JPH0547151B2 - - Google Patents

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 the readout signals. The present invention relates to a signal reading device for a sensor.

(Conventional technology) Conventionally, thin film transistors (hereinafter abbreviated as TFT)
The signal readout circuit of a contact image sensor constructed using
Using TFT, the output signal of the selected photodiode was transferred to multiple 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 magnitude V decreases. Here, the magnitude V of the signal is expressed by the following equation.

V=Q/C (2) Long signal lines have large capacitive coupling with other signal lines, so signal crosstalk occurs.

An object of the present invention is 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 problem) In order to solve the above problem, the present invention provides a signal readout 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 conversion elements; a second signal transfer means for sequentially transferring a plurality of pixel signals transferred by the first signal transfer means; a signal extraction amplifier connected to a signal transfer means, the second signal transfer means comprising a first means consisting of a plurality of elements for converting each of the pixel signals into a voltage signal; The device is characterized in that it is composed of a shift means which connects a plurality of elements of the means to each other and operates in synchronization with a clock having a predetermined frequency, and the 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. Further, FIG. 2 shows a time chart of signals applied to the circuit.

In FIG. 1, D ₁ to D _N are photodiodes that receive pixel information, and the photodiodes operate in a charge accumulation mode. The photodiodes D ₁ -D _N are connected to one terminal of a first signal transfer TFTT _{1 -TN} and a reset switch TFTR _{1 -RN} . Signal transfer TFTT ₁ ~ T _N and each other terminal is the second signal transfer with drain grounded.
Connected to odd numbered gates of TFTS ₁ ~ _{S 2N-1} ,
Further, the drain side terminals, which are the other terminals of the reset switches TFTR ₁ to _RN , are grounded.

The drain grounded second signal transfer TFTS ₁ ~
S _2N-1 and the loads r ₁ to _{r 2N-1} form a so-called source follower circuit. the second signal transfer
Each of the TFT sources has a shift switch TFTU ₁
~ Connected to the gate of the next stage signal transfer TFT via _U2N-1 . In addition, the second signal transfer TFT
TFTS ₁ in the first stage is grounded via reset TFTV ₁ , while the source of TFTS _2N-1 in the final stage is connected to signal extraction amplifier A via shift switch TFTU _2N-1 in the final stage. has been done.

Also, the photodiode is connected to a first common line 1, and the reset switch TFTR ₁
The gate of ~R _N is connected to the second common line 2,
The gates of the first signal transfer TFTT ₁ to T _N are the third
connected to the common line 3 of the second signal transfer
The drain of TFTS ₁ ~ _{S 2N-1} is connected to the fourth common line 4
connected to the shift switch TFTU ₁ ~
The gates of odd stages of U _2N-1 are connected to the fifth common line 5, and the gates of reset TFTV ₁ and the gates of even stages of shift switches TFTU ₁ to _{U 2N-1} are connected to the sixth common line 6. has been done. Also, one end of the reset TFTV ₁ and the loads r ₁ to _{r 2N-1} is connected to the seventh
connected to ground G via a common line 7 of
Grounded.

The first common line 1 is supplied with a photodiode bias voltage V _B , and the fourth common line 4 is supplied with a power supply Vdd. Further, signals φ _R , φ ₀ , φ ₁ and φ ₂ having waveforms shown in FIG. 2 are applied to the second, third, fifth and sixth common lines, respectively.

Next, the operation of this embodiment having the above configuration will be explained. Now, when the time t _{1 to to} signal φ ₀ becomes H level, the first signal transfer TFTT ₁ to _TN is turned on, and the photodiode is switched on according to the amount of light reflected from the original.
The charges accumulated in D ₁ to D _N are transferred to the second signal transfer.
Transferred to odd-numbered gate inputs of TFTS ₁ to _{S 2N-1} . Next, when the signal φ ₀ becomes L level at time t ₂ , the first signal transfer TFTT ₁ to T _N is turned off, and the photodiodes D ₁ to D _N and the second signal transfer
It is blocked from TFTS ₁ to _{S 2N-1} .

Furthermore, when the signals φ _R and φ ₁ become H level at the time t ₂ , the charges remaining in the photodiodes D ₁ to D N are reset, and the charges remaining in the photodiodes D ₁ to D _N are reset.
Accumulation of charges in accordance with the amount of light reflected from the original begins again on D _N.

