Electronic addressing system to read mosaic matrices of optical-electronic elements

An electronic addressing system to read matrices of optical-electronic elements, wherein the optical-electronic elements are of any type, for example photoresistors, photodiodes, light emitters, and the like. The matrices are bi-dimensional and comprise optical-electronic elements arranged according to a row-column structure, without any auxiliary switching an/or commutating means connected therewith. One end of each one of the elements is connected with a corresponding row near each row-column crossover, and the other end is connected with the column related to the crossover. The switching of each one of the optical-electronic elements which is addressed for reading is obtained by an adaptive analog compensation technique, whereby only a single element is read out while all other elements are electrically isolated.

The present invention relates to an electronic addressing system to read 
mosaic matrices of optical-electronic elements of any type, for example 
sensors, light emitters, photodiodes, photoresistors and the like, which 
have a substrate of any dielectric material. The system is mainly 
characterized in being able to carry out addressing in a very short time, 
even in the case of elements having a very high impedance (&gt;&gt;1M .OMEGA.), 
without auxiliary physical switching elements, and can read out mono- or 
bidimensional matrices of any type, having any number of elements to be 
addressed. 
When, for example, reading is limited to sensor or detector mosaics, it is 
known that possible solutions relating to addressing mosaics of sensors 
have until now been limited to arrays of solid state sensors which are 
provided with a silicon substrate (or the like), wherein an auxiliary 
element having the characteristics of a switch (e.g. a diode, a MOS 
transistor, etc.) is used to insulate the selected sensor from the 
surrounding sensors by addressing the row-column cross-over position of 
the sensor to be addressed. Technicians and scientists have, for example, 
made modern image systems in solid state by using phototransistors of 
silicon oxide semiconductors (MOS), and in consequence of the high ON-OFF 
conduction ratio which is possible with field-effect transistors, a 
self-scanned ("integrated") commutation has been obtained (see M. H. 
Crowell et al, Bell Syst. Techn. J., 46, 491-1967). 
The most recent example of self-scanned commutation is due to the charge 
transfer scanning systems by silicon image systems which have many future 
possibilities. These structures, wherein a capacitor of MOS type is 
provided in a simple manner through a structure silicon-dielectric-metal 
gate, may be used as an integrating photoelement similarly to a photodiode 
(see M. H. Boyle & G. Smith, Bell Syst. Techn. J., 49, 587-1970). This 
photosensitive region is obtained by polarization of the metal gate in 
order to remove the free charges from the semiconductor surface. The 
so-called minority charges, which are provided by the active radiation 
under this structure, may be shifted sideways towards an adjacent 
electrode by using a clock voltage, and on the other hand this latter is 
able to maintain the depletion condition of the majority charges all over 
the semiconductor surface. 
This solution has, however, some limitations and drawbacks regarding its 
practical utilization. The limited applicability is principally due to the 
fact that such a solution is possible only when materials having proper 
characteristics of dielectric-semiconductor surface charges are used, and 
these materials, apart from silicon, are difficult to find. A first 
important disadvantage is the loss of transfer efficiency when the number 
of sensors increases (the sensors being the selected representative 
example of optical-electronic elements included in the field of the 
present invention, as said above, while a further disadvantage is the 
dispersion of information in the blooming contour. 
In the particular case of bi-dimensional mosaics, wherein the elements 
comprise sensors of infrared radiation, and when devices are used for 
which a cryogenic cooling is necessary, then it is particularly desirable 
and important to provide electrical scanning elements which are arranged 
outside the substrate wherein the photoelements have been provided. 
Namely, great importance is to be attributed to the possibility of 
providing an addressing system of the single elements with an electronic 
reading which may be set in any desired place. 
The attention of the skilled in the art has already been devoted to the 
solving of such a problem considered at first sight very difficult because 
of the necessity to provide insulating elements in a dynamic sense between 
the element to be read and those other elements which are arranged around 
same. That is to say, no alternative solution has until now been found 
with respect to the above considerations. 
