JP2012115531A - Electronic endoscope and electronic endoscope system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image signal from deteriorating while transmitting the image signal by serial transmission.SOLUTION: The electronic endoscope includes an imaging element, a sample-hold circuit for sampling/holding a signal from the imaging element, a serial cable transmitting a signal from the sample-hold circuit, and a band correction section correcting band of a signal transmitted by the serial cable.

Description

  The present invention relates to an electronic endoscope and an electronic endoscope system, and more particularly, to an electronic endoscope and an electronic endoscope system that can prevent signal deterioration associated with signal transmission using a transmission cable.

  Conventionally, an electronic endoscope that takes an image of an observation target with an imaging element such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) provided at the tip, and light for illuminating the observation target There is known an electronic endoscope system that includes a video processor that supplies an electronic endoscope and processes an image captured by the electronic endoscope and outputs the processed image to a monitor. Such an electronic endoscope system is widely put into practical use in the medical field for observing and treating a site in a body cavity and in the industrial field for observing or inspecting a part.

  As such an electronic endoscope system, one disclosed in Patent Document 1 is known. In Patent Document 1, a signal output from a CCD provided at the distal end portion of an electronic endoscope is transmitted to a control unit through a coaxial cable. The transmitted signal is subjected to correlated double sampling processing and signal amplification processing in an AFE (Analog Front End) of the control unit, and then converted into a digital signal and sent to the signal processing unit. In the signal processing unit, video processing such as white balance and gamma correction, encoding processing such as format processing and compression processing are performed, and the generated image is displayed on a monitor or the like.

JP 2010-78755 A

  In recent years, there has been a demand for high-definition images in electronic endoscope systems, and the number of pixels in an image sensor is increasing. Since the luminance data of each pixel of the image sensor is output based on the drive pulse input to the image sensor, it is necessary to increase the frequency of the drive pulse when the pixel of the image sensor is increased. However, when the frequency of the drive pulse is increased, there is a problem that it is difficult to supply an accurate drive pulse because the signal is deteriorated by the cable serving as the drive pulse transmission means. Therefore, conventionally, it has been attempted to increase the definition of an image without increasing the frequency of the drive pulse by reading out signals in parallel using an imaging device that performs output using a plurality of channels. However, if the imaging device has a plurality of channel outputs, cables for transmitting output signals are required for the number of channels, and the number of wires must be increased. As a result, there is a problem that the cable diameter becomes thick and the insertion portion of the electronic endoscope cannot be reduced in diameter. The reduction in the diameter of the insertion portion is indispensable for reducing the burden on the patient when inserted into the body cavity of the patient.

  Further, in the conventional electronic endoscope system as described above, since the transmission cable is a long cable extending from the distal end portion of the electronic endoscope to the proximal end portion, it is easy to pick up noise that propagates in the air, When the output signal from the CCD is transmitted, the signal deterioration due to the transmission cable can have a great influence.

  When an A / D converter is installed at the distal end of the endoscope where the CCD is provided and the analog signal output from the CCD is converted into a digital signal by A / D conversion and transmitted through a transmission cable, A / D conversion By converting the digital signal converted by the above into a serial signal and outputting it to the control unit, the image signal and the output signal are converted into a digital signal at the tip of the electronic endoscope and then transmitted to the control unit Therefore, it is possible to reduce the deterioration of the image signal due to the transmission as compared with the case where the analog signal is directly transmitted. However, as the number of bits in A / D conversion increases, it is necessary to increase the signal transmission speed in the transmission cable. In serial transmission, the signal base clock has a high frequency, so that waveform distortion occurs in the transmission cable and high-frequency noise occurs in the signal. Accordingly, there are restrictions in achieving EMC (Electromagnetic Compatibility) in the electronic endoscope, and it is not possible to take a good countermeasure against electromagnetic interference, or it is necessary to consider the frequency limitation of the transmission cable. Inconvenience such as doing may occur.

