Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1999-09-03
2004-02-03
Le, Vu (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S308000
Reexamination Certificate
active
06686959
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a drive process for photosensitive devices having a matrix of photosensitive points, of the type which are in particular produced by deposition techniques for semiconductor materials, and its object is to reduce or eliminate the remanence effect occurring in the photosensitive points. The invention relates more particularly (but not exclusively) to the driving of such devices which are used for the detection of radiological images. It also relates to a photosensitive device for implementing this process.
DISCUSSION OF THE BACKGROUND
The techniques for thin-film deposition of semiconductor materials such as hydrogenated amorphous silicon (aSiH) on insulating substrates, for example glass, make it possible to obtain matrices of photosensitive points which can produce an image from visible or near-visible radiation. In order to use these matrices for the detection of radiological images, it is sufficient to interpose a scintillator screen, between the X-radiation and the matrix, to convert the X-radiation to light radiation in the band of wavelengths to which the photosensitive points are sensitive.
The photosensitive points which form these matrices generally comprise a photosensitive element combined with an element fulfilling a switch function.
The photosensitive element commonly consists of a diode, connected in series with the switch element. The switch element may for example be a so-called switching diode whose “closed” or “on” state corresponds to the biasing which sets it in forward conduction, and whose “open” or “off” state corresponds to its reverse biasing. The two diodes are connected with opposite conduction directions, with a so-called “head-to-tail” configuration. Such an arrangement is well-known, in particular from French Patent Application 86 14058 (Publication No. 2 605 166) which describes a matrix of photosensitive points of the type with two diodes in “head-to-tail” configuration, a process for reading the photosensitive points, and a way of producing such a photosensitive device.
FIG. 1
represents a simplified diagram of a photosensitive device, having a conventionally organized matrix
2
. The matrix
2
has photosensitive points P
1
to P
9
, which are each formed by a photosensitive diode Dp and a switching diode Dc that are connected in series with a head-to-tail configuration. The matrix has row conductors Y
1
to Y
3
intersecting with column conductors X
1
to X
3
with, at each intersection, a photosensitive point connected between a row conductor and a column conductor. The photosensitive points P
1
to P
9
are thus arranged along rows L
1
to L
3
and columns CL
1
to CL
3
.
In the example in
FIG. 1
, only 3 rows and 3 columns are represented, which define nine photosensitive points, but such a matrix may have a much larger capacity, which may be as much as several million points. It is common, for example, to produce such matrices having photosensitive points arranged along 2000 rows and 2000 columns (in an area of the order of 40 cm×40 cm), or alternatively arranged along a single line and a plurality of columns in order to form a linear detection array, or else arranged along a single row and a single column in order to form a single photosensitive point.
The photosensitive device has a row drive circuit
3
whose outputs SY
1
, SY
2
, SY
3
are respectively connected to the row conductors Y
1
, Y
2
, Y
3
. The row drive circuit
3
has various elements (not shown) such as, for example, a clock circuit, switching circuits, and a shift register, which allow it to address the row conductors Y
1
to Y
3
sequentially. The photosensitive device furthermore has a voltage source
4
, supplying the row drive circuit
3
with a voltage VP used to define the amplitude of pulses applied to the row conductors.
In each photosensitive point P
1
to P
9
, the two diodes Dp, Dc are connected together either via their anode, or via their cathode as in the example represented. The anode of the photodiode Dp is connected to a column conductor X
1
to X
3
, and the anode of the switching diode Dc is connected to a row conductor Y
1
to Y
3
.
In the image-acquisition or imaging phase, that is to say the phase of illuminating the matrix
2
with a so-called “working” light signal, the two diodes Dp, Dc of each photosensitive point P
1
to P
9
are reverse-biased, and in this state they each constitute a capacitor. It should be noted that the two diodes Dp, Dc are generally designed so that the capacitance exhibited by the photodiode Dp is the larger (by of the order of, for example, 50 times).
During the exposure to a working light signal, the charges are generated in the photodiode Dp by the illumination of the photosensitive point P
1
to P
9
to which it belongs. These charges, the quantity of which depends on the illumination intensity, accumulate at a point “A” on the (floating) node formed at the junction point of the two diodes Dp, Dc. The photosensitive points P
1
to P
9
are read row by row, simultaneously for all the photosensitive points connected to a given row conductor Y
1
to Y
3
. To that end, the row drive circuit
3
applies a so-called reading pulse of a given amplitude to each row conductor Y
1
to Y
3
addressed; the row conductors which are not being addressed are kept at a reference potential Vr or standby potential, which is for example earth, and which may be the same potential as that which is applied to the column conductors X
1
to X
3
.
The possible accumulation of charges at the point “A” of a photosensitive point P
1
to P
9
leads to a reduction in the voltage at this point, that is to say a reduction in the reverse-bias voltage of the photodiode Dp. With certain operating modes, the application of the reading pulse to a row conductor Y
1
to Y
3
has the effect of restoring, to the potential of the point “A” of all the photosensitive points connected to this row conductor, the biasing level which it had before exposure to the working light signal: this results in a current proportional to the charges accumulated at the corresponding point “A” flowing in each of the column conductors X
1
to X
3
.
The column conductors X
1
to X
3
are connected to a reading circuit CL, in the example comprising an integrator circuit
5
, and a multiplexer circuit
6
which is formed, for example, by a shift register with parallel inputs and series output which may be of the CCD type (charge coupled device). Each column conductor is connected to a negative input “−” of an amplifier G
1
to G
3
connected as an integrator. An integration capacitor C
1
to C
3
is connected between the negative input “−” and an output S
1
to S
3
of each amplifier. The second input “+” of each amplifier G
1
to G
3
is connected to a potential which, in the example, is the reference potential Vr, which potential is consequently imposed on all the column conductors X
1
to X
3
. Each amplifier has a so-called resetting switch element I
1
to I
3
(consisting for example of a MOS-type transistor), connected in parallel with each integration capacitor C
1
to C
3
.
The outputs S
1
to S
3
of the amplifiers are connected to the inputs E
1
to E
3
of the multiplexer
6
. This conventional arrangement makes it possible to deliver “in series” and row after row (L
1
to L
3
) at the output SM of the multiplexer
6
, signals which correspond to the charges accumulated at the points “A” of all the photosensitive points P
1
to P
9
.
It should be noted that it is also known, in order to fulfil the switch function which, in the example in
FIG. 1
, is held by the switching diode Dc, to use a transistor; compared with a diode, the latter involves more complicated connection, but provides advantages in the quality of its “on” state, which advantages will be explained in the description below.
FIG. 2
schematically illustrates a photosensitive device
1
′ which differs from the one in
FIG. 1
principally in that it has a matrix
20
in which the switching diodes Dc are replaced by tra
Chaussat Christophe
Ducourant Thierry
Le Vu
Thomson Tubes Electroniques
Whipkey Jason
LandOfFree
Method for controlling a photosensitive device with low... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for controlling a photosensitive device with low..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for controlling a photosensitive device with low... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3341063