, in the low pass filter 4, at the cutoff frequency determined by the capacitor C1. Filtering is performed to remove some of the noise signal included in the input video signal (weakly included noise in the middle electric field).

To the next, if the detected AGC voltage input to the base of the transistor (Q4, Q6) within the differential amplifier (7a, 7b) V2~V _max interval, the transistor (Q5, Q7) are turned off and the transistor (Q4, Q6) Is turned on, and transistors Q2 and Q3 are turned on.

Since no external signal (Video / S-Video) is input to the base of the transistor Q11, the transistor Q11 is turned off, and the reference voltage V4 is input to the base of the transistors Q8 and Q9 so that the transistor is input. (Q8, Q9) is turned on.

Therefore, the current of the constant current source composed of the transistor Q10 and the resistors R18 and R19 flows through the transistor Q4 to the transistors Q8 and Q10 and through the transistor Q6 to the transistors Q9 and Q10. .

On the other hand, when the transistors Q2 and Q3 are turned on, the capacitors C1 and C2 operate, and the low pass filter 4 performs the filtering at the cutoff frequency determined by the capacitors C1 and C2, thereby reducing the input image signal (weak charge). System, which contains a lot of noise, removes a lot of noise signals.

When the received signal is an external video signal, a high potential is input to the base of the transistor Q11, and the transistor Q11 is turned on. At this time, the base voltage V7 of the transistor Q11 is a transistor Q8, Q9. Is set higher than the emitter residual pressure (V6).

Thus, the transistor Q11 is turned on and the transistors Q8 and Q9 are turned off.

On the other hand, when the transistors Q8 and Q9 are turned off, the transistors Q4, Q5, Q6 and Q7 in the differential amplifiers 7a and 7b are turned off.

Accordingly, the current of the constant current sources Q10, R18, and R19 flows through the resistor R6 through the transistor Q12 to the transistor Q11 and through the resistor R9 through the transistor Q13 through the transistor Q11. Will flow into.

On the other hand, when the transistors Q5 and Q7 are turned off, the transistors Q2 and Q3 are turned off and the capacitors C1 and C2 do not operate. Therefore, the external image signal is output through the low pass filter 4 as it is.

As described above, in the present invention, the AGC detection voltage is used to determine the electric field strength of the received signal and variably control the filter time constant of the low pass filter that performs the noise removing operation according to the electric field intensity, thereby making the maximum frequency characteristics of the input signal. When the video noise is eliminated and the external video signal is irrelevant to the electric field strength, the low pass filter is not driven so that the frequency characteristic of the external signal does not drop excessively, thereby providing a clear image to the user. It has an effect.

Claims (2)

An image signal noise canceling circuit using an image detection signal, comprising: an external signal sensing means for detecting whether a received signal is an external signal, and a filtering for selectively controlling filtering characteristics for noise removal under the control of the external signal sensing means A video signal noise canceling circuit comprising a characteristic variable stage. An image signal noise canceling circuit using an image detection signal, comprising: an input field detection means for determining an electric field strength of a received signal from a result of comparing an AGC detection voltage with a reference voltage, and detecting whether the received signal is an external signal And a filtering characteristic variable stage configured to variably control filtering characteristics for noise removal under the control of an external signal sensing means and the input field sensing means and the external signal sensing means.