  The present invention has been made in view of the above circumstances. An object of the present invention is to provide an electronic endoscope and an electronic endoscope capable of preventing deterioration of the image signal while transmitting the image signal by low-frequency serial transmission and further preventing the diameter of the endoscope from becoming thicker. An endoscope system is provided.

  An electronic endoscope according to an embodiment of the present invention that solves the above problems includes an imaging device, a sample-and-hold circuit that samples and holds a signal from the imaging device, a serial cable that transmits a signal from the sample-and-hold circuit, A band correction unit that performs band correction processing on a signal transmitted through the serial cable. As a result, image signals can be transmitted serially in an electronic endoscope, so there is no need to increase the number of cables even when the number of pixels of the image sensor is increased, and signal transmission that does not cause waveform distortion or high-frequency noise. Is realized. Therefore, the diameter of the electronic endoscope is not increased. Further, since the signal sampled and held by the sample and hold circuit is transmitted, it is not necessary to perform high frequency transmission. Further, since band correction is performed on the signal that has been subjected to the sample hold process, it is not necessary to process a complicated signal during band correction. Since the signal change after the sample and hold process is gentle, it is possible to perform A / D conversion using a relatively high speed and low noise A / D converter. In addition, a sample hold circuit is provided at the tip of the electronic endoscope, a band correction unit is provided at the base of the electronic endoscope, and a sample hold circuit is provided at the operation part of the electronic endoscope instead of the tip. It is good also as a structure.

  Further, the band correction unit has an amplifier circuit that amplifies the signal transmitted by the serial cable, the amplifier circuit has a variable resistor, and the electronic endoscope further has a variable resistor according to the cable length of the serial cable. Resistance value control means for changing the resistance value of the. The electronic endoscope further includes a noise measuring unit that measures the amount of noise in the image generated based on the signal output from the band correction unit, and the resistance value control unit is further measured by the noise measuring unit. The resistance value of the variable resistor is adjusted based on the amount of noise.

  An electronic endoscope system according to an embodiment of the present invention includes an image pickup device, a sample hold circuit that samples and holds a signal from the image pickup device, and a serial cable that transmits a signal from the sample hold circuit. And a video processor having a band correction unit that performs band correction processing on a signal transmitted through a serial cable. That is, in the present invention, the band correction unit may be provided in a video processor connected to the electronic endoscope instead of the electronic endoscope. Furthermore, a configuration in which the sample hold circuit is provided at the distal end portion of the electronic endoscope or a configuration in which the sample hold circuit is provided in the operation portion of the electronic endoscope instead of the distal end portion may be employed.

  According to the electronic endoscope and the electronic endoscope system of the present invention, it is possible to prevent the image signal from being deteriorated while transmitting the image signal by low-frequency serial transmission, and to further reduce the diameter of the endoscope tip. Can do.

FIG. 1 is a block diagram showing a schematic structure of an electronic endoscope system according to an embodiment of the present invention. FIG. 2 is a graph showing frequency characteristics of a serial cable used in the electronic endoscope system according to the embodiment of the present invention. FIG. 3 is a graph showing the characteristics of the inverse correction filter of the band correction unit built in the electronic endoscope system according to the embodiment of the present invention. FIG. 4 is a circuit diagram of a band correction unit built in the electronic endoscope system according to the embodiment of the present invention. FIG. 5 is a block diagram showing a modification of the electronic endoscope system shown in FIG. 1 according to the embodiment of the present invention.

  Hereinafter, an electronic endoscope system according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing an outline of an electronic endoscope system 1 in an embodiment of the present invention. The electronic endoscope system 1 of this embodiment is a medical electronic endoscope system for performing observation and treatment in a body cavity of a patient. The electronic endoscope system 1 of this embodiment includes an electronic endoscope 10, a video processor 20, and a monitor 30.

