JPH05103461A - Voltage converting apparatus and video camera using the same - Google Patents

Abstract

PURPOSE:To obtain a voltage converting apparatus and a video camera using the same, wherein the output converting efficiency of the apparatus is not reduced and no fixed-pattern noise is generated on the screen of the video camera, even when using as an external pulse the pulse having a small duty factor. CONSTITUTION:Responding to the high level of a pulse 8 for changing over analog switches, respective common terminals c of analog switches 1, 2, 3 and 4 are connected with respective first change-over terminals a. Also, responding to the low level of the pulse 8 for changing over the analog switches, the respective common terminals c of the analog switches 1, 2, 3 and 4 are connected with respective second change-over terminals b. Thereby, when a load 7 is connected with an output terminal 6, if a capacitor C1 for voltage-charging is being charged, a capacitor C2 for voltage-charging is discharged to the load 7, and also, if the capacitor C2 for voltage-charging is being charged, the capacitor C1 for voltage-charging is discharged to the load 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage converter and a video camera.

[0002]

2. Description of the Related Art In recent years, voltage converters have been used as power sources for consumer equipment such as video cameras. The conventional voltage converter will be described below. FIG. 2 is a circuit diagram showing the configuration of a conventional voltage converter. In FIG. 2, 1
0 and 20 are analog switches, a is analog switch 1
0, 20 first switching terminals, b is analog switch 1
Second switching terminals of 0 and 20, c is analog switch 1
Common terminals of 0 and 20, 30 is an input voltage terminal, 40 is an output voltage terminal, 50 is an output load, and 60 is a pulse input for switching the analog switches 10 and 20 (hereinafter referred to as "analog switch switching pulse"). , C10 is a voltage charging capacitor, and C20 is an output voltage stabilizing capacitor.

As shown in FIG. 2, the voltage charging capacitor C10 has its positive side connected to the common terminal c of the analog switch 10.
, And the negative side is connected to the common terminal c of the analog switch 20. The analog switch 10 is connected so as to switch between the input voltage terminal 30 and the output voltage terminal 40 by the analog switch switching pulse 60, and the analog switch 20 switches between the ground and the input voltage terminal 30 by the analog switch switching pulse 60. Are connected.

The analog switch switching pulse 60 is HI.
At the GH level, the common terminal c of the analog switch 10 is connected to the input voltage terminal 30, and the common terminal c of the analog switch 20 is connected to the ground. Further, when the analog switch switching pulse 60 is at the LOW level, the common terminal c of the analog switch 10 is connected to the output voltage terminal 40, and the common terminal c of the analog switch 20 is connected to the input voltage terminal 30.

The operation of the conventional voltage conversion device thus configured will be described below. A case will be described in which a 5 [V] power supply is connected to the input voltage terminal 3 and a pulse having a duty ratio of 50 [%] is input as the analog switch switching pulse 60 at a frequency that is ½ the horizontal synchronizing signal. .. First, the analog switch switching pulse 60
Is HIGH, the common terminal c of the analog switch 10 is connected to the input voltage terminal 30, and the common terminal c of the analog switch 20 is connected to the ground. Therefore,
The voltage charging capacitor C10 is +5 with respect to the ground
It is charged to [V].

Next, the analog switch switching pulse 60
Is at the LOW level, the common terminal c of the analog switch 10 is connected to the output voltage terminal 40, and the analog switch 2
The common terminal c of 0 is connected to the input voltage terminal 30. At this time, the voltage charging capacitor C1 is charged to +5 [V] with reference to +5 [V]. Therefore, when seen from the ground, the output voltage terminal 4 has +10 [V].
The voltage of [V] is output.

By repeating the above operation, the input voltage +5 [V] is converted to +10 [V] and the load 50
The current will be supplied to.

