JPS6171777A - Differential amplifier - Google Patents

Abstract

PURPOSE:To eliminate completely the noises out of the high frequency messes which are superposed which are superposed on each other in the form of the in-phase components, by using the noise component that cannot be deleted by a differential pair of transistors of the next stage among those high frequency messes superposed on each signal as the feedback signals and reducing the noises superposed on the 1st and 2nd signals with said feedback signals. CONSTITUTION:The 1st and 2nd video signals superposed with noise waveforms P1 and P2 are supplied to the 1st input terminal of the 1st and 2nd subtractors 18 and 19 respectively and subtracted by the feedback signal of the 2nd input terminal. This feedback signal is obtained by adding together the differential outputs amplified by a differential amplifier 20 and therefore used as an addition output of each in-phase noise component that could not be deleted by the amplifier 20. Therefore both subtractors 18 and 19 undergo the substantial differential amplification. The 1st and 2nd video signals perform the subtracting operations only to the noises. While the amplifier 20 lowers the noise level by an amount that cannot be deleted by the amplifier 20.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an endoscope using a solid-state imaging device, for example, when used in combination with a high-frequency cutting and cutting tool, for canceling out noise from the cutting and cutting tool. This invention relates to improvements in differential amplifiers.

[Technical background of the invention]

In recent years, charge-coupled devices (CCDs) and bucket brigade devices (B
BD) and MO8 type sensors, etc., are actively being researched to use as a solid-state image pickup device, especially at the tip of the insertion section of an endoscope.

By the way, when this type of endoscope is used in conjunction with a high-frequency incision and resection instrument (hereinafter referred to as a high-frequency scalpel), the high-frequency current from the scalpel is electromagnetically superimposed on the video signal obtained by the solid-state image sensor, resulting in an image being displayed. There is a known problem that the image becomes unclear.

That is, the high frequency 7. that drives the high frequency scalpel. The frequency of the l'3 flow is set to a value that does not affect the subject (human body), and it is generally considered appropriate for this frequency to be 300 [KHz] or higher. - If the video signal obtained by a solid-state image sensor is a color signal, it has a frequency band of, for example, 4.3 (MHz), and this low frequency component and the high frequency band overlap, causing crosstalk. This is why it occurs. When such a phenomenon occurs, the image becomes unclear, and in severe cases, endoscopic operations such as surgeries and examinations must be stopped.

In order to prevent such external noise, a shield is usually applied, but simply shielding the insertion portion of the endoscope for a very long time has not been able to sufficiently prevent the noise from entering.

Conventionally, as an endoscope with measures against such noise, Japanese Patent Application Laid-Open No. 58-69530 and Japanese Patent Application Laid-open No. 58-6952 have been proposed.
As in Publication No. 8, a system has been proposed in which the part where high-frequency current flows is shielded and the frequency of the high-frequency current is increased to avoid the video signal band), and the high-frequency current band is avoided. However, none of these attempts to actively remove high frequency currents that cause noise in the image signal from the video signal.

On the other hand, in an attempt to eliminate the above-mentioned noise by circuit means, the applicant of the present application proposed the Tokuhara An s 8-
He has already applied for an invention titled Noise Prevention Device for Electronic Scope in No. 163598.

Briefly explaining the contents of this application with reference to FIG. - Introduced via the balanced output amplifier 3 into the double 2-wire shielded cable 4. The terminal end of the insertion part of this cable 4 is connected to a differential amplifier 5.
The output of the differential amplifier 5 is supplied to a video process amplifier circuit (not shown).

By providing the differential amplifier 5 at the terminal end of the cable 4 in this way, each of the first and second signal lines 4. The signals St and S2 appearing at l4t are led with video signal components in opposite phase and noise components in in-phase. The purpose of the next-stage differential amplifier 5 is to differentially amplify the anti-phase component and to differentially amplify the in-phase component. Since the noise is canceled out, the noise from the high-frequency scalpel that is input in the same phase will not appear in the output.

[Problems with background technology]

FIG. 6 shows a specific circuit configuration of the differential amplifier 5 used for the above purpose, and includes transistors TRI and TR.
x constitutes a differential amplifier, and signals Ss and S2 from the shielded cable 4 shown in FIG. 5 are supplied to each pace. The collectors of the differential amplification transistors TR+ and TR2 are respectively connected to a first voltage source that supplies a voltage of +V via load resistors Rsb and R1, while linearity improving resistors R3, R4 and The intermediate resistor R4 is a variable sliding resistor, and its sliding end is a second resistor that supplies a voltage of one through the collector-emitter of the transistor TR and through the resistor R6.
connected to a voltage source. This transistor TRs is
A current source of the differential amplifier has a voltage from the second voltage source applied to its base via resistor R7 and a ground potential via resistor R8.

