JPH04105637A - Camera for electronic endoscope - Google Patents

Abstract

PURPOSE:To transfer a signal charge from a photo detecting section with no charge left at a transfer section by providing a reverse transfer pulse application means at a CCD for vertical transfer to discharge the charge retaining within the transfer section to a drain. CONSTITUTION:When lighting of colors of R, G and B is performed sequentially with interruption periods, a reverse transfer pulse PD is inputted into a CCD5 through a CCD drive circuit 6 from a timing pulse generator 19 immediately before the interruption period begins from the lighting period. An electric charge retaining in a CCD5b for vertical transfer is dischanged sequentially to a drain section 5d as indicated by the arrow D to make the CCD5b for vertical transfer empty with no charge existing. Under such a condition, by applying a light charge transfer pulse P to the CCD5, a signal charge accumulated at a photo detecting section 5a is moved at a stroke to a transfer path 5b. Moreover, the charge transferred the CCD5b for vertical transfer is transferred to a CCD5c for horizontal transfer by a normal transfer pulse PV of a V system clock while being read out from the CCD5c for horizontal transfer as indicated by the arrow T by a horizontal transfer pulse PH to be transmitted to a processor 7.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention is directed to preventing or suppressing the occurrence of smear, etc. in the video signal obtained by the imaging means in electronic endoscopes used for medical, industrial, etc. purposes. The present invention relates to an imaging device for an electronic endoscope that can perform the following operations.

[Prior Art] An endoscope generally has an insertion section inserted into a body such as a human body connected to a main body operation section, and an observation mechanism is provided at the distal end of the insertion section. In recent years, this observation mechanism has been equipped with a solid-state image sensor such as a CCD as an imaging means, and by exposing this solid-state image sensor, the image of the subject is converted into an electrical signal, and this signal is transmitted to a processor. Electronic endoscope systems have come into use in which the processor performs predetermined signal processing to form a composite color video signal, and the video is displayed on a monitor device based on this video signal. It's coming.

Here, solid-state imaging devices are classified into interline transfer method and frame transfer method depending on their signal charge transfer method, and frame interline transfer method is a combination of these interline transfer method and frame transfer method. Solid-state imaging devices have also been developed. here,
In a solid-state image sensor using an interline transfer method, a light receiving section and a vertical transfer CCD are arranged alternately, and a horizontal transfer path is connected to the vertical transfer CCD. After receiving reflected light from the subject through time exposure and accumulating signal charges, the signal charges accumulated in this light receiving section are transferred to a CCD for vertical transfer.
This signal is then read out line by line sequentially via a horizontal transfer CCD and transmitted to the processor. In addition, the frame transfer type has a light receiving section and a storage section, and the signal charges accumulated in the light receiving section are transferred to the storage section at one time, and the signals are sequentially read out from this storage section. This is what I did. Furthermore, the frame interline transfer system has a storage section as in the frame transfer system, in addition to the structure of the interline transfer system described above.

[Problem to be Solved by the Invention 1] When a solid-state image sensor is exposed to light, if light enters a portion other than the light receiving portion, an electric charge is generated in the portion. For example, in an interline transfer type device, when strong light is incident and this light enters a vertical transfer path, charges are generated in the vertical transfer path and remain in the corresponding portion. and,
When charges are transferred from the light receiving section to the vertical transfer path, the charges remaining in the vertical transfer path are added and read out, resulting in a false signal and a deterioration in the image quality of the video. For this reason, it is necessary to prevent light from entering any part of the solid-state image sensor other than the light receiving section.

Therefore, in order to prevent light from entering the transfer section, which consists of a vertical transfer CCD (vertical transfer path), a horizontal transfer CCD (horizontal transfer path), and a storage section, it is generally necessary to install a light shield on these transfer sections. Light is blocked by forming a mask or the like. Here, it is relatively easy to completely block light in the horizontal transfer path (solid-state image sensor using interline transfer method) and storage section (solid-state image sensor using frame transfer method and frame interline transfer method). . However, since the vertical transfer path (solid-state image sensors using interline transfer method and frame interline transfer method) is installed adjacent to the light receiving section, it is extremely difficult to completely shield this vertical transfer path from light. Have difficulty.

As a result, when strong light hits the vertical transfer path during exposure, the strong light also enters the vertical transfer path, causing charge to accumulate, causing so-called smear, in which light stripes appear in the vertical direction. Although it can be expected that such smear can be improved to some extent at the image processing stage, there is a limit to how much smear can be suppressed by such image processing, and in practice, the occurrence of this smear is considered unavoidable. It had been.

