Processor for electronic endoscope, electronic endoscope system

Abstract

To protect an LED when performing lighting control with pulse width modulation to a light emitting element in a processor for an electronic endoscope which includes a light source that has the light emitting element.SOLUTION: A processor for an electronic endoscope according to an embodiment of the present invention which is used in an electronic endoscope including an imaging element configured to perform imaging of a biological tissue, comprises: a light source part which generates illumination light to the biological tissue by combining light emitted from the plurality of light emitting elements; and a current control part which controls current flowing to each light emitting element of the light source part. The current control part includes: a current generation section which generates output current with a duty ratio according to a control signal (PWM control signal) of pulse width modulation and the amplitude according to a signal of low voltage in a first control signal and a second control signal obtained by performing filter treatment to the PWM control signal as the current flowing to each light emitting element; and a feedback circuit section which stabilizes the output current generated by the current generation section by feeding back the current flowing to each light emitting element.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an electronic endoscope processor used in an electronic endoscope having an imaging element configured to capture images of living tissue, and to an electronic endoscope system. [Background technology]

[0002] In the field of medical equipment, an endoscope system is known that can generate images suitable for diagnosing lesions hidden within a body cavity by illuminating biological tissue within the body cavity and capturing an image of the illuminated biological tissue within the body cavity as a subject. Conventionally, lamp light sources such as xenon lamps and halogen lamps that emit white light have been used as illumination light, but recently, instead of lamp light sources, 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.

[0003] For example, Patent Document 1 describes an endoscope system that includes an endoscope having an illumination optical system that irradiates a subject with light from a light source and an imaging optical system that includes an imaging element that images the subject, and a control device to which the endoscope is detachably connected. This system is configured to have multiple control patterns that represent the relationship between a light intensity instruction value and a control output value to the light source, and to have a light source control unit that switches to one of the control patterns based on the identification result of the type of imaging element and control the intensity of light emitted from the light source based on the switched control pattern. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-60860 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, driver ICs (Integrated Circuits) that drive LEDs are sometimes equipped with both a pulse width modulation (PWM) dimming circuit and an analog dimming circuit, and also include a feedback circuit to stabilize the output current flowing to the LED. Such driver ICs are configured to simultaneously perform both PWM and analog dimming control methods, rather than selectively executing either PWM or analog dimming control.

[0006] When such LED driver ICs are used in electronic endoscope systems, the high frequency of the PWM signals used in the system can destroy the LEDs. For example, to capture images of a subject at a high shutter speed (e.g., 1 / 1000 of a second) without blurring the still image under PWM-modulated illumination, the LEDs must be PWM-driven at 10 to 100 times the high shutter speed (e.g., passing a PWM current of 10 to 100 kHz through the LEDs). However, such high-frequency PWM currents cannot be stably controlled due to the response delay of the feedback system, and the peak output current may exceed the rated value of the LED, destroying it.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to protect an LED in a processor for an electronic endoscope equipped with a light source having a light emitting element when dimming the light emitting element by pulse width modulation. [Means for solving the problem]

[0008] One aspect of the present disclosure is a processor for an electronic endoscope used in an electronic endoscope having an imaging element configured to capture images of biological tissue, the processor comprising: a light source unit that combines light emitted from a plurality of light-emitting elements to generate illumination light for the biological tissue; and a current control unit that controls current flowing through each light emitting element of the light source unit. The current control unit a current generating unit that generates, as a current to be passed through each light emitting element, an output current having a duty ratio according to a pulse width modulation control signal (PWM control signal), and an amplitude according to a lower voltage signal of a first control signal and a second control signal obtained by filtering the PWM control signal; and a feedback circuit section that stabilizes the output current generated by the current generating section by feeding back the current flowing through each light emitting element. The current control unit includes, as a circuit for performing the filtering process, a low-pass filter circuit having a cutoff frequency corresponding to the frequency of the PWM control signal.

[0009] The signal level of the second control signal may be 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.

[0010] The range of use of the duty ratio of the PWM control signal may be limited according to the signal level of the first control signal so that the signal level of the first control signal is lower than the signal level of the second control signal.

