JPH0410276B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a differential amplifier device with an improved common-mode component rejection ratio, and is suitable for use in conjunction 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, much research has been conducted to use charge-coupled devices (CCDs), bucket brigade devices (BBDs), MOS sensors, and the like as solid-state imaging devices, especially at the tip of the insertion section of endoscopes.

By the way, when this type of endoscope is used in conjunction with a high-frequency incision and excision tool (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 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 considered appropriate for this frequency to be 300 [KHz] or higher. On the other hand, in the case of a color signal, the video signal obtained by a solid-state image sensor is, for example, 4.3
It has a frequency band of [MHz], and this low-frequency component and the frequency band of the high-frequency current overlap, resulting in crosstalk. 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.

As an endoscope that takes measures against such noise,
Previously, JP-A-58-69530 and JP-A-58-
As in Publication No. 69528, it has been proposed that the part where the high frequency current flows is shielded, and the frequency of the high frequency current is increased to avoid the video signal band, or the high frequency current band is avoided. However, none of these attempts to actively remove high-frequency currents, which 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 has already applied for an invention titled Noise Prevention Device for Electronic Scope in Japanese Patent Application No. 163598-1988 on September 5, 1981. There is.

Briefly explaining the content of this application with reference to FIG. 5, reference numeral 1 indicates the insertion section of the endoscope, and the output of the solid-state image sensor 2 provided at the tip thereof is unbalanced input - balanced output. The signal is introduced into a dual double-wire shielded cable 4 via a type amplifier 3. This cable 4
The terminal end of the insertion part is connected to the first and second terminals of the differential amplifier 5.
are respectively connected to the input terminals of the differential amplifier 5.
The output of is supplied to a video process amplifier circuit (not shown).

In this way, a differential amplifier 5 is installed at the end of the cable 4.
By providing the signals S _{1 and} S ₂ appearing on each of the first and second signal lines 4 ₁ and 4 ₂ of the cable 4, the video signal components are led in opposite phase and the noise components are in the same phase. The purpose of the next stage differential amplifier 5 is to differentially amplify the anti-phase component and cancel the common-mode component.
Noise from the high-frequency scalpel 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.
TR ₁ and TR ₂ constitute a differential amplifier, and signals S ₁ and S ₂ from the shielded cable 4 shown in FIG. 5 are supplied to each base of the differential amplifier. differential amplification transistor
The collectors of TR ₁ and TR ₂ are connected to a first voltage source that supplies +V via load resistors R ₁ and R ₂ , respectively, while the emitters of each are connected to linearity improving resistors R ₃ and R ₄ , respectively. and a portion of resistors R ₅ and R ₄ to the collector of transistor TR ₃ . Note that the resistance R ₄ is a variable sliding resistance. The emitter of the transistor TR ₃ above is a resistor.
It is connected via _R6 to a second voltage source that provides a voltage of -V. This transistor TR ₃ is a current source of the differential amplifier, and is a current source for the differential amplifier, and is a current source for the differential amplifier, and is a current source for the differential amplifier, and is a current source for the differential amplifier, and is a current source for the differential amplifier.
V is applied through resistor _R7 . Incidentally, this base has a resistance of a predetermined value between the opposite ground point.

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 in-phase gain of the in-phase component is, the more suitable it is for preventing noise in an endoscope. This ratio is CMRR
(Common Mode Rejection Ratio)
It is said that the better the characteristics of the differential amplifying transistors TR ₁ and TR ₂ (particularly the AC current amplification factor hfe) are the same, and the larger the output impedance of the current source transistor TR ₃ is, the better.