Moreover, this vertical transfer CCD has a fixed charge capacity, and if a charge exceeding this charge capacity is sent from the light receiving section, so-called blooming will occur. Therefore, it is necessary to adjust the overflow drain voltage for the light receiving section, but as mentioned above, since the transfer section cannot completely block light, the saturation voltage level is
The overflow drain voltage must be set in consideration of the amount of light expected to enter the transfer section, and the overflow drain voltage must be set to a certain low level. As a result, there is also the problem that the dynamic range is reduced.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an electronic endoscope that can transfer signal charges from a light receiving section without any charge remaining in the transfer section. An object of the present invention is to provide an imaging device.

[Means for Solving the Problems 1] In order to achieve the above-mentioned object, the present invention provides a CCD for vertical transfer for transferring signal charges accumulated in a light receiving part in a CCD type solid-state image sensor. The device is characterized in that it includes a reverse transfer pulse applying means that applies a reverse transfer pulse before moving the signal charge and causes the charge accumulated in the transfer section to be swept out to drain.

[Operation] By applying a reverse transfer pulse to the vertical transfer CCD before transferring the signal charges accumulated in the light receiving section, even if light enters the transfer section and charges are generated, , this charge is reliably swept out to the drain by the reverse transfer pulse, leaving the transfer section completely empty. As a result, only the charges accumulated in the light receiving section are transferred, false signal components are removed, and smear and the like are reliably prevented. Also, in this way, C for vertical transfer
Since unnecessary charges are not added to the transferred charges in a CD, the saturation voltage can be set based purely on the signal charge accumulated in the light receiving section, which improves the dynamic range. can be improved.

Here, it is effective to apply the reverse transfer pulse immediately before the movement of the signal charge from the light receiving section, and especially for each wavelength light of R (red), G (green), and B (blue). illumination light,
By sequentially irradiating each with a light blocking area in between, color image signals of the three colors RlG and B are acquired in a sequential manner.
When driving a solid-state imaging device using a so-called field sequential method, it is most preferable to apply a reverse transfer pulse after entering a light-shielding period. Furthermore, if the driving is performed so that the reverse transfer of unnecessary charges and the movement and transfer of signal charges are completed during this light shielding period, there is no room for smear or the like to occur.

In addition, in the case where image signals of each color are obtained by sequential illumination of R, G, and B as described above, two semi-field image signals of an odd field and an even field are obtained. , a reverse transfer pulse may be applied to the vertical transfer CCD before the first read semi-field signal charge moves to the vertical transfer CCD.

[Embodiment 1] Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

First, FIG. 1 shows the overall configuration of an image manipulation device for an electronic endoscope. In the figure, ■ indicates a light source lamp, and 2 indicates a light guide.
A rotary color filter 3 is interposed in the illumination optical path leading to point a. As is well known, this color filter 3 includes an R filter region that transmits light in the R (red) wavelength region;
A G filter region that transmits light in the G (green) wavelength region, and a B
B filter regions that transmit light in the (blue) wavelength range are formed with light shielding regions sandwiched therebetween. Therefore, during one rotation of the color filter 3, sequential illumination with wavelength light of each color of R, G, and B is performed with a light shielding period in between. The R, G, and B illumination lights are sequentially transmitted by the light guide 2 and irradiated from the output end 2b toward the subject via the illumination lens 4.

Next, reference numeral 5 indicates a CCD as a solid-state imaging element. By exposing this CCD 5 to light while the above-mentioned R, G, and B illumination is being performed sequentially, the image of the subject is transferred to the CCD.
The image signals are formed on the imaging plane of CCD 5 and subjected to photoelectric conversion, and by applying clock pulses from CCD drive circuit 6 to CCD 5, the image signals are sequentially read out. This R,G,
The image signals of each color of B are transmitted to the processor 7, and signal processing is performed by the processor 7.

The processor 7 has a first signal processing means 10 that processes the output signal from the CCD 5, and the output signal of the first signal processing means 10 is converted into a digital signal by the A/D converter 11. The data will then be stored in the field memory 12. The data of each color written in the field memory 12 in this way is transferred to D/A converters 13R and 13G.

13B, the signal is converted into an analog signal, further subjected to signal processing by the second signal processing means 14, and sent to the color encoder I5. Then, the color encoder 15
A simultaneous composite color video signal is output.

A memory drive circuit 16 is provided to read data in the field memory 12 described above and drive control of the readout, and the memory drive circuit I
6 detects when each of the R, G, and B filter regions of the color filter 3 faces the illumination optical path and selects the R, G, and B filter regions.
, H, and a synchronizing signal generator 18.