A main object of the present invention is to provide an electronic reading 
system arranged outside the matrix of optical-electronic elements to be 
scanned, wherein the matrix comprises any number of elements. 
Another object of the present invention is to allow the reading of a mosaic 
matrix of optical-electronic elements (which may be sensors of radiation 
in order to simplify the description and illustrate an exemplary 
embodiment) the number of which may be very high, such a matrix using any 
desired dielectric material as a substrate, and following any desired 
technology, which utilizes electrodes having a row-column structure. 
A further object of the present invention is to provide such a mosaic 
matrix which comprises photosensitive elements only; that is, a mosaic 
wherein no insulating element is used. 
A still further object of the present invention is to provide a circuit 
which allows the sequential scanning of matrix structures of above type 
with very high performance relating to: the electronic insulation between 
the one selected sensor and the other sensors; the intrinsic noise of the 
electronic circuitry; and, the reading speed. 
Another object of the present invention is to provide a relatively simple 
reading method which allows the arrangement of the greatest amount of 
active elements (particularly the pre-amplification units) in the 
immediate proximity of the sensor matrix. 
From the previous statement referring to the present technique in the field 
of reading and addressing of matrices of optical-electronic elements, as 
well as from the above objects of the present invention, it should be easy 
to the skilled in the art to understand advantages of such a practical 
realization which may overcome the limitations and drawbacks which have 
been proposed until now by present technology. In order that the invention 
may be better understood in relation to its most important innovative 
characteristics, an embodiment of same will now be described with 
reference to the accompanying drawings. The description refers to an 
illustrating exemplary embodiment of the invention and is not to be 
intended as a limitation thereof. Modifications and/or changes may be made 
by the skilled in the art when supposed as more suitable for particular 
applications. And these modifications and/or changes are also to be 
included within the scope of the claims when based on the ground 
principles of the invention.

Referring now to the drawings, FIG. 1 shows a schematic partial view of a 
matrix 10 of units 11 of sensors 12 with respective insulating element 13 
according to a conventional manner, the connections in a row-columns 
structure having a sequence of rows a, b, c, . . . and columns A, B, C, . 
. . wherein each unit generally indicated by the reference numeral 11 is 
substantially formed by a resistive element R.sub.a-A, R.sub.a-B, . . . 
R.sub.b-A, R.sub.b-B . . . as well as by a corresponding insulating 
element or switch S.sub.a-A, S.sub.a-B . . . , S.sub.b-A, S.sub.b-B . . . 
. 
A set of like resistive elements R.sub.L is provided at the end of each row 
a, b, . . . as a part of row selector (reading circuit) A1, with node 
X.sub.a, X.sub.b . . . preceding said resistive elements R.sub.L of each 
row as a point which is suitable to take out the information from a sensor 
R.sub.i-K having one end connected with row i, while its other end is 
connected with an insulating element S.sub.i-K, which in turn is connected 
with column K. All the columns have their ends in column selector 
(addressing circuit) B1. 
The problem of reading out information from sensor R.sub.i-K of a 
photoresistive type as hereabove supposed is actually very complex, above 
all in the case of high intrinsic impedance, which in addition is almost 
always real. This complexity is above all due to the insulating elements 
S.sub.i-K which follows the respective photoresistive element R.sub.i-K in 
accordance with the techniques of the present time, as schematically shown 
in FIG. 1. 
A very simple but functional circuit has been used satisfactorily, a 
diagram of which is shown in FIG. 2. The following characters are used, 
namely: R.sub.L the load resistor having a common value and referred to 
resistive elements of the information circuit; R.sub.x the resistance of 
the addressed photoresistive element; V.sub.B the supply voltage; v.sub.i 
the information voltage. It is first of all possible to say that the 
maximum sensitivity is obtained when R.sub.L =R.sub.x. In these 
conditions, the partial differential of the information voltage is maximum 
and may be deduced from the following equation: 
##EQU1## 
There are, however, some actual limitations to selecting R.sub.L =R.sub.x 
which depend on the noise as well as on the very high impedance that the 
acquisition system of the analog datum must have. Furthermore, a notable 
limitation is due to the response time of the impulsive excitation system 
which could probably set up the main aspect of the problem. 