However, even if these conditions are ideal,
There are limits 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, the collectors of each differential transistor TR ₁ and TR ₂
A change occurs in the emitter voltage V _CE and the current I _E from the emitter, and the current amplification factor hfe changes accordingly.
This will reduce CMRR. In other words, the signal components amplified by transistors TR ₁ and TR ₂ are output in opposite phases, so when the amplitude of the input signal changes, V _CE1 and I E1 of transistor TR ₁ and V _CE2 and I _E2 of transistor _{TR 2} changes, the amplification factor of the differential amplifier becomes unbalanced, and it becomes 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 points, and
To provide a differential amplifier device that aims to improve the common mode component rejection ratio (CMRR) in a differential amplifier designed to cancel out noise from a noise source such as a high frequency scalpel guided by a common mode component. be.

[Summary of the invention]

In order to achieve the above object, a differential amplifier according to the present invention is configured to feed back noise components remaining in the output after differential amplification to the input as subtraction noise, and is configured to feed back the noise component remaining in the output after differential amplification to the input signal. are derived as first and second signals having opposite phases to each other, and of the noise superimposed on 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 generate the first and second signals. The CMRR of the differential amplifier stage is calculated by subtracting the noise superimposed on the second signal.
This is an improved version of .

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail with reference to illustrated embodiments. 1 and 2 relate to a first embodiment of the present invention, FIG. 1 is a configuration diagram in which the present invention is applied to an endoscope using a solid-state image sensor, and FIG. 2 is a diagram showing the operation of the present invention. FIG. 2 is a waveform diagram for explaining.

In FIG. 1, reference numeral 11 indicates an insertion section of the endoscope, and an objective lens 1 is provided on the observation surface at the distal end of this insertion section.
2 and a diffusing lens 13 are provided. A CCD 14 and an exit surface of a light guide table 15 are arranged at predetermined positions of the objective lens 12 and the diffuser lens 13, respectively, and the light guide table 15 is guided endlessly into the insertion section 11 and has illumination means at an entrance end (not shown). It is designed so that light from the Thereby, the light from the illumination means is transmitted through the light guide table 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 passes through the objective lens 12 to the CCD 14.
The image is formed on the imaging plane. The CCD 14 accumulates the image on the imaging surface as a charge, and reads it out at predetermined intervals in response to a signal from a drive circuit (not shown).

In this way, the video signal read out from the CCD 14 is introduced into the second input terminal of the differential amplification type head amplifier 16 whose first input terminal is connected to the ground point. 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. This cable 17 has two signal lines 17
₁ and 17 ₂ themselves are shielded cables, and have a structure in which a shielding member is further provided to cover them.

This cable 17 leads out the first and second video signals, which are in opposite phases to each other and are formed by the head amplifier 16, to the operating section side of the endoscope or to the outside, and the other ends of the cable 17 are connected to the first and second subtracters 18. , 19. A feedback signal from an adder, which will be described later, is introduced into the second input terminal of each of these subtracters 18 and 19, and each subtracter 18 and 19 subtracts this feedback signal from each of the first and second video signals. It can be carried out. The outputs of these first and second subtracters 18 and 19 are supplied to differential input terminals of a differential amplifier 20 at the next stage. When this differential amplifier 20 leads a signal appearing at one differential output terminal to an output terminal 21 for introducing it into a video process amplifier circuit (not shown),
Each output is supplied to the first and second input terminals of adder 22, respectively. This adder 22 adds the differential signals from the differential amplifier 20 to form a feedback signal _S3 , and applies this signal _S3 to each second input terminal of the first and second subtracters 18, 19. It is commonly introduced.

According to the differential amplifier configured in this way,
The output waveforms of the head amplifier 16 having a differential amplification configuration are in opposite phases to each other as shown in FIGS. 2a and 2b. In addition, 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 the figure P ₁ ,
As shown in P ₂ , they are superimposed on each other in the same phase. The first and second video signals on which the noise waveforms P ₁ and P ₂ are superimposed in this way are sent to the first and second subtracters 18 and 1.
9, and is subtracted from the feedback signal at the second input terminal. 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 subtracts only the noise of the first and second video signals before being differentially amplified, and the differential amplifier 20
The noise level is lowered by a level that cannot be removed by the CMRR of 1, and is 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 _i , 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 set to υ ₀ ( (see FIG. 2c), the gain of the adder 22 is set to α times, and the gain of each subtractor 18, 19 is set to 1 time, then the output of the adder 22 is expressed as υ _i −αυ ₀ . Then, the noise output υ ₀ of the differential amplifier 20 is υ ₀ = (υ _i − αυ ₀ ) β …………(1), and rearranging this, υ ₀ = β/1 + αβυ _i …………(2) becomes. Therefore, CMRR becomes 1/1+αβ from the differential gain υ ₀ /υ _i corresponding to the common mode gain β. This means that when the differential gain is 1, the CMRR is 1/β in the conventional circuit, but it has been improved to 1/1+αβ by the present invention.

