JPH0670243A - Video switch circuit - Google Patents

Abstract

PURPOSE:To make a video switch circuit provided with the limiter and clamper functions simple in configuration and less in signal deterioration. CONSTITUTION:An upper limit transistor TR Q7 and a lower limit TR Q9 are connected to a TR Q8 which takes out the selection output in an emitter follower structure. Thus the upper and lower limit levels of the selection output are limited. Then the output of the TR Q8 is compared with the clamp voltage V4 by an operational amplifier 1. The negative feedback control is applied to the current of a current source I2 based on the comparison output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video switch circuit for selectively outputting a plurality of input video signals.

[0002]

2. Description of the Related Art A circuit diagram of a conventional video switch circuit is shown in FIG. In FIG. 4, one input video signal A is led to the base of the transistor Q ₁ and the other input video signal B is led to the base of the transistor Q ₄ . Switching pulse 1 and switching pulse 2 are selectively input, and when switching pulse 1 is input, transistor Q
₂ and transistor Q ₃ turn on, while transistor Q ₅
And the transistor Q ₆ turns off, the input video signal A
Only is output via transistor Q ₈ . Conversely,
When the switching pulse 2 is input, the transistors Q ₅ and Q ₆ are turned on, while the transistors Q ₂ and Q ₃ are turned off, so that only the input video signal B is output via the transistor Q ₈ .

[0003]

However, the above-mentioned conventional video switch circuit merely selects a video signal. Therefore, when the limiter process or the clamp process is performed on the selected video signal, it is necessary to perform the process after the video switch circuit. The limiter circuit shown in FIG. 5 and the clamp circuit shown in FIG. 6 are separately connected in series. Therefore, there are disadvantages that the number of parts is large, the signal path is long, and the signal deterioration is large.

Therefore, it is an object of the present invention to provide a video switch circuit in which functions of limiter processing and clamp processing are added to simplify the circuit and prevent signal deterioration as much as possible.

[0005]

According to a first aspect of the present invention, there is provided a video switch circuit for selectively outputting a plurality of video input signals in accordance with a switching pulse, and outputting the selection signals. Output through a follower transistor, an emitter is connected to the base of the transistor, and an upper limit transistor for limiting the upper limit level of the transistor output by applying an upper limit level voltage to the base, and the transistor is emitter-coupled. A lower limit transistor for limiting the lower limit level of the transistor output by applying a lower limit level voltage to the base is provided.

The video switch circuit of the invention according to claim 2 is provided with a current source for selectively outputting a plurality of video input signals in response to the switching pulse and for extracting the selected output via the output level adjusting resistor. A clamp circuit is provided to perform negative feedback control of the current of the current source according to the deviation between the clamp voltage and the output taken out from the common connection point of the output level adjusting resistor and the current source.

The video switch circuit of the invention according to claim 3 is provided with a current source for selectively outputting a plurality of video input signals in response to the switching pulse and for extracting the selected output through the output level adjusting resistor. A selected output taken out from a common connection point of the output level adjusting resistor and the current source is output through a transistor of an emitter follower configuration, an emitter is connected to a base of the transistor, and an upper limit level voltage is applied to the base to output the selected output. An upper limit transistor for controlling the upper limit level of the transistor output is provided, an emitter coupling with the transistor is provided, and a lower limit transistor for limiting the lower limit level of the transistor output by applying a lower limit level voltage to the base is provided, and an output of the transistor is provided. A class for negative feedback controlling the current of the current source according to the deviation from the clamp voltage. It is provided with a flop circuit.

[0008]

According to the first aspect of the invention, the selected video signal is guided to the transistor of the emitter follower structure, and the upper and lower limit levels of the selected video signal are limited by the upper limit transistor and the lower limit transistor connected to this transistor. To do.

According to the second aspect of the present invention, the selected video signal is clamped to the clamp voltage by controlling the current source itself for extracting the selected video signal.

According to the third aspect of the present invention, the selected video signal is guided to the transistor having the emitter follower structure, and the upper and lower limit levels of the selected video signal are limited by the upper limit transistor and the lower limit transistor connected to this transistor. In addition, the selected video signal is clamped to the clamp voltage by controlling the current source itself for extracting the selected video signal.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a video switch circuit with a limiter function showing a first embodiment of the present invention. Figure 1
, One input video signal A has a transistor Q ₁
The other input video signal B to the base of the transistor Q
₄ are respectively led to the bases of the respective transistors Q ₁ and Q ₄
Is output by transistors Q ₃ and Q ₆ , respectively. The on / off of each of the transistors Q ₃ and Q ₆ is controlled by the transistors Q ₂ and Q ₅ , respectively, and the switching pulses 1 and 2 are supplied to the bases of the transistors Q ₂ and Q ₅ , respectively. These two switching pulses 1 and 2
Is selectively input.