Such a simple arrangement cannot have the possibility of an immediate 
accomplishment because of the huge complexity resulting from the increase 
in the number of sensors, so that the request of the users is opposed. 
Actually, research on information in sensor mosaics should be directed to 
matrices having a very high number of sensors in respect to the present 
technique, even greater than 1000. 
Sensor structures are arranged in a matrix (n.times.m), wherein the limited 
number of wires (the main source of circuit complexity) is evidenced. This 
relative simplicity is found in the construction of a planar structure 
having photoresistive elements deposited upon a substrate of any type and 
connected as differentiated bus which are just forming the characteristic 
row and column wires, so that one or more wires may be used as a path to 
transmit the information from any of the many sources to any of many 
destinations. 
To this innovative purpose of the present invention, i.e. the use of 
matrixes having high density with (n.times.m) sensors, another feature has 
been added which relates to the acquisition of the necessarily sequential 
information voltage v.sub.i, by insulating [n.times.(m-l)] sensors in a 
desired moment t.sub.i. That is to say, no information is requested of 
these sensors, while only sensor R.sub.i-K is addressed, as only this 
latter is considered important for reading purposes in the moment t.sub.i. 
Such an acquisition of information voltage v.sub.i has been an object of 
analysis and research by those skilled in the art, but considered however 
as a problem which is substantially not resolvable. A not so valid 
solution concerns, for example, the arrangement of as many junctions (p-n) 
on a silicon substrate as there are photosensitive elements, in order to 
embody a matrix of diodes, each one in series connection with a 
corresponding photosensor, the photosensors being, in turn, provided by a 
process of deposition upon another insulating substrate which is placed 
above said diodes. 
It will be evident to those skilled in the art that such a method could be 
possible for sensor mosaics having only a limited density. Moreover, a 
very long stabilization time will be needed because of the high impedance 
of the sensors, so that the equivalent time constants will be very long, 
while using diodes having low doping junctions and consequently limited 
capacities of transition. 
There have been two possible solutions suggested by techniques until now 
for systems of photoresistive sensors of radiation, both solutions having 
however a low degree of functionality. According to a first solution, a 
simple diagrammatic circuit of which is shown in FIG. 2., it is necessary 
to repeat (n.times.m) times said simple circuit. This shows that the 
efficiency of the addressing system is limited to mosaics having a rather 
low sensor number, no more than one hundred. As a matter of fact, when 
this number is increased, the structure complexity will also be increased 
in a drastic manner, which is in contrast with what has been reported 
above. In the second prior art solution, an arrangement is provided of the 
(n.times.m) matrix sensors, wherein each sensor is connected in series 
with a diode to obtain a sufficient electric insulation, like the symbolic 
illustration in FIG. 1. Notable disadvantages are also found in this 
second solution, namely: intrinsic limitations of the scanning velocity; 
complexity of the technological realization; and lack of practical 
convenience in using photoresistive elements only, which are produced upon 
silicon substrates. 
The present invention finally solves the above problems in a completely 
novel manner. 
First of all, there is provided an array of (n.times.m) sensors in a 
matrix, wherein (m-l) sensors of each matrix row which are not addressed 
for information at a desired moment t.sub.i have a positive feedback. This 
is for the purpose of making their output equal to zero and for 
stabilizing the response to the incident radiation in a very short time. 
The stabilization time is essentially dependent on static parameters. 
The basic diagram of such a matrix as well as the provided systems of 
amplification, commutation and feeding to allow the addressing and reading 
of the apparatus will be described hereafter, with reference to FIG. 3. 
As evidenced in FIG. 3, which is clearly different from a conventional 
matrix according to FIG. 1, the novel system of addressing comprises 
sensors R'.sub.a-A, R'.sub.a-B . . . R'.sub.b-A, R'.sub.b-B . . . , 
wherein one end of the photoresistor is directly connected to the proper 
row of the matrix and the other end is connected with the respective 
column, no physical elements of switching being provided as intermediate 
elements. 
