Endoscope system with differential signal transmission

An endoscope system includes: an LVDS driver that outputs a differential signal; a differential transmission line that transmits the differential signal outputted from the LVDS driver; a pulse transformer including, in order to input the differential signal transmitted by the differential transmission line, two input terminals connected to an end of the differential transmission line; a resistor functioning as a bypass impedance element connected on an input side of the pulse transformer, to which the differential signal is inputted, in parallel to the pulse transformer and having, at a predetermined noise frequency of noise mixed in the differential transmission line, impedance smaller than circuit impedance of a circuit to which the pulse transformer, which is connected in parallel to the bypass impedance element, is connected; and a dielectric disposed between the two input terminals of the pulse transformer and between lines of the differential transmission line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an endoscope system and, more particularly, to an endoscope system using a pulse transformer to which a differential signal flowing through a differential signal line is inputted.

2. Description of the Related Art

Conventionally, endoscopes have been widely used in a medical field and an industrial field. In particular, in an endoscope system used in the medical field, in order to secure safety for patients, a part of a CCD driving circuit and a video signal processing circuit are mounted on a patient circuit insulated and separated from a secondary circuit.

For example, as disclosed in International Publication No. 2007/004428 and Japanese Patent Application Laid-Open Publication No. 2007-167590, an endoscope system that uses a differential signal for transmission of a signal between a patient circuit and a secondary circuit is proposed. In those proposals, the differential signal is a signal conforming to a standard of LVDS (Low Voltage Differential Signaling). For insulation, a pulse transformer is used in an LVDS transmission channel.

When external noise is mixed in a differential transmission line that transmits the differential signal, if the external noise is common mode noise, the external noise is cancelled by a subtraction in a termination circuit section. Therefore, the differential signal has a characteristic that the differential signal is robust against the external noise. Usually, a pattern on a substrate on an input side of the pulse transformer is formed such that characteristic impedance is, for example, 100 [Ω], and the common mode noise is cancelled.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, it is possible to provide an endoscope system including: a driver that outputs a differential signal; a differential transmission line that transmits the differential signal outputted from the driver; a pulse transformer including, in order to input the differential signal transmitted by the differential transmission line, two input terminals connected to an end of the differential transmission line; an impedance member including a bypass impedance element connected on an input side of the pulse transformer, to which the differential signal is inputted, in parallel to at least the pulse transformer and having, at a predetermined noise frequency of noise mixed in the differential transmission line, impedance smaller than circuit impedance of a circuit to which the pulse transformer, which is connected in parallel to the bypass impedance element, is connected; and a dielectric disposed between the two input terminals of the pulse transformer and between lines of the differential transmission line such that a distance between the two input terminals of the pulse transformer is equal to inter-line impedance of the differential transmission line.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention is explained below with reference to the drawings.

(Configuration of an Endoscope System)

First, a configuration of an endoscope system according to the present embodiment is explained.FIG. 1is a configuration diagram showing the configuration of the endoscope system according to the present embodiment.

As shown inFIG. 1, an endoscope system1includes an endoscope2and a processor3to which the endoscope2is connected and which performs, for example, signal processing for a video signal from an image pickup device. In the present embodiment, the endoscope2in the endoscope system1is an endoscope including an insertion section provided with the image pickup device at a distal end. However, the endoscope2may be a camera head mounted on a proximal end portion of a rigid endoscope.

The endoscope2includes a CCD11functioning as an image pickup device and a resistor for identification12of the endoscope2. The endoscope2and the processor3are connected by a not-shown signal cable.

The processor3includes a patient side circuit3ato which the endoscope2is connected and a secondary side circuit3belectrically insulated from the patient side circuit3a.

The patient side circuit3aincludes a CCD driver21that drives the CCD11of the endoscope2, a preamplifier22that amplifies an image pickup signal from the endoscope2, and a CDS & A/D section23that subjects the image pickup signal from the preamplifier22to correlated double sampling and digitizes the image pickup signal. The CDS & A/D section23converts the image pickup signal from the endoscope2inputted via the preamplifier22into a parallel signal having a predetermined frequency.