  The electronic endoscope 10 includes an insertion unit 110 to be inserted into a patient's body, an operation unit 120 provided with switches for executing various processes in the electronic endoscope 10 and the video processor 20, and the video processor 20. And a connection portion 130 electrically and optically connected to each other. A light guide 111 for propagating illumination light supplied from the video processor 20 extends from the connection portion 130 to the insertion portion 110 of the electronic endoscope 10. The insertion unit 110 has a light distribution lens 112 for emitting illumination light propagated by the light guide 111 to the observation site, and forms an image of the illumination light reflected by the observation site on the light receiving surface of the image sensor. An objective lens 113 and a CCD 114, which is an image sensor that generates an analog image signal based on the subject image formed on the light receiving surface, are arranged.

  In addition, the electronic endoscope 10 includes a CPU 133 that comprehensively controls each component (for example, the timing generator 136, the band correction unit 135, and the pre-processing unit 132) built in the electronic endoscope 10 and band correction described later. A memory 150 for storing resistance value data of the digital potentiometers 338 to 341 included in the unit 135. The CPU 133 is connected to a system controller 201 built in the video processor 20, and controls each component built in the electronic endoscope 10 in accordance with instructions from the system controller 201.

  The video processor 20 has a system controller 201 that comprehensively controls the electronic endoscope system 1. When the operator turns on the video processor 20, the system controller 201 reads a program from a memory (not shown), turns on the light source 202, and starts an imaging operation. The light source 202 is configured by a high-intensity lamp such as a xenon lamp or a halogen lamp. Then, the light emitted from the light source 202 travels to the incident end of the light guide 111 provided in the electronic endoscope 10 via the condenser lens 203. The light that has traveled to the incident end of the light guide 111 is emitted from the light distribution lens 112 disposed at the distal end of the insertion unit 110 via the connection unit 130 and the operation unit 120 to the observation site in the body. Then, the emitted light is reflected by the observation site and imaged on the light receiving surface of the CCD 114 via the objective lens 113.

  In this embodiment, a single plate simultaneous type is adopted as a color imaging method, and yellow (Ye), cyan (Cy), magenta (Mg), and green (G) color elements are on a checkered pattern on the light receiving surface of the CCD 114. Complementary color filters (not shown) arranged in a line are arranged corresponding to each pixel on the light receiving surface. In the CCD 114, an image signal corresponding to the intensity of light transmitted through the complementary color filter is generated by photoelectric conversion, and one frame of image signal is sequentially read out at a predetermined time interval by a color difference line sequential method. In this embodiment, an interline transfer type CCD is used, and analog image signals for one frame are sequentially read out at intervals of about 1/30 seconds, for example, corresponding to the vertical synchronization frequency of the NTSC system. Is output. In addition, it is also possible to use a primary color CCD or CMOS provided with primary color (R, G, B) color filters instead of the complementary color CCD. It is also possible to adopt a so-called monochrome frame sequential method.

  The timing generator 136 includes a delay time correction circuit 136a. The delay time correction circuit 136a is a circuit that corrects a transmission delay of a signal generated according to the cable length of the serial cable 140, and includes, for example, a plurality of delay lines. The timing generator 136 adjusts the timing of each signal by the delay time correction circuit 136 a and controls the operation of each block in the electronic endoscope 10. For convenience, the connection for connecting the timing generator 136 and each processing block in the connection unit 130 controlled by the timing generator 136 is not shown. The timing generator 136 generates a synchronization signal (SHP pulse and SHD pulse) in which the phase of the transmission delay of the signal by the serial cable 140 is delayed. A CCD driver (not shown) generates a drive pulse based on the synchronization signal from the timing generator 136 and supplies the drive pulse to the CCD 114. The CCD 114 is driven based on the drive pulse, and generates an analog image signal of the captured subject.

