Processor for electronic endoscope and electronic endoscope system

Abstract

One embodiment of the present invention is a processor for an electronic endoscope, which is used in an electronic endoscope provided with an imaging element configured to image a living tissue, and which is provided with: a light source unit that synthesizes light emitted from a plurality of light-emitting elements and generates illumination light for the living tissue; and a current control unit that controls the current flowing into each light-emitting element of the light source unit. The current control unit is provided with: a current generation unit that generates, as a current flowing into each light-emitting element, an output current having an amplitude corresponding to a signal having a lower voltage in a first control signal and a second control signal obtained by filtering the PWM control signal, the output current corresponding to the duty ratio of the PWM control signal; and a feedback circuit unit that feeds back the current flowing into each light-emitting element and stabilizes the output current generated by the current generation unit.

Description

Technical Field

[0001] The present invention relates to a processor for an electronic endoscope, and an electronic endoscope system. The processor for an electronic endoscope is used for an electronic endoscope including an imaging element configured to perform imaging of living tissue. Background Art

[0002] In the field of medical equipment, there is known an endoscope system that can generate an image suitable for diagnosing a lesion hidden in the body cavity by illuminating living tissue in the body cavity and photographing the illuminated living tissue in the body cavity as a subject.

[0003] Conventionally, lamp light sources such as xenon lamps and halogen lamps that emit white light have been used as illumination light. However, recently, semiconductor light sources having light emitting elements such as light emitting diodes (LEDs) and laser diodes (LDs) that emit light in a specific wavelength band have been used instead of lamp light sources.

[0004] For example, Japanese Patent Application Publication No. 2017-60860 describes an endoscope system comprising: an endoscope having an illumination optical system for irradiating light from a light source to a subject, and an imaging optical system including an imaging element for photographing the subject; and a control device detachably connected to the endoscope. In the system, a plurality of control modes are provided to indicate the relationship between a light quantity indication value and a control output value for a light source, and a light source control unit switches to any control mode based on the recognition result of the type of the imaging element, and controls the intensity of the emitted light of the light source based on the switched control mode. Summary of the invention

[0005] Problems to be solved by the invention

[0006] However, there are cases where a driver IC (Integrated Circuit, IC) that drives LEDs is equipped with both a pulse width modulation (PWM) dimming circuit and an analog dimming circuit, and further includes a feedback circuit to stabilize the output current flowing into the LED. Such a driver IC is configured so that both control methods operate simultaneously, rather than selectively executing either the PWM dimming method or the analog dimming method.

[0007] When such a driver IC for LEDs is used in an electronic endoscope system, the LEDs may be damaged due to the high frequency of the PWM signals processed in the electronic endoscope system. For example, in order to shoot at a high shutter speed (e.g., one thousandth of a second) so that a still image of the subject does not blur under PWM dimming illumination, the LEDs are required to be PWM driven at 10 to 100 times the high shutter speed (e.g., a PWM current of 10 to 100 kHz flows into the LEDs). However, such a high-frequency PWM current cannot be stably controlled due to the response delay of the feedback system, and the peak value of the output current may exceed the rated value of the LEDs, thereby damaging the LEDs.

[0008] In view of this, an object of the present invention is to protect an LED when dimming the light emitting element by pulse width modulation in a processor for an electronic endoscope including a light source having a light emitting element.

[0009] Solutions to Solve Problems

[0010] One aspect of the present invention is a processor for an electronic endoscope, which is used in an electronic endoscope having an imaging element configured to perform imaging of living tissue, and comprises:

[0011] a light source unit that synthesizes the lights emitted from the plurality of light emitting elements to generate illumination light for the living tissue; and

[0012] The current control unit controls the current flowing into each light emitting element of the light source unit.

[0013] The current control unit comprises:

[0014] a current generating unit that generates, as a current flowing into each light emitting element, an output current having an amplitude corresponding to a lower voltage signal of a first control signal and a second control signal obtained by filtering the PWM control signal, corresponding to a duty ratio of a pulse width modulated control signal (PWM control signal); and

[0015] The feedback circuit unit feeds back the current flowing into each light emitting element to stabilize the output current generated by the current generating unit.

