JP3006245B2 - Driving method of solid-state image sensor for electronic endoscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic endoscope used for medical, industrial and the like, for driving a solid-state imaging device and reading out signal charges stored in the solid-state imaging device. The present invention relates to a driving method of a solid-state imaging device of an electronic endoscope.

[0002]

2. Description of the Related Art An electronic endoscope is provided with an observation window at a distal end of an insertion portion inserted into a body cavity or the like, and a solid-state image pickup device such as a CCD is provided at an image forming position of an imaging lens attached to the observation window. Arranging the element, irradiating the interior of the body cavity or the like with illumination light, exposing the solid-state imaging device with light reflected from the subject, performing photoelectric conversion, reading out the charge accumulated in this solid-state imaging device,
The signal is transmitted to a processor connected to the endoscope, and a predetermined signal processing is performed by the processor to generate a video signal such as NTSC and display it on a monitor device. Here, in driving the solid-state imaging device,
By applying horizontal and vertical driving pulses to the solid-state imaging device, the electric charges accumulated in the solid-state imaging device are transferred, and the signal transferred in this way is transmitted to the processor via a cable inserted through the insertion portion. It is designed to be transmitted.

[0003]

The endoscope is inserted into a patient's body or the like. From the viewpoints of insertion operability and reduction of patient's pain, the insertion portion has a diameter as small as possible. Need to be The solid-state imaging device is provided at the tip of the insertion portion, and a cable is connected to the solid-state imaging device. The cable also occupies a predetermined space as a built-in component of the insertion portion. Therefore, in order to reduce the diameter of the insertion portion, it is necessary to reduce the number of cables as much as possible. In particular, in recent years, since the diameter of the insertion portion has been reduced to almost the limit, even if one cable is reduced, it is advantageous in reducing the diameter.

In view of the above, the present inventor has conducted intensive studies in order to reduce the number of cables, and focused on cables connected to a horizontal transfer unit. 2. Description of the Related Art In an electronic endoscope, a so-called two-phase driving method in which a transfer is performed by giving a two-phase transfer pulse is generally adopted in a horizontal transfer unit of a solid-state imaging device. That is, as is clear from FIG. 1, the horizontal transfer section in the solid-state imaging device is configured such that a floating diffusion FD is provided at an output stage of a horizontal transfer path HCCD, and the floating diffusion FD is connected to a MOSFET. Then, φ is transferred to the horizontal transfer path HCCD.
Signal charges are sequentially transferred to the output stage by applying two-phase transfer pulses of H1 and φH2, and a + pulse is applied to the diffusion gate to close the gate, thereby setting the potential of the floating diffusion FD to V _DD . Then, with the gate turned off, the signal charge is transferred to the floating diffusion FD via the OG.
, And the change in the signal potential at this time is detected.
By using a floating diffusion amplifier (FDA) having a structure in which a signal is amplified by an FET and output, a high output voltage can be obtained by reducing the output capacitance.

[0005] From the above, as the horizontal transfer system pulse, two transfer pulse signals φ applied to the horizontal transfer path HCCD and having mutually inverted phases and a duty ratio of 50% are provided.
In order to use H1 and φH2 and to output the transferred signal charges, a reset pulse φR for controlling the opening and closing of the gate in the output stage is required. Here, the output signal output waveform in the solid-state imaging device is, as shown in FIG.
Reset period t _R , 0-level period t ₀ , and signal output period t _S (solid line is white level, dotted line is black level output signal)
After the reset operation is performed, a predetermined 0
The level period t ₀ is provided. Therefore, the reset pulse φR is generated when the duty ratio φH is 50%.
1, a different pulse from φH2 is required, and
The horizontal transfer system requires three cables.

