JP3053285B2 - Signal transmission processing circuit of electronic endoscope device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission processing circuit of an electronic endoscope apparatus, and more particularly to a video signal transmission processing circuit in an electronic endoscope apparatus in which a patient circuit is connected to an output circuit by an isolation device. About.

[0002]

2. Description of the Related Art An electronic endoscope apparatus for observing the inside of a body cavity such as a digestive tract or the like by using a CCD (Charge Coupled Device) which is a solid-state image pickup device provided at a distal end portion is well known. In this case, an image of the inside of the body to be observed picked up by the CCD is displayed on a monitor, and diagnosis and various treatments are performed while observing the image displayed on the monitor.

FIG. 10 shows a schematic structure of a conventional electronic endoscope apparatus. As shown, an external endoscope 2 is connected to an external processor 1 as shown in FIG. The CCD 3, which is a solid-state image sensor, is provided at the distal end of the insertion section. On the other hand, in the external processor device 1, a CCD driver 4 and a signal processing circuit 5 for amplifying video signals are provided as patient circuits, and these patient circuits are connected to an output circuit via an isolation device 6. I have. The output circuit includes an A / D (analog / digital) converter 7, a frame memory 8, a D / A (digital / analog) converter 9, a control circuit 10, and the like.

Accordingly, when the CCD 3 is driven by the control circuit 10 and the CCD driver 4, the video signal obtained by the imaging of the CCD 3 is subjected to a process process corresponding to the color display by the signal processing circuit 5. . Thereafter, the video signal is input to the A / D converter 7 via the isolation device 6, and the digital video signal is stored in the frame memory 8. And
The video signal stored in the frame memory 8 is converted into an analog signal by a D / A converter 9 and then output to a monitor (not shown). The image picked up by the CCD 3 is color-coded on the monitor. Is displayed as an image.

[0005] In the above, the isolation device 6 is composed of a photocoupler, a pulse transformer, or the like, and electrically disconnects the patient circuit from the output circuit, thereby increasing the safety when applying the electronic endoscope 2 to a patient. Provided to keep. That is, in the case of the above-described photocoupler, an operation of temporarily converting an electric signal into an optical signal and returning it to an electric signal is again performed, thereby electrically disconnecting between the patient circuit and the output circuit.
A dielectric breakdown voltage of ４4 kV or more is maintained. In the case of a pulse transformer, a predetermined withstand voltage between the two can be maintained by the withstand voltage of the transformer, and electrical safety for a patient or the like is ensured by such an isolation device 6.

[0006]

However, in the conventional signal transmission processing circuit of the electronic endoscope apparatus, the signal transmission processing circuit between the patient circuit and the output circuit depends on the temperature condition and the unique characteristics of the isolation device 6. However, there is a problem that a video signal to be changed fluctuates, and becomes remarkable especially when a photocoupler is used. That is, in the photocoupler, the light emitting diode converts the electric analog signal, which is a video signal, into a light amount corresponding to its magnitude,
This light amount is converted into an electric signal by, for example, a phototransistor. However, the diode and the transistor are affected by the temperature, and the light conversion efficiency varies depending on the temperature condition.

The photocoupler and the pulse transformer as the isolation device 6 vary in the characteristics of individual members depending on the production lot, but the video signal is a plurality of signals, for example, each of RGB signals, or a color difference signal. In addition, since each luminance signal is transmitted using the respective isolation device 6, there is a problem that accurate transmission of the video signal cannot be performed due to variation in characteristics depending on the production lot.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to form a feedback control loop including an isolation device so that the optical conversion efficiency of a photocoupler as an isolation device varies. Another object of the present invention is to provide a signal transmission processing circuit of an electronic endoscope apparatus that can accurately transmit a video signal even when the intrinsic characteristics of an isolation device vary.