[0012] Another aspect of the present disclosure is a method for detecting a signal from an electronic endoscope, comprising: and an electronic endoscope having an imaging element connected to the electronic endoscope processor for acquiring images of the biological tissue. [Effects of the Invention]

[0013] According to the above-described electronic endoscope processor and electronic endoscope system, in an electronic endoscope processor equipped with a light source having a light-emitting element, the LED can be protected when dimming the light-emitting element by pulse width modulation. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing an example of a configuration of an electronic endoscope system according to an embodiment; [Figure 2] FIG. 10 is a block diagram showing the configuration of a reference example of a light source device. [Figure 3]3 is a timing chart showing the operation of the light source device shown in FIG. [Figure 4] 1 is a block diagram showing a configuration of a light source device according to an embodiment; [Figure 5] 5 is a diagram showing an example of the configuration of a filter circuit included in the light source device of FIG. 4. [Figure 6] 5 is a timing chart showing the operation of the light source device shown in FIG. [Figure 7] 5 is a timing chart showing actual waveforms of the light source device shown in FIG. [Figure 8] FIG. 10 is a diagram showing an example of the relationship between the voltage level of a control signal in analog dimming and the duty ratio of a PWM signal that can be set. DETAILED DESCRIPTION OF THE INVENTION

[0015] The electronic endoscope system of this embodiment will be described in detail below with reference to the drawings. Fig. 1 is a block diagram showing an example of the configuration of an electronic endoscope system 1 according to this embodiment. As shown in Fig. 1, the electronic endoscope system 1 is a system specialized for medical use, and includes an electronic scope (endoscope) 100, a processor 200, and a monitor 300.

[0016] The processor 200 includes a system controller 21. The system controller 21 executes various programs stored in a memory 23 and comprehensively controls the entire electronic endoscope system 1. The system controller 21 is also connected to an operation panel 24. The system controller 21 changes each operation of the electronic endoscope system 1 and parameters for each operation in response to instructions from the surgeon input to 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.

[0017] The processor 200 includes a light source device 30. The light source device 30 emits illumination light L for illuminating a subject, such as biological tissue within a body cavity. The illumination light L includes white light, pseudo-white light, or special light. According to one embodiment, the light source device 30 selects one of a mode in which white light or pseudo-white light is constantly emitted as the illumination light L, and a mode in which white light, pseudo-white light, and special light are alternately emitted as the illumination light L, and preferably emits white light, pseudo-white light, or special light based on the selected mode. White light is light with a flat spectral intensity distribution in the visible light band, while pseudo-white light is light with a non-flat spectral intensity distribution that is a mixture of light from multiple wavelength bands. The special light is light in a narrow wavelength band, such as blue or green, within the visible light band. Light in the blue or green wavelength band is used to emphasize and observe specific areas of biological tissue. The illumination light L emitted from the light source device 30 is condensed by the condenser lens 25 onto the incident end surface of the LCB (Light Carrying Bundle) 11 and enters the LCB 11.

[0018] Illumination light L incident on the LCB 11 propagates through the LCB 11. The illumination light L propagates through the LCB 11 and is emitted from the exit end face of the LCB 11 located at the tip of the electronic scope 100, and is irradiated onto the subject via the light distribution lens 12. 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 image sensor 14 via the objective lens 13.

[0019] The solid-state imaging element 14 is a single-plate color CCD (Charge Coupled Device) image sensor with a Bayer pixel arrangement. The solid-state imaging element 14 accumulates an optical image formed at each pixel on its light-receiving surface as an electric charge according to the amount of light, and generates and outputs R (Red), G (Green), and B (Blue) image signals. Note that the solid-state imaging element 14 is not limited to a CCD image sensor, and may be replaced with a CMOS (Complementary Metal Oxide Semiconductor) image sensor or other types of imaging devices. The solid-state imaging element 14 may also be equipped with a complementary color filter.

[0020] A driver signal processing circuit 15 is provided within the connection section of the electronic scope 100. Image signals of a subject are input to the driver signal processing circuit 15 from the solid-state imaging device 14 at a predetermined frame period. The frame period is, for example, 1 / 30 seconds. The driver signal processing circuit 15 performs predetermined processing, including A / D conversion, on the image signals input from the solid-state imaging device 14 and outputs the processed signals to the image processing section 22 of the processor 200. The image processing unit 22 performs predetermined image processing, which will be described later, to generate a video format signal, and outputs it to the monitor 300 .