Therefore, based on the signals from the enable signal generator 17 and the synchronization signal generator 18, writing and reading of data into the field memory 12 is controlled. In addition, the synchronization signal generator 18
The synchronizing signal generated from the CCD drive circuit 6 is converted into a desired pulse signal by a timing pulse generator 19
It is now transmitted to

With this configuration, the CCD 5 is exposed to light during each of the R, G, and B illumination periods by the R filter area, G filter area, and B filter area provided in the color filter 3 with the light shielding area in between, respectively. During the shading period, the C
The signal charge is read out by driving the CD 5 and transmitted to the processor 7 .

By the way, as the above-mentioned CCD 5, for example, as shown in FIG. 2, a large number of light receiving sections 5a each consisting of a large number of photodiodes and a large number of vertical transfer CCDs 5b are arranged alternately in the vertical direction, and this vertical transfer CCD 5b There is a so-called interline transfer system in which a horizontal transfer CCD 5c is connected to the end of the transfer line. This type of CCD 5 first exposes its light-receiving section 5a to light while being irradiated with illumination light to accumulate signal charges, and when it enters a light-blocking period, CCD
Based on the drive signal from the CD drive circuit 6, the light receiving section 5
The charges accumulated in a are transferred to the vertical transfer CCD 5b, and then signal charges are sequentially transferred from the vertical transfer CCD 5b to the horizontal transfer path 5C for each line in the horizontal direction.

Then, signals are sequentially read out from this horizontal transfer CCD 5c and transmitted to the processor 7.

In order to prevent light from entering the vertical transfer CCD 5b and the horizontal transfer CCD 5c while exposing the light receiving section 5a described above, these transfer paths 5b are
, 5c are shielded from light by applying a light shielding mask. However, if strong light hits these transfer paths, especially the vertical transfer CCD 5b installed adjacent to the light receiving section 5a, the light may enter the vertical transfer CCD 5b. When light enters, a photoelectric conversion action is performed within the vertical transfer CCDSb, and charges are generated. If the charges generated in the vertical transfer CCD 5b are sent to the processor 7 along with the signal charges in this way, it will cause smear and the like in the image.

By the way, CCDs are usually structured to have an overflow drain mechanism to drain out the charges when charges exceeding a predetermined value are accumulated. Therefore, in the present invention, this overflow drain mechanism is used to drain the charges accumulated in the vertical transfer CCD 5b to the drain portion 5d of the horizontal transfer CCD 5c.

That is, as shown in FIG. 3(a), R, G.

In the case where the illumination of each color B is performed sequentially with each shading period in between, as shown in FIG.
A reverse transfer pulse PD is inputted to the CCD 5 from time to time via the CCD drive circuit 6. As a result, as shown by the arrows in FIG. 2, the charges accumulated in the vertical transfer CCDSb are sequentially swept out toward the drain section 5d, leaving the vertical transfer CCD 5b in an empty state with no charges. Make it. In this state, by applying a photocharge transfer pulse P to the CCD 5, the signal charges accumulated in the light receiving section 5a are transferred to the transfer path 5.
Move them all at once to b. Furthermore, the charges transferred to the vertical transfer CCD 5b in this way are sequentially transferred to the horizontal transfer CCD 5c by the normal transfer pulse Pv of the system clock.
At the same time, as shown by the arrow T in the figure, the horizontal transfer pulse PH causes the horizontal transfer CC
D5c and transmitted to the processor 7.

In this way, before moving signal charges from the light receiving section 5a to the vertical transfer CCD 5b, the reverse transfer pulse PD can be transmitted to the vertical transfer CCD 5b to sweep the charges to the -H drain section 5d. By leaving the vertical transfer CCD 5b in an empty state, even if light enters the vertical transfer CCD 5b due to being exposed to strong light and generates a charge, this charge will not be transferred from the light receiving section 5a. is not added to the moving charge. As a result, processor 7
The composite color video signal obtained by the processing is free from smear and the like (and its image quality is extremely improved).

Furthermore, this reverse transfer sweeps out the charges from the vertical transfer CCD 5b and moves the signal charges from the light receiving section 5a,
If the transfer and readout are completed within the light shielding period, there is no room for unnecessary charges to be generated in the vertical transfer CCD 5b.

Therefore, this reverse transfer pulse PD is transmitted to the synchronization signal generator 18.
Based on the V-system timing pulse sent from the timing pulse generator 19 to the CCD drive circuit 6, the CCD drive circuit 6 can output it as a pulse signal.

