JP2011010855A - Signal transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To receive the signals of an appropriate waveform in the reception-side end part of a transmission line.SOLUTION: At the distal end of an electronic endoscope insertion part, an imaging element for imaging endoscopic images is disposed. One end of the transmission line 30 having a characteristic impedance Zo different from the input impedance of the load circuit 31 is connected to a load circuit 31 including the imaging element. A drive circuit 20 for outputting the driving pulse signals of the imaging element is connected to another end of the transmission line 30 disposed from the distal end part of an electronic endoscope to a connector part to be used for connection with a processor unit. The drive circuit 20 is provided with the linear amplifier 33 of a low output impedance, and the matching circuit (resistor) of R=Zo is connected between the linear amplifier 33 and the transmission line 30.

Description

  The present invention relates to a signal transmission device for transmitting an electrical signal through a cable, and more particularly to signal transmission related to an imaging element of an electronic endoscope.

  In an electronic endoscope, an image signal from an image sensor provided at the distal end of an insertion portion is sent to a processor device connected to a scope base end portion, subjected to predetermined image processing, and then displayed on a monitor. Since the space at the distal end of the insertion portion is extremely limited, a drive circuit for driving the image sensor is disposed at an appropriate location on the processor device or scope base end side (such as a connector portion for connection to the processor device). . For this reason, a drive signal is sent to an image pick-up element through a signal cable for several meters, for example. Similarly, the detected image signal is sent to a processor device, an analog front end circuit disposed at the base end of the scope, or the like via a signal cable of several meters.

  In signal transmission, the problem of impedance matching generally occurs. However, particularly in an electronic endoscope, since the transmission distance is long, the problem of waveform deterioration due to reflection and loss becomes significant. For this reason, in an electronic endoscope, a matching circuit for matching impedance is provided on the image sensor side, and a switch circuit having a high drive capability (that allows a large amount of current to flow) is provided as a resistor on the drive circuit side. One provided with a damping circuit composed of a capacitor has been proposed (Patent Document 1).

JP 2001-050771 A

  However, impedance matching on the image sensor side is not easy, and it cannot be said that reflection is not sufficiently suppressed. For this reason, a reflected wave is superimposed on the drive signal, and the waveform is distorted. In addition, since the damping circuit provided on the drive circuit side needs to change the constant according to the length of the signal cable, it is necessary to change the capacitor and resistance of the damping circuit for each type of electronic endoscope. . Furthermore, since the transmission distance is several meters, there is waveform degradation due to transmission path loss.

  An object of the present invention is to provide a signal transmission device having a simple configuration capable of receiving a signal having an appropriate waveform at the receiving end of a transmission line.

  The signal transmission device of the present invention is connected to a transmission line having a predetermined characteristic impedance, a load circuit that is connected to the reception side end of the transmission line, and whose input impedance does not match the characteristic impedance, and is connected to the transmission side end of the transmission line The signal transmission circuit includes a low output impedance circuit and a matching circuit that matches the characteristic impedance of the transmission line, and the matching circuit is disposed between the low output impedance circuit and the transmission line. It is characterized by being.

  The signal transmission circuit preferably has a function of shaping the waveform of the output signal in the signal transmission circuit so as to compensate for the distortion of the signal waveform that appears at the receiving end due to transmission loss of the transmission line. For example, a circuit having a characteristic that emphasizes a high frequency component of a signal is used.

  The load circuit includes an image sensor, and a drive pulse signal for the image sensor is output from the signal transmission circuit. The signal transmission device is used, for example, in a scope body of an electronic endoscope.

  ADVANTAGE OF THE INVENTION According to this invention, the signal transmission apparatus of the simple structure which can receive the signal of a suitable waveform in the receiving side edge part of a transmission line can be provided.