Similar to FIG. 1, the end of each row which is directed to the reading 
system is connected with a resistive element R'.sub.L, the resistance 
being equal for all the rows a, b, . . . . A point X.sub.a, X.sub.b . . . 
of the rows is selected to take out the information from one of the 
sensors, e.g. R'.sub.i-K relating to the row i and column K, to be 
addressed. 
It may be assumed, for example, that the scanning operation desires to 
interrogate the sensor R'.sub.i-K and detect the voltage v.sub.i-K in 
point X.sub.i. The addressing and reading system in accordance with the 
present invention provides, first of all, power amplification of the 
v.sub.i-K voltage, by means of pre-amplifying units D1 of low-noise type 
which are realized by a hybrid technology and placed very near the sensors 
of the matrix, so that the noise figure will be particularly low, as the 
output noise voltage may also be &lt;20.mu. VRMS. 
The so amplified voltage v.sub.i-K is then passed to a switching and 
compensation system S1-C1. This is provided by an intermediate signal 
switching network S1 and an active compensation network C1, the scope of 
which is to recover the losses due to gain error of the preamplifying 
units D1, as well as the voltage drops localized on the equivalent 
resistors of the switching devices of intermediate network S1, so that 
voltage v.sub.i-K may be restored to its value as detected at the node 
X.sub.i. The restored voltage v.sub.i-K so reintegrated is then sent to 
the remaining (m-l) columns through the switching network C2, as the 
column K which has been selected for addressing and reading is connected 
with the supply voltage through C2. 
It should be clear to those skilled in the art that, at the reading moment 
t.sub.i, the row i will have (m-l) sensors R' with an equal voltage at 
their ends, while sensor R'.sub.i-k which is the only one selected for 
reading has a voltage equal to the divided voltage between same and the 
common load resistor R.sub.L. 
That operative condition may be considered like the assignment of an 
impedance equivalent to infinity (practically, an impedance of a very high 
value) to the [n=(m-l)] sensors not being selected for reading. That is, 
those non-selected sensors will make no effective contribution to the 
voltage output. 
The structure, which naturally should be nonoscillating, spends a finite 
time to reach the equilibrium state. Referring to common values of the 
parameters which characterize the equivalent circuits of the active 
components used in the circuit, such a time was found to be shorter than 
one .mu.sec, which time is more than acceptable for usual practical 
purposes. 
On the basis of practical experiments, it may also be shown that, by 
improving a hybrid complex of circuit structures by means of active 
components having optimum features, the matrix density may be &gt;&gt;1000 for 
each structure and the number of information wires as well as the 
complexity of the structure in its whole may consequently reach a 
reduction of about 97%. This result is very remarkable and favors the 
embodiment of sensor mosaics of high density, wherein photoresistive 
sensors of a self-scanning type may be used with built-in highly efficient 
circuit system of preamplification. 
On the basis of principles forming the present invention, it is furthermore 
possible to reach high densities of mosaics of photoresistive elements for 
those applications wherein structures with two or more component subarrays 
are required, each substructure having a limited density of photoresistive 
elements. In this manner, however, the circuit structures will be a little 
more complex. There is, however, the advantage of providing systems having 
a remarkable degree of functionality and above all a high reliability. For 
example, the isolation between sensors pertaining to the same row is found 
to be very high, and the isolation between sensors of different rows is 
even higher. 
In other embodiments, when the highest isolation is desired between sensors 
of same row, it was found advantageous to provide matrix structures 
wherein the number of rows and the number of columns are different to each 
other, that is m.noteq.n, and the former may be greater than the latter or 
vice versa. 
It is noted that switching devices S1, SW1 and SW2 need not operate in 
perfect unison. Only the SW1 and SW2 subunits must operate in unison e.g. 
by means of complementary control device (not shown) with the same clock 
timing. Further, the plural contacts of the switching device SW2, the 
compensation de-multiplexer, is selectively switched by means of digital 
logic devices (not shown).