JPS636960A - Signal reader for contact type image sensor - Google Patents

Abstract

PURPOSE:To obtain an output signal from a photodiode without providing plural long common signal lines on an image sensor by sequentially transferring and reading picture element signals as voltage signals. CONSTITUTION:When a signal phio goes to an H level, first signal transfers TFTT1-TN are turned on and a charge stored in the photodiodes D1-DN according to the quantity of reflected light of an original is transferred to the gate input of an odd number of second signal transfers TFTS1-S2N-1. when the H level and the L level of the signals phi1 and phi2 are alternately repeated and switched at a prescribed frequency, the picture elenment signals held by the second signal transfer TFT is transferred one by one to an output amplifier A at a speed corresponding to said frequency and the respective picture element signal is taken out from an output OUT. A reset signal inputted to the gate of the a step of the signal transfer TFTS1 is transferred to the output OUT so as to follow these picture element signals.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a signal readout device for a contact type image sensor, and particularly to a contact type image sensor that has a large readout signal and prevents crosstalk between successive signals. The present invention relates to a signal reading device for an image sensor.

(Prior Art) Conventionally, a signal readout circuit for a contact image sensor configured using thin film transistors (hereinafter abbreviated as TPT) uses TF as a selection switch element for a large number of photodiodes that receive reflected light from an original. The output signal of the selected photodiode was transferred to a plurality of common signal lines, and the signals were sequentially switched and read out using a multiplexer or the like.

(Problems to be Solved by the Invention) The above-described conventional techniques had the following problems.

According to this method, a common signal line with a length comparable to that of the image sensor is required, and the following problems arise due to the length of the common signal line.

(1) Although the capacitance C of the common signal line increases in proportion to the length of the common signal line, the amount of charge Q transferred from the photodiode does not change, so the signal jaggedness V becomes smaller. Here, the major serration V of the signal is expressed by the following equation.

(2) Long signal lines have large capacitive coupling with other signal lines, resulting in signal crosstalk.

The present invention aims to eliminate the above-mentioned problems of the prior art, and to sequentially read output signals from photodiodes without providing a plurality of long common signal lines on an image sensor.

(Means and operations for solving the problems) In order to solve the above problems, the present invention provides a signal readout device for a contact image sensor in which a small number of photoelectric conversion elements are arranged in a row. a first signal transfer means connected to each of the conversion elements; a second signal transfer means for sequentially transferring a plurality of pixel signals transferred by the first signal transfer means; and a second signal transfer means. the second signal transfer means includes a first means comprising a plurality of elements for converting each of the pixel signals into a voltage signal; It is characterized in that it is composed of a plurality of elements connected to each other and a shift means that operates in synchronization with a clock of a predetermined frequency, and pixel signals are sequentially transferred and read out as voltage signals.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention. Also, the second
The figure shows a time diagram of the signals applied to the circuit.

In FIG. 1, D1 to DN are photodiodes that receive pixel information, and these photodiodes operate in a charge accumulation mode. The photodiodes D1 to DN include
The first signal transfer TFTT1 to -[N are connected to one terminal of the reset switches TFTR1 to RN. The other terminal of each of the signal transfer TFTTs T1 to TN is connected to the odd-numbered gate of the second signal transfer TFTS1 to S2 whose drain is grounded, and the reset switch TFT
The drain side terminal, which is the other terminal of R1 to RN, is grounded.

The drain-grounded second signal transfer TFTSi~32N-
1 and the loads '1 to r2N-1 form a so-called source follower circuit. Each of the sources of the second signal transfer TPT includes a shift switch TPTU1~U2N-1
It is connected to the gate of the next stage signal transfer TPT via. Further, the first stage TFT of the second signal transfer TPT
Sl is grounded via reset TFTv1, -
TFTS2 at the end of the 6th layer. , is connected to the signal extraction amplifier A via the final stage shift switch TFTU2N-1.

Further, the photodiode is connected to a first common line 1, the gates of the reset switches TFTR1 to RN are connected to a second common line 2, and the gates of the first signal transfer TPT71 to TN are connected to a third common line 1. Connected to the common line 3, the second signal transfer TPT31 to 32N-1
The drain of the reset TF is connected to the fourth common line 4, the gates of odd-numbered stages of the shift switches TFTU1 to U2N-1 are connected to the fifth common line 5, and the reset TF
TV gate and shift switch TFTU1~U2N
The gates of even-numbered stages of -1 are connected to the sixth common line 6. In addition, reset TFTV1 and load r1~'
One end of 2N-1 is connected to the ground G via the seventh common line 7 and is grounded.

The first common line 1 is supplied with a photodiode bias voltage 8, and the fourth common line 4 is supplied with a power supply Vd.
In addition, signals φ9.φ., φ1 and φ2 having the waveforms shown in FIG. 2 are applied to the common lines 2.3.5 and 6, respectively.

Next, the operation of this embodiment having the above configuration will be explained. Now, time t1-1. signal φ. When becomes the torque level, the first signal transfer TFTs TPT1 to TN are turned on, and the charges accumulated in the photodiodes D1 to DN are transferred to the second signal transfer TFTs TPT31 to 52N-1 according to the amount of reflected light from the original.
is transferred to the odd-numbered gate input. Then, at time t
2, when the signal φ0 becomes a torque level, the first signal transfer TFTT1 to TN are turned off, and the photodiode D
-D and the second signal transfer TFTs 81 to N 82N-1 are cut off.