[0008]

However, when the conventional voltage converter having such a structure is used as a power source for driving a solid-state image pickup element of a video camera, the analog switch switching pulse 60 has a half of the horizontal synchronizing signal. Since the pulse has a double frequency and a duty ratio of 50%, the charging / discharging operation of the voltage charging capacitor C10 is performed during the video period. In such a case, there is a possibility that the solid-state image sensor is affected via the ground line, and vertical stripe-shaped fixed pattern noise is generated on the screen.

On the other hand, in order to prevent the occurrence of this fixed pattern noise, the analog switch switching pulse 60 is
When a pulse whose logic level changes during the blanking period (for example, a horizontal synchronizing signal) is used, the duty ratio is 50
Since it is not [%] but small, the voltage charging capacitor C1
0 and the charging / discharging time of the output voltage stabilizing capacitor C20 becomes unbalanced, and there is a problem that the output conversion efficiency decreases.

An object of the present invention is to solve the above-mentioned conventional problems. Even if a pulse having a small duty ratio is used as an external pulse, the output conversion efficiency does not decrease, and a power source for driving a solid-state image pickup device of a video camera. Even when used as
It is an object of the present invention to provide a voltage conversion device that does not generate fixed pattern noise on a screen and a video camera using the voltage conversion device.

[0011]

According to a first aspect of the present invention, there is provided a voltage conversion device comprising: a first changeover switch having a first changeover terminal connected to an input voltage terminal and a second changeover terminal connected to an output voltage terminal; A capacitor having one end connected to the common terminal of the changeover switch of No. 1 and a second changeover switch having a common terminal connected to the other end of the capacitor, the first changeover terminal grounded, and the second changeover terminal connected to the input voltage terminal; A third changeover switch having a first changeover terminal connected to the output voltage terminal and a second changeover terminal connected to the input voltage terminal, and a second capacitor having one end connected to a common terminal of the third changeover switch, A fourth changeover switch in which a common terminal is connected to the other end of the second capacitor, a first changeover terminal is connected to an input voltage terminal, and a second changeover terminal is grounded is provided. Then, in response to the first logic level of the external pulse, the common terminals of the first, second, third and fourth changeover switches are connected to the respective first changeover terminals, and the second external pulse is inputted.
The common terminals of the first, second, third and fourth changeover switches are connected to the respective second changeover terminals in response to the logic level of.

A video camera according to a second aspect is the first aspect.
According to another aspect of the present invention, the voltage conversion device described above is provided, and a pulse for switching the first, second, third and fourth changeover switches during a blanking period of an image is used as the external pulse.

[0013]

According to the structure of the present invention, the common terminals of the first, second, third and fourth changeover switches are connected to the respective first changeover terminals in response to the first logic level of the external pulse. , The common terminals of the first, second, third and fourth changeover switches are connected to the respective second changeover terminals in response to the second logic level of the external pulse, so that a load is applied to the output voltage terminals. When connected, the second capacitor discharges to the load while the first capacitor is charging, and
When the second capacitor is charging, the first capacitor will discharge to the load. That is, the first and second capacitors complementarily charge and discharge, and the load is discharged regardless of the logic level of the external pulse. Therefore, even if a pulse with a small duty ratio is used as the external pulse, the output conversion efficiency does not decrease.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of a voltage converter according to an embodiment of the present invention. In FIG.
1, 2, 3, and 4 are analog switches serving as first, second, third, and fourth changeover switches, a is each first changeover terminal of analog switches 1, 2, 3 and 4, and b is analog switch 1 , 2, 3 and 4 second switching terminals, b common terminals of analog switches 1, 2, 3 and 4, 5 input voltage terminal, 6 output voltage terminal, 7 output load, 8 analog External pulse for switching the switches 1, 2, 3 and 4 (hereinafter referred to as "analog switch switching pulse"), C1 is a capacitor for voltage charging, C2
Is a voltage charging capacitor, and C3 is an output voltage stabilizing capacitor.