By the way, it is possible to use one of the transfer pulses as a reset pulse and perform a reset operation using one of the pulses φH1 or φH2 (for example, φH1). Can be reduced. However,
If a horizontal transfer pulse having a duty ratio of 50% is used as a reset pulse as it is, the 0 level period t ₀ cannot be provided. As mentioned above,
A floating diffusion amplifier is provided at the output stage of the horizontal transfer path HCCD, and the junction capacitance of the floating diode is set to 0. Although a few PF, for protecting the solid-state imaging device, generally diffused resistor shown in FIG. 1 with R _P is inserted in series to the reset gate. For this reason, a time constant is formed in the reset circuit by the resistance _RP and the junction capacitance, and a pulse is delayed. Here, if a horizontal transfer pulse having a duty ratio of 50% is used as it is as a reset pulse, the reset period t _R ′ is reduced as shown in FIG. 3 due to this delay and the finite rising characteristic of the floating diffusion amplifier itself. This results in limiting the signal output period t _S ′. For this reason, if the 0 level period t ₀ is eliminated, the cable length and the drive impedance affect the waveform of the horizontal transfer pulse, and the stability of the reset operation is impaired. As shown by the phantom line in FIG. The output period t _S is substantially limited, causing a decrease in output level, ie, a decrease in sensitivity.

On the other hand, focusing on the transfer pulse,
The transfer of the accumulated charge is performed almost instantaneously, and the pulse width of the transfer pulse is sufficiently longer than the time required for the actual transfer. Further, if the duty ratio of the two-phase transfer pulse is not 50%, the transfer operation is not hindered.

The present invention has been made based on such knowledge, and it is an object of the present invention to stabilize a reset operation and reduce an output level without providing a cable for transmitting a reset pulse separately. An object of the present invention is to enable a solid-state imaging device to be driven without lowering.

[0009]

In order to achieve the above-mentioned object, the present invention provides a horizontal transfer unit of a solid-state image sensor with a two-phase pulse signal having a duty ratio other than 50%. Is a horizontal transfer pulse signal, and a narrow pulse having a duty ratio of 50% or less is used as a reset pulse signal.

[0010]

In order to stabilize the reset operation, it is necessary to provide a zero-level period (feed-through period) in the output amplifier.
This is for giving 0% duty. Therefore,
The duty ratio of the horizontal transfer pulse signal is set to a value other than 50%, and a narrow pulse of 50% or less is used as a reset pulse, and the reset pulse is applied to the reset gate. As a result, the signal output period can be lengthened by an amount corresponding to the reduced pulse width.
Even in the signal output period, it is possible to prevent a situation in which the reset operation affects and the signal output level decreases. Usually, the reset pulse has a duty ratio of 2
It is preferable to set the duty ratio of the horizontal transfer pulse to one of the pulses (for example, φH1).
Is set to 25%, and the other pulse (for example, φH2) is set to 75%. As a result, as shown in FIG. 4, the reset period t _R ″ has a 25% duty, the signal output period t _S ″ has a 75% duty, and a sufficient signal output period can be obtained. Further, since the transfer operation of the signal charge is performed almost instantaneously, the transfer can be sufficiently performed even with the shorter pulse of 25% duty, and even if such an uneven transfer pulse is used, The transfer operation itself is performed without any trouble.

Therefore, only two cables are required to transmit the pulse signal in the horizontal transfer unit, and the reset operation can be performed smoothly, and the signal output can be stabilized. As a result, not only a cable for transmitting the reset pulse but also a circuit configuration for generating the reset pulse is not required, so that the diameter of the insertion portion can be reduced and the circuit configuration of the solid-state imaging device drive circuit is simplified. can do. Normally, this solid-state image sensor driving circuit is arranged at a position as close as possible to the solid-state image sensor from the viewpoint of shortening the cable length and minimizing the deterioration of signals transmitted through the cable. It is often necessary to mount it on a relay board or the like built in the main body operation unit,
When the circuit configuration of the solid-state imaging device drive circuit is simplified,
Since the size and weight can be reduced, it is advantageous from the viewpoint of the operability of the main body operation unit.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, FIG. 5 shows the overall configuration of an imaging system for an electronic endoscope. In the drawings, reference numeral 1 denotes an endoscope, the endoscope 1 has a main body operation unit 2, and an insertion unit 3 inserted into a body cavity or the like is connected to the main body operation unit 2;
A connection cord 6 detachably connected to the light source device 4 and a video signal processing circuit 5 provided integrally with or separately from the light source device 4 is continuously provided. The light source device 4 has a light source lamp 10, and in the optical path of the light source lamp 10, a light amount stop member 11, a condenser lens 12, and a rotating color filter 13 are sequentially provided. The R, G, and B illuminations are sequentially performed at a predetermined light amount. The entrance end 14a of the light guide 14 faces the illumination light path. Light guide 1
4 is routed from the connection cord 6 to the insertion section 3 through the main body operation section 2, and its emission end 14 b faces the illumination lens 15 provided at the tip of the insertion section 3.