On the other hand, when the odd-numbered shift switches TFTU ₁ , U ₃ , U ₅ , ..., U _2N-1 are turned on by the signal φ 1, the odd-numbered stages _{S 1 ,} S ₃ , S _Five ,
..., the pixel signal input to the gate of S _2N-1 is
The signals are transferred to the gate inputs of the next stages S ₂ , S ₄ , S ₆ , . . . , respectively. At this time, the pixel signal input to the gate of the final stage TFTS _2N-1 is taken out through the final stage shift switch TFTU _2N-1 and amplifier A.

Next, at time _t3 , when the signals φ _R and φ ₁ go low and the signal φ ₂ goes high, the reset TFTV ₁ is activated.
and odd-numbered shift switches TFTU ₂ , U ₄ ,
_{U 6 , . _ _} The pixel signals that were previously sent to the next stage S ₃ ,
It is shifted to S ₅ , S ₇ , ...

Next, when the H level and L level of the signals φ ₁ and φ ₂ are alternately and repeatedly switched at a predetermined frequency, the pixel signals held in the second signal transfer TFT are changed one by one to the corresponding frequency. The signals are transferred to the output amplifier A at a corresponding speed, and each pixel signal is extracted from the output OUT. At the same time, the reset signal input to the gate of the first stage signal transfer TFTS ₁ is transferred toward the output OUT so as to follow these pixel signals.

Therefore, when the pixel signal detected by the first stage photodiode _D1 is taken out through the output amplifier A, all gate inputs of the second signal transfer TFT have been reset.

Next, when the signal φ ₀ becomes H level at time t _o , the pixel information accumulated in the photodiodes D ₁ to D _o between times t ₃ to _{t o} is transferred to the first signal transfer TFTT ₁
~T _N and is transferred to the odd-numbered gate of the second signal transfer TFTS ₁ ~S _2N-1 , and thereafter the same operation as described above is performed.

According to this embodiment, the second signal transfer TFTS ₁ ~
A source follower circuit consisting of S _2N-1 and loads r ₁ to _{r 2N-1} , and a shift switch TFTU ₁ to connect them.
Since the pixel information detected by the photodiodes _D1 to _DN is transferred by U2N _-1 ,
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 in FIGS. 3 and 4.
This will be explained using figures. 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 TFT that connects it, whereas in this embodiment, the pixel signal is transferred from the source This is done by using an inverter circuit using grounded TFTS ₁ to _{S 2N-1} and shift switches TFTU ₁ to _{U 2N-1} that connect the inverter circuit. Note that the same reference numerals as in FIG. 1 indicate the same or equivalent components as in FIG. 1.

Therefore, in the operation of this embodiment, in the process of shifting the pixel signal one stage 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 pixel signals detected by the photodiodes D ₁ to D _N are not directly read out using long signal lines as in the conventional device, but are Since the information is converted into information and sequentially transferred and read out, 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 photodiodes D ₁ to D _N are not read out via multiple long lines, but are converted into voltage information and the voltage information is transferred. Since it is being read, the signal level is high and 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 signals applied thereto, and FIG.
The figure shows a circuit diagram of a second embodiment of the present invention, and FIG. 4 shows a time chart of signals applied thereto. D ₁ ~D _N ...Photodiode, _S1 ~ _S2N-1 ...
Second signal transfer TFT, U ₁ to _{U 2N-1} ... shift switch TFT, V ₁ ... reset TFT.

Claims (1)

[Scope of Claims] 1. A signal readout device for a contact image sensor in which a plurality of photoelectric conversion elements are arranged in a row, comprising: a first signal transfer means connected to each of the photoelectric conversion elements; a second signal transfer means for sequentially transferring a plurality of pixel signals transferred by the signal transfer means; and a signal extraction amplifier connected to the second signal transfer means; The signal transfer means connects a first means comprising a plurality of elements for converting each of the pixel signals into a voltage signal, and a plurality of elements constituting the first means and synchronizes with a clock of a predetermined frequency. 1. A signal reading device for a contact image sensor, comprising a shift means that operates. 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. The signal reading device for a contact image sensor according to claim 1, wherein the second signal transfer means transfers a reset signal subsequent to the transfer of the pixel signal.