In order to achieve the above object, the present invention provides an electronic endoscope in which a patient circuit on an electronic endoscope applied to a patient and an output circuit for processing / outputting a video signal are connected by an isolation device. In a signal transmission processing circuit of an endoscope apparatus, an amplitude detection circuit provided on the output circuit side for detecting an amplitude level of a video signal transmitted via an isolation device, and an output of the amplitude detection circuit is output to a patient circuit side. A conversion circuit for converting the converted signal into a digital predetermined signal in order to restore the original signal; a reconversion circuit provided on the patient circuit side for reconverting the converted signal input via the isolation device into the original signal; And a level control circuit for controlling the level of the video signal by feeding back the output of the circuit. The conversion circuit and the re-conversion circuit may be a voltage-frequency conversion circuit and a frequency-voltage conversion circuit, an A / D converter, a D / A converter, and the like. A modulation circuit and a demodulation circuit that modulate and demodulate the output of the amplitude detection circuit based on the frequency signal can be used.

[0010]

According to the above arrangement, the amplitude level of the video signal subjected to the predetermined processing is detected after being transmitted through the isolation device, and the amplitude level is detected, for example, by the voltage-frequency conversion circuit. Is converted into a frequency signal. When this frequency signal is returned to the patient circuit via the isolation device, it is converted to the original voltage signal by the frequency-voltage conversion circuit.

The voltage signal, which is a detection signal of the amplitude level, is supplied in a form of being fed back to the level control circuit. For example, by inputting this voltage signal to the emitter side of the transistor whose video signal is supplied to the base side, The amplitude of the output video signal is controlled. Therefore, even when the amplitude of the video signal fluctuates due to the isolation device, the operation is performed to compensate for the fluctuation. For example, even if the optical conversion efficiency of the photocoupler fluctuates due to the temperature, the conversion efficiency does not change. Can be controlled to be constant.

[0012]

FIG. 1 shows a configuration of a signal transmission processing circuit of an electronic endoscope apparatus according to a first embodiment, that is, a signal transmission processing circuit including an isolation device. Is composed of a photocoupler and is provided for each of a plurality of video signals to be transmitted. That is, it is composed of a light emitting diode D1 for converting an electric signal into an optical signal, a photodiode D2 for converting an optical signal into an electric signal, and a transistor TR1. On the patient circuit side electrically disconnected from the output circuit by the isolation device 12, connected to an input terminal A, a capacitor C1 for cutting a DC component of a video signal, and a current proportional to the video signal to a photodiode D
1 is provided with a control transistor TR2.

On the other hand, on the output circuit side, the transistor T
Output transistor for converting the output current of R1 to voltage
A transistor TR3 is provided, and the output transistor TR3
The output terminal B is connected to the collector terminal side.
An amplitude detection circuit is provided between the terminal B and the output transistor TR3.
13 are provided. The amplitude detection circuit 13 has an input
A level that detects the amplitude level of a signal and converts it to a predetermined level.
The level converter 14 and the reference level (black level) of the video signal
A clamp circuit that clamps the
The detection signal is transmitted by the frequency converter 14 to a frequency signal described later.
It is converted to a level that enables transmission. And this amplitude
The detection circuit 13 has a voltage-frequency conversion (V
-F conversion) circuit 16 is connected to the V-f conversion circuit 1.
6 converts the output voltage of the amplitude detection circuit 13 into a frequency signal
You. FIG. 2 shows the conversion characteristics of the Vf conversion circuit 16.
As shown in the figure, the Vf conversion circuit 16
If V L to V_P Proportional to the voltage of the video signal
Output frequency f_L To f_P Can be obtained.

In order to return the output of the Vf conversion circuit 16 to the patient circuit side, an isolation device 17 is provided.
And the isolation device 17 is constituted by a pulse transformer. This isolation device 17 has a frequency-voltage conversion (f
A -V conversion circuit 18 is connected, and the fV conversion circuit 18 converts a frequency signal output from the isolation device 17 into a voltage. The fV conversion circuit 18 is connected to the emitter side of a control transistor TR2 as the level control circuit, and an input video signal is supplied to the base side of the control transistor TR2. Therefore, this control transistor TR
According to FIG. 2, when the output voltage of the fV conversion circuit 18 becomes low, a high-level video signal corresponding to the output voltage is output to the collector side, and when the output voltage becomes high, a low-level video signal corresponding thereto is output. Will be output.

