Control circuit for video endoscope

Disclosed is a control circuit which is connected to a video endoscope, having a CCD in the distal end thereof. The control circuit supplies driving clock pulses to the CCD, and converts a picture element signal pulses from the CCD into a continuous image signal, by clamping, or sampling and holding, the signal pulses. The converted signals are further subjected to video processing. A scope discrimination resistor is contained in the endoscope, in the vicinity of a connector thereof, which connects the endoscope and the control circuit. The resistance value of the resistor depends on the length of the endoscope. When the endoscope is connected to the control circuit, the resistor is connected in series with a constantcurrent source in a scope discrimination circuit. The discrimination circuit discriminates the scope length by detecting the resistance value of the resistor as a terminal voltage. The waveform of the driving clock pulses for the CCD is modified in accordance with the result of the discrimination, and the timing for clamping, or sampling and holding, the picture-element signal pulses from the CCD (10), is determined by the discrimination result.

BACKGROUND OF THE INVENTION 
The present invention relates to a control circuit for video endoscope. 
Improved video endoscopes have recently been developed with the progress of 
solid-state pickup elements. In these endoscopes, a solid-state pickup 
element, such as a charge-coupled device (CCD), is contained in the distal 
end of the endoscope, and used to pick up an image of the interior of the 
body cavity. The image from the pickup element is transmitted, through a 
signal line in the endoscope, to an outside display unit, whereupon it is 
displayed. 
Conventionally, a light source of an endoscope is provided as a light 
source unit, independent of the body of the endoscope, and the endoscope 
is connected to the unit by means of a universal cord, which extends from 
the endoscope body. An illumination light from the light source unit is 
transmitted through a light guide fiber in the universal cord and the 
endoscope body, and is then applied to an object. 
Video endoscopes of this type require a driver circuit for generating clock 
pulses, used to drive the solid-state pickup element, a video processing 
circuit for video-processing an image signal from the pickup element, and 
other circuits. Usually, these circuit units are disposed in the light 
source unit. The clock pulses for the pickup element and image signals 
from the element are transferred between the light source unit and the 
pickup element, by means of a signal line in the universal cord. 
In general, endoscopes are available with various lengths and diameters, 
depending on the region into which the endoscope is to be inserted. 
Meanwhile, in order to commonly use the aforesaid circuit units for the 
various endoscopes, the same solid-state pickup element is used in all 
types of video endoscopes. If the length of an endoscope is different from 
that of another, however, the length of the signal line, extending from 
the circuit units in the light source unit to the distal end of the 
endoscope, varies correspondingly, thus resulting in the following awkward 
situations. 
If the signal line is lengthened, the waveform of the clock pulses, 
supplied from the driver circuit to the solid-state pickup element, is 
deteriorated and ceases to be an exactly square one. Accordingly, the 
pickup element cannot be driven correctly. Further, the transmission of 
the image signals, from the element to the video processing circuit, is 
delayed. The image signals delivered from the pickup element are 
intermittent picture-element signal pulses. Therefore, the video 
processing circuit must first convert them into continuous image signals 
by clamping them, or by sampling and holding them. Such a process must be 
synchronized with the generation timing of the drive clock pulses. If the 
transmission of the image signals is delayed, the synchronism cannot be 
maintained, so that extra data, not including the picture-element 
information, will be clamped, or sampled and held. Thus, accurate image 
signals cannot be obtained. Moreover, the influences of the delay of 
transmission on the signal line vary according to the endoscope length. 
Conventionally, therefore, two or more different types of video 
endoscopes, with different lengths, cannot be connected to a single light 
source unit. 
With use of these prior art video endoscopes, furthermore, diagnoses are 
made frequently on the basis of the color of a displayed image of the 
affected part, rather than its shape. Accordingly, the 
color-reproducibility of the display unit should be considerably accurate, 
and its color adjustment must be performed carefully. In a conventional 
method of color adjustment, a color chart is picked up in advance, and the 
image color is adjusted in accordance with the chart, displayed on a 
screen. However, the distal end portion of the video endoscopes has a 
diameter of a little more than ten millimeters, and the angle of view is 
very wide. Therefore, the photographing of the color chart is a delicate 
work, so that the color adjustment cannot be performed with speed. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a control circuit for 
video endoscope, connectible with any types of video endoscopes. 
Another object of the invention is to provide a control circuit for video 
endoscope, capable of speedy color adjustment of a display screen. 
According to the present invention, there is provided a control circuit for 
video endoscope, which comprises means for detecting the type of a video 
endoscope connected to the control circuit; means for modifying the 
waveform of clock pulses in accordance with the result of detection by the 
detecting means, and supplying the modified clock pulses to a solid-state 
pickup element in the endoscope; and means for converting image signal 
pulses, supplied from the pickup element, into a continuous image signal, 
by clamping, or sampling and holding the pulses, with a timing 
corresponding to the detection result given by the detecting means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of a control circuit for video endoscope according to the 
present invention will be described in detail with reference to the 
accompanying drawings. FIG. 1 is a block diagram of the control circuit, 
to which a video endoscope is connected. Charge-coupled device (CCD) 10, 
as a solid-state pickup element, is contained in a distal end portion of 
the endoscope, whereby an image of the interior of the body cavity is 
picked up. Light from a lamp (not shown) is transmitted through a light 
guide fiber, to illuminate the inside of the body cavity. Resistor 12 for 
scope discrimination is contained in the endoscope, in the vicinity of a 
connector, which connects the endoscope and the control circuit. The 
resistor 12 indicates the length of the endoscope, or more exactly, the 
length of a signal line extending from the connector to CCD 10. The 
resistance 12 value of resistor 12 depends on the endoscope length. 
