JP3332800B2 - CCD camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CCD camera,
More particularly, the present invention relates to a CCD camera having a CCD panel and a driver for receiving a positive power supply voltage and a negative power supply voltage from a power supply circuit, respectively, and applying a sweep pulse from an output terminal of the driver to a substrate voltage terminal of the CCD.

[0002]

2. Description of the Related Art Referring to FIG.
The camera 10 includes a power supply circuit 12.
Outputs two power supply voltages of 15 V and -7.5 V in this embodiment. That is, the power supply circuit 12 includes a switching controller 14, which is activated by a power-on signal from a microcomputer (not shown) and deactivated by a power-off signal. Switching controller 14
Receives a power supply voltage VB from, for example, a battery (not shown), and when activated, outputs a switching signal to the base of pnp transistor Q1 according to, for example, a PWM method. The emitter-collector of the transistor Q1 is connected between the power supply voltage from the battery and the first terminal of the primary winding of the transformer T, and the ground terminal of the primary winding of the transformer T is grounded.

Two circuits 16 are provided on the secondary winding side of the transformer T.
And 18 are formed, and circuit 16 generates a positive voltage, for example, 15V. The circuit 18 generates a negative voltage, for example, -7.5V. 15 generated by the first circuit 16
V is output from the first terminal 16a, and -7.5V generated by the second circuit 18 is output from the second terminal 18a.

The first circuit 16 is a so-called flyback circuit, and includes a rectifying diode D1 connected to a first terminal of a secondary winding of the transformer T, a smoothing capacitor C11 for receiving a DC voltage from the diode D1, and a smoothing capacitor. Choke coil L1 and capacitor C connected to C11
12 is included. The second circuit 18 is also a flyback circuit, and includes a rectifier diode D2 connected to a second terminal of the secondary winding of the transformer T and a smoothing capacitor C
21 and a filter composed of a choke coil L2 and a capacitor C22.

The first terminal 16a and the second terminal
15V output from terminal 18a and -7.
5V is applied to a V driver 22 and a CCD panel 24 included in the camera circuit 20. From the output terminal SUB of the V driver 22, a sweep pulse of the electronic shutter is supplied to the CCD.
The voltage is supplied to the substrate voltage terminal VSUB of the panel 24. In the CCD panel 24, a substrate voltage terminal VSUB is used.
Through a diode (not shown), for example, 5V
Is applied. Therefore, between the output terminal SUB and the substrate voltage terminal VSUB, a 15V clamper composed of the capacitor C3, the diode D3 and the resistor R1, and a 5V clamper composed of the capacitors C4, R2 and C5 are inserted. A sweep pulse of, for example, 6 to 12 V is applied from output terminal SUB to substrate voltage terminal VSUB.

[0006] As the V driver 22, "CXD
An IC such as “1267AN” or “CXD1250N” may be used, or may be built in a timing generator such as “CXD2485AR”.

[0007]

On the other hand, such a CC
When driving the CCD panel 24 in the D camera 10, a voltage range which can be taken between the terminals or between the terminals is defined as an absolute maximum rating. For example, at the substrate voltage terminal VSUB, the lower limit of the absolute maximum rating is-
0.3 to -0.5 V or more. Such a rating is naturally complied with in a steady state, but may deviate from the standard when a power switch (not shown) of the CCD camera is turned on / off.

[0008] In the prior art shown in FIG.
+ V (for example, 15 V) output from the terminal 16a is
Since it is the main power supply of the CCD panel 24, the capacitance of the noise removal filter capacitors C11 and C12 is changed to the capacitance of the -V (for example, -7.5V) noise removal filter capacitors C21 and C22 output from the second terminal 18a. Is larger. Therefore, in the power supply circuit 12 of the prior art in FIG. 1, as shown in FIG. 2, when the power is turned on, the rise of + V (start-up time) tends to be later than the rise of -V. Further, since the load of -V is smaller (approximately 1/5) than that of + V, the fall (discharge time) of -V when the power is turned off tends to be later than the fall of -V.