Next, the operation according to the configuration of FIG. 1 will be described with reference to FIG.
It will be described based on. FIG. 3 (a) shows a video signal input to the input terminal A on the patient circuit side in FIG. 1, and this video signal passes through the capacitor C1 and the control transistor TR2, and passes through an isolation device (photocoupler). The signal is supplied to the output circuit side via the line 12. And
On the output circuit side, the video signal is supplied to the output terminal B via the output transistor TR3, and the amplitude detection circuit 1
3 is also input. In the amplitude detection circuit 13, the level converter 14 detects the amplitude level of the video signal, and converts the amplitude level into a detection signal having the level shown in FIG. When this detection signal is supplied to the clamp circuit 15, its reference level is DC-reproduced by the clamp pulse shown in FIG. That is, an optically black portion (black level signal) is included in the video signal.
Exists as a reference level of the video signal, accurate detection is performed by clamping the detection signal, and the clamped signal is as shown in FIG.

The output of the clamp circuit 15 in the amplitude detection circuit 13 is converted into a frequency signal by a Vf conversion circuit 16 at the next stage, and this frequency signal is returned to the patient circuit via an isolation device 17. The purpose of the frequency conversion of the voltage signal is to convert the voltage signal into a digital signal by the frequency conversion, so that the signal transmitted through the isolation device 17 does not fluctuate. In the patient circuit, the frequency signal converted by the Vf conversion circuit 16 is converted into an original voltage signal by the fV conversion circuit 18, and this voltage signal is input to the emitter side of the control transistor TR2.

When the output voltage of the Vf conversion circuit 16 is input to the emitter of the control transistor TR2, the amplitude of the video signal input to the base is adjusted to a level corresponding to the input voltage. Output to the side. For example, when the video signal fluctuates due to the isolation device 12 and the level of the video signal decreases, a signal voltage proportional to the reduction is supplied, thereby lowering the emitter voltage of the control transistor TR2. Therefore, a voltage compensated for the above-mentioned decrease is output to the collector side. Conversely, when the amplitude of the video signal rises, the emitter voltage of the control transistor TR2 rises, so that a voltage reduced in the rise is output to the collector side.

In this manner, even when the video signal fluctuates due to the isolation device 17, the fluctuation can be compensated for, and when the isolation device 12 for each line is affected differently by the temperature, or Even when each device has a different characteristic, it is possible to prevent the transmitted video signal from fluctuating.

FIG. 4 shows an equivalent circuit of the circuit of FIG.
And why the above video signal does not fluctuate
Will be described. In the figure, A₁ Is the control transistor TR
Gain of 2, H₁ Is voltage-current conversion efficiency, Hp is light conversion
Efficiency, H_feIs the current amplification factor of the transistor TR1 (optical base).
Of collector current to source current), A_Two Is current-current
Pressure conversion efficiency, D₁ Is the transfer function of the amplitude detection circuit, H_A Is V
The conversion efficiency of the −f conversion circuit 16 (corresponding to the slope in FIG. 2)
R), H_Two Is the conversion effect of the isolation device 17.
Rate, H_B Is the conversion efficiency of the fV conversion circuit 18. Soshi
As is clear from the figure,₀ = A₁ ・ H₁ ・ Hp ・
H_fe・ A_Two And β = D₁ ・ H_A ・ H_B ・ H 2
You. Then, when the input voltage is V_INAnd the output voltage as Vo
And (V_IN-ΒVo) A₀ = Vo. Therefore, the output
Voltage Vo and input voltage V_INRatio Vo / V with_INIs the following formula
1.

