Sense and inject moving target indicator apparatus

A moving target indicator apparatus utilizing charge injector device (CID) sensors to detect the presence or absence of a moving target. A signal from a possible target site in the sensor array is measured during a flow scan and is processed with the signal return from a second scan to determine absence or presence and direction.

BACKGROUND OF THE INVENTION 
The present invention relates broadly to a moving target indicator 
apparatus, and in particular to a sense and inject moving target indicator 
apparatus. 
In the prior art, the signl processing for moving target indicators (MTI) 
is remote or off chip with respect to the MTI unit. In the memory unit, 
the signal from each site in field one is stored, and then compared with 
the signals from field two. This method of signal processing requires a 
good deal of memory, especially if a large number of bits are required and 
utilized. The sense and inject method uses the sensing array itself as the 
memory. With this method it is possible to use MTI cells of special design 
in which the charge from the first field is collected and stored in an 
adjacent storage pad. After the second field charge is collected, the two 
charge packets may be differentially compared. Although the use of the MTI 
cell in this manner looks attractive in principle, the fabrication of an 
array of such cells would be extremely difficult and costly. The present 
sense and inject apparatus accomplishes the same on-chip storage with a 
conventional CID cell and does not require difficult fabrication 
processes. 
SUMMARY OF THE INVENTION 
The present invention utilizes a sense and inject moving target indicator 
(MTI) apparatus in conjunction with charge injector device (CID) sensors 
which is capable of yielding a signal that is the difference between the 
charge collected during the first and second fields. The sense and inject 
apparatus measures the signal at a site after the first field, and 
re-introduces the complement of the field one signal, by injecting twice 
the charge collected in the first field from a reference charge in the 
site. After integrating for the second field, the combined signal is 
measured. If the charge collected during the two fields is the same, the 
net signal is zero. If different, the signal will be positive or negative 
depending upon whether the target moves into or out of the site. 
It is one object of the present invention, therefore, to provide a new and 
improved sense and inject moving target indicator apparatus. 
It is another object of the invention to provide a new and improved sense 
and inject moving target indicator apparatus utilzing charge injector 
device sensors to determine a moving target presence or absence. 
It is still another object of the invention to provide a new and improved 
sense and inject moving target indicator apparatus wherein the signal and 
twice its complement are combined with a second signal to provide a moving 
target indication. 
It is yet another object of the invention to provide a new and improved 
sense and inject moving target indicator apparatus which is economical to 
produce and utilizes currently available components that lend themselves 
to standard mass production manufacturing techniques. 
These and other advantages, objects and features of the invention will 
become more apparent after considering the following description taken in 
conjunction with the illustrative embodiment in the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the FIGURE there is shown a sense and inject moving target 
indicator apparatus wherein the inject unit 10 is connected to the CID 
(charge injector device) array 14 which in turn is shown connected to the 
sense unit 12. The inject unit 10 comprises a plurality of adder and 
difference units which are arranged to provide the voltage potentials 
shown on the respective output lines labelled set 1, 2 and 3. The CID 
array 14 is represented by a plurality of lines in which the sensor units 
(not shown) are arranged to form a matrix. The CID array 14 includes a 
reference row and a transistor gate for each of the plurality of sensor 
lines. The transistor gates are connected to a shift register (not shown). 
The sense unit 12 is connected to receive signals from the reference row 
which may be read differentially with any one selected sensor row of the 
CID array unit 14. 
The operation of the present apparatus will be more fully understood and 
explained in the following example. The present apparatus is called the 
sense and inject apparatus because the storage is accomplished by 
injecting at each CID array site a charge that is twice the first field 
charge at the site. After second field integration, the detected signal 
will be zero at the site if the optical signal has been invariant during 
the two fields. The present sense and inject MTI (memory target indicator) 
apparatus requires an opaque reference row such that each active row may 
be compared differentially with the opaque row in order to obtain 
cancellation of any fixed pattern noise which may be introduced by 
feed-through of the column drive pulses. However, in order to be able to 
inject a charge which is equivalent to the first field signal, a large 
bias charge must be present in all the sites on the CID array. The amount 
of signal injected depends upon the specific site capacitance which may 
vary due to site area and oxide variation. A voltage applied to the column 
drives may inject different amounts of charge from each site and thus, 
these variations will introduce an uncertainty into the stored signal 
charge. However, this uncertainty can be reduced by rereading the stored 
charge and adjusting the stored charge by successive injections. The 
corrected sense and inject apparatus operates on the principle that a 
charge packet can be sensed more accurately than it can be set. It is 
believed that two corrections are needed to restore the field one signal 
charge. Furthermore, the initial bias charge must be set accurately and it 
therefore, requires two corrections. The wells in the CID array would be 
filled by flashing a light at the beginning of the cycle. Since there is 
no simple way of adding charge after the initial light flash, it is 
necessary to approach the desired bias charge levels by injecting 
increments of charge, being careful not to overshoot the desired charge 
level. As a result, the initial injection must always be less than the 
desired level by the expected uncertainty due to capacitance variations. 
