Impedance matching apparatus and endoscope including the same
An impedance matching apparatus includes: a cable that transmits a rectangular wave outputted from a solid image pickup device; a correlated double sampling circuit that performs scanning of the rectangular wave by sampling the rectangular wave with a timing of a signal clamp pulse being changed, based on a timing of the feed-through sampling pulse fixed at a timing at which the rectangular wave by the cable indicates a high value; a variable resistance provided at a tail end side of the cable; and a resistance value varying unit that, that performs the scanning with a resistance value of the variable resistance being changed, based on a signal outputted from the correlated double sampling circuit, changes a resistance value of the variable resistance so as to match a characteristic impedance of the cable.
1. An impedance matching apparatus comprising:
a solid image pickup device;
a driving portion that drives the solid image pickup device so that the solid image pickup device outputs a rectangular wave;
a cable that transmits the rectangular wave outputted from the solid image pickup device;
a correlated double sampling circuit that performs correlated double sampling by fixing a timing of a feedthrough sampling pulse to a timing at which the rectangular wave transmitted by the cable indicates a high value, and with the fixed timing of the feedthrough sampling pulse as a basis, sampling the rectangular wave with a timing of a signal clamp pulse being changed to scan the rectangular wave;
a variable resistance provided at a tail end side of the cable and having a variable resistance value; and
a resistance value varying portion that based on a signal outputted from the correlated double sampling circuit, changes a resistance value of the variable resistance so that a resistance value of the variable resistance matches a characteristic impedance of the cable.
2. The impedance matching apparatus according to claim 1 , wherein the resistance value varying portion differentiates twice a signal outputted from the correlated double sampling circuit, and determines a resistance value of the variable resistance to a resistance value at which an absolute value of a result obtained by the differentiation is a value closest to 0, as a resistance value matching the characteristic impedance of the cable.
3. The impedance matching apparatus according to claim 1 , wherein the resistance value varying portion differentiates twice a signal outputted from the correlated double sampling circuit, and determines a resistance value of the variable resistance to a resistance value at which a number of peaks of square values of second derivatives within a predetermined period is a predetermined number, as a resistance value matching the characteristic impedance of the cable.
4. An endoscope including an impedance matching apparatus according to claim 1 , wherein the endoscope further comprises compensating means that compensates a length of the cable so that the cable length substantially becomes a predetermined length.