In such a configuration, as already mentioned, the differential
Since the equipment attempts to cancel the output when the in-phase and equal amplitude inputs are input, and output the full output when the anti-phase inputs are input, the ratio of the differential gain of the anti-phase component to the common-mode gain of the common-mode component is a measure of its performance. The larger the size, the more suitable it is for preventing noise from the endoscope. This ratio is CMRR (Common Mode Rejectron
Ratio), and the differential amplification transistor TR
1. It is said that the better the characteristics of TRx (especially the alternating current amplification factor hfe) are, and the greater the output impedance of the current source transistor TR3, the better.

However, even if these conditions are ideal, there is a limit to the value of CMRR. The main reason for this is variations in input voltage due to temperature drift and the like. When this input voltage changes, each differential transistor TR
A change occurs in the collector-emitter voltage VCE of I, T& and the current IE from the emitter, and the current amplification factor hfe changes accordingly, reducing the CMRR. In other words, the signal components amplified by transistors TRI and T& are output in opposite phases, so when the amplitude of the input signal changes, VCEI and Igt of transistors TR and VCE2 and IF5 of transistor TR1 change, and the differential amplifier The amplification factors become unbalanced, making it impossible to cancel the common-mode noise component superimposed on the signal.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned points, and is a differential amplifier that completely cancels out noise from a noise source such as a high-frequency scalpel guided by a common-mode component.
An object of the present invention is to provide a differential amplifier device that can improve MRR.

[Summary of the invention]

In order to achieve the above object, a differential amplifier device according to the present invention has the following features:
The noise component remaining in the output after differential amplification is fed back to the input as subtraction noise, and the signal from the solid-state image sensor is converted into first and second signals with opposite phases to each other. Out of the noise from the high-frequency scalpel that is derived and superimposed on each of these signals, the noise component that cannot be removed by the next-stage differential pair transistor is formed as a feedback signal, and this signal is superimposed on the first and second signals. The CMRR'& of the differential pair transistors described above is improved by subtracting the noise.

[Embodiments of the invention]

Hereinafter, fully illustrated embodiments of the present invention will be described in detail.

FIG. 1 and FIG. 2 relate to a first embodiment of the present invention.
The figure is a configuration diagram in which the present invention is connected before endoscopy using a solid-state image sensor, and FIG. 2 is a waveform diagram for explaining the present invention in detail.

In FIG. 1, reference numeral 11 indicates an insertion section of the endoscope, and an objective lens 12 and a diffusion lens 13 are provided on the distal end observation surface of this insertion section. At predetermined positions iM of these objective lens 12 and diffuser lens 13, there are CCDs 14, respectively.
and an exit surface of the light guide cable 15 are arranged,
The light guide cable 15 is continuously guided into the insertion portion 11 so that the light from the illumination means can be incident at an entrance end (not shown). Thereby, the light from the illumination means is transmitted through the light guide cable 15 and emitted from the output end, and is distributed by the diffusion lens 13 to illuminate the subject. The reflected light from the subject is imaged on the imaging surface of the CCD 14 via the objective lens 12. C.C.
D14 accumulates the image on this image plane as a charge, and reads it out at any time by a signal from an allegation circuit (not shown).

In this way, the video signal read out from the CCD 14 is
Differential amplification type head amplifier 1 whose input end is connected to the ground point
6 into the second input terminal. The differential output of this head amplifier 16 is introduced into each one end of the double, two-wire shielded cable 17 and led out to the other end. This cable 17 has a structure in which the two signal lines 171 and 172 are themselves shielded cables, and a shield member is further provided to cover them.

The cono cable 17 is connected to a first head amplifier formed by the head amplifier 16 and having opposite phases to each other. The second video signal is led out to the operating section side of the endoscope or to the outside, and each other end is connected to each first input end of the first and second subtracters 18 and 19. A feedback signal from an adder, which will be described later, is introduced into each second input terminal of each of these subtracters 18, 19, and each subtractor 7J, 18, 19 inputs this feedback signal and each first . Subtraction with the second video signal can be performed.

These first. The outputs of the i2 subtracters 18 and 19 are supplied to the differential input terminals of the differential amplifier 20 at the next stage.