  The analog image signal generated by the CCD 114 is sent to a CDS (Correlated Double Sampling) 115 that performs correlated double sampling processing as a sample and hold circuit. In the CDS 115, the output of the analog image signal from the CCD 114 during the feedthrough period and the video signal output period is clamped by the clamp pulse output from the timing generator 136.

  In the CDS 115, the output signal level is further sampled and held, and a signal from which amplifier noise and reset noise have been removed is sent to the buffer 116. The analog image signal from the CCD 114 is sent to the connection unit 130 via the CDS 115 and the buffer 116 via the operation unit 120 by the serial cable 140.

  The analog image signal sent from the insertion unit 110 to the connection unit 130 via the serial cable 140 is sent to the band correction unit 135. Here, the band correction in the present embodiment will be described with reference to the graph of FIG. FIG. 2 is a graph showing the frequency characteristics of the serial cable 140 of this embodiment, and the vertical axis represents the gain of the serial cable 140 (that is, the ratio of the output side voltage Vout to the input side voltage Vin (Vout / Vin)). The horizontal axis represents the frequency of the signal transmitted by the serial cable 140.

  As shown in FIG. 2, the serial cable 140 having a specific cable length has a frequency characteristic because it has resistance, inductance, and capacitance components. This frequency characteristic indicates a characteristic in which the gain is attenuated as the frequency of the signal to be transmitted becomes higher, and generally has a gentle downward curve. Therefore, when the frequency of the signal transmitted by the serial cable 140 is high, the signal input to the serial cable 140 cannot be reproduced unless the signal attenuated on the output side of the serial cable 140 is corrected. Here, the analog image signal output from the CCD 114 includes an output signal in the feedthrough period and an output signal in the video signal output period, and becomes a signal in a wide frequency band from low frequency to high frequency. For this reason, when this analog image signal is transmitted by the serial cable 140 and is to be reproduced on the output side, it is necessary to correct a signal attenuated in a wide frequency band from a low frequency to a high frequency. Therefore, in the electronic endoscope 10 of the present embodiment, the analog image signal output from the CCD 114 is once sampled and held by the CDS 115 and the sampled and held transmission signal is transmitted by the serial cable 140. That is, the CDS 115 samples a signal necessary for image reproduction (that is, the output of the feedthrough period and the video signal output period of the analog image signal) and holds it for a certain period, thereby reducing the high frequency component included in the analog image signal. The signal is converted into a frequency component, and only the signal required by the A / D converter 134 at the subsequent stage is transmitted by the serial cable 140. With such a configuration, the signal transmitted by the serial cable 140 can be reproduced only by correcting the low frequency band on the output side of the serial cable 140, so that the correction can be made compared with the case where the analog image signal is directly transmitted. It becomes easy. In addition, as shown in FIG. 2, the low frequency band has less gain attenuation than the high frequency band and can be corrected with a small correction amount, so that a signal with a good S / N ratio can be obtained. As described above, in the electronic endoscope 10 according to the present embodiment, the analog image signal is sampled and held by the CDS 115 and the transmission signal thus sampled and held is transmitted by the serial cable 140. A band correction unit 135 that is arranged at the tip and corrects a transmission signal is arranged in the connection unit 130.

  The band correction unit 135 corrects the transmission signal transmitted by the serial cable 140 using an inverse correction filter. FIG. 3 is a graph showing the characteristics of the inverse correction filter of the band correction unit 135 of the present embodiment. 3 represents the gain of the band correction unit 135 (that is, the ratio of the output side voltage Vout to the input side voltage Vin (Vout / Vin)), and the horizontal axis represents the frequency of the signal corrected by the band correction unit 135. 3, the band correction unit 135 performs correction so as to compensate for the gain attenuation of the serial cable 140 shown in Fig. 2, and outputs a signal required by the A / D conversion unit 134 in the subsequent stage. In a band up to the frequency fo necessary for reproduction (that is, a low frequency band), it is configured to obtain a flat characteristic (such that the gain is 1). It is not necessary to correct high frequency components (frequency higher than the frequency fo indicated by the dotted line in FIG. 3) unnecessary in the A / D converter 134 in the subsequent stage, and for signals in a band that does not need to be corrected. For example, after the processing by the band correction unit 135, processing for cutting a high-frequency component of a signal by an LPF (Low-pass Filter) (not shown) can be performed. 135, an appropriate band correction is performed on the output signal in the feedthrough period of the analog image signal and the output signal in the video signal output period required by the A / D conversion unit 134 in the subsequent stage according to the cable characteristics. However, the band correction process can be simplified.

