JPH0616575B2 - Slice circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a slice circuit.

Background Art and Problems When shooting with a color video camera, chroma noise (noise included in a color signal) is conspicuous on a playback screen in a dark part of a subject.

Therefore, it is considered that the chroma noise is made inconspicuous by reducing the color signal level in the dark part of the subject, that is, in the part where the luminance signal level is low.

FIG. 1 shows an example of a camera configured to perform such processing.

That is, in FIG. 1, (1) shows a single-tube color image pickup tube such as a Trinicon system (Trinicon is a registered trademark). From this image pickup tube (1), a luminance signal Sy and a carrier color signal are shown. A composite signal of Sc and the index signal Si is taken out, and this signal is supplied to the preamplifier (2) and the AG.
It is supplied to the low-pass filter (4) through the C amplifier (3) to extract the luminance signal Sy, and this signal Sy is supplied to the NTSC encoder (6) through the gamma correction circuit (5).

Further, the composite signal from the AGC amplifier (3) is supplied to the band pass filter (11) to extract the carrier color signal Sc and the index signal Si, and these signals Sc, Si
Is supplied to a separation circuit (12) to be separated into signals Sc and Si, and the signal Sc is supplied to a demodulation circuit (15) through a gamma correction circuit (13) and a variable attenuator circuit (14),
The signal Si is supplied to the demodulation circuit (15), the red and blue color difference signals are demodulated from the signal Sc, and these color difference signals are encoded.
Supplied to (6).

Then, an NTSC color video signal is formed from the luminance signal and the color difference signal in the encoder (6), and this signal is taken out to the terminal (7).

Further, in this case, the luminance signal Sy from the filter (4) is supplied to the base of the transistor Q ₁ . The transistor Q ₁ constitutes a slice circuit (16), and therefore the resistors R ₁ and R ₂ and the reference voltage source V _S for setting the slice level are connected. Therefore, if the base-emitter voltage of the transistor Q ₁ is V _BE , then the transistor Q 1
₁ is turned on when its base voltage is below (V _S -V _BE), the off-time of the above (V _S -V _BE).

Therefore, the base of the transistor Q ₁ is, for example, shown in FIG.
When a luminance signal Sy having a negative sync polarity is supplied as shown in FIG. 2, its collector receives the signal Sy as shown in FIG. 2B.
level (V _S -V _BE) black side portion than the y is retrieved is inverted as the output signal Ss.

Then, this signal Ss is supplied to the variable attenuator circuit (14) as its control signal, and as shown in FIG. 2C,
The attenuation amount of the attenuation circuit (14) is controlled to be large when the level of the signal Ss is high and small when the level of the signal Ss is low.

Accordance connexion, when the luminance signal Sy is below the level (V _S -V _BE), the higher the level becomes smaller, Sc of the carrier chrominance signal
Since the level of is reduced, the color noise in the dark part of the subject does not stand out.

In this way, the camera of FIG. 1 can provide a reproduction screen in which color noise is inconspicuous.

However, since the signal Sy is sliced by using the voltage V _BE of the transistor Q ₁ in the slice circuit (16) in FIG. ₁ , the signal Sy has a slice level (V _S −V _BE ).
On the other hand, if it changes gradually, that is, if the shaded portion of the signal Sy in FIG. Further, in general, it is difficult to perform processing in a state where the signal level is high inside the IC. Especially, since the portable video camera is in a battery operation and the power supply voltage is about 5V, the signal level is even higher. Processing is difficult. Therefore, the slice level (V _S −V _BE ) for the signal Sy becomes about 0.2t (a value of about 10% from the black side of the signal Sy), and this uses the voltage V _BE of the transistor Q _1. If you slice by using this method, the accuracy will deteriorate. Further, in the slice circuit (16), the gain of the transistor Q ₁ is R ₂ / R ₁ , but when the peak-to-peak level V _{PP of the} signal Ss is 100% (specified value), the attenuator circuit (14 ) Becomes a specified value, and if the peak-to-peak level V _{PP of the} signal Ss varies,
The attenuation of the attenuator circuit (14) will be insufficient or excessive. Therefore, the peak of the signal Ss
The peak level V _PP should be 100%.

However, in the slice circuit (16) of FIG. 1, when the gain R ₂ / R ₁ is adjusted so that the maximum value of the signal Ss becomes 100%,
Actually, the slice level of the transistor Q ₁ is the resistor R ₁
Also changes, the slice level changes by adjusting the peak-to-peak level V _PP of the signal Ss. Alternatively, conversely, if the slice level is adjusted, the peak-to-peak level V _{PP of the} signal Ss will change. ……… Also, when the 0 level of the signal Ss fluctuates, the attenuation amount of the attenuator circuit (14) fluctuates, so the attenuator circuit (1
In 4), the signal Ss must be clamped, but for this purpose, it is necessary to form horizontal and vertical blanking periods in the signal Ss. That is, the clamp is performed during this blanking period. The object of the present invention is to solve the above-mentioned points (1) to (5) in particular so as to obtain an appropriate color video signal.