Moreover, as described above, when charge is transferred to the vertical transfer CCD 5b, since no charge remains in the vertical transfer CCD 5b, the overflow drain voltage is set to the maximum charge capacity of the vertical transfer CCD 5b. As a result, the dynamic range can be improved.

By the way, in the above case, the reverse transfer pulse PD is applied to the vertical transfer CCD 5b during the exposure period, but after the reverse transfer pulse PD is applied, the charge transfer pulse P is transmitted. CCD5 for vertical transfer
There is a risk that charge may be stored in b. Considering this point, it is preferable to apply the reverse transfer pulse PD after the light shielding period has started. For this purpose,
As shown in FIG. 3(C), the reverse transfer pulse PD may be applied at the same time as the exposure period ends and the light shielding period begins. However, by performing this reverse transfer, the vertical transfer CC
A predetermined time is required until the charges in DSb are discharged to the drain. Therefore, the light shielding period must also be made longer by this reverse transfer time. In order to avoid a prolonged light-blocking period due to this, the clock frequency of the reverse transfer pulse is increased to perform highway transfer.

Next, as an imaging means, a CCD 5 shown in FIG.
0 can be used. That is, as is clear from the figure, this CCD 50 has a light receiving section 50a and a light receiving section 50a.
The CCD 5 is similar to the CCD 5 described above in that a vertical transfer CCD 50b is provided adjacent to the CCD 50b, but a storage section 50c is further provided. The number of pixels in the storage section 50c is half the number of pixels in the light receiving section 50a.

Note that the sensitivity of the light receiving section 50a is the same as that of the conventional C.
Use one that has twice the sensitivity of a CD. As a result, the number of pixels in the vertical direction of the light receiving section 50a can be approximately half that of those commonly used in conventional endoscopes. However, in order to maintain good resolution in the horizontal direction, it is preferable that the number of pixels in the horizontal direction is not much different from that of a conventional CCD.

This CCD 50 uses a frame interline transfer method.
This type of CCD is normally driven as follows. First, as shown in FIG. 5(a), charges are accumulated in the light receiving section 50a during the exposure period, and when the light-shielding period begins, the first charge is accumulated as shown in FIG. 5(b). The signal charges of odd lines in the vertical direction in the light receiving section 50a are moved all at once to the vertical transfer CCD 50b by the charge transfer pulse P1, and then the signal charges are sent to the storage section 50c. Next, by applying the second charge transfer pulse P2, the signal charges of the even lines are transferred to the CC for vertical transfer.
1 from the storage unit 50c.
The signals are read out line by line continuously to obtain an odd semi-field image signal (here, as the semi-field image signal, in addition to reading out every other line in the horizontal direction, 2-line mixed reading is also performed). When performing this two-line mixed readout, one line and the previous line should be added and read out to form an odd semi-field image signal, and the line and the line after it should be added and read out. ) When reading out the odd semi-field image signal is completed, the vertical transfer CCD 50
The signals of even lines located within b are transferred to the storage section 50c, and the signals are sequentially read line by line from this storage section 50c, thereby obtaining even semifield image signals. Once these odd semi-field image signals and even semi-field image signals are stored in the field memory 12, and when read from the field memory I2, as shown in FIG. 5(C), the odd and even semi-field image signals are By alternately reading out the image signals line by line, one field image signal can be obtained.

If this CCD 50 is used, the number of pixels can be reduced as a whole, so the imaging means can be made smaller, and there are advantages such as an increase in the readout speed of signals from the CCD 50.

Therefore, when using this CCD 50, as shown in FIG.
), after entering the shading period,
At a stage before the first charge transfer pulse P is applied, a reverse transfer pulse PD is supplied to the vertical transfer CCD 50b,
The charge accumulated in the vertical transfer CCD 5 (Ib) can be swept out to the drain.If the charge is swept out at high speed by this reverse transfer pulse PD, the vertical transfer can be completed in a short time. The transfer CCD 50b can be emptied, and the light receiving section 50b has a small number of pixels in the vertical direction, and since the storage section 50c is provided in addition to the vertical transfer CCD 50b, a short light-shielding period can be achieved. In the meantime, after emptying the vertical transfer CCD 50b, the odd semi-field image signal and the even semi-field image signal can be read out.

Here, the operation of the CCD 50 in FIG. 4 has been explained using the waveform diagram in FIG. 5, but the number of pixels of the CCD 5 in FIG.
When the number of pixels is relatively small, such as 20,000 pixels, the operation shown in FIG. 5 can be similarly performed. That is, in the CCD 5 of FIG. 2, as shown in FIG. 5(a), charge is accumulated in the light receiving part 5a during the exposure period, and as shown in FIG. 5(b) during the light-blocking period, First charge transfer pulse P
.