[0016] The signal level of the second control signal may be adjusted in such a manner that the signal level of the second control signal when the duty ratio of the PWM control signal is 100% is higher than the maximum value of the signal level of the first control signal.

[0017] The use range of the duty ratio of the PWM control signal may be limited according to the signal level of the first control signal in such a manner that the signal level of the first control signal is lower than the signal level of the second control signal.

[0018] The current control unit may include a low-pass filter circuit having a cutoff frequency corresponding to a frequency of the PWM control signal as a circuit for performing the filtering process.

[0019] Another aspect of the present invention is an electronic endoscope system comprising:

[0020] The electronic endoscope processor; and

[0021] The electronic endoscope is connected to the electronic endoscope processor and includes an imaging element for acquiring an image of the living tissue.

[0022] Effects of the Invention

[0023] According to the electronic endoscope processor and the electronic endoscope system, in the electronic endoscope processor including the light source having the light emitting element, when dimming the light emitting element by pulse width modulation is performed, the LED can be protected. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a block diagram showing an example of the configuration of an electronic endoscope system according to an embodiment.

[0025] Figure 2 It is a block diagram showing the structure of a reference example of a light source device.

[0026] Figure 3 Yes means Figure 2 A timing diagram of the operation of the light source device is shown.

[0027] Figure 4 This is a block diagram showing the structure of a light source device according to one embodiment.

[0028] Figure 5 Yes means Figure 4 A diagram showing a configuration example of a filter circuit included in a light source device.

[0029] Figure 6 Yes means Figure 4 A timing diagram of the operation of the light source device is shown.

[0030] Figure 7 Yes means Figure 4 The timing diagram of the actual waveform of the light source device shown.

[0031] Figure 8 This is a diagram showing an example of the relationship between the voltage level of the control signal and the duty ratio of the PWM signal that can be set in analog dimming. DETAILED DESCRIPTION

[0032] Hereinafter, the electronic endoscope system according to the present embodiment will be described in detail with reference to the drawings.

[0033] Figure 1 1 is a block diagram showing an example of the structure of the electronic endoscope system 1 according to the present embodiment. Figure 1 As shown, the electronic endoscope system 1 is a system dedicated to medical use, and includes an electronic scope (endoscope) 100 , a processor 200 , and a monitor 300 .

[0034] The processor 200 includes a system controller 21. The system controller 21 executes various programs stored in the memory 23 and centrally controls the entire electronic endoscope system 1. In addition, the system controller 21 is connected to the operation panel 24. The system controller 21 changes various operations of the electronic endoscope system 1 and parameters corresponding to each operation according to instructions input by the operator into the operation panel 24. The system controller 21 outputs clock pulses to each circuit in the electronic endoscope system 1 to adjust the timing of the operation of each part.

[0035] The processor 200 is provided with a light source device 30. The light source device 30 emits an illumination light L for illuminating a subject such as living tissue in a body cavity. The illumination light L includes white light, pseudo white light, or special light. According to one embodiment, preferably, the light source device 30 selects any one of a mode of continuously emitting white light or pseudo white light as the illumination light L and a mode of alternately emitting white light or pseudo white light and special light as the illumination light L, and emits white light, pseudo white light, or special light according to the selected mode. White light is light having a flat spectral intensity distribution in the visible light band, and pseudo white light is light having an uneven spectral intensity distribution and mixed with light of multiple bands. Special light is light of a narrow band in the visible light band, such as blue or green. When enhancing and observing a specific part in living tissue, light of a blue or green band is used. The illumination light L emitted from the light source device 30 is focused on the incident end face of the light carrying bundle (LCB) 11 by a condenser lens 25 and then incident into the LCB 11.