The parallel signal from the CDS & A/D section23is inputted to an LVDS conversion section24. The LVDS conversion section24converts the inputted parallel signal into a serial signal for LVDS transmission.

The CCD driver21and the CDS & A/D section23are controlled by a drive control section25. The drive control section25generates a CCD control signal on the basis of a reference clock from a clock circuit (CLK)27provided in the secondary side circuit3bvia a photocoupler26and controls the CCD driver21and the CDS & A/D section23. The LVDS conversion section24and the drive control section25include FPGAs (field programmable gate arrays).

The serial signal for the LVDS transmission converted by the LVDS conversion section24is transmitted to an LVDS modulation section29of the secondary side circuit3bvia an LVDS transmission section28.

The LVDS modulation section29subjects the serial signal inputted via the LVDS transmission section28to conversion opposite to the conversion performed by the LVDS conversion section24and converts the serial signal into a predetermined parallel signal. The converted parallel signal is subjected to color separation processing, synchronization processing, and the like by a color processing section30and stored in an image memory31as image data.

The image data stored in the image memory31is subjected to image signal processing by an HD signal processing section32or an SD signal processing section33and outputted to a not-shown monitor.

The color processing section30, the HD signal processing section32, or the SD signal processing section33are controlled by a control section34. The control section34detects the resistor for identification12of the endoscope2via a photocoupler35to perform control of video processing corresponding to a type of the endoscope2. The HD signal processing section32is a processing section that performs video signal processing at high resolution and the SD signal processing section33is a processing section that performs video signal processing at standard resolution. The LVDS modulation section29, the color processing section30, the HD signal processing section32, and the SD signal processing section33include FPGAs (field programmable gate arrays).

The control section34includes an interface with not-shown peripheral apparatuses such as a keyboard, a printer, a PCMCIA, a LAN, and a foot switch and includes an interface with a front panel36. Further, the control section34includes a character generator34aon an inside. The control section34can generate a message corresponding to necessity and cause a monitor to display the message.

FIG. 2is a configuration diagram showing a configuration of the LVDS transmission section28. The LVDS transmission section28includes an LVDS driver41, a pulse transformer42, and an LVDS receiver43.

The pulse transformer42includes a primary side coil42aand a secondary side coil42b. A serial signal from the LVDS conversion section24is inputted to the LVDS driver41. The LVDS driver41is a driver that outputs a differential signal. The LVDS driver41supplies an LVDS signal to the coil42aon an input side (i.e., the primary side) of the pulse transformer42.

The coil42bon an output side (i.e., the secondary side) of the pulse transformer42is connected to the LVDS receiver43. The LVDS receiver43outputs the received LVDS signal to the LVDS modulation section29.

(Connecting Structure of a Differential Transmission Line and the Pulse Transformer)

FIG. 3is a perspective view of a connecting portion of a differential transmission line50, which transmits an LVDS signal from the LVDS driver41, and the pulse transformer42.

As shown inFIG. 3, two wiring patterns (hereinafter referred to as differential patterns)51,52forming the differential transmission line50are provided on a substrate53. The differential transmission line50is a micro strip line that transmits a differential signal outputted from the LVDS driver41. Further, the pulse transformer42, which is a chip component, is also mounted on the substrate53. The pulse transformer42is connected to an end of the differential transmission line50. The differential signal transmitted by the differential transmission line50is inputted to the pulse transformer42.

Two input terminals44,45of the pulse transformer42are respectively connected to end portions (hereinafter referred to as connection end portions)51a,52aof the two differential patterns51,52formed in parallel to each other. A distance between the two input terminals of the pulse transformer42is formed to be equal to inter-line impedance of the differential transmission line50.