  The signal subjected to the band correction by the band correction unit 135 is sent to the A / D conversion unit 134 and converted into a digital signal. The A / D conversion unit 134 performs sampling and quantization of the analog signal at a predetermined sampling frequency and a predetermined number of bits according to the clock pulse supplied from the timing generator 136. The image signal converted into a digital signal by the A / D conversion unit 134 is sent to the pre-processing unit 132. The pre-processing unit 132 converts the input image signal into an image signal composed of a luminance signal Y and color difference signals Cb and Cr. Then, after the amplified luminance signal Y and color difference signals Cb, Cr are respectively amplified, they are sent to a matrix circuit (not shown), and the matrix coefficient value for determining the conversion characteristics is changed according to the filter characteristics of the CCD 114, Perform color correction on the image signal. The matrix circuit converts the input luminance signal Y and color difference signals Cb and Cr into three primary color signals R, G and B having no mixed colors and outputs them. The R, G, B image signals converted by the matrix circuit are amplified and adjusted to an appropriate signal level, and then stored in an image memory (not shown) for each color.

  The image signal read from the image memory is converted to an analog signal by the D / A conversion unit 131 and then sent to the subsequent processing unit 204 of the video processor 20. The post-processing unit 204 converts the image signal sent from the image memory into a digital video signal, an RGB video signal, a composite video signal, a Y / C signal, and the like, and then outputs the image to the monitor 30 as an observation image. The surgeon observes and treats a site in the body cavity while checking the observation image displayed on the monitor 30.

  FIG. 4 is a circuit diagram of the band correction unit 135 built in the electronic endoscope system 1 of the present embodiment. As shown in FIG. 3, the band correction unit 135 includes operational amplifiers (OP) 336 and 337 and digital potentiometers (DPM) 338 to 341 which are variable resistors. The memory 150 (FIG. 1) stores preset values for each digital potentiometer so that appropriate band correction can be performed based on the frequency characteristics determined according to the cable length of the serial cable 140. . That is, in this embodiment, the resistance values of the digital potentiometers 338 to 341 are determined according to the frequency characteristics of the serial cable 140 shown in FIG. 2, and the data of each resistance value is stored in the memory 150. When the electronic endoscope system 1 is activated, the CPU 133 reads the data of each resistance value from the memory 150 as resistance value control means, and sets the resistance values of the digital potentiometers 338 to 341, respectively. Therefore, the band correction unit 135 can perform band correction by setting a filter characteristic in accordance with the length of the serial cable.

  As described above, the signal whose band has been corrected by the band correction unit 135 is sent to the A / D conversion unit 134, converted into a digital signal, and then sent to the pre-processing unit 132 (FIG. 1).

  The above is the description of the embodiment of the present invention. However, the present invention is not limited to the above-described configuration, and various modifications can be made within the scope of the technical idea of the present invention. For example, in the present embodiment, the band correction is performed using the resistance values of the digital potentiometers 338 to 341 determined in advance according to the frequency characteristics of the serial cable 140 shown in FIG. It is also possible to adopt a configuration in which the resistance values of the digital potentiometers 338 to 341 are feedback-controlled based on the amount.