As a result, the signal charges of the odd lines are transferred all at once from the light receiving section 5a to the vertical transfer CCD 5b, and the signal charges are normally transferred using the vertical transfer pulse PVI. Next, by applying the second charge transfer pulse P2, charges on even lines are transferred all at once to the vertical transfer CCD 5b, and then normal transfer is performed sequentially in the vertical transfer CCDSb using the vertical transfer pulse PV2, and from the horizontal transfer CCD 5c. Take it out as a signal.

Then, when these odd semi-field signals and even semi-field signals are once stored in the field memory 12 and read out from the field memory 12, they are stored in the field memory 12 as shown in FIG.
), one frame image is formed by alternately and sequentially reading odd and even semifield signals one line at a time. Here, as is clear from FIG. 5, after entering the light shielding period, the first charge transfer pulse P
, is applied to the vertical transfer CCD 5b, and the smear component charges accumulated in the vertical transfer CCD Sb are swept out to the drain portion 5d.

[Effect of the Invention 1] As explained above, the present invention provides reverse transfer pulse applying means to transfer the signal charges accumulated in the light receiving section to the transfer section for transferring the signal charges from the light receiving section. Since the configuration is configured to apply a sending pulse, unnecessary charges generated in the vertical transfer CCD are not added when signal charges are moved, and false signals such as smear are no longer generated. In addition, it is possible to raise the level of the overflow drain voltage in the light receiving section, thereby improving the dynamic range and improving the image quality of the image obtained by the imaging means.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an imaging device for an electronic endoscope showing one embodiment of the present invention, and FIG. An explanatory diagram of the configuration of the solid-state image sensor used in the second embodiment, FIG. 3(a) is a timing chart regarding illumination light irradiation, and FIG. 3(b) is a diagram showing the V of the solid-state image sensor in the first embodiment. 3(c) is a drive timing chart of the system clock of the solid-state image sensor in the second embodiment. FIG. 4 is a drive timing chart of the system clock used in the third embodiment of the present invention. FIGS. 5(a), 5(b), and 5(c) are explanatory diagrams of the configuration of the image sensor, and irradiation of illumination light in the third embodiment of the present invention;
FIG. 3 is a timing chart regarding driving of the system clock of the solid-state image sensor and reading of signals from the field memory. 5.50: CCD, 5a, 50a: Light receiving section, 5b. 50b: CCD for vertical transfer, 5C: CCD for horizontal transfer,
5d: drain section, 50c: storage section, 6: CCD drive circuit, 7: processor, IO: first signal processing means, 12:
field memory, 14: second signal processing means, 16.
Memory drive circuit, 18: synchronous signal generator, J9: timing pulse generator.

Claims (4)

[Claims] (1) Equipped with a CCD-type solid-state image sensor as an imaging means provided at the tip of the insertion section and a processor that processes signals from this solid-state image sensor, and captures a subject image under illumination light from an illumination device. In an image capturing device, a reverse transfer pulse is applied to a vertical transfer CCD for transferring signal charges accumulated in a light receiving section of the solid-state image sensor before moving the signal charges from the light receiving section, and the vertical transfer CCD is transferred to the vertical transfer CCD. What is claimed is: 1. An imaging device for an electronic endoscope, comprising a reverse transfer pulse applying means for sweeping out charges accumulated in the drain section. (2) The illumination device sequentially illuminates with wavelength light of each color of R, G, and B with a shading period in between, and after the shading period starts after this illumination period, the reverse transfer pulse applying means The imaging device for an electronic endoscope according to claim 1, wherein a reverse transfer pulse is applied. (3) The configuration is such that, during the light shielding period, accumulated charges are swept out from the vertical transfer CCD, signal charges are moved and transferred from the light receiving section to the vertical transfer CCD, and signals are read from the transfer section. The imaging device for an electronic endoscope according to claim (2), characterized in that: (4) Two types of image signals, odd-numbered lines and even-numbered lines, are read out from the solid-state image sensor during the light-blocking period after the illumination period by the illumination device, and the first signal of these two line image signals is read out from the solid-state image sensor. Claims (1) and (2), characterized in that the reverse transfer pulse is applied to the transfer section by the reverse transfer pulse applying means before the charge is transferred from the light receiving section to the vertical transfer CCD. (3)
An imaging device for an electronic endoscope according to any one of the above.