1 is a schematic external view showing a configuration of an electronic endoscope using a transmission apparatus according to an embodiment of the present invention. It is a block diagram which shows typically the electrical and optical structure of the scope main body shown by FIG. It is a block diagram which shows the structure of the transmission path of 1st Embodiment. A state of signal reflection when impedance matching is not taken at both ends of the transmission line is schematically shown. 6 is a graph showing time-series changes in voltages Vmo and VL at ends P1 and P2 when a step signal Vout is output from the output end P of the linear amplifier of FIG. The state of signal reflection in the signal transmission device of this embodiment is schematically shown. 7 is a graph showing time-series changes in voltages Vmo and VL at ends P1 and P2 when a step signal Vout is output from the output end P of the linear amplifier of FIG. The time series changes of the voltage waveforms Vmo and VL at the end P1 and the end P2 with respect to the pulse signal (Vout) with a constant period are schematically shown for each of the cases where there is reflection at the end P1 and the case where there is no reflection. It is a graph. It is a block diagram of the signal transmission apparatus of 2nd Embodiment which considered the impedance matching of the signal transmission circuit. FIG. 5 is a graph showing waveforms of voltages Vout, Vmo, and VL at points P, P1, and P2 that are affected by transmission loss when impedance matching is considered but waveform shaping is not performed on an output pulse signal. . It is a graph which shows the waveform of voltage Vout, Vmo, VL when the waveform shaping of this embodiment which considered impedance matching and transmission loss is given to the output pulse signal. It is a block diagram of the modification of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic external view showing a configuration of an electronic endoscope using a transmission apparatus according to an embodiment of the present invention.

  The electronic endoscope system is connected to the scope main body 10 and the scope main body 10 to perform various types of image processing, and to supply illumination light to the scope main body 10. The electronic endoscope system is connected to the processor apparatus and is photographed by the scope main body 10. Generally, it is composed of a monitor device or the like for displaying the recorded video. FIG. 1 shows the appearance of the scope body 10.

  The scope main body 10 connects a tubular insertion portion 11 to be inserted into a body or a tube hole, an operation portion 12 provided at a proximal end portion of the insertion portion 11, and the operation portion 12 to a processor device (not shown). Connector part 13 for connecting, and connecting pipe 14 which connects between operation part 12 and connector part 13 is constituted. As is conventionally known, an imaging element (see FIG. 2) is provided at the distal end portion 11A of the insertion portion 11, and an image of the subject is captured by the imaging element by illumination light emitted from the distal end portion 11A. The illumination light is normally supplied from the processor device through a light guide disposed in the scope body 10.

  FIG. 2 is a block diagram schematically showing an electrical and optical configuration of the scope main body 10 shown in FIG.

  The connector unit 13 of this embodiment includes, for example, an I / O port 15, a control circuit 16, a system clock generator 17, a signal processing circuit (DSP) 18, a power supply circuit 19, a drive circuit 20, an analog front end (AFE) 25, and the like. Is provided. The connector unit 13 is electrically connected to a processor device (not shown) via an I / O port 15, and the I / O port 15 includes a control circuit 16, a system clock generator 17, and a signal processing circuit (DSP). 18 and a power supply circuit 19 are connected.

  The control circuit 16 controls the scope main body 10 in general, and the system clock generator 17 generates various clock pulses required in the scope main body 10. For example, the system clock generator 17 outputs necessary timing signals to the drive circuit 20, the signal processing circuit (DSP) 18, the analog front end (AFE) 25, and the like.

  An imaging element 21 such as a CCD or a CMOS is provided at the distal end portion 11A of the insertion portion 11 (see FIG. 1). The subject image is picked up by the image pickup device 21 via the image pickup lens 22. The image sensor 21 is connected to the drive circuit 20 via a signal cable (sensor clock transmission path) 23 wired through the communication tube 14, the operation unit 12, and the insertion unit 11, and drive pulses such as a vertical synchronization signal and a horizontal synchronization signal. The signal is transmitted from the drive circuit 20. For example, a coaxial cable having a predetermined characteristic impedance is used as the signal cable.

  An image signal picked up by the image pickup device 21 is an analog front end (AFE) 25 of the connector section 13 via a signal cable (video signal transmission path) 24 wired through the insertion section 11, the operation section 12, and the connecting pipe 14. Is transmitted to. The analog front end 25 includes, for example, a first stage amplifier circuit, a correlated double sampling circuit, and an AD converter, samples an image signal at a predetermined timing, and converts an analog image signal received through the signal cable 24 into a digital signal. The video signal digitized in the analog front end 25 is subjected to signal processing in a signal processing circuit (DSP) 18 and output to a processor device (not shown) via the I / O port 15.

  Note that power is supplied from the power supply circuit 19 to the image sensor 21. Illumination light is supplied from a light source unit provided in a processor device (not shown), and is provided from the connector unit 13 to the distal end portion 11A through the connecting tube 14, the operation unit 12, and the insertion unit 11. The light is transmitted to the distal end portion 11A through 26 and irradiated through the illumination lens 27 provided on the distal end portion 11A.