When the power supply circuit 12 is used as described above, when the power supply is turned on / off, as shown in FIG.
A negative voltage may be generated from the output terminal SUB of the substrate voltage, and a negative voltage lower than the rated voltage (−VL) may be applied to the substrate voltage terminal VSUB due to the negative voltage. That is, as shown in FIG. 2, when the negative voltage -V is started before the positive voltage + V, a negative voltage is generated from the output terminal SUB of the V driver 22,
This negative voltage is applied to the substrate voltage terminal VSUB of the CCD panel 24 before the positive voltage rises. Therefore, the potential of the substrate voltage terminal VSUB becomes equal to the rated voltage −VL
It becomes smaller.

For this purpose, it is conceivable to turn on the positive voltage and the negative voltage in the order of turning on the power switch and turn off the power supply in the reverse order when turning off the power.
In the case of 2, since both the first circuit 16 and the second circuit 18 are realized by the flyback method, that is, one transformer T is provided with the first and second taps to generate both positive and negative voltages. Therefore, it is not always easy to output the positive and negative voltages in the above-described order, and it is easily affected by the capacitance of the above-mentioned capacitor.

Therefore, the prior art shown in FIG.
A two-stage voltage clamper (capacitor) is interposed between the output terminal SU and the substrate voltage terminal VSUB.
Although the time during which a negative voltage lower than the rating from B is applied to the terminal VSUB is delayed as much as possible, in the prior art shown in FIG. 1, the potential of the substrate voltage terminal VSUB is not rated when the power is turned on / off. There is a problem that the voltage becomes lower than -VL.

[0012] Therefore, a main object of the present invention is to provide a CCD camera in which the substrate voltage terminal potential does not become lower than the lower limit of the rated voltage.

[0013]

SUMMARY OF THE INVENTION The present invention provides a power supply circuit for outputting a positive power supply voltage and a negative power supply voltage, and a CCD for receiving the positive and negative power supply voltages from the power supply circuit, respectively.
A CCD camera comprising a panel and a driver, wherein a sweep pulse is applied from an output terminal of the driver to a substrate voltage terminal of the CCD panel. The CCD camera conducts between a substrate voltage terminal and a ground potential by a negative voltage of the substrate voltage terminal. like,
A CCD camera characterized in that a diode is connected.

[0014]

For example, when the power switch of the camera is turned on, a power-on signal is output from the microcomputer of the camera.
In response to the power-on signal, the power circuit is activated,
The negative voltage −V and the positive voltage + V are output from the second terminal and the first terminal in this order, respectively. Therefore, a negative voltage is output from the output terminal of the driver. At this time, since the positive voltage has not been applied yet, the negative voltage is applied to the substrate voltage terminal of the CCD panel.

On the other hand, the diode connected between the substrate voltage terminal of the CCD panel and the ground is forward biased by this negative voltage. Therefore, the diode is turned on, and the potential of the substrate voltage terminal becomes lower than the ground voltage by the forward voltage of the diode. Therefore, if the magnitude (absolute value) of the forward voltage of the diode is set smaller than the lower limit voltage (absolute value) of the absolute maximum rating, a negative voltage larger than the lower limit voltage is applied to the substrate voltage terminal of the CCD panel. Can be prevented.

When the power switch is turned off, the positive voltage + V falls earlier than the negative voltage -V, so that a negative voltage may be applied to the substrate voltage terminal of the CCD panel in the same manner as when the power is turned on. However, even in this case, it is possible to prevent a negative voltage larger than the lower limit voltage from being applied to the substrate voltage terminal of the CCD panel by the action of the diode described above.