[0020]

[Formula 1] Vo / V _IN = A ₀ / (1 + A ₀ β) Here, if A ₀ β >> 1, then

[0021]

[Formula 2] Vo / V _IN = 1 / β = 1 / (D ₁ · _HA · H _B · H ₂ )

As understood from the result of the above equation (2),
The output Vo of the control loop is determined by the parameter D₁ ・ H_A ・ H_B 
・ H_Two Will be determined by That is,
A 0 is the gain A of the control transistor TR2₁ And output
Current-voltage conversion efficiency A of transistor TR3_Two Increase
In this case, the light conversion efficiency Hp and the transistor TR1
Current amplification factor H_feChanged greatly depending on conditions such as temperature
Is determined by the feedback amount β. And
The above parameter D₁ ・ H_A ・ H_B ・ H_Two Is the temperature change
Unaffected by the isolation device
Transmission due to differences in temperature conditions and variations in characteristics
Video signal that compensates for the fluctuation even if it occurs
To obtain a video signal with a good SN ratio.
It becomes possible.

Next, the overall configuration of an actual electronic endoscope device incorporating the above-described signal transmission processing circuit will be described with reference to FIGS. As shown in FIG. 5, a processing unit 23 is connected to the external processor device 1 via a connector 22, and the electronic endoscope 2 is connected to the processing unit 23 integrally or by a connector. A CCD 3 is connected to a distal end of the electronic endoscope 2 and a light guide 24 for emitting observation light from the distal end is provided. In the embodiment, the CCD driver 4 and the first signal processing circuit 25 are provided in the processing unit 23 (or in the operation unit of the electronic endoscope).

FIG. 6 shows a detailed circuit of the first signal processing circuit 25 including the CCD driver 4. In the first signal processing circuit 25, correlated double sampling (CDS) is included. -Correlated Double Sampling), an automatic gain control unit (AGC) 27, a process processing unit 28 for performing clamp processing, matrix processing, gamma correction, blanking, etc., and a timing generator for supplying timing pulses to each unit including the CCD driver 4. The output of the CCD 3 is input to the automatic gain control unit 27. Further, a microcomputer 30 and an interface 31 are provided for efficiently performing each processing in the process processing unit 28. Therefore, according to the CCD driver 4 and the first signal processing circuit 25 provided in the processing unit 23, the driving of the CCD 3 is controlled by the CCD driver 4, and the video signal in the body to be observed obtained by the CCD 3 is applied to the video signal. On the other hand, the first signal processing circuit 25 performs image processing up to the preceding stage of the memory described later.

A signal transmission processing circuit 33 including the above-described isolation device of FIG. 1 is provided in the external processor device 1.
For example, RGB video signals are transmitted from the first signal processing circuit 25 via a first group of isolation devices 12 provided respectively. A frame memory 35 is connected to the signal transmission processing circuit 33 via an A / D converter 34.
To the second signal processing circuit 37 via the D / A converter 36
Are connected, and the second signal processing circuit 37 performs output processing for outputting to a monitor.

Further, a second group of isolation devices 38 and a third group of isolation devices 39 are provided in the external processor device 1, and the second group of isolation devices 38 are provided with a timing pulse generation circuit 4.
0 is connected to the third group of isolation devices 39
Is connected to an operation unit (control panel) 41.
The timing pulse generation circuit 40 outputs a timing pulse to each of the components, and outputs a synchronization signal (C-SYNC) and a blanking signal (C-SYNC) to the electronic endoscope 2 via the second group of isolation devices 38. C-BL
K), and supply pulses such as an operation control signal (4f _SC ).
On the other hand, a control signal for performing operations such as freeze, partial enlargement, electronic shutter, and setting of γ value is supplied from the operation unit 41 to the electronic endoscope 2 via the third group of isolation devices 39. You. A transformer 43, a first power supply circuit 44, and a second power supply circuit 45 are provided. The first power supply circuit 44 is connected to the CCD driver 4 and the first signal processing circuit 25 disposed in the electronic endoscope 2. , The second power supply circuit 45 supplies power to each processing circuit in the external processor device 1.

Further, a light source 46 optically connected to the light guide 24 in the electronic endoscope 2 is provided, and a light source power supply 47 is connected to the light source 46. The light source 46 is controlled by a light source control unit 48. For example, in the case of the frame sequential method, the RGB filters are driven and the RGB light is sequentially output.