Furthermore, even if the input voltage of the differential amplifier 20 changes due to a change in ambient temperature and the value of β increases, α
By setting the value of α≫β, there is almost no change in the value of CMRR.

Figure 3 shows CMRR on the vertical axis and β on the horizontal axis.
A characteristic diagram of CMRR is shown, and β due to temperature drift is shown.
This shows that even if the value of CMRR changes, the range of change in the CMRR value is +1/α to -1/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 ₁ , TP ₂ , TP ₃ ,
TP ₄ is an unbalanced input terminal into which the first and second video signals from the shielded cable 17 are introduced, TP ₂ and TP ₄ are connected to the ground point, and TP ₁ and TP ₂
are resistors R ₁₃ , each connected at one end to ground via the lug connections of resistor R ₁₁ and coupling capacitor C ₁ and resistor R ₁₂ and coupling capacitor C ₂ , respectively;
Connected to each other end of _R14 . The coupling capacitors C ₁ and C ₂ are connected in parallel to the electrolytic capacitors C ₃ and C ₄
have. Signals appearing at the other ends of the resistors R ₁₃ and R ₁₄ are respectively introduced into the bases of the transistors TR ₁₁ and TR ₁₂ forming a differential pair via resistors R ₁₅ and R ₁₆ , respectively. these transistors
Each collector of TR ₁₁ and TR ₁₂ has a load resistance R ₁₇ ,
It is connected to the first power supply line _L1 via _R18 , and its emitter is connected to the collector of the current source transistor _TR13 via the series connection of resistors _R19 , _R20 and _R21 , _R22, respectively. . A sliding resistor R ₂₃ is interposed at the intersection of each of these series connections, and the sliding end of this resistor R ₂₃ is connected to the collector of the transistor TR ₁₃ via the intersection of resistors R ₂₀ and R ₂₂ . connected to. This transistor TR ₁₃ has a resistor at its base.
_R24 , a resistor _R25 , _a capacitor _C5 , and _an electrolytic capacitor _C6 . Voltage from power line L ₂ is applied. Also, transistor
The emitter of TR ₁₃ is connected to the second power supply line L 2 through a resistor R ₂₇ , and one end is connected to the second power supply line L ₂ through a parallel connection consisting of a resistor R ₂₈ and a capacitor C ₇ and an electrolytic capacitor C ₈ . The voltage across the resistor R ₂₉ connected to L ₂ is supplied. This resistor _R29 is the load resistance of the emitter follower transistor _TR14 . The collector of this emitter follower transistor TR ₁₄ is the power line.
_L1 , and its base is configured to receive a signal from the collectors of differential pair transistors _TR15 and _TR16 forming an adder through a resistor _R30 , and the collectors of each of these transistors _TR15 and _TR16 are connected to ,resistance
Connected to ground via R ₃₁ . In addition, each emitter of transistors TR ₁₅ and TR ₁₆ is connected to a resistor.
It is connected to the power supply line L ₁ via R ₃₂ and R ₃₃ , and the signals from the collectors of the differential pair transistors TR ₁₁ and TR ₁₂ are differentially input to each base via resistors R ₃₄ and R ₃₅ , respectively. . Therefore, one transistor of the adder differential pair transistors TR ₁₅ and TR _16
TR16 functions as a buffer element and is supplied from its emitter to the base of an output emitter follower transistor _TR17 via a resistor _R30 . The emitter of this transistor _TR17 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 _TR17 .