  Next, the signal transmission apparatus of the first embodiment will be described with reference to FIG. In FIG. 3, a transmission line 30 is a transmission line having a characteristic impedance Zo included in the sensor clock transmission path 23. One end of the transmission line 30 is connected to the load circuit 31 including the imaging device 21, and the other end is connected to the drive circuit 20. In the first embodiment, the drive circuit 20 includes a matching circuit 32 and a low output impedance circuit 33 such as a linear amplifier.

  The load circuit 31 is not provided with a termination circuit that matches the impedance of the transmission line 30, and impedance matching is not performed. On the other hand, in the drive circuit 20, the matching circuit 32 (resistor R = Zo) that matches the characteristic impedance Zo of the transmission line 30 is positioned in the vicinity of the low output impedance circuit 33 between the transmission line 30 and the low output impedance circuit 33. Be placed.

  That is, the drive pulse signal of the image sensor 21 sent from the logic circuit of the system clock generator 17 is amplified by the linear amplifier 33 with low output impedance, and then output to the transmission line 30 via the matching circuit 32 for transmission. The signal is transmitted to the load circuit 31 including the image sensor 21 through the line 30.

  Next, with reference to FIGS. 4-8, an effect | action and effect at the time of using the signal transmission apparatus of 1st Embodiment are demonstrated.

  FIG. 4 schematically shows a state of signal reflection when impedance matching is not performed at both ends of the transmission line 30. In the example of FIG. 4, the impedance ZL of the load circuit 34 including the image sensor 21 is larger than the characteristic impedance Zo of the transmission line 30 and the impedance Zm of the matching circuit 36 of the drive circuit 35 is smaller than the characteristic impedance Zo. Assumed (ZL> Zo> Zm).

  Therefore, signal reflection is repeatedly generated at the end P1 on the drive circuit 35 (matching circuit 36) side and the end P2 on the load circuit 34 side, which are both ends of the transmission line 30. In the example of FIG. 4, the reflection coefficient ρm = (Zm−Zo) / (Zm + Zo) at the end P1, and the reflection coefficient ρL = (ZL−Zo) / (ZL + Zo) at the end P2. Since Zo> Zm, the reflected wave has an opposite phase in the reflection at the end P1.

  FIG. 5 is a graph showing time-series changes in the voltages Vmo and VL at the ends P1 and P2 when the step signal Vout is output from the output terminal P of the linear amplifier (low output impedance circuit) 33 in FIG. .

  As shown in FIG. 4, time T11 indicates the time when the step signal is output from the end P1 (corresponding approximately to the time when the step signal is output from the output terminal P). It shows the time when the signal first reaches the end P2 through the transmission line 30 and is reflected. T12 is the time when the step signal reflected at the end P2 at the time T21 reaches the end P1 through the transmission line 30 and is reflected again. Similarly, the time when the reflected signal reaches the end P2 and is reflected is sequentially expressed as T22, T23,..., And the time when the reflected signal reaches the end P1 and is reflected is sequentially expressed as T13, T14,. ing. The time Td shown in FIG. 5 is a propagation time required for a signal to be transmitted through the signal cable (transmission line 30). 4 and 5, it is assumed that there is no loss in the transmission line 30.

  As shown in FIG. 5, when the impedance is not matched at both ends of the transmission line 30, the transmitted signal is repeatedly reflected at both ends P1 and P2, and they are superimposed on the original signal. The signal waveform greatly collapses and an appropriate signal cannot be transmitted to the load circuit 34.

  On the other hand, in the present embodiment, impedance matching is not performed for the load circuit 31 and the impedance ZL remains larger than the characteristic impedance Zo of the transmission line 30 (ZL> Zo). The impedance Zm of the matching circuit 32 is equal to the characteristic impedance Zo of the transmission line 30 (Zm = Zo).

  As a result, in the present embodiment, signal reflection occurs at the end portion P2 of the transmission line 30, but no signal reflection occurs at the end portion P1. That is, the reflection coefficient ρL = (ZL−Zo) / (ZL + Zo) at the end P2 and the reflection coefficient ρm = 0 at the end P1. FIGS. 6 and 7 correspond to FIGS. 4 and 5, respectively, and FIG. 6 schematically illustrates signal reflection in the signal transmission device of the present embodiment. FIG. 7 is a graph showing time-series changes in the voltages Vmo and VL at the ends P1 and P2 when the step signal Vout is output from the output terminal P of the linear amplifier (low output impedance circuit) 33 at that time. .