According to the above configuration, the light output from the light source 46 under the control of the light amount control unit 48 is transmitted to the electronic endoscope 2.
The light is transmitted through the inside by a light guide 24, whereby the observation light is emitted from the distal end portion into the body to be observed. Then,
The CCD 3 driven and controlled by the CCD driver 4 captures the image of the object to be observed illuminated by the above-described observation light.
A video signal is supplied from the CD 3 to the first signal processing circuit 25. In the first signal processing circuit 25, predetermined processing such as amplification, clamping, γ correction, blanking, and the like is performed on the video signal, and, for example, RGB video signals are supplied to the external processor device 1.

The video signal thus input is
As shown in FIG. 1, after being supplied to the control transistor TR2 via the capacitor C1, it is outputted to the isolation device 12. In the isolation device 12, an input signal is subjected to electro-optical conversion by a light emitting diode D1, and further, is converted to an optical signal by a photodiode D2.
The electric signal is converted and amplified by the transistor TR1, and the amplified video signal is output to the output transistor TR3 on the output circuit side. Therefore, the isolation circuit 12 electrically disconnects the patient circuit from the output circuit. Then, the output of the output transistor TR3 is supplied to an amplitude detection circuit 13, where the amplitude level of the video signal is detected and converted to a voltage of a predetermined level. After the output of the amplitude detection circuit 13 is converted into a frequency signal, the output is returned to the patient circuit side via the isolation device 17, and is again converted into a voltage signal indicating an amplitude level. Output to TR2. Therefore,
The signal voltage controls the level of the video signal,
When the video signal fluctuates due to the influence of the isolation device 12, the video signal is controlled to eliminate the fluctuation.

As described above, the video signal transmitted between the patient circuit and the output circuit is temporarily stored in the frame memory 35 via the A / D converter 34, and when read out thereafter, the D / D The signal is input to the second signal processing circuit 37 via the A converter 36, and the RGB signal, the Y / C signal, and the like are output from the second signal processing circuit 37 to the monitor. Note that a synchronization signal is output from the timing pulse generation circuit 40 to the monitor. In this way, an image of the inside of the body to be observed is displayed in color on the monitor.

According to the signal transmission processing circuit 33, since the fluctuation of the amplitude level of the video signal is detected, the temperature condition of the environment in the electronic endoscope apparatus changes, and the characteristic of the isolation device 12 is changed. Even if a change occurs, and even if the characteristics of the individual isolation devices 12 are different, the video signal can be transmitted in a stable state.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 7, a control amplifier 50 having the same configuration as the control transistor is connected to an input terminal A on the patient circuit side.
On the output side, an output amplifier 51 having the same configuration as the output transistor is connected to the output terminal B. An A / D converter 52 is provided as a conversion circuit for converting the output of the amplitude detection circuit 13, and a D / A converter 53 is provided on the patient circuit side corresponding to the analog-digital conversion.

According to the configuration of the second embodiment, the voltage signal corresponding to the amplitude level of the video signal detected by the amplitude detection circuit 13 on the output circuit side is converted into a digital signal by the A / D converter 52. This digital signal is transmitted to the patient circuit via the isolation device 17. After being converted to the original voltage signal by the D / A converter 53, the voltage signal is supplied to the control amplifier 50. In this control amplifier 50, the level of the video signal is reduced in the same manner as in the first embodiment. Controlled. Therefore, even if a change occurs in the isolation device 12, a video signal free of the change can be obtained. In this case, a photocoupler can be used as the isolation device 17.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 8 shows an example in which an amplitude modulation (FM modulation) circuit is used as a conversion circuit for converting the output of the amplitude detection circuit 13, and a mixer 55 for amplitude modulation is provided on the output circuit side.
And an oscillator 56, and a mixer 57 and an oscillator 58 for demodulation are provided on the patient circuit side.

According to the third embodiment, the amplitude detection circuit 1
The voltage signal corresponding to the amplitude level of the video signal detected in 3 is amplitude-modulated by the carrier of the oscillator 56, and the signal transmitted through the isolation device 17 is demodulated by the carrier of the oscillator 57. Become. In this case, as in the second embodiment, a video signal having no fluctuation can be obtained.

