Contact-type linear image sensor

Claim 2

A contact-type image sensor comprising a linear array of amorphous semiconductor photoconductive cells (D1, D2, ..., Dnm) formed on a substrate (10), said photoconductive cells being divided into cell units (U1, U2, ..., Um) each of which has a predetermined number of cells, drive means (12, 14) connected to said photoconductive cells, for sequentially selecting said cell units, and for generating drive voltage signals for sequentially activating the cells of a selected cell unit, and signal readout means (S1, S2, ..., Sm, LO, 16) connected to said cell units, for generating a series of pixel voltage signals from pixel currents sequentially supplied from the cells of the selected cell unit, characterized in that said signal readout means comprises: a common signal output line (LO) connected to said cell units; capacitor means (CL) connected to said common signal output line (LO), for sequentially accumulating said pixel currents; and analog switch means (SR) connected to said common signal output line, for resetting said common signal output line every time one of the cells of each cell unit is designated after a pixel current read out from another cell adjacent to this cell has been accumulated in said capacitor means.

Claim 3

The image sensor according to claim 1, characterized in that said analog switch means comprises a switching transistor (SR) connected between said common signal output line (LO) and a reference voltage, and being driven and rendered conductive every time one cell of each cell unit is designated after a pixel current read out from another cell, adjacent to this cell, has been accumulated in said capacitor means, thereby to reset said common signal output line (LO) and initialize said capacitor means (CL).

Claim 4

The image sensor according to claim 2, characterized in that said signal readout means further comprises controller means (20) connected to said switching transistor (SR), for generating a pulse signal for controlling the switching operation of said transistor (SR).

Claim 5

The image sensor according to claim 3, characterized by further comprising noise-eliminating means (50, 50ʹ) connected to said common signal output line (LO), for sampling and holding a switching noise voltage corresponding to reset noise generated by said analog switch means (SR) and contained in each pixel voltage signal at an initial part of a signal readout period of the selected cell, and for detecting a difference between a voltage appearing on said common signal output line (LO) at a final part of the signal readout period and the switching noise voltage, to output said difference as an effective pixel signal, thus removing the reset noise from each pixel voltage signal.

Claim 6

The image sensor according to claim 4, characterized in that said noise-eliminating means comprises a sample-and-hold circuit (52) connected to said common signal output line (LO), and a differential amplifier (A1) having an inverting input connected to said sample-and-hold circuit (52), and a noninverting input connected to said common signal output line (LO).

Claim 7

The image sensor according to claim 5, characterized in that said sample-and-hold circuit includes second analog switch means (SC), connected between said common signal output line (LO) and the inverting input of said differential amplifier (A1), for performing a sampling operation, and a capacitive element connected to the inverting input of said differential amplifier (A1).

Claim 8

The image sensor according to claim 6, characterized in that said noise-eliminating means further comprises a second sample-and-hold circuit (54), connected to the output of said differential amplifier (A1), and a buffer amplifier (A2) having a noninverting input connected to said sample-and-hold circuit, and an output fed back to an inverting input of said buffer amplifier (A2).

Claim 9

The image sensor according to claim 7, characterized in that said second sample-and-hold circuit (54) includes third analog switch means (SS), connected between the output of said differential amplifier (A1) and the noninverting input of said buffer amplifier (A2), for performing a sampling operation, and a capacitive element (CH) connected to the noninverting input of said differential amplifier (A1).

Claim 10

The image sensor according to claim 4, characterized in that said noise-eliminating means comprises a first sample-and-hold circuit (52ʹ) connected to said common signal output line (LO), a second sample-and-hold circuit (54ʹ) connected to said common signal output line (LO), and a differential amplifier (A2) having an inverting input connected to said second sample-and-hold circuit (54ʹ), and a noninverting input connected to said common signal output line (LO), for functioning as a buffer amplifier.

Claim 11

The image sensor according to claim 9, characterized in that said first sample-and-hold circuit (52ʹ) comprises a holding capacitive element (CC) connected in series to said common signal output line (LO), and an analog switch (SC) connected to said signal-holding capacitive element (CC) and having one end connected to the reference voltage, for sampling an input signal.

Claim 12

The image sensor according to claim 10, characterized in that said second sample-and-hold circuit includes a sampling analog switch (SS) connected to said common signal output line (LO) by the signal-holding capacitive element (CC) of said first sample-and-hold circuit (52ʹ), and a capacitive element (CH) connected to the noninverting input of said buffer differential amplifier (A2).

Claim 13

The image sensor according to claim 4, characterized by further comprising a voltage-amplifying circuit (16) connected to said common signal output line (LO), for amplifying an image signal supplied from said photoconductive cells, and a plurality of analog switches (S1, S2, ..., Sm) provided between said cell units (D1, D2, ..., Dnm), on the one hand, and said common signal output line (LO), on the other.