An imaging lens 16 is provided at the end of the insertion section 3 for photographing a subject such as a body cavity under irradiation of illumination light irradiated through the light guide 14. A solid-state image sensor 17 composed of a CCD or the like is mounted at an image forming position of the lens 16. Therefore, an image of a subject is captured by the solid-state imaging device 17. The signal obtained by the photoelectric conversion by the solid-state imaging device 17 is transmitted to the video signal processing circuit 5 via the signal cable 18, and after performing predetermined signal processing by the video signal processing circuit 5, The image is displayed on the monitor device 7 as an image. In order to read out signals by driving the solid-state imaging device 17, a relay board is mounted on the main body operation unit 2, and a solid-state imaging device driving circuit 19 is provided on the relay board. Then, the synchronization signal provided in the video signal processing circuit 4 is input to the solid-state imaging device driving circuit 19, and a pulse signal necessary for driving the solid-state imaging device 17 is generated based on the synchronization signal. This pulse signal is applied to the solid-state imaging device 17.

Here, in the horizontal transfer section of the solid-state imaging device 17, two-phase transfer pulses φH1 and φH2
Although a reset pulse φR is required, one of the transfer pulses φH1 and φH2 is shared with the reset pulse φR. For this reason, the transfer pulse φH1 is not a pulse having a duty ratio of 50%, but a pulse having an optimum duty of 25% as a reset pulse. As a result, the reset operation becomes stable, the signal output period is not restricted, and the loss of the signal can be prevented, so that the sensitivity is maintained in a good state.
In addition, the transfer of the signal charge is performed almost instantaneously, and the transfer is sufficiently performed even when the duty ratio is 25%. Further, the pulse width becomes non-uniform, for example, the transfer pulse φH1 is 25% and φH2 is 75%. However, if the pulse width is only as long as the time required for the transfer, it will not hinder the special transfer. Absent.

Therefore, based on the synchronizing signal from the signal processing circuit 5, one of the 25% duty transfer from the two-phase pulse signal generated by the solid-state imaging device driving circuit 19 and having a duty ratio of 50% φH1 and φH2. A duty conversion unit 20 that converts the pulse and reset pulse φH1 ′ into the other transfer pulse φH2 having a 75% duty is provided on the output side of the solid-state imaging device drive circuit 19. Therefore, based on FIG.
An example of the circuit configuration will be described. FIG. 7 shows the waveforms of the signals of the respective parts indicated in the circuit diagram of FIG.

Φ output from the solid-state image sensor driving circuit 1
The two-phase pulses H1 and φH2 are 50% duty pulses whose phases are inverted. These two pulses are shaped by the waveform shaping circuit 21 and the TTL
By converting the signal into a signal of a level suitable for driving the gate circuits 23, 26, and 29 by the level converter 22, signals having waveforms shown in FIGS. 7A and 7B are obtained. Of these signals (a) and (b), the signal (a) is input to the gate circuit 23 and is delayed by a 1/4 cycle by the delay circuit 24, and the signal shown in FIG. It is said. The AND circuit 25 performs an AND operation on the delayed signal (c) and the signal (a) to obtain an AND signal as shown in FIG.
(D) is obtained. On the other hand, the signal (a) is inverted by the inverting amplifier 26, and the signal (e) is obtained as shown by (e) in FIG. The signal (d) shown in FIG. 7 (f) is obtained by passing the signal (d) and the signal (e) through the OR circuit 27. Further, when this signal (f) is inverted by the inverting amplifier 28, one pulse φH1 ′ shown in FIG. 7 (g) is obtained. On the other hand, the signal (b) is compared with the signal (d) described above via the NOR circuit 29, thereby obtaining the signal (b) of FIG.
The signal (h) shown in FIG. When this signal (h) is inverted by the inverting amplifier 30, FIG.
The other pulse .phi.H2 'is obtained.