A resistor54to which the two differential patterns51,52are connected is provided near the connection end portions51a,52a. The resistor54, which is a chip component, is an impedance member that electrically connects the two input terminals44,45of the pulse transformer42, to which a differential signal is inputted, and has impedance smaller than impedance of the pulse transformer42at a predetermined noise frequency in noise mixed in the differential transmission line50. In other words, the resistor54is an impedance member including a bypass impedance element connected in parallel to the pulse transformer42. The impedance of the resistor54is smaller than circuit impedance on the pulse transformer42side connected in parallel to the resistor54at the predetermined noise frequency in the noise mixed in the differential transmission line50.

As indicated by a dotted line inFIG. 3, the resistor54may be provided in the pulse transformer42.

FIG. 4is a diagram for explaining the connecting portion of the differential transmission line, which transmits the LVDS signal from the LVDS driver41, and the pulse transformer42.FIG. 5is a diagram for explaining a flow of charges of a differential signal.

As shown inFIG. 5, the substrate53on which the differential transmission line50is provided is a multilayer substrate. The two differential patterns51,52are formed on a top layer. A ground (GND) layer55is formed in the substrate53.

Usually, the two differential patterns51,52formed on the substrate53are designed while performing various simulations based on physical structures such as width of a pattern, thickness of an insulating layer, and a distance between the insulating layer and a ground (GND) and an inter-pair distance d1between the two differential patterns51,52is determined such that impedance of the differential transmission line50from a transmission position to a reception position of the differential signal is desired impedance.

In the present embodiment, as shown inFIGS. 3 and 4, the differential transmission line50and the pulse transformer42are connected such that the inter-pair distance d1between the two differential patterns51,52and a distance d2between the two input terminals44,45of the pulse transformer42are equal. In other words, the distance d2between the two input terminals of the pulse transformer42is formed to be equal to the inter-line impedance of the differential transmission line50.

This is to prevent impedance mismatch from occurring in the connecting portion of the differential transmission line50and the pulse transformer42.

This point is specifically explained. It is assumed that the differential transmission line50and the pulse transformer42are connected such that the distance between the two input terminals44,45of the pulse transformer42and the inter-pair distance between the two differential patterns51,52are different. For example, as indicated by a dotted line inFIG. 4, it is assumed that the inter-pair distance between the two differential patterns51,52increases toward the connection end portions51a,52a.

When positive charges of a P channel flow to the differential pattern52, negative charges are excited in an N channel and flow to the differential pattern51. Between the two differential patterns51,52in which the inter-pair distance d1determined by design is kept, since magnetic fields generated in the two differential patterns51,52are in opposed directions, radiation of noise does not occur.

However, as indicated by dotted lines inFIGS. 4 and 5, when the distance d2between the connection end portions51a,52aof the differential patterns51,52is larger than the inter-pair distance d1, the differential patterns51,52are formed to expand toward the connection end portions51a,52a. Mismatch of impedance occurs in a portion where the distance between the differential patterns expands.

As the distance between the patterns expands, in some case, the negative charges corresponding to the positive charges flowing to the differential pattern52do not flow to the differential pattern51and are generated and flow to the ground (GND) layer55closer from the differential pattern52than the differential pattern51. In that case, a leak of the negative charges occurs in the ground (GND) layer and radiation from the ground (GND) layer55occurs. Since the mismatch of impedance occurs, the differential patterns51,52are easily affected by noise from an outside.

Therefore, as indicated by solid lines inFIGS. 3 to 5, the inter-pair distance d1between the differential patterns51,52are kept up to the connection terminal sections51a,52a. To keep the inter-pair distance d1, the distance d2between the input terminals44,45of the pulse transformer42is set equal to the inter-pair distance d1.

Instead of fixing the inter-pair distance between the differential patterns51,52, in a region expanding toward the connection end portions51a,52ain the differential patterns51,52, a dielectric may be provided to set the distance between the two input terminals of the pulse transformer42equal to the inter-line impedance of the differential transmission line50.