[0036] The illumination light L incident on the LCB 11 propagates in the LCB 11. The illumination light L propagating in the LCB 11 is emitted from the emission end face of the LCB 11 disposed at the front end of the electronic scope 100, and is irradiated on the subject via the light distribution lens 12. The return light from the subject illuminated by the illumination light L from the light distribution lens 12 forms an optical image on the light receiving surface of the solid-state imaging element 14 via the objective lens 13.

[0037] The solid-state imaging element 14 is a single-plate color charge coupled device (CCD) image sensor with a Bayer-type pixel configuration. The solid-state imaging element 14 accumulates the optical image formed on each pixel of the light-receiving surface as an electric charge that varies with the amount of light, and generates R (Red), G (Green), and B (Blue) image signals and then outputs them. In addition, the solid-state imaging element 14 is not limited to the CCD image sensor, and can also be replaced by a complementary metal oxide semiconductor (CMOS) image sensor or other types of imaging devices. The solid-state imaging element 14 can also be a device equipped with a complementary color filter.

[0038] A driver signal processing circuit 15 is provided in the connection part of the electronic scope 100. The image signal of the subject from the solid-state imaging element 14 is input to the driver signal processing circuit 15 at a predetermined frame cycle. The frame cycle is, for example, 1 / 30 seconds. The driver signal processing circuit 15 performs predetermined processing including A / D conversion on the image signal input from the solid-state imaging element 14, and outputs it to the image processing unit 22 of the processor 200.

[0039] The image processing unit 22 performs the following predetermined image processing to generate a video format signal, and outputs the signal to the monitor 300 .

[0040] In addition, the driver signal processing circuit 15 accesses the memory 16 and reads the unique information of the electronic scope 100. The unique information of the electronic scope 100 recorded in the memory 16 includes, for example, the number of pixels and sensitivity of the solid-state imaging element 14, the operable frame rate, the model, etc. The driver signal processing circuit 15 outputs the unique information read from the memory 16 to the system controller 21. The unique information may include, for example, the number of pixels and resolution of the solid-state imaging element 14, and the element-specific information, and further includes the field angle, focal length, depth of field, etc. related to the optical system.

[0041] The system controller 21 performs various operations based on the unique information of the electronic scope 100 and generates control signals. The system controller 21 uses the generated control signals to control the operation and timing of various circuits in the processor 200 so as to perform processing suitable for the electronic scope 100 connected to the processor 200.

[0042] The system controller 21 supplies a clock pulse to the driver signal processing circuit 15. The driver signal processing circuit 15 drives and controls the solid-state imaging element 14 at a timing synchronized with the frame rate of the image processed by the processor 200 side based on the clock pulse supplied from the system controller 21.

[0043] Next, the light source device 30 built in the processor 200 will be described.

[0044] Generally speaking, in a light source device, a plurality of LEDs are used as light sources to obtain white illumination light, and the emitted light of the plurality of LEDs is synthesized. For example, as a light source, sometimes three LEDs, namely a blue LED, a green LED, and a red LED, are used, and sometimes five LEDs, namely an ultraviolet (UV) LED, a blue LED, a green LED, an amber LED, and a red LED, are used.

[0045] Each LED can be dimmed by analog and PWM. Analog dimming is to control the light intensity of the LED by the size of the current flowing into the LED. On the other hand, PWM dimming is to set the current flowing into the LED to a current of PWM (Pulse Width Modulation) waveform, and control the light intensity of the LED by the duty cycle of PWM.

[0046] The light source device 30 is configured to be able to independently perform analog dimming and PWM dimming.

[0047] Before describing the structure of the light source device 30 of the present embodiment, Figure 2 and Figure 3 A reference example of the light source device will be described to facilitate understanding of the light source device 30 of the present embodiment.

[0048] Figure 2 It is a block diagram showing a reference example of a light source device. Figure 3 1 is a timing chart showing the operation of a reference example of a light source device. Figure 2 , only the structure of the light source device for a single LED 32 is shown.

[0049] Reference Figure 2 The reference example of the light source device includes an LED control unit 31R that controls the current flowing into the LED 32. The LED control unit 31R includes an LED driver circuit 35, a sense resistor Rs, and a metal oxide semiconductor (MOS) transistor Q1.