[0021] The driver signal processing circuit 15 also accesses the memory 16 to read out information specific to the electronic scope 100. The information specific to the electronic scope 100 stored in the memory 16 includes, for example, the number of pixels and sensitivity of the solid-state image sensor 14, the operable frame rate, the model number, etc. The driver signal processing circuit 15 outputs the information read out from the memory 16 to the system controller 21. This information may include, for example, information specific to the solid-state image sensor 14, such as the number of pixels and resolution, as well as information related to the optical system, such as the angle of view, focal length, and depth of field.

[0022] The system controller 21 performs various calculations based on the unique information of the electronic scope 100 and generates control signals. Using the generated control signals, the system controller 21 controls the operation and timing of various circuits within the processor 200 so that processing appropriate for the electronic scope 100 connected to the processor 200 is performed.

[0023] The system controller 21 supplies clock pulses to the driver signal processing circuit 15. In accordance with the clock pulses supplied from the system controller 21, the driver signal processing circuit 15 drives and controls the solid-state imaging device 14 at a timing synchronized with the frame rate of the video processed on the processor 200 side.

[0024] Next, the light source device 30 built into the processor 200 will be described. Generally, in light source devices, multiple LEDs are used as light sources to obtain white illumination light, and the light emitted from the multiple LEDs is combined. For example, three LEDs (blue, green, and red) may be used as the light source, and five LEDs (UV (Ultra Violet) LED, blue, green, amber, and red) may be used. Each LED is capable of analog dimming and PWM dimming. Analog dimming is the process of controlling the intensity of the light emitted by the LED by changing the amount of current flowing through the LED. On the other hand, PWM dimming is the process of passing a current through the LED with a PWM (Pulse Width Modulation) waveform, and controlling the intensity of the light emitted by the LED by changing the PWM duty ratio. The light source device 30 is configured to be able to perform analog dimming and PWM dimming independently of each other.

[0025] Before describing the configuration of the light source device 30 of this embodiment, a reference example of the light source device will be described below with reference to FIGS. 2 and 3 to facilitate understanding of the light source device 30 of this embodiment. Fig. 2 is a block diagram showing a reference example of a light source device. Fig. 3 is a timing chart showing the operation of the reference example of the light source device. As mentioned above, the light source device has multiple LEDs, but Fig. 2 shows only the configuration of the light source device for a single LED 32. 2, the reference example of the light source device has an LED control unit 31R that controls the current flowing through the LED 32. The LED control unit 31R has an LED driver circuit 35, a sense resistor Rs, and a MOS transistor Q1.

[0026] The LED driver circuit 35 receives a control signal CTRL1 and a PWM signal (PWM) supplied from the system controller, and outputs a PWM output PWM_OUT that controls the MOS transistor Q1 and an output current I_OUT that flows through the LED 32. The LED driver circuit 35 is configured by a hardware module configured, for example, by an FPGA (Field-Programmable Gate Array). The LED driver circuit 35 includes an analog dimming driver 41, a PWM driver 42, and a current control circuit 43. 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. The PWM driver 42 generates a PWM output PWM_OUT by amplifying the PWM signal to a voltage that can drive the MOS transistor Q1, and supplies the generated PWM output PWM_OUT to the gate of the MOS transistor Q1 and also outputs it to the current control circuit 43.

[0027] The current control circuit 43 amplifies the current output from the analog dimming driver 41 and generates the output current I_OUT based on the duty ratio 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 ratio of the PWM signal. Therefore, the waveform of the output current I_OUT is a pulse waveform determined by the duty ratio of the PWM signal, and the amplitude of the pulse waveform has a value corresponding to the voltage level of the control signal CTRL1. 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 made variable. That is, when the duty ratio of the PWM signal is 100%, the PWM output PWM_OUT becomes H level, the MOS transistor Q1 turns ON, and an output current I_OUT according to the amplitude of the control signal CTRL1 flows to the LED 32. When performing PWM dimming, the voltage level of the control signal CTRL1 is kept constant and the duty ratio of the PWM signal is made variable. In this case, the output current I_OUT is kept constant, and the MOS transistor Q1 is turned ON / OFF according to the level of the PWM output PWM_OUT, which has the same duty ratio as the duty ratio of the PWM signal, so that the output current I_OUT based on the duty ratio of the PWM signal flows through the LED 32.