Claim 14

A matrix-driven contact-type linear image sensor comprising an array of amorphous semiconductor photo­conductive cells (D1, D2, ..., Dnm) formed on an elongated substrate (10) and made of, said photocon­ductive cells being divided into a first number (m) of cell units (U1, U2, ..., Um) each having a second number (n) of cells which have first ends electrically connected to each other by a common wiring line (LA), and second ends, drive means (12, 14) connected to the second ends of the cells of each cell unit, for sequentially selecting a cell unit from among said cell units, and for generating matrix-drive voltage signals for sequentially activating the cells of a selected cell unit, and signal readout means (S1, S2, ..., Sm, LO, 16) connected to said cell units, for generating a series of pixel voltage signals from pixel currents sequentially supplied from the cells of the selected cell unit, characterized in that said signal readout means comprises: a common signal output line (LO) connected to said cell units; a first number (m) of selecting analog switches (S1, S2, ..., Sm) provided between said cell units, on the one hand, and said common signal output line (LO), on the other hand, and being sequentially rendered conductive; capacitor means (CL) connected to said common signal output line (LO), for sequentially accumulating said pixel currents, said capacitor means (CL) being an internal electrostatic capacitance including a coupling capacitance inherently present between said common signal output line (LO) and said substrate (10), and parasitic capacitance components of said selecting analog switches (S1, S2, ..., Sm); analog switch means (SR) connected to said common signal output line (LO), for resetting said common signal output line (LO) every time one of the cells of each cell unit is designated after a pixel current read out from another cell, adjacent to this cell, has been accumulated, thereby to initialize said capacitor means (CL); and noise-eliminating means (50, 50ʹ) connected to said common signal output line (LO), for sampling and holding a switching noise voltage corresponding to a reset noise generated by said analog switch means (SR) and contained in each pixel voltage signal, during a first part of a period for reading the pixel voltage signal from a cell, and for detecting the difference between said switching noise voltage and the voltage appearing on said common signal output line (LO) during the last part of the period for reading the pixel voltage signal from the cell, and then outputting this difference as an effective pixel signal, thereby to remove the reset noise from the pixel voltage signal.

Claim 15

A matrix-driven contact-type linear image sensor comprising an array of amorphous semiconductor photo­conductive cells (D1, D2, ..., Dnm) formed on an elongated substrate (10) and made of, said photocon­ductive cells being divided into a first number (m) of cell units (U1, U2, ..., Um) each having a second number (n) of cells which have first ends electrically connected to each other by a common wiring line (LA), and second ends, drive means (12, 14) connected to the second ends of the cells of each cell unit, for sequentially selecting a cell unit from among said cell units, and for generating matrix-drive voltage signals for sequentially activating the cells of a selected cell unit, and signal readout means (S1, S2, ..., Sm, LO, 16) connected to said cell units, for generating a series of pixel voltage signals from pixel currents sequentially supplied from the cells of the selected cell unit, characterized in that said signal readout means comprises: a common signal output line (LO) connected to said cell units; a first number (m) of selecting analog switches (S1, S2, ..., Sm) provided between said cell units, on the one hand, and said common signal output line (LO), on the other hand, and being sequentially rendered conductive; capacitor means (CL) connected to said common signal output line (LO), for sequentially accumulating said pixel currents, said capacitor means (CL) being an internal electrostatic capacitance including a coupling capacitance inherently present between said common signal output line (LO) and said substrate (10), and parasitic capacitance components of said selecting analog switches (S1, S2, ..., Sm); analog switch means (SR) connected to said common signal output line (LO), for resetting said common signal output line (LO) every time one of the cells of each cell unit is designated after a pixel current read out from another cell, adjacent to this cell, has been accumulated, thereby to initialize said capacitor means (CL); and noise-eliminating means (50, 50ʹ) connected to said common signal output line (LO), for sampling and holding a switching noise voltage corresponding to a reset noise generated by said analog switch means (SR) and contained in each pixel voltage signal, during a first part of a period for reading the pixel voltage signal from a cell, and for detecting the difference between said switching noise voltage and the voltage appearing on said common signal output line (LO) during the last part of the period for reading the pixel voltage signal from the cell, and then outputting this difference as an effective pixel signal, thereby to remove the reset noise from the pixel voltage signal.

Claim 16

The contact-type image sensor according to claim 13, characterized in that said noise-eliminating means (50, 50ʹ) comprises a sample-and-hold circuit (52) having an analog switch (SC) and a capacitor (CC).

Claim 17

The contact-type image sensor according to claim 13, characterized in that said noise-eliminating means (50, 50ʹ) comprises a sample-and-hold circuit (52, 52ʹ) having an analog switch (SC) and a capacitor (CC), and a differential amplifier (A1) connected to the sample-and-hold circuit (52, 52ʹ) and having an inverting input and a noninverting input.

Claim 18

The contact-type image sensor according to claim 15, characterized in that said capacitor (CC) is connected between the ground and the inverting input of said differential amplifier (A1).

Claim 19

The contact-type image sensor accoridng to claim 15, characterized in that said capacitor (CC) is connected in series to said common signal output line (LO).