In addition, a voltage source ±V is applied to each power supply line L ₁ and L ₂ via AC blocking coils L ₃ and L ₄ , respectively, and smoothing capacitors C ₉ to _{C 15} are connected between the ground and the ground. There is.

According to the above configuration, the signal from the cable 17 is directly transmitted to the differential pair transistors TR ₁₁ and TR ₁₂
supplied to the base of The current source transistor _TR13 corresponds to the subtracters 18 and 19 in FIG. That is, the transistor TR ₁₃ receives the feedback signal S ₃ from the emitter of the emitter follower transistor TR ₁₄ via the capacitor C ₇ and the resistor R ₂₆ , and the resulting current change is transmitted to the differential pair transistors TR ₁₁ and TR ₁₂ . is superimposed on the collector current of Thus, transistor TR ₁₁ ,
In TR ₁₂ , each collector current is reduced by the common mode component that cannot be removed due to its own CMR action, and the resulting differential output is generated by the buffer transistors TR ₁₅ ,
It is supplied to the base of the output transistor TR ₁₇ via TR ₁₆ , and taken out as the voltage across resistor R ₃₇ .

Furthermore, in the above-mentioned Japanese Patent Application No. 163598/1983, a head amplifier with an unbalanced output is used, and one end of the shielded cable 17 receives a signal from this head amplifier, and the other end is grounded. Although an embodiment is shown, the present invention can also be applied to an endoscope having such a configuration. Furthermore, the present invention is not limited to application to endoscopes, and can be broadly applied to, for example, video cameras using solid-state image sensors, audio circuits, measurement circuits, and the like.

〔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,
Since the signal from which the noise contained in the input is subtracted by the feedback amount is differentially amplified, it is possible to reliably remove the noise from the high frequency scalpel superimposed as an in-phase component.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a differential amplifier according to the present invention, FIG. 2 is an operating waveform diagram for explaining the operation of the present invention, and FIG. 3 is a common-mode component rejection ratio characteristic. 4 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 superimposed on the output of a conventional solid-state image sensor, and FIG. 6 is a circuit diagram showing a second embodiment of the present invention. 5 is a circuit diagram showing an example of a differential amplifier used in FIG. 5. FIG. 14...Solid-state image sensor, 16...Head amplifier, 1
7...Double 2-wire shielded cable, 18, 19...Subtractor, 20...Differential amplifier, 22...Adder, TR ₁₁
~ _TR17 ...Transistor, _R11 ~ _R37 ...Resistor, _C1 ~
C ₁₅ ...Capacitor.

Claims (1)

[Claims] 1. First and second signals having a phase inversion component as a main component and including an in-phase component are supplied to one input terminal,
first and second analog subtracting means, the other input terminal of which is supplied with a feedback signal for subtracting the in-phase component from the first and second signals;
and differential amplifier means into which the signal from the second subtracting means is differentially introduced, and the differential output of this amplifying means is supplied, and the outputs are added together to differentially amplify the in-phase component. analog addition means for obtaining residual components that cannot be removed by the means as the feedback signal;
A differential amplifying device comprising output means for amplifying one of the differential outputs of the differential amplifying means and outputting the amplified signal as an output signal. 2. First and second differential pairs whose bases are supplied with first and second signals whose main component is a phase inversion component and which includes an in-phase component, and whose collectors are respectively connected to the first voltage source via a load resistance. A differential amplifier consisting of a transistor and a differential output from the differential amplifier are supplied, and the outputs are added together to form a residual component that cannot be removed by the differential amplifier among the in-phase components as a feedback signal. means and
A current that is interposed between each emitter of the differential amplifier and a second voltage source, and that removes the residual component from the output of the differential amplifier so that the feedback signal is superimposed on the output current. What is claimed is: 1. A differential amplifier device comprising: a source; and output means for amplifying one of the differential outputs of the differential amplifier to produce an output signal.