  As shown in FIG. 6, since the signal is reflected only at the end portion P2 and not reflected at the end portion P1, the influence of reflection appears only at the end portion P1. That is, the voltage Vmo at the end portion P2 is once affected by the reflection at the end portion P2 at time T12, but is not affected by the reflected wave at the end portion P2. In the present embodiment, since a low output impedance circuit such as a linear amplifier is used for the drive circuit 20, even if the reflected wave returns to the end P1 side, the waveform is not affected.

  For example, as in the present embodiment, in the transmission of drive pulses of the image sensor, even if the waveform on the transmission end (end P1) side is broken, the image is captured if the waveform on the reception end (end P2) side is in place. There is no problem in driving the element, and the purpose of signal transmission can be achieved. In FIG. 8, the voltages at the end P1 and the end P2 when the transmission signal (Vout) is a pulse signal with a constant period for each of the cases where there is reflection at the end P1 and when there is no reflection. Waveforms Vmo and VL are shown as time series graphs. In the voltage waveforms Vmo and VL of FIG. 8, a broken line indicates a case where there is reflection at the end P1 (without transmission-side impedance matching), and a solid line indicates a case where there is no reflection (with transmission-side impedance matching).

  As shown in FIG. 8, even in the pulse signal, if the impedance matching by the matching circuit 32 (see FIG. 6) is not performed, the pulse waveform is disturbed at the receiving end P2. However, even if impedance matching is not performed on the receiving side, if impedance matching is performed on the transmitting side, the voltage Vmo at the transmitting end P1 is affected by reflection, but the voltage at the receiving end P2 is not affected. As for VL, the same waveform as the pulse waveform output from the logic circuit is maintained.

  As described above, in the signal transmission device according to the first embodiment, a damping circuit is provided on the transmission end side as in the prior art, and the reception end side is not impedance-matched with the transmission line, but the transmission side is connected via the matching circuit. By adopting a configuration connected to the low output impedance circuit, it is possible to prevent the reception side from being affected by the reflection of the transmission line without performing matching on the reception end side. This makes it possible to eliminate the influence of reflection from the receiving side with a very simple configuration. Further, it is not necessary to change the constant corresponding to the length of the transmission line as in the case of using a damping circuit.

  In the above description, the impedance Zm of the matching circuit is assumed to be equal to Zo on the assumption that the output impedance of the low output impedance circuit is extremely smaller than the resistance of the matching circuit. However, the impedance of the matching circuit may be set so that the impedance when the transmission end side is viewed from the transmission line side is substantially equal to the characteristic impedance of the transmission line.

  Further, although the impedance ZL of the load circuit 31 is larger than the characteristic impedance Zo of the transmission line 30 (ZL> Zo), even when “ZL <Zo”, only the phase of the reflected wave on the receiving end side is reversed. Thus, the effect of impedance matching on the transmitting end side is not lost. That is, it is not necessary to consider the impedance of the load circuit.

  Next, a signal transmission device according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a block diagram of a signal transmission apparatus according to the second embodiment. In the second embodiment, the configuration of the drive circuit is different from that of the first embodiment. That is, the drive circuit 20 of the first embodiment includes a matching circuit 32 and a low output impedance circuit (for example, a linear amplifier) 33. In the drive circuit 40 of the second embodiment, a low output impedance circuit (for example, a linear amplifier). A waveform shaping circuit is provided between 33 and the logic circuit. Other configurations are substantially the same as those of the first embodiment. In the following description, the same reference numerals are used for the same configurations, and the description thereof is omitted.

  In the first embodiment, the transmission line 30 has been described as having no transmission loss. However, since the transmission line 30 is several meters long, distortion occurs in the pulse waveform due to the transmission loss. In the second embodiment, in consideration of the distortion of the pulse waveform at the receiving end due to transmission loss (for example, based on the length of the transmission line), the pulse signal is generated in the waveform shaping circuit on the transmission side so as to compensate for this. Shape in advance. That is, when the pulse signal that has been shaped and output reaches the receiving end through the transmission line 30, the pulse signal from the logic circuit in the waveform shaping circuit is such that its waveform becomes the waveform of the pulse signal output from the logic circuit. Is formatted.

  FIG. 10 shows the influence of transmission loss when the waveform shaping is not performed on the output pulse signal as waveforms of voltages Vout, Vmo, and VL at points P, P1, and P2 (see FIG. 6). Here, a waveform when there is a transmission loss is indicated by a solid line, and an ideal waveform when there is no transmission loss is indicated by a broken line. Here, the description is based on the assumption that impedance matching is performed on the transmission end side and re-reflection does not occur at the transmission end.