[0050] The LED driver circuit 35 inputs the control signal CTRL1 and the PWM signal (PWM) supplied from the system controller, and outputs the PWM output PWM_OUT of the control MOS transistor Q1 and the output current I_OUT flowing into the LED 32. The LED driver circuit 35 is composed of a hardware module composed of, for example, a Field-Programmable Gate Array (FPGA).

[0051] The LED driver circuit 35 includes an analog dimming driver 41 , a PWM driver 42 , and a current control circuit 43 .

[0052] The analog dimming driver 41 generates a current that changes according to the voltage level of the control signal CTRL1 and outputs the current to the current control circuit 43 .

[0053] The PWM driver 42 generates a PWM output PWM_OUT by amplifying the PWM signal to a voltage capable of driving the MOS transistor Q1 , and supplies the generated PWM output PWM_OUT to the gate of the MOS transistor Q1 and outputs it to the current control circuit 43 .

[0054] The current control circuit 43 amplifies the current output from the analog dimming driver 41, and generates an output current I_OUT based on the duty cycle of the PWM output PWM_OUT supplied from the PWM driver 42. The output current I_OUT generated by the current control circuit 43 is based on both the voltage level of the control signal CTRL1 and the duty cycle of the PWM signal. Therefore, the waveform of the output current I_OUT is a pulse waveform determined by the duty cycle of the PWM signal, and the amplitude of the pulse waveform becomes a value corresponding to the voltage level of the control signal CTRL1.

[0055] When analog dimming is performed, the duty ratio of the PWM signal is set to 100%, and the voltage level of the control signal CTRL1 is variable. That is, when the duty ratio of the PWM signal is 100%, the PWM output PWM_OUT becomes H level and the MOS transistor Q1 is turned on, and the output current I_OUT corresponding to the amplitude of the control signal CTRL1 flows to the LED 32.

[0056] When PWM dimming is performed, the voltage level of the control signal CTRL1 is fixed and the duty cycle of the PWM signal is variable. In this case, the output current I_OUT becomes a fixed value, and the MOS transistor Q1 is turned on / off according to the level of the PWM output PWM_OUT having the same duty cycle as the duty cycle of the PWM signal, thereby the output current I_OUT based on the duty cycle of the PWM signal flows to the LED 32.

[0057] In addition, the current control circuit 43 detects the current (output current I_OUT) flowing through the LED 32 by sensing the voltage drop in the resistor Rs, and performs feedback control for stabilizing the output current I_OUT based on the detection result. In this feedback control, control is performed in such a way that the average output current I_OUT over a predetermined time is converged to the target current as the control amount.

[0058] exist Figure 3In FIG. 4 , (a) is a timing chart showing the output current I_OUT (LED current) when a PWM signal having a frequency sufficiently low relative to the response characteristics of the feedback control in the current control circuit 43 is input to the LED driver circuit 35 . Figure 3 In the formula, T1, T2, ... correspond to one cycle respectively, and CT is the prescribed time for determining the control amount.

[0059] like Figure 3 As shown in (a), when a relatively low frequency PWM signal is input to the LED driver circuit 35, since the pulse width is longer than the prescribed time CT even when the duty cycle is small, the average output current I_OUT can be roughly consistent with the target current. That is, the amplitude levels A1, A2, ... of the average output current I_OUT for the prescribed time CT in the period T1, T2, ... are roughly close to the target current, and the output current I_OUT can be converged to the target current in a timely manner. In addition, the output current I_OUT overshoots instantly after the pulse rises, but since the pulse width is relatively long, it can converge to the target current within the pulse width.

[0060] exist Figure 3 In FIG. 1 , (b) is a timing chart showing the output current I_OUT (LED current) when a PWM signal having a higher frequency with respect to the response characteristic of the feedback control in the current control circuit 43 is input to the LED driver circuit 35 .