This differential amplifier 20 outputs a differential output to an adder 22 when the signal appearing at one differential output terminal is led to an output terminal 21 for introduction into a video process amplifier circuit (not shown).
are supplied to the first and second input terminals it, respectively. The differential signals from the adder 22 and the difference amplifier 20 are added together to form a feedback signal S3, and this signal Ssk is common to each second input terminal of the first and second subtracters 18 and 19. has been introduced.

According to the differential amplifier circuit configured in this way, the output waveform r! of the head amplifier 16 having a differential amplification configuration is obtained. , Figure 2(a)
, have opposite phases to each other as shown in (b). Also,
The waveform of the noise from the high-frequency scalpel arriving at the cable 17 in the insertion section of the endoscope is shown in P1. As shown in Pz, they are superimposed on each other in the same phase. In this way, the noise waveform P1. P
The first and second video signals superimposed with
It is subtracted from the feedback signal at the input end. Since this feedback signal is the sum of the differential outputs after differential amplification by the differential amplifier 20, it becomes the summed output of each in-phase noise component that could not be completely removed by the differential amplifier 20. Therefore, each subtractor 18,19 is substantially differentially amplified [7
It subtracts only the noise of the first and second video signals of the iT, reduces the noise level by a level that cannot be removed by the CMRR of the differential amplifier 20, and supplies it to the differential amplifier 20. . However, according to the present invention, the feedback effect only acts on noise.

Now, focusing only on the external noise superimposed on the signal, its amplitude is set to υ, the common mode gain of the differential amplifier 20 is set to β times, and the noise component that cannot be completely removed in common mode by the differential amplifier 20 is υ.

(see FIG. 2(c)), the gain of the adder 22 is α times, and the gains of each subtractor 18 and 19 are 1 times, then the subtracter 2
The output of 2 is expressed as V, -αv0. Then, the noise output v0 of the differential amplifier 20 is v6==(υ, -αv0)β ・・・・・・・・・・・・
......fil, and rearranging this gives β υ. Ni vi ・・・・・・・・・・・・・・・・・・
・・・・・・f2)1+αβ. Therefore, CMRR is the difference W= for the common mode gain β
= Even if the input voltage of C changes and the value of β increases,
By setting the value of α to α)β, there is almost no change in the value of CMRR.

FIG. 3 shows a characteristic diagram of CMRR in which CMRR is plotted on the vertical axis and β is plotted on the horizontal axis, showing that the value of β varies depending on temperature drift.

Incidentally, since the video signal is removed by the adder 22, it is not included in the feedback signal.

Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment is constructed using a transistor circuit, and has a simpler structure than the previous embodiment since each subtracter is also used as a current source of a differential amplifier.

In FIG. 4, each terminal TP1. TP2, TP3
, TP4 is an unbalanced input terminal to which the first and second video signals from the shielded cable 17 are received;
TPl, TP4 are connected to the ground point, TPl, T
Pl is a resistor Rt31R whose one end is connected to the ground point through a lug connection of a resistor Ru and a coupling capacitor C1, and a resistor Rtz and a coupling capacitor C2, respectively.
14. Note that the coupling capacitor C+, (:2 is the electrolytic capacitor Cs,
It has C4. The signals appearing at the other ends of the resistors R13+R14 are transmitted to the transistors TRu and TRtz forming a differential pair via resistors R14 and Rlg, respectively.
will be introduced at each page. These transistors TR
The collectors of II and TRtz each have a load resistance Rsy
+Re5t" to the first power supply line L, and the emitters are resistors Rts and Rz, respectively.

and R21+R22, which are connected in series to the collector of the current source transistor TRxs. still,
A sliding resistor R1m is interposed at the intersection of each of these series connections, and the sliding end of this resistor R4m is connected to the resistor R20 and R
22 to the collector of the transistor TR13. This transistor TR, +3 is connected to the ground via a parallel connection consisting of a resistor 1'h4, a resistor R25, a capacitor C5, and an electrolytic capacitor C6, and a resistor is connected to the intersection of these parallel connections and the resistor R4. A voltage from the second power supply line L is applied via R26. Also, transistor TR1g
The emitter of is connected to the second power supply line L via the resistor R27.
2 and resistor R28 as well as capacitor C7
The voltage across the resistor Rte, one end of which is connected to the second power supply line L2, is supplied through a parallel connection consisting of the electrolytic capacitor C8 and the electrolytic capacitor C8. This resistance R29
is the load resistance of the emitter follower trough system It TR14. The collector of this emitter follower transistor TR14 is connected to the power supply line Ll, and the pace is connected to the resistor R.
Differential pair transistor TR for buffer amplification via 3°
5s, '1rRH, and these transistors TRts + TR
Each collector of III is connected to a ground point via a resistor R31ff. Also, transistors T&i, T
Each emitter of Rts is connected to the power supply line L1 through a resistor R31+R33, and each pace is connected to a resistor an
41 The differential pair transistor TRo via R2H
, TRtx are differentially input. Therefore, the buffer output is taken out from the emitter of the buffer transistor TR1g, and the resistor R46'
It is supplied to the output emitter follower transistor TR1t via C. The emitter of this transistor T Rry is connected to the power supply line L1, and the emitter is connected to a ground point via a resistor R37.