[0028] The current control circuit 43 also detects the current (output current I_OUT) flowing through the LED 32 from the voltage drop across the sense resistor Rs, and performs feedback control to stabilize the output current I_OUT based on the detection result. In this feedback control, the average output current I_OUT over a predetermined time is used as a control amount to converge to a target current.

[0029] 3(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. In Fig. 3, T1, T2, ... each correspond to one period, and CT is a predetermined time when the control amount is determined. As shown in Figure 3(a), when a relatively low-frequency PWM signal is input to the LED driver circuit 35, the pulse width is longer than the predetermined time CT, even if the duty ratio is small, so the average output current I_OUT can be made to roughly match the target current. That is, the amplitude levels A1, A2, ... of the average output current I_OUT over the predetermined time CT in periods T1, T2, ... are roughly close to the target current, allowing the output current I_OUT to converge to the target current in a timely manner. Note that although there is a momentary overshoot immediately after the rising edge of the output current I_OUT pulse, the relatively long pulse width allows it to converge to the target current within the pulse width.

[0030] 3(b) is a timing chart showing the output current I_OUT (LED current) when a PWM signal with a high frequency relative to the response characteristics of the feedback control in the current control circuit 43 is input to the LED driver circuit 35. As shown in Fig. 3(b), when a PWM signal with a high frequency and a small duty ratio is input to the LED driver circuit 35, the pulse width is shorter than the predetermined time CT when setting the target current, so the average output current I_OUT set as the controlled variable does not reflect the pulse amplitude and is lower than the pulse amplitude. In Fig. 3(b), the average output current I_OUT set as the controlled variable in periods T1 to T6 are denoted as A1 to A6, respectively.

[0031] 3(b), although the pulse amplitude of the output current I_OUT roughly matches the target current, the average output current I_OUT (control amount) within the predetermined time CT is low, so the LED driver circuit 35 generates the output current I_OUT so that the pulse amplitude increases in period T2 to bring the control amount closer to the target current. Similarly, the output current I_OUT is generated in periods T3 to T5, with the pulse amplitude gradually increasing. In period T5, the average output current I_OUT within the predetermined time CT roughly matches the target current, but at this point the pulse amplitude of the output current I_OUT exceeds the rated current of the LED, which may damage the LED 32. Furthermore, when a PWM signal with a high frequency and a small duty ratio is input to the LED driver circuit 35, there is a problem in that the overshoot immediately after the rise of the pulse of the output current I_OUT cannot be converged within the short pulse width.

[0032] Next, the configuration of the light source device 30 of this embodiment will be described with reference to FIG. Fig. 4 is a block diagram showing the configuration of a light source device 30 according to one embodiment. As can be seen from a comparison of Fig. 2 and Fig. 4, the LED control unit 31 of the light source device 30 differs from the reference example of the light source device in that a filter circuit 37 is added. The filter circuit 37 receives the PWM signal and outputs a control signal CTRL2 to the analog dimming driver 41A. The analog dimming driver 41A generates a current based on the lower voltage of the control signals CTRL1 and CTRL2 and outputs the current to the current control circuit 43. That is, the LED control unit 31 performs analog dimming based on the lower voltage of the control signals CTRL1 and CTRL2.

[0033] An example of the filter circuit 37 is shown in FIG. 5, filter circuit 37 includes an integrating circuit 371 and a voltage dividing unit 372. Integration circuit 371 is made up of resistors R1 and R2 and capacitors C1 and C2, and forms a low-pass filter circuit with a cutoff frequency (e.g., 2 to 3 kHz) according to the frequency of the PWM control signal. Voltage dividing unit 372 has resistors R3 and R4 for dividing the output voltage of integration circuit 371, and forms a voltage dividing circuit for adjusting the DC level of control signal CTRL2. The specific circuit shown in FIG. 5 is merely an example, and a person skilled in the art can appropriately set a low-pass filter with the required cutoff frequency.