[0061] like Figure 3 As shown in (b), when a PWM signal with a high frequency and a small duty cycle is input to the LED driver circuit 35, since the pulse width is shorter than the prescribed time CT when setting the target current, the average output current I_OUT set as the control amount does not reflect the pulse amplitude and becomes a value lower than the pulse amplitude. Figure 3 In (b), in the periods T1 to T6, the average output current I_OUT set as the control amount is set to A1 to A6, respectively.

[0062] exist Figure 3 In cycle T1 of (b), although the pulse amplitude of the output current I_OUT is roughly consistent with the target current, since the average output current I_OUT (control amount) within the specified time CT is low, the LED driver circuit 35 generates the output current I_OUT in cycle T2 with an increased pulse amplitude to make the control amount close to the target current. Similarly, in cycles T3 to T5, an output current I_OUT with a gradually increasing pulse amplitude is generated. In cycle T5, the average output current I_OUT within the specified time CT is roughly consistent with the target current, but at this point in time, the pulse amplitude of the output current I_OUT exceeds the rated current of the LED, which may damage the LED 32.

[0063] In addition, when a PWM signal with a high frequency and a small duty cycle is input to the LED driver circuit 35 , there is also a problem that the overshoot of the output current I_OUT immediately after the pulse rises cannot be converged within a shorter pulse width.

[0064] Secondly, refer to Figure 4 The structure of the light source device 30 according to the present embodiment will be described.

[0065] Figure 4 is a block diagram showing the structure of a light source device 30 according to one embodiment. Figure 2 and Figure 4 It can be seen that the LED control unit 31 of the light source device 30 is different from the reference example of the light source device in that a filter circuit 37 is added.

[0066] The filter circuit 37 inputs the PWM signal and outputs the control signal CTRL2 to the analog dimming driver 41A. The analog dimming driver 41A generates a current based on the signal with a lower voltage among the control signals CTRL1 and CTRL2, and outputs the current to the current control circuit 43. That is, in the LED control unit 31, analog dimming is performed based on the control signal with a lower voltage among the control signals CTRL1 and CTRL2.

[0067] An example of the filter circuit 37 is shown in Figure 5 .

[0068] exist Figure 5 In the example shown, the filter circuit 37 includes an integration circuit 371 and a voltage divider 372. The integration circuit 371 is composed of resistors R1 and R2 and capacitors C1 and C2, and constitutes a low-pass filter circuit with a cutoff frequency (e.g., 2 to 3 kHz) corresponding to the frequency of the PWM control signal. The voltage divider 372 has resistors R3 and R4 for dividing the output voltage of the integration circuit 371, and constitutes a voltage divider circuit for adjusting the direct current (DC) level of the control signal CTRL2.

[0069] Figure 5 The specific circuit shown is only an example, and those skilled in the art can appropriately set the required cutoff frequency of the low-pass filter.

[0070] In the LED control unit 31, the filter circuit 37 and the analog dimming driver 41A provide an LED protection function so that when a high-frequency and low-duty PWM signal is input to the LED driver circuit 35, the amplitude of the pulse of the output current I_OUT does not exceed the rated current of the LED 32. Figure 6 The timing diagram is used to illustrate this.

[0071] exist Figure 6In the timing diagram, (a) represents the control signal CTRL1, (b) represents the PWM signal, (c) represents the control signal CTRL2, and (d) represents the output current I_OUT.

[0072] exist Figure 6 In the case where a PWM signal having a frequency higher than the cut-off frequency set in the filter circuit 37 and a small duty cycle is input to the LED driver circuit 35, as shown in FIG. Figure 6 As shown in (c), the filter circuit 37 attenuates the high frequency component of the PWM signal and outputs the control signal CTRL2 having a frequency component close to DC to the analog dimming driver 41A.