Clock pulses from a pulse generator (not shown), used to drive CCD 10, are 
applied to the input of driver 16 through isolation transformer 14, and 
their voltage is raised to a predetermined level. In this case, driver 16 
is an amplifier. The waveform of the output of driver 16 is modified by 
matching circuit 18 (shown in detail in FIG. 3), and the modified output 
signal is supplied to CCD 10. Although the clock pulses for CCD 10 are 
shown in the form of a single signal in FIG. 1, they actually are signals 
of a plurality of phases, e.g., three-phase signals. 
Image signal pulses from CCD 10 are applied to the input of clamp circuit 
24, through preamplifier 20 and isolation transformer 22. The level of the 
image signal pulses is fetched with predetermined timing, and maintained 
as it is. The clamping timing of circuit 24 is controlled by timing 
generator 32, which produces timing pulses in accordance with the output 
of timing controller 30, to which clamp pulses are supplied from a control 
circuit (not shown). The output of clamp circuit 24 is supplied to a video 
process circuit. 
When video endoscope is connected to the connector, resistor 12 for scope 
discrimination is connected to scope discrimination circuit 26 (shown in 
detail in FIG. 2). Circuit 26 discriminates the length of a scope by 
detecting the resistance value of resistor 12. Based on the discrimination 
result, matching circuit 18 and timing controller 30 are controlled. 
FIG. 2 shows scope discrimination circuit 26 in detail. Circuit 26 is 
provided with current source 40, which is connected in series with 
resistor 12. Thus, the resistance value of resistor 12 is detected as a 
terminal voltage. The terminal voltage of resistor 12 is applied to the 
positive input terminals of seven comparators 48a to 48g, which constitute 
comparator circuit 48. The negative input terminals of comparators 48a to 
48g are supplied with voltages at voltage-dividing points of voltage 
divider 44, which is formed of eight resistors, connected in series 
between positive and negative power sources. The voltage dividing points 
correspond to nodes between the resistors. The voltages applied to the 
negative input terminals become lower in the order of comparators 48a to 
48g. The outputs of comparators 48a to 48g, all together, constitute a 
seven-bit binary signal. The outputs of comparators 48a and 48g are 
assigned to MSB (most significant bit) and LSB (least significant bit), 
respectively. In response to the resistance value of resistor 12, 
comparator circuit 48 deliver the binary signal, whose zeroth (LSB) to nth 
bits are 1 (n is any integral number from zero to six), and whose (n+1)th 
to sixth (MSB) bits are 0. 
The zeroth, first, and second bits, corresponding to the outputs of 
comparators 48g, 48f and 48e of comparator circuit 48, respectively, are 
applied to input terminals A2, A3 and A4 of adder circuit 54, 
respectively. The third, fourth, fifth, and sixth bits, corresponding to 
the outputs of comparators 48d, 48c, 48b and 48a, respectively, are 
applied to input terminals A1, A2, A3 and A4 of adder circuit 52, 
respectively. Adder circuits 52 and 54 cooperate and add one to the 
outputs of comparator circuit 48. In the outputs of circuit 48, the 
higher-order bits are 1, and the lower-order bits are 0. If one is added 
to the outputs, therefore, all the bits but one are 0. Thus, the position 
of the bit being 1, out of the outputs of circuits 52 and 54, indicates 
the resistance value of resistor 12. If the comparator output is 0001111, 
for example, it becomes 0010000 after one is added to it. If the 
comparator output is 1111111, it becomes 10000000 after one is added to 
it. Thus, eight binary identification signals ID1 to ID8, which are all 0 
except one, are delivered from adder circuits 52 and 54. 
In this manner, the type (scope length) of the video endoscope can be 
discriminated with use of a simple arrangement, by supplying constant 
current to resistor 12 in the endoscope, and detecting the resistance 
value of resistor 12 as a terminal voltage. Although the identification 
signals are more than one in number, they can be used directly for the 
switching of switching elements, since all of them, except one, are 0. 
Referring now to FIG. 3, matching circuit 18 will be described in detail. 
Isolation transformer 14 is connected to driver 16 through capacitor 60. 
