Large area infrared scene emitter RIIC

Details Large area infrared scene emitter RIIC Large area infrared scene emitter RIIC

1999-09-08

2002-10-15

Anderson, Bruce (Department: 2881)

Radiant energy

Radiant energy generation and sources

Plural radiation sources

C250S494100

Reexamination Certificate

active

06465798

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to resistively heated microemitter arrays, particularly to the incorporation of sample-and-hold, and snapshot circuitry into read-in-integrated-circuits (RIICs) for use with microemitter arrays.
BACKGROUND
Infrared (IR) scene generation is presently a critical technology for testing of IR imaging systems, for example in IR-guided missile systems. By artificially generating a changing IR scene and projecting it into the IR sensing system of a missile, the various performance elements of the missile can be evaluated in a laboratory setting, reducing the need for costly missile test firings. This same IR scene generation technology is also being adapted for portable field testing of missiles and FLIR (Forward Looking InfraRed) systems.
Two-dimensional arrays of resistively heated microemitter elements are one type of device used to create and display infrared scenes. A microemitter element is generally a small two-terminal thin film resistor, that is deposited onto a thin silicon nitride or silicon dioxide substrate, that is supported from a base structure by thermally insulating legs or posts that also typically provide electrical connections to supply current to the element. Fabrication typically employs micromachining technology.
To simulate an entire IR scene, it is desirable to integrate the microemitter elements into a two-dimensional array. For adequate resolution, the array typically contains at least
512
elements in each of the x and y dimensions.
FIG. 1A
is a perspective view illustrating for clarity a 3×3 array segment
100
of microemitter elements
102
. For this configuration, two electrical connections
104
are provided to each element. For example, an array segment
100
of 3×3 =9 elements
102
requires eighteen electrical connections
104
. Extrapolating the 3×3 array example to an array of 512×512 elements would produce a requirement for 524,288 electrical connections.
Emitted infrared power increases monotonically with increasing temperature. An electrical current through a specific emitter element
102
determines its temperature and therefore the infrared power that it emits. A single element
102
thus provides a single pixel (spatial resolution element) of an IR scene. By performing this process with every individual element
102
in an array, an infrared scene is generated pixel by pixel. The scene can then be updated at high speed to simulate a moving target that can be viewed by a remote IR imaging system.
A typical 512×512 microemitter array measures on the order of 30 mm on a side. Each emitter element
102
typically measures tens of microns on a side and has a dynamic range of several hundreds of degrees C. The temperature of the emitter element is proportional (to first order) to the power dissipated in the element. Therefore emitter element temperature has the same relationship as does the emitter element power dissipation to applied signal voltage. To attain the needed output temperature range, the range of currents supplied to an emitter element must be capable of changing dynamically by more than four orders of magnitude.
After the applied current is removed, a resistive emitter element cools by radiation and by heat conduction and/or convection through a surrounding gas atmosphere and/or mechanical support structure. The time constant for heating and cooling is typically a few msec, and can be selected by specifying the mass (heat capacity) of the emitter and the thermal conductance of the structure and surroundings.
To facilitate the required multiple electrical connections to emitter elements
102
, a read-in-integrated-circuit (RIIC)
106
is employed. This integrated circuit provides electronic timing and output signals to the emitter array, as well as electric interconnects and support structure for each emitter element
102
. RIIC
106
typically employs CMOS technology, and includes signal multiplexing, control, and power circuitry (see for example Cole et al., “512×512 WISP (Wide Band Infrared Scene Projector) Arrays,” SPIE vol. 2741, Orlando, Fla., 1996, p. 83).
As shown in
FIG. 1A
, emitter elements
102
are supported on RIIC
106
by thermally insulating legs, which also provide electrical connections
104
to the resistor body
108
(large central thin film deposition) of emitter element
102
. Emitted IR radiation is shown by arrows
110
from a representative resistor body
108
. Slots between adjacent emitter elements
102
minimize thermal crosstalk (i.e., pixel signal distortion caused by interelement heat conduction). Electrical connectors
104
can contact RIIC
106
directly or can contact supporting structures attached to that substrate (see Cole et al., U.S. Pat. No. 5,600,148, Issued Feb. 4, 1997).
It is desired for RIIC
106
to provide a unique signal voltage specific to each emitter element
102
, thus causing each element to emit a unique and controlled amount of IR radiation. This element-specific interface-circuitry is contained in a portion of RIIC
106
called a unit cell
112
. For a large array of emitter elements
102
, each supporting unit cell
112
typically is physically located directly beneath its respective emitter element
102
.
FIG. 1B
is a simplified block diagram of the major circuitry blocks associated with conventional RIIC
106
. Analog signal data are received at an analog signal interface
140
, and are distributed by an analog signal multiplexer
148
through column interconnect lines
114
to individual unit cells
112
as addressed by a column multiplexer
142
and a row multiplexer
144
. Unit cells
112
are configured in a two-dimensional array of unit cells
150
. Typically, analog signal interface
140
can consist of 32 or more parallel analog input lines, and analog signal multiplexer
148
can consist of 32 or more parallel multiplexers, each associated with one of a plurality of off-RIIC digital-to-analog converters (not shown).
FIG. 1C
is a simplified schematic block diagram of the conventional RIIC circuitry of
FIG. 1B
, showing an expanded view of two unit cells
112
,
113
. Unit cells
112
,
113
are configured identically and are located in the same column but in differing rows in array of unit cells
150
. In the architecture illustrated, analog signal interface
140
includes 32 parallel signal input lines. Column multiplexer
142
addresses analog signal multiplexer
148
, causing analog pixel data to load onto 32 parallel column interconnect lines
114
. Then row multiplexer
144
provides an address signal on a row enable line
124
, which momentarily closes a sample-and-hold switch
120
, charging a sample-and-hold capacitor
116
to a signal voltage V
1
in 32 representative unit cells
112
in a selected row. An appropriate combination of column multiplexers
142
and row multiplexers
144
provide addressing for other unit cells
112
in RIIC
106
. Again, according to conventional system architecture, no more than 32 unit cells can be addressed simultaneously.
Sample-and-hold capacitor
116
in the 32 representative unit cells
112
of the selected row is connected between a circuit ground node
130
and an input terminal of a transconductance amplifier
126
. The output terminal of transconductance amplifier
126
is connected to resistor body
108
of emitter element
102
through electrical connection
104
. Thus voltage V
1
on sample-and-hold capacitor
116
will give rise to a corresponding current
132
from transconductance amplifier
126
through emitter element
102
, heating the emitter element and generating infrared radiation (see FIG.
1
A). Current
132
will remain steady until the next row enable signal refreshes the charge on sample-and-hold capacitor
116
in the next frame cycle.
Prior emitter arrays that have been used for IR scene generation have updated their display information one line or a portion of a line at a time. A number of organizations (see for example Cole et al., SPIE 1996, cited above; Cole et al., “Recent Progress In Large Dynamic

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