The emitter sides of the transistors Q ₃ and Q ₆ are both connected to the current source I ₂ via the diodes D ₁ and D _2, and the selective output is taken out from the current source I ₂ . A common connection point between the current source I ₂ and the diodes D ₁ and D ₂ is connected to the base of a transistor Q ₈ having an emitter follower structure, and a selected video signal is output via this transistor Q ₈ .

The upper limit transistor Q ₇ has its emitter side connected to the base of the transistor Q ₈ via a diode D ₃ and has an upper limit level voltage V ₂ applied to its base. Lower limit transistor Q ₉ is transistor Q ₈
And emitter-coupled to the base of the lower limit level voltage V ₃
Is being applied. The diodes D ₁ , D ₂ and D ₃ are for matching the input and output biases.

In the above structure, when the switching pulse 1 is input, the transistors Q ₂ and Q ₃ are turned on while the transistors Q ₅ and Q ₆ are turned off and only the input video signal A is supplied to the base of the transistor Q _8. To be done. When the base voltage becomes higher than V ₂ + 2V _be (base-emitter voltage), the upper limit transistor Q ₇ is turned on, and the base voltage does not become higher than V ₂ + 2V _be . When the base voltage becomes lower than V ₃ , the lower limit transistor Q ₉ turns on.

Therefore, the video signal A limited by the upper limit voltage V ₂ + V _be and the lower limit voltage V ₃ -V _be is output to the emitter side of the transistor Q ₈ .

FIG. 2 is a circuit diagram of a video switch circuit with a clamp function showing a second embodiment of the present invention. In FIG. 2, parts having the same configurations as those of the first embodiment are designated by the same reference numerals in the drawing, the description thereof will be omitted, and only different configurations will be described. That is, the upper limit for the transistor Q _7, are not provided lower transistor Q _9, etc., the current source I ₂ the output level adjusting resistor R ₂ connected in series, via the output level adjusting resistor R ₂ The selected output is taken out from the current source I ₂ . The emitter side of the transistor Q ₈ is connected to the + input terminal of the operational amplifier 1. A clamp voltage V is applied to the-input terminal of the operational amplifier 1.
₄ is being applied. The operational amplifier 1 supplies an output according to the deviation of both input voltages to the current source I ₂ , and the current source I ₂ controls the current amount in inverse proportion to this output. A clamp circuit 2 is configured by the operational amplifier 1, the current source I _{2, and the} like. still,
In the figure, C is a condenser for integration.

In the above structure, when the switching pulse 1 is input, the video signal A is supplied to the base of the transistor Q ₈ as in the first embodiment, and the video signal A is output via the transistor Q _8. It Then, an output corresponding to the deviation between the video signal A and the clamp voltage V ₄ is supplied to the current source I ₂ , and negative feedback control is performed. That is, assuming that the DC level of the input video signal A is 0V, the DC level DC of the output is given by the following equation.

[0018] _{DC = -V be -R 1 · I} 1 + V be + R 2 · I 2 -V be = in _{-V be -R 1 · I 1 +} R 2 · I 2 above expression to control the value of I ₂ Output DC level D
Since C is closed is equal so that the loop and the clamp voltage V _4, the output is clamped to the clamp voltage V _4.

FIG. 3 is a circuit diagram of a video switch circuit having a limiter function and a clamp function according to a third embodiment of the present invention. In FIG. 3, parts having the same configurations as those of the second embodiment are designated by the same reference numerals in the drawing, the description thereof will be omitted, and only different configurations will be described. That is, the transistor Q
The ₈ upper transistor Q ₇ as in the first embodiment, the lower limit for the transistor Q ₉ and the like are added.

In the above structure, the selected video signal A or B is limited by the upper limit transistor Q ₇ and the lower limit transistor Q ₉ and clamped to the clamp voltage V ₄ by the clamp circuit 2 and output.

According to the first to third embodiments, the two input video signals A and B are selected.
It can be configured to allow selecting the three or more input video signal by adding a set of such transistors _{Q 1, Q 2, Q 3} .

[0022]

As described above, according to the first aspect of the present invention, since the upper limit transistor and the lower limit transistor are connected to the transistor of the emitter follower structure and the limiter function is added, the circuit can be simplified and the signal deterioration can be achieved. The effect that can be prevented as much as possible.