FIG. 6is a diagram showing a state in which a dielectric member is provided between the connection end portions51a,52aof the differential patterns51,52. As shown inFIG. 6, a dielectric member57is provided in a region56between patterns expanding toward the connection end portions51a,52ain the pair of differential patterns51,52.

A dielectric constant ∈2of the dielectric member57provided in the region56is a value at which the distance between the patterns in the expanding portion is seemingly the same as the inter-pair distance d1of the differential pattern50. The dielectric constant ∈2is larger than a dielectric constant ∈1between the patterns in a region where the differential patterns51,52are parallel. As a material of the dielectric, for example, there is a ceramic material having a dielectric constant higher than a dielectric constant of an epoxy material in a normal region.

Next, action of the resistor54is explained.

FIG. 7is a circuit diagram for explaining the action of the resistor54. As shown inFIG. 7, an LVDS signal source SS corresponding to the LVDS driver41is connected between the differential patterns51,52. The coil42acorresponding to primary winding in the pulse transformer42is connected between the connection end portions51a,52aof the differential patterns51,52. Further, the resistor54connected in parallel to the coil42ais connected between the differential patterns51,52. Impedance Z of the pulse transformer42including the coil42ais different according to a frequency of a signal.

InFIG. 7, noise due to static electricity, an electric knife, or the like is shown as a noise source NS connected between each of the differential patterns51,52and a substrate ground (GND(P)) of the patient side circuit3a. Further, impedance Z0between the differential patterns51,52and the ground layer (GND(S))55is shown as an impedance element61.

When noise is mixed in the differential transmission line50, the impedance of the pulse transformer42changes to impedance corresponding to a frequency of the noise. For example, when a frequency of a noise signal is 30 [MHz] and the coil42ahas 50 [μH], impedance Z of the pulse transformer42including the coil42ais 95 kΩ (=50×(2×π×300)).

On the other hand, impedance Z1of the resistor54is selected to be smaller than the impedance Z of the pulse transformer42at a predetermined frequency of noise mixed in the differential patterns51,52.

For example, the impedance Z0of the impedance element61(i.e., between the differential patterns51,52and the ground (GND(S)) layer55) is high impedance, for example, 30 [kΩ]. The impedance Z1of the resistor54is low impedance, for example, 100 [Ω].

The impedance Z1of the resistor54is selected to be larger than the impedance Z of the pulse transformer42at a frequency of a differential signal of LVDS to be transmitted. Consequently, an electric current of the differential signal flows to the coil42aof the pulse transformer42.

However, when a noise signal is mixed in the differential patterns51,52, the impedance Z1of the resistor54at the noise frequency of the noise of the electric knife or the like is smaller than the impedance Z2of the coil42a. In the example explained above, the impedance Z1of the resistor54is 100Ω and the impedance Z of the pulse transformer42is 15 kΩ. Therefore, an electric current I including a noise current In does not flow to the coil42aand flows to the resistor54having the low impedance.

InFIG. 7, a solid line indicates a case in which the electric current I including the noise current In flows to the resistor54in a direction indicated by an arrow A of the slid line. A dotted line indicates a case in which the electric current I including the noise current In flows to the coil42ain a direction indicated by an arrow B of the dotted line.

When the noise having the predetermined frequency is mixed, compared with a potential difference (I×15 kΩ) between both ends of the coil42ain the case in which the electric current I flows to the coil42a, a potential difference (I×100Ω) between both the ends of the coil42ain the case in which the electric current I flows to the resistor54is low. Therefore, deterioration in a differential signal, which is an actual signal, is substantially suppressed.

In other words, since most of the electric current I flows to the resistor54connected in parallel to the coil42a, it is possible to substantially suppress deterioration in the actual signal on the differential patterns51,52due to the noise current In.

Therefore, it is possible to suppress the deterioration in the actual signal during mixing of noise by setting, on the basis of the frequency of the noise due to the static electricity, the electric knife, or the like, the impedance of the pulse transformer42and the impedance of the resistor54in the relation described above. As a result, according to the embodiment explained above, it is possible to realize an endoscope system having improved immunity tolerance.