An output signal is obtained from the emitter of this transistor TR1□.

In addition, each power line LhL is provided with an AC blocking coil L.
A voltage source ±V is applied through 3 and L4k, and smoothing capacitors C9 to C15 are connected between the grounding points.

According to the above configuration, the signal from the cable 17 is directly supplied to the differential pair of transistors TRII and TRtz. And the subtractor 18.19 in FIG.
The equivalent is the one-channel current source transistor TR1s. That is, the transistor TR13 receives the feedback signal S from the emitter of the emitter 5 follower transistor TR5s,
is received at the emitter via the capacitor C7 and the resistor R48tl, thereby superimposing the storm current change on the collector currents of the differential pair transistors TRII and TRtz. Thus, transistors TRII, TRtz are
Each collector current is reduced by the common mode component that cannot be removed by its own CMR action, and the resulting differential output is supplied to the output transistor TRt7 through the buffer transistors TR15ITR1g, and the resistor &
70 is taken out as a voltage across both ends.

Furthermore, the aforementioned 41! Japanese Patent No. 58-163598 discloses an embodiment in which a head amplifier with an unbalanced output is used, and one end of a shielded cable 17 receives a signal from the head amplifier, and the other end is grounded. Although shown, the present invention can also be applied to a bell with such a number of grooves. Further, the present invention may also be applied to a video camera using a solid-state image sensor.

〔Effect of the invention〕

As explained above, according to the present invention, the noise component appearing in the output of the differential amplifier is fed back to the input, and the signal from which the noise included in the input is subtracted by the feedback amount is differentially amplified. This has the effect of reliably removing noise from the high d-wave scalpel that is superimposed as an in-phase component.

[Brief explanation of the drawing]