  Also, in FIG. 11, the shapes of the voltages Vout, Vmo, and VL when the waveform shaping of the present embodiment in consideration of transmission loss is applied to the output pulse signal are indicated by solid lines, and the voltage when the waveform shaping is not performed. The shapes of Vout, Vmo, and VL are indicated by broken lines.

  The waveform shaping circuit 41 according to the second embodiment includes a circuit that passes or emphasizes a high-frequency component of a signal generally called a high-pass filter, such as a differential configuration circuit. The pulse signal from the logic circuit of the system clock generator 17 is shaped by the waveform shaping circuit 41, amplified by the linear amplifier 33, and output to the transmission line 30 via the matching circuit 32. In the waveform shaping circuit 41 of the second embodiment, for example, a CR circuit which is a passive differentiation circuit is included, and converted into a waveform in which the high frequency component of the pulse signal from the logic circuit is emphasized.

  As described above, according to the second embodiment, as in the first embodiment, the influence of reflection at the receiving end can be removed from the pulse signal transmitted with a simple configuration, and in the second embodiment, Further, distortion of the pulse waveform at the receiving end due to the influence of transmission loss can be removed.

  Next, a modification of the second embodiment will be described with reference to FIG. In the second embodiment, the CR circuit, which is a passive differentiation circuit, is arranged in front of the amplifier. However, in the drive circuit 42 according to this modification, a waveform using an operational amplifier instead of the linear amplifier 33 and the CR circuit 41 is used. A shaping circuit 43 is used. That is, in the modification, the waveform shaping circuit 43 that serves as both amplification and waveform shaping corresponds to the low output impedance circuit of the second embodiment. Other configurations are the same as those of the second embodiment.

  As described above, the same effect as that of the second embodiment can be obtained in the modified example, and the reflection at the transmission end is suppressed and the transmission loss is corrected, so that the input to the reception end is performed as shown in FIG. It is possible to maintain the waveform of the pulse signal to be output as the waveform output from the logic circuit. Further, instead of the second embodiment or the modification, it is possible to adopt a configuration in which waveform formation is performed using a D / A converter or the like.

  In the present embodiment, the transmission line for transmitting the driving pulse of the image sensor has been described. However, the signal transmission device of the present invention is not limited to this, and impedance matching on the reception side of the transmission line is performed. This is effective when it is difficult to maintain only the waveform at the receiving end, and is particularly effective when the transmission path is long. That is, it is effective for transmission of an image signal, and can be applied to the video signal transmission path 24 in FIG. 2 if the space of the endoscope distal end portion 11A permits.

  Note that the circuit configuration, optical configuration, light source arrangement, and the like described in this specification are also exemplary and are not limited to the present embodiment. The signal transmission device of the present invention can also be applied to devices other than electronic endoscopes having a long transmission distance, for example.

DESCRIPTION OF SYMBOLS 10 Scope main body 11 Insertion part 11A Tip part 12 Operation part 13 Connector part 14 Connection pipe 20, 35, 40, 42 Drive circuit 21 Image sensor 23 Sensor clock transmission path 30 Transmission line 31 Load circuit 32 Matching circuit 33 Linear amplifier (low output) Impedance circuit)
41, 43 Waveform shaping circuit

Claims (5)

A transmission line having a predetermined characteristic impedance;
A load circuit connected to the receiving end of the transmission line, the input impedance of which does not match the characteristic impedance;
A signal transmission circuit connected to the transmission side end of the transmission line,
The signal transmission circuit includes a low output impedance circuit and a matching circuit for matching with the characteristic impedance, and the matching circuit is disposed between the low output impedance circuit and the transmission line. Signal transmission device.   The signal transmission circuit has a function of shaping a waveform of an output signal in the signal transmission circuit so as to compensate for distortion of the signal waveform appearing at the reception side end due to transmission loss of the transmission line. The signal transmission device according to claim 1.   3. The signal transmission device according to claim 2, wherein a circuit having a characteristic that emphasizes a high frequency component of a signal is used for shaping the waveform.   The signal transmission device according to claim 2, wherein the load circuit includes an image sensor, and a drive pulse signal of the image sensor is output from the signal transmission circuit.   The signal transmission device according to claim 4, wherein the signal transmission device is used in a scope body of an electronic endoscope.

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