  FIG. 5 is a block diagram showing a modification of the electronic endoscope system shown in FIG. 1 according to the embodiment of the present invention. In this modification, a noise measurement unit 132a is added to the pre-processing unit 132 of the embodiment of the present invention shown in FIG. In FIG. 5, in order to describe only the parts different from the above-described embodiment, the band correction unit 135, the A / D conversion unit 134, the pre-stage processing unit 132 </ b> M, the CPU 133, and the memory 150 are built in the electronic endoscope 10. Only shows. In FIG. 5, the same reference numerals as those in FIGS. 1 and 4 are assigned to configurations common to the above-described embodiment.

  As shown in FIG. 5, the pre-stage processing unit 132M of the present modification has a noise measurement unit 132a. The noise measuring unit 132a acquires data regarding noise occurring in the image. Based on the noise measurement result obtained from the noise measuring unit 132a, the CPU 133 adjusts the digital potentiometers 338 to 340 so that the noise (dispersion, deviation, etc.) in the whitest region is minimized during white balance adjustment in the electronic endoscope system. 341 is configured to adjust the resistance value. The noise at the time of white balance adjustment is generated because the band correction by the band correction unit 135 is not properly performed (that is, the filter characteristic of the band correction unit 135 is not optimal). By performing feedback control of the resistance values of the digital potentiometers 338 to 341 based on the amount of noise included in the obtained image, real-time and more accurate band correction can be executed.

  In the above description, the CDS 115 is provided in the insertion unit 110 of the electronic endoscope 10, but the CDS 115 may be provided in the operation unit 120. In this case, since the signal line connecting the timing generator 136 and the CDS 115 can be shortened, the diameter of the insertion portion 110 can be expected to be reduced. The effect of the present invention can also be obtained by using a sample and hold amplifier instead of the CDS 115. Further, each processing block after the band correction unit 135 may be configured to be included in the video processor 20.

DESCRIPTION OF SYMBOLS 1 Electronic endoscope system 10 Electronic endoscope 20 Video processor 110 Insertion part 114 CCD
115 CDS
120 Operation unit 130 Base unit 132, 132M Pre-processing unit 132a Noise measurement unit 133 CPU
135 Band Correction Unit 140 Serial Cable 338 to 341 Digital Potentiometer

Claims (8)

An image sensor;
A sample-and-hold circuit that samples and holds a signal from the image sensor;
A serial cable for transmitting a signal from the sample and hold circuit;
A band correction unit that performs band correction processing on a signal transmitted by the serial cable,
An electronic endoscope characterized by that. The sample hold circuit is provided at the tip of the electronic endoscope,
The band correction unit is provided at the base of the electronic endoscope.
The electronic endoscope according to claim 1.   The electronic endoscope according to claim 2, wherein the sample hold circuit is provided in an operation unit of the electronic endoscope instead of the tip portion. The band correction unit has an amplification circuit that amplifies a signal transmitted by the serial cable,
The amplifier circuit has a variable resistor,
The electronic endoscope further includes a resistance value control unit that changes a resistance value of the variable resistor according to a cable length of the serial cable.
The electronic endoscope according to any one of claims 1 to 3, wherein the electronic endoscope is characterized in that The electronic endoscope has a noise measurement unit that measures a noise amount of an image generated based on a signal output from the band correction unit,
The resistance value control means further adjusts the resistance value of the variable resistor based on the amount of noise measured by the noise measurement unit,
The electronic endoscope according to claim 4. An electronic endoscope having an image sensor, a sample hold circuit that samples and holds a signal from the image sensor, and a serial cable that transmits a signal from the sample hold circuit;
A video processor having a band correction unit that performs band correction processing on a signal transmitted by the serial cable,
An electronic endoscope system characterized by that. The sample and hold circuit is provided at a distal end portion of the electronic endoscope.
The electronic endoscope system according to claim 6.   8. The electronic endoscope system according to claim 7, wherein the sample hold circuit is provided in an operation unit of the electronic endoscope instead of the distal end portion.

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