Further, when the signals φR and φ1 reach the torque level at the time t2, the charges remaining in the photodiodes D1 to DN are reset, and the accumulation of charges in the photodiodes D1 to DN according to the amount of light reflected from the original starts again.

On the other hand, the signal φ1 causes the odd-numbered stage shift switch TFT to
U1, u3. u5. . . . When U2N-1 is turned on, the odd-numbered stages S1°S3 .
S5. . . . , the pixel signals input to the gates of 52N-1 are respectively input to the next stage S2. S4. S6゜...
Transferred to the gate input of .... At this time, the final stage T
The pixel signal input to the gate of FTS2N-1 is taken out through the final stage shift switch TFTU2N-1 and amplifier A.

Next, at time t3, the signals φ8 and φ1 become the torque level, and when the signal φ2 becomes the torque level, the reset TFTV1 and the odd-numbered shift switches FTU2 . U4. U6.・
..., U2N is turned on, the gate signal of the second signal transfer TFTS of the first stage is reset, and the signal transfer TPTS, S4. S6.・・・・・・
The pixel signals transferred to the next stage S3 and 3 respectively
5, S7. It will be shifted to...

Next, when the trubels of the signals φ1 and φ2 are alternately and repeatedly switched at a predetermined frequency, the pixel signals held in the second signal transfer TPT are changed one by one to a speed according to the frequency. The pixel signals are transferred to the output amplifier A, and each pixel signal is taken out from the output OUT.

At the same time, following these pixel signals, a set signal is input to the gate of the first stage signal transfer TFTS1 and transferred toward the output OUT.

Therefore, when the pixel signal detected by the first stage photodiode D1 is extracted through the output amplifier A,
All gate inputs of the second signal transfer TPT have been reset.

Next, at time t, the signal φ. When becomes Trubel, time t
3-t7. The pixel information stored in the photodiodes r)1 to DN during the period is transferred to the first signal transfer TFT Tl to
It passes through TN and is transferred to the odd-numbered gates of the second signal transfer TFTs 81 to 32N-1, and thereafter the same operation as described above is performed.

According to this embodiment, the second signal transfer TPT31 to S
and the load '''' 2N-1.
-11 Olower circuit and shift switch TF”ru that connects them
-u, the photodiode D11
Since the pixel information detected at 2N-1 to DN is transferred, a common line for signal readout is not required. Therefore, the problems that the conventional device had are solved.

Next, a second embodiment of the present invention will be described using FIGS. 3 and 4. FIG. 3 shows a circuit diagram, and FIG. 4 shows a time chart of signals applied thereto.

The difference between this embodiment and the first embodiment is that in the first embodiment, the pixel signal is transferred by a source follower circuit and a shift switch TPT that connects the pixel signal, whereas in this embodiment, the pixel signal is transferred from the source Grounding TPT31~32N-1
This is done by using the inverter circuit used and the shift switches TFTU1 to U2N-1 that connect the inverter circuit. Note that the same reference numerals as in FIG. 1 indicate the same or equivalent parts as in FIG.

Therefore, in the operation of this embodiment, in the process of shifting the pixel signal one step at a time toward the output amplifier, the pixel signal is always inverted and sent.

Note that since the operations other than this are the same as those of the first embodiment, detailed explanation will be omitted.

As described above, according to the embodiment of the present invention described above, the foot
The pixel signals detected by the diodes D1 to DN are not directly read out using long signal lines as in conventional devices, but are converted into voltage information and sequentially transferred and read out, so the signal level is high. And crosstalk is reduced.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

According to the present invention, the pixel signals detected by the foot diodes D1 to DN are not read out via a plurality of long lines, but are converted into voltage information, and the voltage information is transferred and read out. The signal level is very high because
Moreover, there is an effect that crosstalk is reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the first embodiment of the present invention, Fig. 2 is a time chart of the signals applied to it, Fig. 3 is a circuit diagram of the second embodiment of the invention, and Fig. 4 is the signal applied to it. This figure shows the time chart of the signal. D1~DN...Photodiode, S1~S2 Todo・
・Second signal transfer TPT, u1 to U 2N-1...Shift switch TPT, V1...Reset TPT Agent Patent attorney Michito Hiraki Outside 18 Figure 1 Figure 2

Claims (3)

[Claims] (1) In a signal reading device for a contact image sensor in which a plurality of photoelectric conversion elements are arranged in a row, a first signal transfer means connected to each of the photoelectric conversion elements, and a first signal transfer means connected to each of the photoelectric conversion elements; a second signal transfer means that sequentially transfers a plurality of pixel signals transferred by the second signal transfer means, and a signal extraction amplifier connected to the second signal transfer means; A first means comprising a plurality of elements that convert each pixel signal into a voltage signal; and a shift means that connects the plurality of elements constituting the first means to each other and operates in synchronization with a clock of a predetermined frequency. A signal reading device for a contact image sensor, characterized in that: (2) The signal readout device for a contact type image sensor according to claim 1, wherein the photoelectric conversion element is composed of a photodiode, and the photodiode is driven in a charge accumulation mode. (3) Signal reading of the contact type image sensor according to claim 1, wherein the second signal transfer means transfers a reset signal subsequent to the transfer of the pixel signal. Device.