Circuit 18 includes relay switches S1 to S8, and CR differentiation 
circuits DL1 to DL8 connected to switches S1 to S8, respectively. The 
output of driver 16 is supplied to circuits DL1 to DL8 via switches S1 to 
S8. The time constants of circuits DL1 to DL8 are different from one 
another. Switches S1 to S8 are controlled by identification signals ID1 to 
ID8, and closed by a identification signal being 1. As mentioned before, 
only one of signals ID 1 to ID 8 is 1, so that only one of switches S1 to 
S8 is closed. Accordingly, the clock pulses for CCD 10 are differentiated 
by one of differentiation circuits DL1 to DL8, using a time constant 
corresponding to the scope length. As a result of this differentiation, 
the clock pulses take a waveform such that a differential component is 
added to the leading edge of an original square waveform. The waveform of 
the added differential component is deteriorated while the clock pulses 
are being transmitted through the signal line. When the clock pulses are 
applied to CCD 10, the waveform restores the original square waveform. In 
short, the differentiation circuits, in matching circuit 18, serve to 
previously compensate the waveform components, which are to be 
deteriorated while the clock pulses are being transmitted through the 
signal line. Thus, according to this embodiment, the solid-state pickup 
element is prevented from being driven in a wrong manner, due to waveform 
deterioration during the transmission of the clock pulses, by previously 
modifying the waveform of the clock pulses according to the scope length. 
FIG. 4 is a detail circuit diagram of clamp circuit 24. Image signal pulses 
from isolation transformer 22 are supplied to a video processing circuit 
through impedance converter 68, capacitor 70, and impedance converter 74. 
Dynamic clamp circuit 72 is connected between capacitor 70 and converter 
74. Circuit 72 includes analog switch 75, formed of bridge connected 
diodes, and self-bias transformer 76 for supplying a bias current pulse to 
switch 75. The timing pulses from timing generator 32 are supplied to 
transformer 76. In response to these pulses, image signal pulses from CCD 
10 are clamped and converted into a continuous image signal. 
As mentioned before, the clamping timing is delayed for the same duration 
as the delay of the image signal pulses caused by the signal line, 
depending on scope-length identification signals ID1 to ID8. Thus, the 
image signal pulses can be clamped with a correct timing, without being 
affected by the delay time during the transmission of the signal through 
the signal line. 
Timing controller 30, which is constructed in substantially the same manner 
as matching circuit 18 shown in FIG. 3, comprises eight one-shot 
multivibrators with different time constants, in place of CR 
differentiation circuits DL1 to DL8. Clamp pulses (synchronous with the 
clock pulses) are supplied to the multivibrators through relay switches. 
Any one of the switches is closed in response to scope-length 
identification signals ID1 to ID8, and an output pulse signal from any one 
of the multivibrators is supplied to timing generator 32. A timing pulse 
is produced at the trailing edge of the pulse signal. 
Image signal pulses can be converted into a continuous signal with use of a 
sampling/holding circuit, in place of clamp circuit 24. 
FIG. 5 is a block diagram of a video process circuit connected to the 
output of clamp circuit 24, shown in FIG. 1. The output of circuit 24 is 
applied to frame memories 82 through pre-process circuit 80. Memories 82 
are provided individually for three colors; red (R), green (G), and blue 
(B). Image signals of these colors are stored in their corresponding 
memories. The R, G and B image signals, read out from memories 82, are 
supplied to a first input terminal of switch 86, via gamma compensator 84. 
RGB signal generator 92 is connected to a second input terminal of switch 
86. The output of switch 86 is supplied to color display 90 via NTSC 
decoder 88. The switching control of switch 86 is executed by scope 
detector 94, which is supplied with scope identification signals ID1 to 
ID8. 
Referring now to the flow chart of FIG. 6, operation for color adjustment 
of the display screen will be described. When the power is turned on in 
step S10, switch 86 is connected to RGB signal generator 86 in step S20. 
Generator 92 generates R, G and B standard-color signals forming a 
predetermined color bars in synchronism with the V and H sync. signals. R, 
G and B standard-color signals are applied to the input of NTSC decoder 
88, via switch 86, to be converted into NTSC signals, which are supplied 
to color display 90. Display 90 indicates RGB color bars, as shown in 
FIGS. 7A and 7B. In this case, the color bars are displayed in the central 
portion or at the bottom of a screen. In step S30, an operator performs 
color adjustment while watching the color bars. Thus, the color adjustment 
does not require any color chart to be picked up. After the adjustment, 
the operator connects the video endoscope to the control circuit. It is 
assumed that the video endoscope is not connected to the control circuit 
during color adjustment. 
In step S40, scope detector 94 determines whether or not the connection of 
the endoscope is detected. In doing this, detector 94 indicates the 
connection if any one of scope identification signals ID 1 to ID 8 is 1. 
If the connection is not detected, the processes from step S20 to S40 are 
repeated. If the connection is detected, switch 86 is connected to gamma 
compensator 84, in step S50. In this state, image signals from memories 82 
are applied to the input of NTSC decoder 88, via gamma compensator 84, and 
switch 86. Thus, an image of the interior of the body cavity appears on 
color display 90. 
According to the present invention, as described above, there is provided a 
control circuit for video endoscope, which can be connected with any types 
of video endoscopes, and can effect speedy color adjustment of displayed 
pictures. 
It is to be understood that the present invention is not limited to the 
embodiment described above, and that various changes and modifications may 
be effected therein by one skilled in the art without departing from the 
scope or spirit of the invention.