As shown in FIG. 1, the positive side of the voltage charging capacitor C1 is connected to the common terminal c of the analog switch 1, and the negative side thereof is connected to the common terminal c of the analog switch 2. Similarly, the positive side of the voltage charging capacitor C2 is connected to the common terminal c of the analog switch 3, and the negative side is connected to the common terminal c of the analog switch 4.

The analog switches 1 and 3 are connected so as to switch between the input voltage terminal 5 and the output voltage terminal 6 by the analog switch switching pulse 8. When the analog switch switching pulse 8 is HIGH level, the common terminal c of the analog switch 1 is connected to the input voltage terminal 5, and the common terminal c of the analog switch 3 is connected to the output voltage terminal 6. Also, the analog switch switching pulse 8 is LOW.
At the time of level, the common terminal c of the analog switch 1 is connected to the output voltage terminal 6 and the common terminal c of the analog switch 3
Are wired so as to be connected to the input voltage terminal 5.

The analog switches 2 and 4 are connected so as to switch between the ground and the input voltage terminal 5 by the analog switch switching pulse 8. When the analog switch switching pulse 8 is HIGH level, the common terminal c of the analog switch 2 is connected to the ground, and the common terminal c of the analog switch 4 is connected to the input voltage terminal 5. Further, when the analog switch switching pulse 8 is at the LOW level, the common terminal c of the analog switch 2 has the input voltage terminal 5
, And the common terminal c of the analog switch 4 is wired so as to be connected to the ground.

The operation of the voltage conversion device thus configured will be described below. A 5 [V] power supply was connected to the input voltage terminal 5, and a pulse (horizontal synchronizing signal) whose state changed between the blanking period and the video period was used as the analog switch switching pulse 8. As a result, the charging / discharging switching time for the large-capacity output voltage stabilizing capacitor C3 is excluded from the video period, and the occurrence of fixed pattern noise is prevented.

First, when the HIGH level of the horizontal synchronizing signal is input as the analog switch switching pulse 8, the common terminal c of the analog switch 1 is the input voltage terminal 5
, And the common terminal c of the analog switch 2 is connected to the ground. Therefore, the voltage charging capacitor C1
Is charged to +5 [V] with respect to the ground. Next, as the analog switch switching pulse 8, L of the horizontal synchronizing signal
When the OW level is input, the common terminal c of the analog switch 1 is connected to the output voltage terminal 6, and the common terminal c of the analog switch 2 is connected to the input voltage terminal 5. At this time, the voltage charging capacitor C1 is charged to +5 [V] with reference to +5 [V]. Therefore, when viewed from the ground, the output voltage terminal 6 has +10 [V].
The voltage of [V] is output. At the same time, the common terminal c of the analog switch 3 is connected to the input voltage terminal 5, and the common terminal c of the analog switch 4 is connected to the ground. Therefore, the voltage charging capacitor C2 is charged to +5 [V] with respect to the ground.

When the analog switch switching pulse 8 becomes HIGH again, the analog switch 1
The common terminal c of the analog switch 2 is connected to the input voltage terminal 5, and the common terminal c of the analog switch 2 is connected to the ground. As a result, the voltage charging capacitor C1 stops discharging the load 7 and the output voltage stabilizing capacitor C3, and is charged to +5 [V] with respect to the ground. At the same time, the common terminal c of the analog switch 3 is connected to the output voltage terminal 6,
The common terminal c of the analog switch 4 is connected to the input voltage terminal 5. At this time, the voltage charging capacitor C2 is +5
Since it is charged to +5 [V] with reference to [V], the output voltage terminal 6 is seen from the ground.
A voltage of +10 [V] is output to.