SUMMARY OF THE INVENTION Therefore, in the present invention, the level control of the signal Ss is performed in accordance with the slice level.

Example Namely, in FIG. 3, between the power supply terminal T ₁₁ and the ground, with a resistor R ₂₁ and the constant current source Q ₁₄ are connected in series, the gamma correction circuit to the constant current source Q ₁₄ (5 The luminance signal Sy is supplied to the signal Sy and the signal Sy becomes a constant current signal.

Further, a resistor R ₂₂ and a collector-emitter of a transistor Q ₂₃ for a constant current source are connected in series between the terminal T ₁₁ and the ground, and the midpoint of this connection is the bases of the transistors Q ₁₁ and Q ₁₂ . connected, between the ground and the emitters of the transistors Q _11, Q _12, together with the collector-emitter of the transistor Q _21, Q ₂₂ is connected to constant current source, the emitter of the transistor Q _11, Q ₁₂ To resistor R ₁₁
Are connected. Further, the collector-emitter of the current-voltage converting transistor Q ₃₁ is connected between the terminal T ₁₁ and the collector of the transistor Q ₁₁ , and the collector-emitter of the transistor Q ₁₃ is connected in parallel between the transistor Q ₁₂ mitter. Connected, terminal T ₁₁ and transistors Q ₁₂ and Q ₁₃
Transistor Q ₃₂ for current-voltage conversion between the collector and
Is connected between the collector and the emitter, and a constant bias voltage is supplied to the bases of the transistors Q ₃₁ and Q ₃₂ . Further, the base of the transistor Q ₁₃ is connected to the resistor R _21.
And a constant current source Q ₁₄ are connected. The transistor Q ₁₁ is always on (active region).

Further, between the ground and the terminal T _11, with between the constant current source Q ₂₅ and the transistor Q ₂₄ collector-emitter is connected in series, the collector of the transistor Q ₂₄ is, the transistor Q ₂₁
A current mirror circuit (21) is formed by being connected to the bases of Q ₂₄ to Q ₂₄ .

Further, a double balance type multiplication circuit (22) is configured. That is, the emitters of the transistors Q ₄₁ and Q ₄₂ are connected to the constant current Q ₄₃ , the negative horizontal and vertical blanking pulse ▲ ▼ is supplied to the base of the transistor Q ₄₁ through the terminal T ₁₂ , and at the same time, the transistor Q ₄₂ A constant bias voltage is supplied to the base.

Further, the emitters of the transistors Q ₅₁ and Q ₅₂ are connected to the collector of the transistor Q ₄₁ , and the transistors Q ₅₁ and Q ₅₂ are connected.
Is connected to the emitters of the transistors Q ₃₂ and Q ₃₁ , and resistors R ₃₁ and R ₃₂ (R ₃₁ = R ₃₂ ) are connected between the collectors of the transistors Q ₅₁ and Q ₅₂ and the terminal T _11. It Further, the emitters of the transistors Q ₅₃ and Q ₅₄ are connected to the collector of the transistor Q ₄₂ ,
_53, with the base at a constant bias voltage of Q ₅₄ is supplied, the collector of the transistor Q _53, Q ₅₄ is connected to the resistor R _31, R _32, collector output of the transistor Q _51, Q ₅₃ is variable Atsuteneta circuit It is supplied to (14) as a control signal.

With such a configuration, if the luminance signal Sy from the filter (4) has a waveform as shown in FIG. 2A, the luminance signal Sy from the gamma correction circuit (5) has its gamma correction characteristic. The waveform becomes as shown in FIG. 2D depending on (for example, 1 / 2.2 rideability). The signal Sy is supplied to the constant current source Q ₁₄ and converted into a constant current signal, and the constant current signal flows through the resistor R ₂₁ , so that the base of the transistor Q ₁₃ is shown in FIG. 2E. The luminance signal voltage Vy having such a waveform is supplied.

The transistors Q ₂₃ and Q ₂₄ are connected to the current mirror circuit (2
Since constitute a 1), if the constant current I ₂₅ of the constant current source Q _25, resistors constant current I ₂₅ flows in R _22, the base voltage V _B of the transistor Q _11, Q ₁₂ is, V _B = V _CC −R ₂₂ I ₂₅ ……………… (i).

Accordance connexion, these voltages Vy, V _B is the transistors Q ₁₁ to Q ₁₃
The voltages are compared by Vy as shown in FIGS. 2E and 2F.
When ≧ V _B , the transistor Q ₁₂ is off, the transistor Q ₁₃ is on, and the transistor Q ₁₁ is on (normally on). Therefore, at this time, the transistors Q ₁₁ and
Q ₁₃ works as a differential amplifier. Accordance connexion, the collector current I ₁₁ of the transistor Q ₁₁ as shown in FIG. 2 G signal Vy
And the collector current I ₁₂ of the sum of the transistors Q ₁₂ and Q _{13 has} a waveform opposite to the current I ₁₁ (in-phase with the signal Vy).