Further, according to the second aspect, since the clamp function is added by controlling the current source itself for extracting the selected video signal, it is possible to simplify the circuit and prevent the signal deterioration as much as possible. Play.

Further, according to claim 3, by connecting the upper limit transistor and the lower limit transistor to the transistor of the emitter follower structure to add a limiter function and controlling the current source itself for extracting the selected video signal. Since the clamp function is added, the circuit can be simplified and the signal deterioration can be prevented as much as possible.

[Brief description of drawings]

FIG. 1 is a video switch circuit diagram with a limiter function (first embodiment).

FIG. 2 is a video switch circuit diagram with a clamp function (second embodiment).

FIG. 3 is a video switch circuit diagram with a limiter function and a clamp function (third embodiment).

FIG. 4 Video switch circuit diagram (conventional example)

FIG. 5: Limiter circuit diagram (conventional example)

FIG. 6 is a clamp circuit diagram (conventional example).

[Explanation of symbols]

Q ₇ ... upper transistor Q ₈ ... transistors Q ₉ ... lower transistor V ₂ ... upper-level voltage V ₃ ... lower level voltage I ₂ ... current source 2 ... clamp circuit

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

FIG. 2 is a circuit diagram of a video switch circuit with a clamp function showing a second embodiment of the present invention. In FIG. 2, parts having the same configurations as those of the first embodiment are designated by the same reference numerals in the drawing, the description thereof will be omitted, and only different configurations will be described. That is, the upper limit for the transistor Q _7, are not provided lower for Taranjisuta Q _9, etc., the current source I resistor R ₂ output level settling for ₂ are connected in series, via the output level adjusting resistor R ₂ The selected output is taken out from the current source I ₂ . Also, the transistor Q ₈
The emitter side of the operational amplifier 1 through the switch SW of the -
Connected to the input terminal, the switch SW is a clamp pulse
Switch on. The clamp voltage V ₄ is applied to the + input terminal of the operational amplifier 1. The operational amplifier 1 is resistance
It is a Miller integrating circuit consisting of anti-R ₃ and capacitor C
Ri, and supplies an output corresponding to the deviation of both the input voltage to the current source I _2, the current source I ₂ controls the amount of current in inverse proportion to the output. A clamp circuit 2 is configured by the operational amplifier 1, the current source I _{2, and the} like.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

Further, according to the second aspect, since the clamp function is added by controlling the current source itself for extracting the selected video signal, it is possible to simplify the circuit and prevent the signal deterioration as much as possible. Play. Again negative
V _be of the transistor by a clamp circuit for feedback control
Variation, temperature becomes a particularly strong circuit .

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

Further, according to claim 3, by connecting the upper limit transistor and the lower limit transistor to the transistor of the emitter follower structure to add a limiter function and controlling the current source itself for extracting the selected video signal. Since the clamp function is added, the circuit can be simplified and the signal deterioration can be prevented as much as possible. Also, with a clamp circuit that controls negative feedback
Variability of V _be of the transistor, temperature becomes a particularly strong circuit.
It

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

[Procedure Amendment 5]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

[Procedure correction 6]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

Claims (3)

[Claims] 1. A plurality of video input signals are selectively output according to a switching pulse, the selection signals are output via a transistor having an emitter follower structure, an emitter is connected to a base of the transistor, and an upper limit is applied to the base. An upper limit transistor for applying a level voltage to limit the upper limit level of the transistor output, and a lower limit transistor for emitter-coupled with the transistor and applying a lower limit level voltage to the base to limit the lower limit level of the transistor output. A video switch circuit characterized by being provided. 2. A current source for selectively outputting a plurality of video input signals in response to a switching pulse and extracting the selected output via an output level adjusting resistor, the output level adjusting resistor and the current source. The video switch circuit is provided with a clamp circuit for performing negative feedback control of the current of the current source according to a deviation between an output taken out from the common connection point and the clamp voltage. 3. A current source for selectively outputting a plurality of video input signals in response to a switching pulse and extracting the selected output via an output level adjusting resistor, the output level adjusting resistor and the current source. For outputting the selected output from the common connection point of the transistors through the transistor of the emitter follower configuration, connecting the emitter to the base of the transistor, and applying the upper limit level voltage to the base to control the upper limit level of the transistor output. A transistor is provided, which is emitter-coupled to the transistor and has a lower limit transistor that limits the lower limit level of the transistor output by applying a lower limit level voltage to the base, and the current depending on the deviation between the output of the transistor and the clamp voltage. Video featuring a clamp circuit for negative feedback control of the source current Switch circuit.