In the embodiment explained above, as an example of the impedance member, the resistor, which is a passive component, having the impedance smaller than the impedance of the pulse transformer at the predetermined noise frequency of the noise mixed in the differential pattern is explained. However, instead of the resistor, a capacitor or a coil may be used as the passive component as long as the capacitor or the coil has such impedance. Further, the passive component may be a passive component including a combination of two or more components selected out of the resistor, the capacitor, and the coil. In other words, the impedance member may be a passive component including at least one of the resistor, the capacitor, and the coil.

FIG. 8is a diagram showing an example of a circuit in a case in which a circuit including a capacitor and a coil is used as the impedance member.

As shown inFIG. 8, a coil71functioning as a bypass impedance element is connected between the differential patterns51,52. A capacitor72is connected between a connection point P1of the coil71and the differential pattern51and one end of the coil42a.

For example, it is assumed that a noise frequency is 10 MHz, a frequency of a differential signal is 300 MHz, an inductor of the coil71functioning as the bypass impedance element is 200 μH, capacitance of the capacitor72is 0.1 pF, and impedance between a differential pattern and a ground (GND(S)) layer is 1 MΩ.

In this case, at the noise frequency (10 MHz), whereas impedance of the coil71is 12 kΩ, a sum of impedance on a pulse transformer side and impedance of the capacitor is 162 kΩ.

On the other hand, at the signal frequency (300 MHz), whereas a sum of impedance on the pulse transformer side and impedance of the capacitor is 99 kΩ, impedance of the coil71is 376 kΩ. Further, as explained above, the impedance between the differential pattern and the ground (GND(S)) layer is 1 MΩ.

Therefore, at the signal frequency (300 MHz), the sum of the impedance on the pulse transformer side and the impedance of the capacitor72is smaller than the impedance of the coil71. Therefore, a signal current flows to the pulse transformer42. On the other hand, at the noise frequency (10 MHz), the impedance of the coil71is smaller than the sum of the impedance on the pulse transformer side and the impedance of the capacitor72. Therefore, a noise current does not flow to the pulse transformer42and flows to the coil71.

As explained above, in the case ofFIG. 8, at the noise frequency, the impedance of the coil71functioning as the bypass impedance element is smaller than impedance of a circuit (a circuit including the capacitor72and the coil42a) connected in parallel to the coil71. As a result, the noise current flows to the coil71functioning as the bypass impedance element. However, a differential signal current flows to a circuit on the pulse transformer side.

Furthermore, in the embodiment explained above, an example in which the differential signal is the LVDS signal is explained. However, the configuration of the embodiment explained above is also applicable to differential signals of RS-422, DVI, eDP, V-by-One Hs, and the like.

In the embodiment explained above, an example of the differential signal flowing to the patterns provided on the substrate is explained. However, a technique of the embodiment explained above can also be applied to a differential signal flowing to a twist pair line.

As explained above, with the endoscope system according to the embodiment explained above, when the differential signal is transmitted via the pulse transformer, it is possible to suppress deterioration in the actual signal of the differential signal using the impedance member having impedance smaller than the impedance of the pulse transformer at the noise frequency between lines of the differential transmission line.

In the past, in some case, impedance due to an inductance component between the terminals of the primary side coil in the pulse transformer is high depending on a frequency of noise. Therefore, there is a problem in that, when external noise of static electricity, an electric knife, or the like flows to the primary side coil, a large potential difference occurs between both ends of the primary side coil and the actual signal in the differential signal is deteriorated. However, according to the embodiment explained above, it is possible to realize an endoscope system having improved immunity tolerance.

Therefore, according to the embodiment explained above, it is possible to realize an endoscope system having improved immunity tolerance.

The present invention is not limited to the embodiment explained above. Various changes, modifications, and the like are possible in a range in which the spirit of the present invention is not changed.