In this way, in response to the HIGH level of the analog switch switching pulse 8, the analog switches 1,
The common terminals c of 2, 3, and 4 are connected to the first switching terminals a, and the common terminals c of the analog switches 1, 2, 3, and 4 are connected to the first switching terminals a in response to the low level of the analog switch switching pulse 8. When the load 7 is connected to the output voltage terminal 6, the voltage charging capacitor C2 is discharged to the load 7 while the voltage charging capacitor C1 is being charged. When the voltage charging capacitor C2 is being charged, the voltage charging capacitor C1 is discharged to the load 7. Ie 2
By complementarily charging and discharging the individual capacitors (voltage charging capacitors C1, C2), the imbalance of the charging / discharging time is compensated for, and each analog switch 1, 2, 3 and 4 is pulsed with a low duty ratio. The voltage conversion efficiency does not decrease even if the drive circuit is driven.

As a result, the voltage converter is used as a power source for driving a solid-state image pickup device of a video camera, and as an analog switch switching pulse 8, a horizontal synchronization for switching the analog switches 1, 2, 3 and 4 during a blanking period of an image. By using the signal, it is possible to prevent the output conversion efficiency of the voltage conversion device from being lowered and to eliminate the fixed pattern noise on the screen.

In this embodiment, the voltage converter for generating a positive voltage has been described, but it can be realized by a voltage converter for generating a negative voltage. Further, in this embodiment, the case where the voltage conversion is performed by using one voltage conversion device has been described, but it is also possible to perform the voltage conversion by using a plurality of voltage conversion devices. Further, in this embodiment, the voltage conversion device using two voltage charging capacitors has been described.
A plurality of voltage charging capacitors may be used.

[0024]

According to the voltage converter of the present invention, the common terminals of the first, second, third and fourth changeover switches are connected to the first changeover terminals in response to the first logic level of the external pulse. Since the common terminals of the first, second, third and fourth changeover switches are connected to the respective second changeover terminals in response to the second logic level of the external pulse, they are connected to the output voltage terminals. With the load connected, the second capacitor discharges to the load while the first capacitor is charging,
Moreover, when the second capacitor is being charged, the first capacitor is discharged to the load. That is, the first and second capacitors complementarily charge and discharge, and the load is discharged regardless of the logic level of the external pulse. Therefore, even if a pulse with a small duty ratio is used as the external pulse, the output conversion efficiency does not decrease.

As a result, this voltage conversion device is used as a power source for driving a solid-state image pickup device of a video camera, and a pulse for switching the first, second, third and fourth changeover switches during an image blanking period as an external pulse. By using, it is possible to prevent the output conversion efficiency of the voltage conversion device from decreasing and to eliminate the occurrence of fixed pattern noise on the screen.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a voltage converter according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional voltage conversion device.

[Explanation of symbols]

 1 analog switch (first changeover switch) 2 analog switch (second changeover switch) 3 analog switch (third changeover switch) 4 analog switch (fourth changeover switch) 5 input voltage terminal 6 output voltage terminal 8 analog Switch switching pulse (external pulse) C1 voltage charging capacitor (first capacitor) C2 voltage charging capacitor (second capacitor) a first switching terminal b second switching terminal c common terminal

Claims (2)

[Claims] 1. A first changeover switch having a first changeover terminal connected to an input voltage terminal and a second changeover terminal connected to an output voltage terminal; and a capacitor having one end connected to a common terminal of the first changeover switch. Connecting a common terminal to the other end of this capacitor, grounding the first switching terminal and connecting a second switching terminal to the input voltage terminal, and connecting the first switching terminal to the output voltage terminal A third changeover switch having a second changeover terminal connected to the input voltage terminal, a second capacitor having one end connected to a common terminal of the third changeover switch, and a common terminal to the other end of the second capacitor And a fourth change-over switch in which the first change-over terminal is connected to the input voltage terminal and the second change-over terminal is grounded, in response to the first logic level of the external pulse. , The common terminals of the third and fourth changeover switches are connected to the respective first changeover terminals, and in response to the second logic level of the external pulse, the first, second, third and fourth changeovers are performed. A voltage converter in which each common terminal of the switch is connected to each second switching terminal. 2. A video camera comprising the voltage conversion device according to claim 1, wherein the external pulse is a pulse for switching the first, second, third and fourth changeover switches during a blanking period of an image. ..