[0073] The voltage level of the control signal CTRL2, which is a frequency component close to DC, is lower than that of the control signal CTRL1. In this way, since the analog dimming driver 41A generates a current from the lower voltage signal of the control signals CTRL1 and CTRL2 and outputs it to the current control circuit 43, analog dimming is performed based on the control signal CTRL2. As a result, Figure 6 As shown in (d), the amplitude of the pulse of the output current I_OUT generated by the current control circuit 43 is suppressed to a low level, and does not exceed the rated current of the LED 32 to protect the LED 32. In addition, at this time, the amplitude of the pulse of the output current I_OUT does not reach the target current and dimming cannot be performed, but the LED 32 can be protected from unexpected overcurrent.

[0074] Figure 7 Yes means Figure 4 The timing diagram of the actual waveform of the light source device 30 is shown.

[0075] exist Figure 7 , (a) is the waveform of the control signals CTRL1 and CTRL2, and (b) is the waveform of the output current I_OUT.

[0076] exist Figure 7 In the example, before time t1, only control signal CTRL1 is used to perform analog dimming (that is, the duty cycle of the PWM signal is 100%). After time t1, it is assumed that a PWM signal with a high frequency and a small duty cycle is input to the LED driver circuit 35. In this case, after time t1, control signal CTRL2 attenuates the high-frequency component of the PWM signal, making it a signal with a lower voltage and a lower frequency component than control signal CTRL1. In this way, after time t1, the analog dimming driver 41A performs analog dimming based on control signal CTRL2. As a result, as shown in FIG. Figure 7 As shown in (b) of FIG. 1 , the pulse amplitude of the output current I_OUT gradually decreases similarly to the control signal CTRL2 , thereby protecting the LED 32 .

[0077] As described above, the electronic endoscope system 1 according to the present embodiment is provided with an LED control unit 31 (an example of a current control unit) configured to simultaneously perform both analog dimming and PWM dimming on each LED of the light source device 30. The LED control unit 31 is input with a control signal CTRL1 (an example of a first control signal) for performing analog dimming, a PWM signal, and a control signal CTRL2 (an example of a second control signal) for filtering the PWM signal. The LED control unit 31 generates an output current of an amplitude corresponding to the signal with a lower voltage among the control signals CTRL11 and CTRL2. The duty ratio of the output current is determined by the duty ratio of the above-mentioned PWM signal. In addition, the LED control unit 31 (an example of a feedback circuit unit) performs feedback control to feed back the current flowing into each LED to stabilize the output current.

[0078] In the above-described structure, when a PWM signal with a high frequency and a small duty cycle is input, the control signal CTRL2 attenuates the high frequency component of the PWM signal and becomes a signal with a frequency component close to DC, and its voltage level is lower than that of the control signal CTRL1. Therefore, analog dimming is performed based on the lower control signal CTRL2. Therefore, even if feedback control is performed in a manner that the average output current I_OUT over a predetermined period of time converges to the target current as the control amount, the output current I_OUT does not exceed the rated current of the LED and protects the LED.

[0079] In the light source device 30 of the present embodiment, the protection function protects the LED 32 when a PWM signal with a very high frequency and a small duty cycle is input, but when such an abnormal PWM signal is not input, it is preferable to perform analog dimming according to the control signal CTRL1. Figure 7 As shown in FIG. 1 , before time t1 (that is, before the protection function takes effect), the control signal CTRL2 is preferred to be higher than the control signal CTRL1. That is, in the case of analog dimming, in order not to be affected by the control signal CTRL2, it is preferred to make the voltage of the control signal CTRL2 higher than the control signal CTRL1. For example, the voltage of the control signal CTRL2 is about 10-20% higher than the control signal CTRL1, but this is not limited. The voltage value of the control signal CTRL2 is adjusted in Figure 5 In the example of the filter circuit 37 , this is performed by the voltage divider 372 .

[0080] In summary, in one embodiment, the signal level of the control signal CTRL2 is adjusted so that the signal level of the control signal CTRL2 when the duty ratio of the PWM signal is 100% is higher than the maximum value of the signal level of the control signal CTRL1 .