When Vy <V _B , the transistor Q ₁₂ turns on,
Transistor Q ₁₃ is off and transistor Q _{13
Since 11} is on, at this time, the transistors Q ₁₁ and Q
₁₃ acts as a differential amplifier and its transistor Q
_Since the base inputs of ₁₁ and Q ₁₂ are both voltage V _B , the current I
₁₁ and I ₁₂ are constant values. The magnitudes of the currents I ₁₁ and I ₁₂ at this time are equal to the current I ₂₅ by the current mirror circuit (21).

Therefore, in the collectors of the transistors Q ₁₁ and Q ₁₂ , Q ₁₃ , as shown in FIG. 2G, the signal currents I ₁₁ and I _{12 of} opposite phases obtained by slicing the signal Vy at the level V _B are obtained. become.

The signal currents I ₁₁ and I ₁₂ are transferred to the transistors Q ₃₁ and
After being converted into a voltage by Q ₃₂ , it is supplied as a control signal Ss to the variable attenuator circuit (14) through the double balance type multiplication circuit (22), and the carrier color signal Ss is attenuated.

At this time, the blanking pulse of the terminal T ₁₂ ▲
A blanking period is formed in the signal Ss by ▼.

Thus, according to the present invention, the slice signal Ss for controlling the attenuation amount can be obtained. In this case, the slice level is the voltage V _{B as} shown in FIG. 2, and this voltage V _B
Can be arbitrarily set by the constant current source Q ₂₅ as shown in the equation (i), and accordingly, the slice level V _B can be arbitrarily set.

If the constant current of the constant current source Q ₄₃ is I ₄₃ , the circuit (2
The total gain A of 1) and (22) is Is. Therefore, the peak-to-peak level V _PP of the signal Ss is Therefore, regardless of the change of the current I ₂₅ , the peak-to-peak level V _PP of the signal Ss does not change even if the slice level V _B is adjusted.

Furthermore, since the gamma-corrected luminance signal Vy (Sy) is sliced to form the signal Ss, the change in the signal Vy at the slice level V _B becomes sharp and clear as shown in FIG. 2E. You can slice. Also, at this time,
Since the carrier color signal Sc is also gamma-corrected, the signal S is converted from the luminance signal Vy (Sy) that has been gamma-corrected.
Getting s is more appropriate. Furthermore, without using the V _BE of the transistors, the transistors Q _{11 to} Q
_Since slicing is performed by the voltage comparison by ₁₃ , the slice level accuracy can be increased and the power supply voltage V _CC can be increased.
Can be as low as 5V, for example, and it is suitable not only for IC, but also for a battery-operated camera.

Further, since the signal Ss is blanked, the attenuator circuit (14) can be easily clamped.

In the above description, the variable attenuator circuit (14) is a signal line of the color difference signal demodulated in the demodulation circuit (15),
Alternatively, it may be provided in the signal line of the carrier color signal in the encoder (6). Further, instead of the gamma correction circuit (13), a control signal having a predetermined characteristic may be added to the signal Ss to give a gamma characteristic to the color signal (carrier color signal).

EFFECTS OF THE INVENTION A highly accurate slice signal Ss can be obtained, and even if the slice level is changed, the peak-to-peak level V _{PP of the} slice signal Ss does not change. Further, a blanking period can be formed in the signal Ss.

[Brief description of drawings]

1 and 2 are views for explaining the present invention, and FIG. 3 is a connection diagram of an example of the present invention. (5) is a gamma correction circuit, and (14) is a variable attenuator circuit.

Front Page Continuation (72) Inventor, Jouichi Sato, 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo, Soni-Inc. (72) Inventor, Mitsuru Sato, 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Soni- Within the corporation (56) References Japanese Patent Publication No. 5-7887 (JP, B2)

Claims (1)

[Claims] 1. An input signal and a reference level set by a current mirror including a first auxiliary current path through which an auxiliary current equal to a main current controlled by a variable constant current source flows. When it is lower, a current is set by the main current from the variable constant current source, a sub-current equal to the main current flows, and when the input signal is higher than the reference level, a second amplification operation is performed. After the voltage is compared by the differential current mirror circuit having the sub-current path, the input signal is sliced at the reference level, the currents in the second and third current paths are voltage-converted, and a pair of inputs is input. Section and a differential amplifier circuit having a constant current source in the common emitter connection section to obtain a slice output, so that the input level is below the reference level regardless of the change of the reference level by the variable constant current source. When the slice circuit, characterized in that as an output having a predetermined constant voltage level at the output of the differential amplifier circuit is obtained.