8g11A is a 4-゛ζ configuration diagram showing the first embodiment of the differential amplifier according to the present invention. FIG. 2 is an operating waveform diagram for explaining the present invention in detail, and FIG. 3 is a common-mode component removal ratio temporal characteristic. FIG. 4 is a circuit diagram showing the second embodiment of the present invention, and FIG.
This figure is a block diagram showing an example of a structure for removing noise superimposed on the output of a conventional solid-state image sensor, and FIG. 6 is a circuit diagram showing an example of a differential amplifier used in FIG. 5. 14... Solid-state image sensor, 16... Head amplifier, 17... Double 2-wire shielded cable, 18.19.
...Subtractor, 20...Differential amplifier, 22...Adder, TRII~TRty...Transistor, R11%R3? ...Resistance, Ct-CLs
−=capacitor. Figure 5 Figure 6 1 Procedural amendment (voluntary) November 6, 1980 1 Display of the case 1988 Patent Application No. 193304 2 Title of the invention Differential amplifier device 3 Relationship with the person making the amendment Patent Applicant [1: Address: 2-43 Cangaya, 1F, Shibuya-ku, Tokyo
No. 2 Trap ui'H (Masterpiece) (037) Olympus Optical Industry Co., Ltd. Representative Satoshi Shimoyama Department 4, Agent 160 '' (7623) Patent Attorney Susumu Ito. 5 Date of correction order Spontaneous 8rl Oral correction content correction specification 1, Title of invention Differential amplifier 2, Claims First and second analogs to which feedback signals for subtracting phase components are supplied a subtracting means, a differential amplifying means into which signals from the first and second subtracting means are differentially introduced, and a differential output of the amplifying means; one of the differential outputs of the differential amplifying means; 1. A differential amplifier comprising: output means for amplifying and producing an output signal. (2) first and second signals whose main components are phase inverted components and which include an in-phase component; the bases are supplied with the first and second signals, and the collectors are respectively connected to the first voltage source via load resistors; A differential amplifier consisting of a dynamic pair of transistors and a differential output from the differential amplifier are supplied, and the outputs are added together to amplify one of the differential outputs of the common mode width amplifier and output as an output signal. 1. A differential amplifier comprising: means. 3. Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a differential amplifier device that improves the common-mode component rejection ratio, and is suitable for use in combination with a high-frequency cutting and cutting tool, for example, in an endoscope using a solid-state image sensor. , relates to a differential amplification device suitable for canceling out noise from this cutting tool. [Technical background of the invention] In recent years, charge-coupled devices (CCDs) and bucket brigade devices (B
BD) and MO8 type sensors, etc., are actively being researched to use as a solid-state image pickup device, especially at the tip of the insertion section of an endoscope. By the way, when this type of endoscope is used in conjunction with a high-frequency incision and resection instrument (hereinafter referred to as a high-frequency scalpel), the high-frequency current from the scalpel is electromagnetically superimposed on the video signal obtained by the solid-state image sensor, resulting in an image being displayed. There is a known problem that the image becomes unclear. In other words, the frequency of the high-frequency current that drives the high-frequency scalpel is set to a value that does not affect the subject (human body), and it is generally said that a frequency of 300 (KHz) or higher is appropriate.On the other hand, solid-state imaging devices In the case of a color signal, the video signal obtained in this case has a frequency band of, for example, 4.3 MHz, and this low-frequency component and the frequency band of the high-frequency current overlap, causing crosstalk. When such a phenomenon occurs, the image becomes unclear and, in severe cases, the operation of the endoscope, such as surgery or examination, must be stopped.To prevent such extraneous noise, a shield is usually applied. However, simply shielding the insertion part of the endoscope for an extremely long time was not sufficient to prevent noise from entering. Conventionally, as an endoscope that took measures against such noise, there was a Publication No. 69530 and JP-A-58-6952
As in Publication No. 8, it has been proposed to shield the part where the high frequency current flows, and to raise the frequency of the high frequency current to avoid the video signal band, or to avoid the high frequency current band. However, none of these attempts to actively remove high-frequency current, which causes noise in the image signal, from the video signal. On the other hand, in an attempt to eliminate the above-mentioned noise by circuit means, the applicant filed a patent application No. 58-1 on September 5, 1983.
No. 63598 has already been filed for an invention entitled Noise Prevention Device for Electronic Scope. The content of this application will be briefly explained with reference to Figure 5.
Reference numeral 1 indicates an insertion section of an endoscope, and the output of a solid-state image pickup device 2 provided at the distal end thereof is introduced into a dual two-wire shielded cable 4 via a balanced output amplifier 3. The terminal ends of the insertion portion of the cable 4 are connected to the first and second input terminals of a differential amplifier 5, respectively, and the output of the differential amplifier 5 is supplied to a video process amplification circuit (not shown). By providing the differential amplifier 5 at the end of the cable 4 in this way, the signals S, , S appearing on the first and second signal lines 4t and 4t of the cable 4 have video signal components in reverse phase and are noise. The components are derived in phase. The purpose of the next stage differential amplifier 50 is to differentially amplify the anti-phase component.
Since the purpose is to cancel out the in-phase components, noise from the high-frequency scalpel input in the same phase will not appear in the output. [Problems in the Background Art] FIG. 6 shows a specific circuit configuration of the differential amplifier 5 used for the above purpose, and includes transistors TR and TR.
, constitute a differential amplifier, and signals S, , S, from the shielded cable 4 shown in FIG. 5 are supplied to each pace. The collectors of the differential amplification transistors TR, , TR, are respectively connected to a first voltage source that supplies a voltage of +■ through a load resistor R1 and an island, while the emitters are connected to a linearity improving resistor R1 and a first voltage source, respectively. Part of the horse and resistance R