Thus, it may be clearly understood that the present apparatus is based 
upon the premise that it is possible to read, non-destructively, and with 
high precision the difference in the voltages on two lines, one a 
reference row and the other a selected row from the imaging array. This 
difference voltage may then be used to correct the charge on the selected 
row to make it read the same as the charge on the reference row. The 
reason for the use of a reference row, rather than a simple reference 
voltage, is to achieve the advantages demonstrated by differential 
readouts in rejecting electrical interference signals that are coupled 
into the rows. The present apparatus operates in the specific manner set 
forth by performing the following steps: 
(1) All wells are filled (a light is flashed). 
(2) Charge is set in a reference row by injecting to a voltage V.sub.1 
-V.sub.o. 
(3) Charge is set in the selected row by injecting to voltage V.sub.1. 
V.sub.o is selected so that, at every array site, the charge will exceed 
the charge at any site in the reference row. This is required because the 
array charge will be adjusted to be equal to the reference charge in the 
same column and it is only possible to reduce charge. 
(4) The reference row and selected row are read out differentially. 
(5) As each column site is read, the differential voltage is observed, 
multiplied by a gain factor, and an approximately equivalent charge is 
injected from the selected site. Since an injection voltage .DELTA.V 
results in a charge change .DELTA.Q=C.DELTA.V, and this results in a 
change in output voltage of approximately .delta.V=.DELTA.Q/C.sub.output, 
it is clear that the gain should be approximately 
.DELTA.V/.delta.V=C.sub.out /C, where C is the site capacitance. 
(6) After such a correction the differential voltage is read again and, if 
necessary, a second correction can be made. It is obviously essential to 
have remembered the first correction since charge is injected only by 
successively decreasing the gate voltage. Thus, the nth injection voltage 
is 
EQU V.sub.n =V.sub.1 +.DELTA.V.sub.1 +.DELTA.V.sub.2 --+.DELTA.V.sub.n-1 
where the .DELTA.V are calculated from the readout differential voltages. 
It is believed that two corrections are required to achieve 100 electron 
accuracy. 
(7) Having established reproducible bias charges through the array (all the 
charges in a column will be equal to the reference charge in that column), 
the array is allowed to integrate the first field. 
(8) The array is read out, site by site. For each site the differential 
output voltage (the first field signal) is temporarily stored. 
(9) A correction to the injection voltage (again G.delta.V.sub.1) is 
generated and the first attempt to set Q.sub.R -Q.sub.1 is made by 
injecting to V.sub.1 +G.delta.V.sub.1. It turns out, however, that some of 
the charge will be inaccessible unless a d-c offset voltage is also 
included. This should be about 2.times.V.sub.o. Thus the first injection 
voltage, after field 1, is 
V.sub.1 -2V.sub.o +G.delta.V.sub.1 ; wherein V.sub.1 and V.sub.o are 
negative in P-channel devices. 
(10) The reference row and selected row are read differentially, yielding 
some residual voltage, presumably negative (i.e., there will be less 
charge in the selected row than in the reference row). This is multiplied 
by the gain and added to -2V.sub.o +G.delta.V. The net will be further 
added to yield the next injection voltage: 
V.sub.1 -2V.sub.o +G.delta.V.sub.1 +(-2V.sub.o +G.delta.V.sub.1 
+G.delta.V.sub.2). 
(11) A further iteration may be necessary. 
(12) The second field is integrated. 
(13) The array is read out in a normal manner and the bias voltage 2V.sub.o 
subtracted. Only the difference charge -Q.sub.1 +Q.sub.2 results in an 
output signal. 
Although the invention has been described with reference to a particular 
embodiment, it will be understood to those skilled in the art that the 
invention is capable of a variety of alternative embodiments within the 
spirit and scope of the appended claims.