Further, in each of the above embodiments, an example was described in which a photocoupler was used as the isolation device 12, but the same effect can be obtained by using a pulse transformer.

Further, the amplitude detection circuit 13 can have a configuration other than the above-described embodiment shown in FIG. That is, in the case of FIG. 9A, a peak hold circuit 60 is provided at the subsequent stage of the level converter 14, and the peak hold circuit 60 detects the peak value of the amplitude of the video signal. This is to grasp the fluctuation of the signal. In the case of FIG. 9B, the clamping process performed in the first embodiment is eliminated, and the amplitude level of the video signal can be detected also by this.

[0038]

As described above, according to the present invention,
The amplitude level of the video signal transmitted via the isolation device is detected, and the detected signal is converted into, for example, a frequency signal, a digital signal, etc., and returned to the patient circuit via the isolation device. Since the level of the video signal is controlled based on the converted detection signal, even when a variation in light conversion efficiency in the photocoupler or a variation in the intrinsic characteristic of the isolation device occurs, the variation due to the variation is compensated. A video signal can be formed, and the video signal can be accurately transmitted from the patient circuit to the output circuit.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram illustrating a configuration of a signal transmission processing circuit of an electronic endoscope apparatus according to a first embodiment of the present invention.

FIG. 2 is a graph illustrating Vf conversion characteristics of the Vf conversion circuit of FIG. 1;

FIG. 3 is a waveform chart showing the operation of each component of the embodiment of FIG.

FIG. 4 is a block diagram illustrating an equivalent circuit of the signal transmission processing circuit of FIG. 1;

FIG. 5 is a circuit block diagram illustrating an overall configuration of the electronic endoscope apparatus according to the embodiment.

FIG. 6 is a circuit block diagram showing a configuration inside a first signal processing circuit in the circuit of FIG. 5;

FIG. 7 is a circuit block diagram showing a configuration of a second embodiment.

FIG. 8 is a circuit block diagram showing a configuration of a third embodiment.

FIG. 9 is a block diagram showing another configuration in the amplitude detection circuit.

FIG. 10 is a block diagram illustrating a schematic configuration of a conventional electronic endoscope apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... External processor apparatus, 2 ... Electronic endoscope, 3 ... CCD, 6, 12, 17, 38, 39 ... Isolation device, 13 ... Amplitude detection circuit, 14 ... Level conversion circuit, 15 ... Clamp circuit, 16 ... Voltage-frequency (V-f) conversion circuit, 18 frequency-voltage (f-V) conversion circuit, 25 first signal processing circuit, 33 signal transmission processing circuit, 52 A / D converter, 53 ... D / A converter, 55, 57: Mixer, 56, 58: Oscillator, D1: Light-emitting diode, D2: Photodiode, TR1, TR2, TR3: Transistor.

Claims (3)

(57) [Claims] 1. A signal transmission processing circuit of an electronic endoscope apparatus, wherein a patient circuit on an electronic endoscope side applied to a patient and an output circuit for processing / outputting a video signal are connected by an isolation device. An amplitude detection circuit provided on the output circuit side for detecting the amplitude level of a video signal transmitted via the isolation device, and a digital predetermined signal for returning the output of the amplitude detection circuit to the patient circuit side A conversion circuit for converting, a re-conversion circuit provided on the patient circuit side, for re-conversion of the conversion signal input via the isolation device into the original signal, and an output of the re-conversion circuit being fed back to convert the video signal A signal transmission processing circuit for an electronic endoscope device, comprising a control loop including a level control circuit for controlling a level. 2. The method according to claim 1, wherein the converting circuit is a voltage-frequency converting circuit for converting a voltage signal into a frequency signal, and the re-converting circuit is a frequency-voltage converting circuit for converting a frequency signal into a voltage signal. The signal transmission processing circuit of the electronic endoscope apparatus according to claim 1. 3. The conversion circuit replaces an output of the amplitude detection circuit with a modulation circuit that modulates the output with a predetermined frequency signal.
2. The signal transmission processing circuit according to claim 1, wherein said reconversion circuit is replaced with a demodulation circuit for demodulating said modulated signal into an original signal.