[0034] In the LED control unit 31, the filter circuit 37 and the analog dimming driver 41A provide an LED protection function that prevents the amplitude of the pulse of the output current I_OUT from exceeding the rated current of the LED 32 when a PWM signal with a high frequency and a small duty ratio is input to the LED driver circuit 35. This LED protection function will be described below with reference to the timing chart of FIG.

[0035] In the timing chart of FIG. 6, (a) indicates the control signal CTRL1, (b) indicates the PWM signal, (c) indicates the control signal CTRL2, and (d) indicates the output current I_OUT. In FIG. 6, when a PWM signal having a higher frequency than the cutoff frequency set in the filter circuit 37 and a small duty ratio is input to the LED driver circuit 35, the filter circuit 37 attenuates the high frequency components of the PWM signal and outputs a control signal CTRL2 having a frequency component close to DC to the analog dimming driver 41A, as shown in FIG. 6(c). The voltage level of the control signal CTRL2, which has a frequency component close to DC, becomes lower than that of the control signal CTRL1. The analog dimming driver 41A then generates a current based on the lower voltage of the control signals CTRL1 and CTRL2 and outputs the current to the current control circuit 43, thereby performing analog dimming based on the control signal CTRL2. As a result, as shown in FIG. 6(d), the pulse amplitude of the output current I_OUT generated by the current control circuit 43 is kept low, preventing the rated current of the LED 32 from being exceeded and protecting the LED 32. Note that the pulse amplitude of the output current I_OUT at this time does not reach the target current, preventing dimming, but protecting the LED 32 from unintended overcurrent.

[0036] FIG. 7 is a timing chart showing actual waveforms of the light source device 30 shown in FIG. In FIG. 7, (a) shows the waveforms of the control signals CTRL1 and CTRL2, and (b) shows the waveform of the output current I_OUT. In FIG. 7, it is assumed that analog dimming is performed using only the control signal CTRL1 (i.e., the duty cycle of the PWM signal is 100%) before time t1, and that a PWM signal with a high frequency and a low duty cycle is input to the LED driver circuit 35 after time t1. In this case, after time t1, the control signal CTRL2 attenuates the high-frequency components of the PWM signal and becomes a signal with a lower voltage and lower frequency components than the control signal CTRL1. Then, after time t1, the analog dimming driver 41A performs analog dimming based on the control signal CTRL2. As a result, as shown in FIG. 7(b), the pulse amplitude of the output current I_OUT gradually decreases in the same way as the control signal CTRL2, and the LED 32 is protected.

[0037] As described above, the electronic endoscope system 1 of this embodiment includes 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 receives a control signal CTRL1 (an example of a first control signal) for analog dimming, a PWM signal, and a control signal CTRL2 (an example of a second control signal) obtained by filtering the PWM signal. The LED control unit 31 generates an output current having an amplitude corresponding to the lower voltage of the control signals CTRL11 and CTRL2. The duty ratio of this output current is determined by the duty ratio of the PWM signal. The LED control unit 31 (an example of a feedback circuit unit) also performs feedback control to stabilize the output current by feeding back the current flowing through each LED. In the above configuration, when a PWM signal with a high frequency and a small duty cycle is input, the control signal CTRL2 attenuates the high-frequency components of the PWM signal to become a signal with frequency components close to DC, and its voltage level becomes lower than that of the control signal CTRL1. Therefore, analog dimming is performed based on the lower control signal CTRL2. Therefore, even when feedback control is performed to converge the average output current I_OUT over a predetermined time to the target current as a control variable, the output current I_OUT will not exceed the rated current of the LED, and the LED will be protected.

[0038] The protection function described above in the light source device 30 of this embodiment is to protect the LED 32 when a PWM signal with an extremely high frequency and a small duty ratio is input. However, when such an abnormal PWM signal is not input, it is preferable to perform analog dimming in accordance with the control signal CTRL1. From this perspective, as shown in FIG. 7, it is preferable that the control signal CTRL2 be higher than the control signal CTRL1 before time t1 (i.e., before the protection function is activated). That is, when analog dimming is being performed, it is preferable that the voltage of the control signal CTRL2 be higher than the control signal CTRL1 so as not to be affected by the control signal CTRL2. Although not limited thereto, for example, the voltage of the control signal CTRL2 is set to be approximately 10 to 20% higher than the control signal CTRL1. The voltage value of this control signal CTRL2 is adjusted by the voltage divider 372 in the example of the filter circuit 37 of FIG. 5. In short, 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.