[0017]

According to the present invention, it is possible to prevent a voltage lower than the lower limit of the absolute maximum rating from being applied to the substrate voltage terminal of the CCD panel with a simple configuration. Therefore,
There is no need to strictly design or adjust the rise and fall of the positive voltage and the negative voltage, and a component such as a capacitor having an optimum capacitance value can be used for the power supply circuit.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0019]

Referring to FIG. 3, a CCD camera 10 of this embodiment is the same as the prior art of FIG. 1 except for the following, and therefore, the same or similar parts are denoted by the same reference numerals. Therefore, duplicate description will be omitted. That is, in the embodiment of FIG. 3, the substrate voltage terminal VSU of the CCD 24 is used.
A diode D5 is connected between B and ground. That is, the cathode of the diode D5 is connected to the substrate voltage terminal VSUB.
And the anode is connected to the ground potential.

As the diode D5, the diode D5
Where VF is the absolute value of the forward voltage of, and VL is the absolute value of the lower limit of the absolute maximum rating, VF <VL (−VF> −V
A diode satisfying L), for example, a Schottky diode is used. In a CCD camera using an electronic shutter, if the reverse blocking voltage of the diode D5 is Vr, the amplitude of the sweep pulse of the electronic shutter is Ves, and the maximum value of the substrate voltage terminal VSUB is Vmax, Vr> Ve
It is necessary to select a diode that further satisfies s + Vmax. That is, at the time of the electronic shutter operation, since the reverse voltage of the maximum Ves + Vmax is applied to the diode D5, the reverse blocking voltage Vr of the diode D5 becomes the voltage Vr.
Must be greater than es + Vmax.

In operation, for example, the CCD camera 10
When a power switch (not shown) is turned on, a power-on signal is output from a microcomputer (not shown) of the camera. In response to this power-on signal, power supply circuit 12 is activated, and as shown in FIG. 4, negative voltage -V and positive voltage +
V is output from the second terminal 18a and the first terminal 16a in this order. Therefore, a negative voltage is first output from the output terminal SUB of the V driver 22. At this time, since the positive voltage has not been applied yet, the negative voltage is applied to the substrate voltage terminal VSUB of the CCD panel 24.

On the other hand, the substrate voltage terminal V of the CCD panel 24
The diode D5 connected between SUB and ground is forward biased by this negative voltage. Therefore, the diode D5 turns on and the substrate voltage terminal VSUB
Is lower than the ground voltage (0 V) by the forward voltage (VF) of the diode D5. And the diode D
5 is VF <VL (-VF) as described above.
> -VL), so that a large negative voltage lower than the lower limit voltage VL is prevented from being applied to the substrate voltage terminal VSUB of the CCD panel 24. That is, the forward voltage of the diode D5 can prevent the substrate voltage terminal VSUB from lowering below the lower limit.

When the power switch is turned off, the positive voltage + V falls earlier than the negative voltage -V, so that a negative voltage is applied to the substrate voltage terminal VSUB of the CCD panel 24 in the same manner as when the power switch is turned on. However, even in this case, the action of the diode D5 prevents the application of a large negative voltage lower than the lower limit voltage VL to the substrate voltage terminal VSUB.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of the related art.

FIG. 2 is a waveform diagram showing that a negative voltage less than the rated voltage is applied to a substrate voltage terminal of a CCD panel in the prior art.

FIG. 3 is a circuit diagram showing one embodiment of the present invention.

FIG. 4 is a waveform diagram showing that a negative voltage lower than the rated voltage is not applied to the substrate voltage terminal of the CCD panel in the embodiment of FIG. 1;

[Description of References] 10: CCD camera 12: Power supply circuit 16a: First terminal 18a: Second terminal 20: Camera circuit 22: V driver 24: CCD panel SUB: Output terminal VSUB: Substrate voltage terminal D5: Diode

Claims (1)

(57) [Claims] A power supply circuit for outputting a positive power supply voltage and a negative power supply voltage; and a CCD panel and a driver for receiving the positive power supply voltage and the negative power supply voltage from the power supply circuit, respectively. In a CCD camera to which a sweep pulse is applied to a substrate voltage terminal of a CCD panel, a diode is connected between the substrate voltage terminal and a ground potential so as to conduct by a negative voltage of the substrate voltage terminal. CCD camera.