Line sensor apparatus

Abstract: There is provided a color line sensor apparatus comprising color line sensors consisting of a plurality of lines and a selecting circuit which can select a desired one of a plurality of lines, wherein the line selected by the selecting circuit is scanned on the basis of a scan pulse from a scanning circuit.

Description: The present invention relates to an apparatus for driving sensors consisting of a plurality of lines and, more particularly, to a sensor drive apparatus to realize a miniaturization of the apparatus scale, a high speed operation, and the like. Fig. 4 is a diagram showing a schematic arrangement of a conventional sensor drive circuit. In the conventional example, scanning circuits 1 to 3 are provided for color line sensors 1 to 3, respectively. Therefore, the line sensors can be independently driven by shifting the timings of start pulses  s1 to  s3 of the scanning circuits. That is, by supplying the start pulse  s1 and drive pulses ₁ and ₂, the scanning circuit 1 is made operative and the line sensor 1 is driven and a sensor signal O₁ is output through an amplifier A₁. Subsequently, by supplying the start pulses  s2 and  s3 , the sensor signals of the line sensors 2 and 3 are similarly output through amplifiers A₂ and A₃, respectively. However, in the conventional drive apparatus, as many scanning circuits as lines are needed, so that there are problems such that the circuit scale enlarges, the bus line capacitances of the scanning circuits increase, and it is difficult to drive at a high speed. On the other hand, there is also a problem such that the pitch among the line sensors is decided by the size of scanning circuit and can be hardly set to a small pitch. Since the pitch cannot be reduced, for instance, in the case of constructing a 3-line colour sensor of RGB, the optical characteristics deteriorate and the scale of the signal processing system increases. JP-A-61-288576 discloses a plurality of rows of horizontal tranfer CCDs provided with a common scanning circuit. The common scanning circuit receives two clock signals, and passes these on to the top horizontal CCD for one horizontal line period, so as to transfer the charges in the top horizontal CCD along it. During the next horizontal line period the scanning circuit passes the clock signals to the second horizontal CCD to clock it, and this process continues down to the lower most horizontal CCD. According to the present invention there is provided line sensor apparatus as set out in claim 1. The remaining claims set out optional features. By providing the selecting means, a plurality of lines can be independently driven by one scanning circuit. As compared with the conventional apparatus, the circuit scale can be reduced and the high speed operation can be accomplished in an embodiment of the present invention. The pitch among the lines can be also reduced. Fig. 1 is a schematic arrangement diagram for explaining the fundamental operation of a sensor dirve apparatus according to the present invention; Fig. 2 is a schematic circuit diagram of an embodiment of the sensor drive apparatus of the invention; Fig. 3 is a timing chart for explaining the operation of the embodiment; and Fig. 4 is a schematic arrangement diagram of a conventional sensor drive circuit. An embodiment of the present invention will be described in detail hereinbelow with reference to the drawings. Fig. 1 is a schematic arrangement diagram for explaining the fundamental operation of a sensor drive apparatus according to the invention. The case of three line sensors will be described as an example. In the diagram, when a start pulse  s is input to a scanning circuit 101, the scanning circuit sequentially outputs n scan pulses to a phase control circuit 102 as selection means in response to the drive pulses ₁ and ₂. The phase control circuit 102 selects an arbitrary line sensor on the basis of selection signals TG₁ to TG₃. Only the selected line sensor is scanned by the scan pulse from the scanning circuit 101 and a sensor signal from the line sensor is sequentially output. For instance, when only the selection signal TG₁ is supplied, only the line sensor 1 is driven and the phase control circuit 102 sequentially outputs scan pulses to only the line sensor 1. Thus, the sensor signal of the line sensor 1 is sequentially read out through the amplifier A₁. Tha same shall also apply with regard to the line sensors 2 and 3. Fig. 2 is a schematic circuit diagram of an embodiment of the sensor drive apparatus according to the invention. When the start pulse  s is input, the scanning circuit 101 successively outputs scan pulses ₁₁, ₂₁, ₁₂, ₂₂, ...  1n , and  2n synchronously with the drive pulses ₁ and ₂. The phase control circuit 102 consists of n stages of circuits. Either one of the R, G, and B signals is selected by selection signals STR, STG, and STB and the scan pulse is output from each stage. In the circuit of the first stage, the scan pulse ₁₁ of the scanning circuit 101 becomes either one of R₁, G₁, and B₁ signals through transistors Q₁ to Q₃. Bootstrap capacitors C₁ to C₃ are connected between gate and source of the transistors Q₁ to Q₃. On the other hand, a grounding voltage GND is applied to each gate electrode of the transistors Q₁ to Q₃ through transistors Q g1 to Q g3 and a voltage VDD is also applied thereto through transistors Q s1 to Q s3 . The scan pulse ₂₁ is commonly input to gate electrodes of the transistors Q g1 to Q g3 . The selection signals STR, STG, and STB are input to gate electrodes of the transistors Q s1 to Q s3 , respectively. The outputs R₁, G₁, and B₁ are input to the gate electrodes of the transistors Q s1 , Q s2 , and Q s3 of the subsequent second stage. In a manner similar to the above, the second to nth stages are constructed. Either one of the R, G, and