The transistor TR8 is connected to the collector of the transistor TR8 through a portion of the transistor TR8. Note that the resistance R4 is a variable sliding resistance. The emitter of the transistor TR is connected via a resistor R6 to a second voltage source supplying a partial voltage. This transistor TR8 is a current source of the differential amplifier, and a portion of the second voltage source is applied via a resistor R7. Note that this base has a resistance of M i value between the ground point and the resistance. In such a configuration, as mentioned above, the differential amplifier attempts to cancel the output with the in-phase equal amplitude input and output the anti-phase input, so as a measure of its performance, the difference The larger the ratio of the gain to the common mode gain of the common mode component is, the more suitable it is for noise prevention in the endoscopic sight 3. This ratio is CΔ(RR(CommonMode Rejecti
on Itatio), and the characteristics of the differential amplification transistors TR, TR, (especially the AC current amplification factor hf
e) are uniform and the output impedance of the current source transistor TR is larger, the better. However, even if these conditions are ideal, there is a limit to the value of CMRR. The main reason for this is changes in input voltage due to temperature drift and the like. When this input voltage changes, each differential transistor TR,
, the collector-emitter voltage VCE of TR2 and the current from the emitter 1. A change occurs, and the current amplification factor hfe changes accordingly, reducing the CMRR. In other words, the signal components amplified by transistors TR and TR are output in opposite phases, so when the amplitude of the input signal changes, VCEl and IΣ1 of transistor TR and VCl2 and IE2 of transistor TR2 change, The amplification factors of the differential amplifier become unbalanced, making it impossible to cancel the common mode noise component superimposed on the signal. [Object of the Invention] The present invention has been made in view of the above-mentioned points, and is a differential amplifier designed to cancel out noise from a noise source such as a high-frequency scalpel guided by a common-mode component. C
An object of the present invention is to provide a differential amplifier device that aims to improve MRR). [Summary of the Invention] In order to achieve the above object, a differential amplifier device according to the present invention has the following features:
The noise component remaining in the output after differential amplification is fed back to the input as subtraction noise, and the input signals are derived as first and second signals with opposite phases to each other. , among the noise superimposed on each of these signals in the same phase, the component that cannot be removed by the differential amplification stage is formed as a feedback signal, and this signal is used to subtract the noise superimposed on the first and second signals. This improves the CMRR' of the differential amplifier stage. [Embodiments of the Invention] The present invention will be described in detail below with reference to illustrated embodiments. FIG. 1 and FIG. 2 relate to the first implementation of the present invention.
The figure is a configuration diagram in which the present invention is applied to an endoscopic chain using a solid-state image sensor, and FIG. 2 is a waveform diagram for explaining the operation of the present invention. In FIG. 1, reference numeral 11 indicates an insertion section of the endoscope, and an objective lens 12 and a diffusion lens 13 are provided on the distal end observation surface of this insertion section. The exit surfaces of the CCD 14 and the light guide cable 15 are disposed at predetermined positions of the objective lens 12 and the diffuser lens 130, respectively, and the light guide cable 15 is guided endlessly into the insertion section 11 and exits from the illumination means at the entrance end (not shown). of light is incident on it. Thereby, the light from the illumination means is transmitted through the light guide cable 15 and emitted from the output end, and is distributed by the diffusion lens 13 to illuminate the subject. The reflected light from this object is reflected by the objective lens 1.
2 to the imaging surface of the CCD 14. CCD1
Reference numeral 4 stores the image on the imaging surface as a charge, and reads it out at predetermined intervals by a signal from a drive circuit (not shown). In this way, the video signal read out from the CCD 14 is
Differential amplification type head amplifier 1 whose input end is connected to the ground point
6 into the second input terminal. The differential output of the head amplifier 16 is introduced into each one end of the double, two-wire shielded cable 17 and led out to the other end 91. This cable 17 is
Book signal F917. . 17 is a shielded cable itself, and has a structure in which a shielding member is further provided to cover the cable. This cable 17 is connected to a first . The second video signal is led out to the operating section side of the endoscope or to the outside, and each other end is connected to each first input end of the first and second subtracters 18 and 19. A feedback signal from an adder, which will be described later, is introduced into each second input terminal of each of these subtracters 18, 19, and each subtractor 18, 19 inputs this feedback signal and each first . Subtraction with the second video signal can be performed. These first. The outputs of the second subtracters 18 and 19 are supplied to the differential input terminals of the differential amplifier 20 at the next stage. This differential amplifier 20 connects each output to the first and second terminals of an adder 22 when guiding a signal appearing at one differential output terminal to an output terminal 21 for introducing into a video process amplifier circuit (not shown). Supplied to each input terminal. The adder 22 adds the differential signals from the differential amplifier 20 to form a feedback signal S, and passes this signal S to the first and second subtracters 18.
19 second input terminals in common. According to the differential amplifier configured in this way, the output waveform of the head amplifier 16 having the differential amplification configuration is as shown in FIG.
), the phases are opposite to each other. Furthermore, the waveforms of the noise from the high-frequency scalpel arriving at the cable 17 in the insertion section of the endoscope are shown in P and P of the same figure. As shown in , they are superimposed on each other in the same phase. The first and second video signals on which the noise waveforms P, , P, are superimposed are input to the first input terminals of the first and second subtracters 18 and 19, respectively, and the feedback signals at the second input terminals are is subtracted. Since this feedback signal is the sum of the differential outputs after differential amplification by the differential amplifier 20, it becomes the summed output of each in-phase noise component that could not be completely removed by the differential amplifier 20. Therefore, each of the subtracters 18 and 19 substantially subtracts only the noise of the first and second video signals before being differentially amplified, and the CMRR of the differential amplifier 20 cannot remove the noise. The noise level is lowered by a certain level and then supplied to the differential amplifier 20. In other words, the present invention has a feedback effect only on noise. Now, focusing only on the external noise superimposed on the signal, its amplitude is set to υ, the common mode gain of the differential amplifier 20 is multiplied by β, and the noise component that cannot be completely removed in common mode by the differential amplifier 20 is υ. . (see FIG. 2(c)), the gain of the adder 22 is α times, and the gains of each subtractor 18 and 19 are 1 times, then the subtracter 2