[0081] As described above, when the protection function is in effect, the output current I_OUT cannot be controlled to the target current, and dimming of the control signal CTRL1 cannot be performed. Therefore, when it is desired to continue with the intended dimming operation, PWM dimming should not be performed when the voltage level of the control signal CTRL1 is high. That is, when reducing the light intensity of the emitted light of LED32, first reduce the voltage level of the control signal CTRL1 for dimming, and preferably adjust the duty ratio of the PWM signal only when the voltage of the control signal CTRL1 has been sufficiently reduced.

[0082] Figure 8 An example of the relationship between the voltage level of the control signal CTRL1 (CTRL1 level) in analog dimming and the duty ratio of the PWM signal that can be set is shown.

[0083] In addition, here as an example, it is assumed that when the CTRL1 level is at the maximum value (100%), the voltage of the control signal CTRL2 with a duty ratio of 100% is 10% higher than that of the control signal CTRL1. In this case, if the duty ratio of the PWM signal is in the range of approximately 90% to 100%, then CTRL2 > CTRL1, so analog dimming can be performed using the control signal CTRL1. When the voltage level of the control signal CTRL1 is low, the duty ratio of the PWM signal for maintaining the relationship CTRL2 > CTRL1 and enabling analog dimming using the control signal CTRL1 is relaxed. For example, when the voltage level of the control signal CTRL1 is approximately 55%, the duty ratio can be made variable in the range of 50% to 100% (set as the "actual use area") to maintain the relationship CTRL2 > CTRL1.

[0084] In Figure 8 the "actual use area" is defined as the area where analog dimming can be performed using the control signal CTRL1. When CTRL2 < CTRL1, since analog dimming cannot be performed using the control signal CTRL1, it is set as the "non-dimming area".

[0085] Therefore, in one embodiment, the use range of the duty ratio of the PWM signal is limited according to the signal level of the control signal CTRL1 so that the signal level of the control signal CTRL1 is lower than the signal level of the control signal CTRL2. Thereby, it is prevented that analog dimming cannot be performed using the control signal CTRL1 due to the duty ratio of the PWM signal.

[0086] As described above, the processor for an electronic endoscope and the electronic endoscope system of the present invention have been described in detail. However, the processor for an electronic endoscope and the electronic endoscope system of the present invention are not limited to the above-described embodiments, and various improvements and changes can be made without departing from the gist of the present invention.

[0087] The present invention relates to a patent application of Japanese Patent Application No. 2022-134492 filed with the Japan Patent Office on August 25, 2022, and the entire contents of the application are incorporated into this specification by reference.

Claims

1. A processor for an electronic endoscope, which is used in an electronic endoscope having an imaging element configured to perform imaging of living tissue, and comprises: a light source unit that synthesizes the lights emitted from the plurality of light emitting elements to generate illumination light for the living tissue; and a current control unit for controlling the current flowing into each light emitting element of the light source unit; The current control unit comprises: a current generating unit that generates, as a current flowing into each light emitting element, an output current having an amplitude corresponding to a lower voltage signal of a first control signal and a second control signal obtained by filtering the PWM control signal, corresponding to a duty ratio of a pulse width modulated control signal (PWM control signal); and The feedback circuit unit feeds back the current flowing into each light emitting element to stabilize the output current generated by the current generating unit.

2. The processor for an electronic endoscope according to claim 1, wherein: The signal level of the second control signal is adjusted so that the signal level of the second control signal when the duty ratio of the PWM control signal is 100% is higher than the maximum value of the signal level of the first control signal.

3. The processor for an electronic endoscope according to claim 2, wherein: The use range of the duty ratio of the PWM control signal is limited according to the signal level of the first control signal in such a manner that the signal level of the first control signal is lower than the signal level of the second control signal.

4. The processor for an electronic endoscope according to claim 1, wherein: The current control unit includes a low-pass filter circuit having a cutoff frequency corresponding to the frequency of the PWM control signal as a circuit for performing the filtering process.

5. An electronic endoscope system comprising: The processor for an electronic endoscope according to any one of claims 1 to 4; and The electronic endoscope is connected to the electronic endoscope processor and includes an imaging element for acquiring an image of the living tissue.

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