B signals selected by the selection signals is output from each of the stages. Fig. 3 is a timing chart for explaining the operation of the embodiment. First, after the start pulse  s was supplied to the scanning circuit 101, the selection signal STB is set to 1, so that the transistor Q s3 of the first stage is turned on. The voltage VDD is input to the gate electrode of the transistor Q₃. Thus, the conductance of the transistor Q₃ rises. When the signal STB is set to 0, the gate electrode of the transistor Q₃ is set to the floating state. When the drive pulse ₁ is input to the scanning circuit 101, the scan pulse ₁₁ synchronized with the drive pulse ₁ is output. Since the transistors Q₁ and Q₂ are in the off state, the scan pulse ₁₁ appears as an output B₁ through the transistor Q₃. At that time, the "1" level output B₁ further increases the gate potential of the transistor Q₃ through the bootstrap capacitor C₃. Thus, almost all of the voltage of the scan pulse ₁₁ appears as the output B₁ without decreasing. At the same time, the transistor Q s3 of the second stage is turned on by the output B₁. The voltage VDD is applied to the gate electrode of the transistor Q₃ of the second stage. The conductance of the transistor Q₃ rises. The transistor Q s3 is turned off by the "0" level output B₁. The gate electrode of the transistor Q₃ is set to the floating state. Subsequently, when the scan pulse ₂₁ is output synchronously with the drive pulse ₂, the transistors Q g1 to Q g3 of the first stage are turned on. All of the gate potentials of the transistors Q₁ to Q₃ are reset to the grounding potential. Thus, the transistors Q₁ to Q₃ are turned off. Next, when the scan pulse ₁₂ is set to 1 synchronously with the drive pulse ₁, the pulse ₁₂ passes through the transistor Q₃ whose conductance has increased. The scan pulse ₁₂ appears as an output B₂ due to the bootstrap effect. In a manner similar to the above, outputs B₃, B₄, ..., B n are successively output synchronously with the scan pulses ₁₃, ₁₄, ...,  1n . That is, in the embodiment, the color line sensor of B is scanned and its sensor signal is sequentially output. Next, to select and scan the color line sensor of G, the start pulse  s is supplied to the scanning circuit 101 and, thereafter, the selection signal STG is set to 1. Thus the transistor Q s2 of the first stage is turned on, the gate potential of the transistor Q₂ rises, and the conductance of only the transistor Q₂ increases. When the scan pulse ₁₁ is output, an output G₁ appears through the transistor by the bootstrap effect. In a manner similar to the above, G₂, G₃, ... are sequentially output synchronously with the scan pulses ₁₂, ₁₃, ..., the color line sensor of G is scanned, and its sensor signal is sequentially output. The same shall also apply to the case of selecting the color line sensor of R. The transistor Q s1 of the first stage is turned on by setting the selection signal STR to 1. As mentioned above, according to the embodiment, either one of the line sensors of R, G, and B can be selected by the selection signal STR, STG, or STB. Only the selected line sensor can be scanned by the scanning circuit 101. Although the embodiment has been described with respect to the case of the color line sensors of RGB, the invention is not limited to this example but can be obviously applied to a general sensor having a plurality of lines. The invention can be also applied to a construction such that a plurality of lines are selected and signals are read out by a plurality of signal lines. As described in detail above, since the sensor drive apparatus according to the invention has selection means which can select desired one of a plurality of lines, a plurality of lines can be independently driven by one scanning circuit. As compared with the conventional apparatus, the circuit scale can be reduced and the high speed operation can be accomplished. Since the pitch among the lines can be set to a small pitch, in the case of the photosensors, the resolution can be improved. On the other hand, in the case of the color sensor, a color signal can be derived without deteriorating the optical characteristics of RGB.

Claims: Line sensor apparatus having a plurality of line sensors, each line sensor having a plurality of portions, and readout means for reading signals from the line sensors, characterised in that the readout means comprises line sensor scanning means for scanning along a line sensor by providing scan signals in turn to respective said portions of the line sensor, the line sensor scanning means being common to a plurality of line sensors, and the readout means further comprises selection means for selecting a line sensor to be scanned by the line sensor scanning means. Apparatus according to claim 1 in which the selection means receives said scan signals from the scanning means and passes them on to the selected line sensor. Apparatus according to claim 1 or claim 2 in which the line sensors are colour line sensors. An apparatus according to claim 3, wherein different colour filters are provided for different said line sensors, respectively. An apparatus according to any one of the preceding claims, wherein said line sensors have independent output terminals, respectively. An apparatus according to any one of the preceding claims, wherein said selection means is arranged to one side of said plurality of line sensors. An apparatus according to claim 6, wherein said scanning means is arranged on the side opposite to said line sensors of said selection means. An apparatus according to any one of the preceding claims in which the selection means selects an arbitrary line sensor to be scanned on the basis of selection signals.

Inventors: OHZU HAYAO, OHZU, HAYAO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: H04N9
IPC codes: H04N1, H01L27, H04N9, H04N3