The output of 2 is expressed as V, -αvo. Then, the noise output υ0 of the differential amplifier 20 is t+0=(υi−αυ.)β...
・・・α), and rearranging this, β v0=□ ν ・・・・・・・・・・・・・・・−・・・・
(2) 1+αβ 4 . Therefore, CMRR is the difference in common mode gain β,
According to the present invention, the value has been improved to +4β, and even if the value of β increases due to changes in the differential amplifier 200 Å voltage due to changes in ambient temperature, by setting the value of α to α>β, There is almost no change in the CMRRO value. Figure 3 shows (CMRR with JiRR on the vertical axis and β on the horizontal axis)
Even if the value of β fluctuates due to temperature drift, the range of change in the CMIIR value is from 10 to 1.
It shows that there is α. Note that the video signal is removed by the adder 22, so it is not included in the feedback signal. Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the present invention is implemented using a transistor circuit, and compared to the previous embodiment, each subtracter is also used as a current source of a differential amplifier, making the structure simpler. In Fig. 4, each terminal TP+, TP2- TPs
, TP4 is an unbalanced input terminal into which the first and second video signals from the shielded cable 17 are introduced,
TP2 and TP4 are connected to the ground point, and TP, , T
P, are the resistor R11 and the coupling capacitor CI, respectively.
and resistance R1! and resistors R, 8, R, each one end connected to the ground point through the lug connection of the coupling capacitor C7.
4 are connected to each other end. Note that the coupling capacitors C, , C, have electrolytic capacitors C5, C, in parallel. The signals appearing at the other ends of the resistors R1, R, and 4 are respectively introduced into the bases of the transistors TRu to TRu forming a differential pair via resistors R111 and R1, respectively. These transistors TRII, TR+t
Each collector has a load resistance RI? y is connected to the first power supply line LL via R18, and the emitters are resistors R, I, , R, respectively. and R, , R, , are connected to the collector of the current source transistor TR+s through series connections. A sliding resistor R2 is interposed at the intersection of each of these series connections, and the sliding end of this resistor R7 is a resistor R, ! . and R are connected to the collector of the transistor TR1s through which intersection. The base of this transistor TR, is connected to the ground via a parallel connection consisting of a resistor Ru, a resistor R2, a capacitor C6, and an electrolytic capacitor C6, and a resistor R is connected to the intersection of these parallel connections and the resistor R2. A voltage from the second power supply line L2 is applied via the second power supply line L2. Further, the emitter of the transistor TR,3 is connected to the second power supply line L2 via a resistor R4, and one end is connected to the second power line L2 via a parallel connection consisting of a resistor R2, a capacitor C7, and an electrolytic capacitor C8.
power line L. The voltage across the resistor R5 connected to the resistor R5 is supplied to the resistor R5. This resistor R2,l is a load resistance of the emitter follower transistor TR, . The emitter follower transistor TR,4 has a collector connected to the power supply line L1, and a base that receives a signal from the collectors of the differential pair transistors TR15, TRta forming an adder via a resistor R3. Hey, transistor TR+
! , TR, , are connected to a ground point via a resistor R8. Also, the transistor 'l'R
Each emitter of 15+ TR+6 has a resistor R321R1 respectively.
3 to the power supply line L1, and signals from the collectors of the differential pair transistors TR, . . . , Tn, .quadrature. Therefore, the adder differential pair transistor TR,
,. One transistor TR of TRta. acts as a buffer element, and from its emitter there are resistors R,,! , to the bases of the output emitter follower transistors TR, . The emitter of this transistor TR, is connected to the power supply line L, while the emitter is connected to the resistor R.
It is read directly to the ground point via vy. This transistor T
R1? An output signal is obtained from the emitter of. In addition, each power line L1. A voltage source ±V is applied to L through AC blocking coils Ls and R4, respectively, and smoothing capacitors C, .about.cps are connected between the grounding points. According to the above configuration, the signal from the cable 17 is directly supplied to the bases of the differential pair transistors TR, , TR, , □. The current source transistor TR+s corresponds to the subtracters 18 and 19 in FIG. That is, the transistor TR, receives the feedback signal S from the emitter of the emitter follower transistor TR14 at its emitter via the capacitor C7 and the resistor R2,';e, and the resulting current change is transmitted to the differential pair transistor TRo.
, superimposed on the collector current of TRI2. Thus, transistors TRu and TR12 have their own CMR
As a result, each collector current is reduced by the common mode component that cannot be removed, and the resulting differential output is transmitted to the output transistor T via buffer transistors TR, 1, TR+a.
R, , and is taken out as a voltage across the resistor R570. In addition, in the above-mentioned Japanese Patent Application No. 163598/1983, a head amplifier with unbalanced output is used, and a shielded cable 17 is used.
Although an embodiment is shown in which one end of the head amplifier receives a signal from the head amplifier and the other end is grounded, the present invention can also be applied to an endoscope with such a configuration. It is possible. Further, the present invention is not limited to use in endoscopes, but can also be applied to, for example, video cameras using solid-state image sensors, audio circuits, measurement circuits, etc. [Effects of the Invention] As explained above, according to the present invention, the noise component appearing in the output of the differential amplifier is fed back to the input, and a signal from which the noise included in the input is subtracted by the feedback amount is differentially amplified. This has the effect of reliably removing noise from the high frequency scalpel superimposed as an in-phase component. 4. Brief description of the drawings FIG. 1 is a configuration diagram showing a first embodiment of a differential amplifier according to the present invention, FIG. 2 is an operation waveform diagram for explaining the present invention in detail, and FIG. 3 is a characteristic diagram showing the in-phase component rejection ratio characteristic, and the fourth
The figure is a circuit diagram showing a second embodiment of the present invention, FIG. 5 is a configuration diagram showing an example of a configuration for removing noise that overlaps the output of a conventional solid-state image sensor, and FIG. 6 is a circuit diagram used in FIG. 5. FIG. 2 is a circuit diagram showing an example of a differential amplifier. 14... Solid-state image sensor, 16... Head amplifier,
17...Double 2-wire shielded cable, 18, 19.
...Subtractor, 20...Differential amplifier -122...
Adder, TRII~TR17...Transistor, R11~R57...Resistor, 01~CI,
...Capacitor.