The above two pulses φH1 ′ and φH2 ′ are:
When the duty ratio of the pulse φH1 ′ is 25%,
The pulse shown in FIG. 7 (j), which alternately goes to the high level and the low level at the duty ratio of 2 'of 75%, is generated. Of these two pulses, φH1 ′ is shared by the transfer pulse and the reset pulse φR. Thereby, in the horizontal transfer section, the reset pulse φH having the most preferable 25% duty can be applied, and a sufficient signal output period can be provided after the reset period.
As a result, the reset operation is stabilized, and the reset period does not affect the signal output period, so that the signal output level can be prevented from lowering. Also, one of the transfer pulses is 25% duty and the other pulse is 75%.
Although the transfer is performed at the% duty, the time required for the charge transfer is sufficiently ensured. Therefore, if the voltage is alternately applied, there is no particular trouble in the transfer.

As a result, a cable for independently transmitting the reset pulse φR is not required. As a result, the number of cables can be reduced and the diameter of the insertion section 3 can be reduced. Further, since it is not necessary to provide a circuit for generating the reset pulse in addition to the circuit for generating the transfer pulse, the circuit mounted on the relay board in the main body operation unit 2 can be simplified. At the same time, the size and weight can be reduced.

In the above-described embodiment, the duty converter 20 is provided, and φH1 ′ and φH2 ′ are formed from φH1 and φH2 in the duty converter 20, but the duty ratio is not limited to 50%. If a pulse signal having a duty ratio of 50% or less can be used for both the reset pulse and the transfer pulse, φH1,
The reset pulse may be generated from any of φH2, and if the horizontal transfer is not hindered and the signal output period can be sufficiently secured, the duty ratio of the narrow pulse is not limited to 25%. Absent. Further, the duty conversion is performed in the main body operation unit 2,
For example, it is also possible to provide a connector portion of the connection cord 6 connected to the video signal processing device 5.

[0020]

As described above, according to the present invention, in addition to the horizontal transfer section of the solid-state imaging device provided at the tip of the insertion section, a two-phase pulse signal for transferring signal charges is subjected to a duty cycle. Since the ratio is set to a value other than 50% and a narrow pulse having a duty ratio of 50% or less is used as the reset pulse signal among the two-phase pulse signals, the horizontal transfer system can be performed without lowering the signal output level. Can reduce the number of cables for transmitting the drive signal by one, and eliminate the need for a separate circuit for generating a reset pulse, thereby simplifying the circuit configuration of the solid-state imaging device drive circuit. Has various effects.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a horizontal transfer unit of a solid-state imaging device.

FIG. 2 is a diagram illustrating a waveform of an output signal of a solid-state imaging device.

FIG. 3 is a diagram illustrating a waveform of an output signal of a solid-state imaging device when a duty ratio of a reset pulse is set to 50%.

FIG. 4 is a diagram showing a waveform of an output signal of a solid-state imaging device when a reset operation is performed according to the method of the present invention.

FIG. 5 is a schematic configuration diagram of an imaging system of the electronic endoscope.

FIG. 6 is a circuit configuration diagram of a duty conversion unit according to the first embodiment of the present invention.

FIG. 7 is a signal waveform diagram of each unit in the duty conversion unit.

[Description of Signs] 1 Endoscope 2 Main body operation unit 3 Insertion unit 4 Video signal processing device 17 Solid-state imaging device 18 Signal cable 19 Solid-state imaging device drive circuit 20 Duty conversion unit

Claims (3)

(57) [Claims] 1. A solid-state imaging device is provided at a distal end of an insertion portion for performing imaging of a body cavity or the like, and the solid-state imaging device is driven by a driving pulse signal transmitted from a solid-state imaging device driving circuit via a cable inserted into the insertion portion. In an electronic endoscope configured to read out signal charges stored in an element, two-phase pulse signals having a duty ratio other than 50% are supplied to a horizontal transfer unit of the solid-state imaging element, and these two-phase pulse signals are supplied. Is a horizontal transfer pulse signal and the duty ratio is 50
%, Wherein a narrow pulse of not more than% is used as a reset pulse signal. 2. The duty ratio of the narrow pulse is about 2
2. The driving method for a solid-state image pickup device of an electronic endoscope according to claim 1, wherein the driving voltage is 5%. 3. The solid-state imaging device driving method for an electronic endoscope according to claim 1, wherein a duty conversion section for a pulse signal is provided in a main body operation section of said electronic endoscope.