[0039] As described above, when the protection function is activated, the output current I_OUT cannot be controlled to the target current, and dimming using the control signal CTRL1 becomes impossible. Therefore, if you want to continue the intended dimming operation, you must avoid performing PWM dimming while the voltage level of the control signal CTRL1 is high. In other words, when reducing the light intensity of the light emitted from the LED 32, it is preferable to first perform dimming by lowering the voltage level of the control signal CTRL1, and then adjust the duty ratio of the PWM signal only when the voltage of the control signal CTRL1 has sufficiently decreased.

[0040] FIG. 8 shows an example of the relationship between the voltage level (CTRL1 level) of the control signal CTRL1 in analog dimming and the settable duty ratio of the PWM signal. Here, as an example, when the CTRL1 level is at its maximum value (100%), it is assumed that 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 within the range of approximately 90% to 100%, then CTRL2 > CTRL1, so analog dimming by the control signal CTRL1 is possible. When the voltage level of the control signal CTRL1 is low, the duty ratio of the PWM signal for enabling analog dimming by the control signal CTRL1 while maintaining the relationship of CTRL2 > CTRL1 is relaxed. For example, when the voltage level of the control signal CTRL1 is approximately 55%, the duty ratio can be made variable (referred to as the "actual usage area") within the range of 50% to 100% in order to maintain the relationship of CTRL2 > CTRL1. In FIG. 8, the "actual usage area" is defined as the area where analog dimming by the control signal CTRL1 is possible. When CTRL2 < CTRL1, it is referred to as the "non-dimming area" because analog dimming by the control signal CTRL1 is not possible. Therefore, in one embodiment, the usage range of the duty ratio of the PWM signal is restricted according to the signal level of the control signal CTRL1 such 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 by the control signal CTRL1 becomes impossible due to the duty ratio of the PWM signal.

[0041] 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 embodiments, and of course, various improvements and modifications may be made without departing from the gist of the present invention.

Explanation of Reference Numerals

[0042] 1... Electronic endoscope system LCB... 11 Light distribution lens... 12 Objective lens... 13 Solid-state imaging device... 14 Driver signal processing circuit... 15 16...Memory 21...System controller 22...Image processing unit 23...Memory 24...Operation panel 30…Light source device 31,31R…LED control section 32...LED 35...LED driver circuit 37...Filter circuit 371...Integrator circuit 372...Voltage divider 41...Analog dimming driver 42...PWM driver 43...Current control circuit Q1...MOS transistor 100...Electronic scope 200...processor 300...Monitor

Claims

1. A processor for an electronic endoscope used in an electronic endoscope having an imaging element configured to capture images of biological tissue, a light source unit that combines light emitted from a plurality of light-emitting elements to generate illumination light for the biological tissue; a current control unit that controls a current flowing through each light emitting element of the light source unit, The current control unit a current generating unit that generates, as a current to be passed through each light-emitting element, an output current having a duty ratio according to a pulse width modulation control signal (PWM control signal), and an amplitude according to a lower voltage signal of a first control signal and a second control signal obtained by filtering the PWM control signal; a feedback circuit unit that stabilizes the output current generated by the current generating unit by feeding back the current flowing through each light emitting element; the current control unit includes, as a circuit for performing the filtering process, a low-pass filter circuit having a cutoff frequency corresponding to the frequency of the PWM control signal; Processor for electronic endoscopes.

2. 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.

2. The processor for an electronic endoscope according to claim 1.

3. limiting a range of use of the duty ratio of the PWM control signal in accordance with the signal level of the first control signal so that the signal level of the first control signal is lower than the signal level of the second control signal; 3. A processor for an electronic endoscope according to claim 2.

4. A processor for an electronic endoscope according to any one of claims 1 to 3; an electronic endoscope including an image sensor connected to the electronic endoscope processor and configured to acquire an image of the biological tissue; An electronic endoscope system comprising:

Images