Claims (2)

[Claims] (1) Signals obtained by a solid-state image sensor are derived as first and second signals whose phases are inverted, and noise arriving from the outside is superimposed on the first and second signals in the same phase. the first and second signals on which these noises are superimposed are respectively guided to a first input terminal, and a feedback signal for subtracting the noise by a predetermined amount is introduced to a second input terminal; first and second analog subtracting means to be inputted, an amplifying means to which signals from the first and second subtracting means are differentially introduced, and a differential output of the amplifying means; The present invention is characterized by comprising: analog addition means for forming residual components of the noise appearing in the feedback signal at a predetermined level; and output means for amplifying one of the differential outputs of the differential amplifier to produce an output signal. differential amplifier. (2) Deriving the signals obtained by the solid-state image sensor as first and second signals whose phases are inverted, and superimposing noise arriving from the outside in the same phase on the first and second signals. a first and a second signal deriving means, each of which has a first and second signal from the signal deriving means, the base of which is supplied to the base and the collector of which is connected to the first voltage source via a load resistor, respectively; a differential amplifier comprising a differential pair of transistors; an analog addition means to which a differential output from the differential amplifier is supplied; and an analog addition means for forming a residual component of the noise appearing at the output as a feedback signal at a predetermined level; and the addition means is interposed between each emitter of the differential amplifier and a second voltage source, and subtracts a predetermined amount of the noise component from the signal amplified by the differential amplifier. What is claimed is: 1. A differential amplification device comprising: a current source transistor capable of converting the differential output from the differential amplifier; and output means for amplifying one of the differential outputs of the differential amplifier to produce an output signal.