JPS626774Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diode slicing circuit used to remove noise components contained in a reproduced signal of a VTR (video tape recorder), for example.

FIG. 1 shows a conventional noise removal circuit. The input terminal 1 is supplied with a video signal _S1 obtained by demodulating a reproduced signal from a VTR. Video signal S ₁ has
As shown in FIG. 2A, noise components are included. The video signal _S1 is supplied to a low pass filter 2 and a high pass filter 3, and the low pass filter 2
As shown in Figure 2B, a signal _S2 with a rounded waveform and no noise component is generated from the high-pass filter 3, and as shown in Figure 2C, a signal S2 is generated at a rapid level change portion. A signal _S3 is generated in which a noise component is superimposed on the overshoot and undershoot. By supplying this signal _S3 to the diode slice circuit 4 shown surrounded by a broken line,
Only the signal S ₃ ' with a level exceeding the range of ±Vf centered on 0 [V] is taken out from the diode slice circuit 4. This signal S ₃ ′ does not contain any noise components, and by adding the signals S ₂ and S ₃ ′ by the adder 5, the video signal S 3 from which the noise components have been removed is output to the output terminal 6 as shown in FIG. 2D. You can get ₄ .

The diode slice circuit 4 includes two diodes 7a and 7b connected in opposite directions, capacitors 8 and 9, and a resistor 10.
This is the forward voltage drop between a and 7b, which is approximately 0.7 [V] in the case of a silicon diode and 0.4 [V] in the case of a Schottky diode. By the way, in the above-described noise removal circuit, the slice level of the diode slice circuit 4 may be large if only the noise components are removed, but as a result, the high-frequency components of the video signal that are lost are large. As a result, the waveform of the resulting output video signal _S4 differs from the original waveform. Assuming that the slice level determined based on such considerations is around -26 [dB], when silicon diodes are used, the level of the input video signal to the diode slice circuit 4 is ±Vf × 20 = ± 14V=28
[V _pp ], and even if a Schottky diode is used, the input video signal must be as large as 16 [V _pp ]. However, handling such large-level signals requires the use of a high-voltage power supply, which is difficult to implement, especially when integrated into an IC.

The present invention eliminates the drawbacks of such conventional diode slice circuits.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 3, 11 indicates a power supply terminal to which a positive DC voltage (+Vcc) is applied, and a series circuit of a variable resistor 12 and resistors 13, 14, and 15 is inserted between this power supply terminal 11 and the ground. . A connection point between the variable resistor 12 and the resistor 13 is grounded via a capacitor 16. Also, the first connection point 17 of the resistors 13 and 14 and the resistor 1
4 and 15 are connected to the input terminal 20 via capacitors 19a and 19b, respectively. Further, diodes 22a and 22b are inserted between the connection points 17 and 18 and the output terminal 21, respectively, in opposite directions. As the diodes 22a and 22b, silicon diodes, Schottky diodes, etc. can be used.

In the above configuration, the resistance value of the variable resistor 12 is R ₁₂ , and the values of the resistors 13, 14, and 15 are R ₁₃ , respectively.
Assuming R ₁₄ and R ₁₅ , the voltage across the resistor 14 (potential difference between connection points 17 and 18) E ₁₄ is E ₁₄ = R ₁₄ · Vcc/R ₁₂ + R ₁₃ + R ₁₄ + R ₁
It becomes ₅ . As an example, if a sinusoidal voltage is applied from the input terminal 20, as shown in FIG _.
Sinusoidal voltages Ea and Eb appear with a difference of . This potential difference E ₁₄ can be determined by selecting the value of each resistor so _that [0<E ₁₄ <( _{V f
a} + V _fb )].
These sinusoidal voltages Ea and Eb are connected to the diode 22a.
and 22b, so that its V-I
The shaded portion is output according to the characteristics 23a and 23b, and the output voltage E ₀ can be taken out to the output terminal 21.

As can be understood from the above description, according to the present invention, the voltage E ₁₄ is varied by varying the value R ₁₂ of the variable resistor 12, thereby changing the slice level from [0 to (V _fa + V _fb )]. Therefore, the slice level can be made smaller than (±Vf), and as mentioned at the beginning, it is suitable for use when removing sufficiently low level noise components. Furthermore, if the slice level is simply to be reduced, the value of any one of the resistors 13, 14, and 15 may be changed without providing the variable resistor 12 and the capacitor 16. However, since signal components flow through the resistors 13, 14, and 15, if any of these were made externally adjustable as a variable resistor, the lead wires through which the signal components would flow would become long, and the signal components would be Degradation or interference with other circuits may occur. According to the present invention, since the capacitor 16 is connected, the signal component is bypassed, and only the DC component flows through the variable resistor 12, so that there is no influence at all even when the variable resistor 12 is separated by a lead wire. do not have.

In addition, especially when the slice level is small,
It is important that the slice levels of the two diodes 22a and 22b are symmetrical in positive and negative directions, but in the present invention, the diodes 22a and 22b are directly connected between the output end 21 and the connection points 17 and 18. Therefore, these diodes 22a and 2
2b have the same characteristics, the voltage E ₁₄ across the resistor 14 is divided by these two diodes, and the DC level at the output terminal 21 is always (V ₁₇ +V ₁₈ )/2 (V ₁₇
and V ₁₈ is the voltage at connection points 17 and 18).
Therefore, the slice levels of the diodes 22a and 22b can always be made symmetrical in positive and negative directions even if there are errors in the resistance values of the resistors 13, 14, and 15.

In addition, in the present invention, the input terminal 20 and the two diodes 22a and 22b are each connected to a capacitor 1.
9a, 19b and DC cut, the DC level of input terminal 20 and connection point 1
There is no need to relate the DC levels of 7 and 18.
The resistance values of the resistors 13, 14, and 15 can be easily set because only the bias values for the diodes need to be considered.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram showing the configuration of a conventional noise removal circuit, Fig. 2 is a waveform diagram of each part used for its explanation, Fig. 3 is a connection diagram of an embodiment of the present invention, and Fig. 4 is an explanation of its operation. FIG. 12 is a variable resistor, 17 is a first connection point, 18
is the second connection point, 19a and 19b are the first and second connection points.
20 is an input terminal, 21 is an output terminal, and 22a and 22b are first and second diodes.

Claims (1)

[Scope of utility model registration request] One end 11 of the DC power source is connected to the other end of the DC power source via a series circuit connected in sequence to a variable resistor 12, a first resistor 13, a second resistor 14, and a third resistor 15. A connection point between the resistor 12 and the first resistor 13 is connected to the other end of the DC power supply via a capacitor 16, and the first resistor 13 is connected to the other end of the DC power supply through the capacitor 16.
The first connection point 17 of the second resistor 14 and the second connection point 18 of the second resistor 14 and third resistor 15 are connected to the first and second capacitors 19, respectively.
a, 19b, and the first connection point 17 is connected to the anode of the first diode 22a.
The cathode of the second diode 22b is connected to the anode of the second diode 22b, the cathode of the second diode 22b is connected to the second connection point 18, and the cathode of the first diode 22a and the second diode 22b are connected to each other. The connection point with the anode is output end 2
A diode slice circuit connected to 1.