1964 PROCEEDINGS O F THE IEEE 1731

by a more sophisticated >IT1 technique. These reduc- tions in the size and weight of a typical radar receiver can be obtained by the hybrid thin-film approach a t a production cost equivalent to standard component equipment. In large quantities, such a receiver can be produced at a cost below that of its equivalent MIL- type component system.

TABLE 11 INTEGRATED ELECTRONIC RADAR RECEIVER

I Present R-979/UPS-l I Microelectronic Receiver

Volume Weight Circuit Types Adjustments

Trimmer Panel 1

12 ,OOO in3 150 Ib 100

I 10

100 in3 4 lb

20

9 6

ACKNOWLEDGMENT The authors acknowledge the helpful guidance re-

ceived from Commander R. E. Bodamer and Com- mander D. J. Yuengling of the Office of Naval Research Washington, D. C., J. W. Brush, J. A. Cauffman, Com- mander B. D. Williams, S. D. Keim, and A. B. Sahagian of the Navy Bureau of Ships, Washington D. C., J.

Purdy of Rome Air Development Center, Rome, N. Y . , J. J. Donovan of the Department of Defense, Washing- ton, D. C., and W. Shiff of Ft. Monmouth Signal Corps Laboratories, Red Bank, N. J.

The authors also acknowledge the efforts of the engi- neers of the Solid State Technology Section of the West- inghouse Surface Division.

REFERENCES [I] “Ultra-Reliable Tactical Command Transceiver,” Office of Naval

Research, Washington, D. C., Contract NOnr-4189(00)-DOC-9;

[2] Study of Fabrication of Microeleponic Assemblies for Fre- luly, 1963.

quency and Time Control Systems, Bureau of Ships, Washing- ton, D. C., Contract NObsr 87593; June, 1962.

[3] “Lightweight Techniques Study for AN/UPS-1 Class Radars,” Bureau of Ships, \\’ashington, D. C., Triservice Contract NObsr

[4] E. F. Horsey and P. J. Franklin, “Status of microminiaturiza- 98533; June, 1963.

tion,” IRE TRANS. ON COMPONENT PARTS, vol. CP-9, pp. 3-19; March, 1962.

[SI D. C. Englebart, “Microelectronics and the Art of Similitude,” 1960 Internat1 Solid-State Circuits Conf. Digest, p: 76.

[6] J. J . Suran, Circuit considerations relating to microelectronics,”

A. P. Stern, “Some general considerations of microelectronics, PROC. IRE, vol. 49, pp. 420-429; October, 1960.

1960 Proc. Nat’! Electronics Conf., vol. 16, pp. 194-198. [7] J . D. Meindl, Power Dissipation in Microelectronic Transmis-

sion Circuits,” Proc. 5th Mil-E-Con Conf., IRE PROF. GROUP ON

[8] “A Guide Manual of Cooling Methods for Electronic Equipment,” MILITARY ELECTRONICS, pp. 4-16; June, 1960.

Dept. of the Navy, Bureau of Ships, NAVSHIPS 900, 194, U. S. Govt. Printing Office; April, 1964.

Application of Molecular Engineering Techniques to Infrared Systems

C. P. HOFFMAN, MEMBER, IEEE, AND R. F. HIGBY

Summary-This paper presents basic design details and con- cepts used when applying molecular engineering techniques to the development of a high-performance infrared subsystem using a mosaic detector. Some of the advantages of using mosaic detectors are discussed. In many aerospace applications the size, weight, reli- ability, and power consumption requirements of the redundant circuits required with a mosaic detector cannot be met with conven- tional components. New techniques were developed to obtain high- performance molecular circuits that were applied in a subsystem con- cept to demonstrate that mosaic subsystems were practical. Details of the individual circuits and the over-all subsystem are described.

INTRODUCTION HE T R E N D in aerospace applications of infrared systems is toward high sensitivity, search rates, tracking accuracy and reliability simultaneously

work was supported by the Electronic Technology Division, Avion- Manuscript received June 3, 1964; revised August 24, 1964. This

ics Lab., Rright-Patterson AFB, Ohio, Contract AF33 (616)-8449 directed by J . B. LaGrange.

Defense and Space Center, Baltimore, Md. The authors are with the Aerospace Division, Westinghouse

with lower weight, volume, and power consumption. I t was the purpose of the program described herein to demonstrate the advantages derived from the applica- tion of molecular engineering techniques to achieve these goals when using IR equipments having mosaic detectors. In such applications, the size, weight, relia- bility and, in some instances, power consumption re- quirements cannot be met with conventional compo- nents.

An I R subsystem with a mosaic detector can continu- ously surveil a wide field-of-view with many individual detector elements thereby eliminating mechanical scan- ning. Detection sensitivity is enhanced by v’T, where N is the number of detector elements, when compared to a single detector covering the same field-of-view. The small size of the detector elements enhances resolution and background discrimination, and the electronics can be designed for multiple target tracking. By making use of molecular circuits, the multiple channel amplifiers

1732 PROCEEDINGS O F THE IEEE December

( IR preamplifiers) and signal processing circuits become practical with small size, weight, and high reliability.

A fully molecular I R subsystem, designed for the use of a 100 element mosaic detector, was developed and has the performance parameters given in Table I. The 100 elements and their associated signal amplifiers (channel amplifiers) adequately demonstrate the advantages of using molecular circuits in IR subsystems with mosaic detectors. Advances in the fabrication technology of mosaic detectors make mosaic detectors with more than 100 elements feasible. Molecular circuit technology im- provements make systems based on the use of mosaic detectors practical for aerospace applications.

TABLE I

detector acts as a reticle, and a signal of alternating polarity is obtained when a point target image is nutated on the mosaic detector. A molecular circuit channel amplifier is used with each detector element to provide separate amplification channels associated with that element. I t is in this application that the advan- tage of the molecular circuit over a conventional com- ponent counterpart becomes most evident.

The IR channel amplifier shown in Fig. 2 was designed using five of the basic stages in an RC coupled circuit. All of the channel amplifiers provided the desired tem- perature stable-gain characteristics of 93 1 db with less than 5 mw of power dissipation when using a single supply of +6 volts dc. Comparable gain character- istics were also demonstrated with a Dower dissiDation of

SYSTEM PAR-4lrETERS 1 mw by reducing the supply voltage. These channel _ _ Field-of-View 0.4"/Element

grams and could be designed for a maximum total power approximately 30 cubic inches, weigh less than 1500 1 x lo-'* c ) Cooled Lead Selenide a t 4.3 Microns

5 x 10-14 veloped, the associated amplifiers could be packaged in b) Cooled Lead Sulfide a t 2.5 Microns fore, if a system using a 1000 element mosaic were de-

5 X 10+ a ) Uncooled Lead Sulfide a t 2.5 Microns Sensitivity (Q'atts/cm*nep)

1 Mil rms cubic inch and weigh less than 1.5 grams each. There- Tracking Accuracy amplifier packages, including leads, occupy less than 0.03

Power Input 6.2 Watts

SUBSYSTEM DESCRIPTION A functional block diagram of the molecular IR sub-

system developed to demonstrate that the use of molecu- lar techniques is both feasible and practical is shown in Fig. 1.

All of the electronics circuits used in the subsystem were obtained almost exclusively by using a basic stage developed on the program. Standard functional blocks for linear circuit application were not readily useable in the subsystem due to considerations of low noise, high gain, temperature stability, and power dissipation, espe- cially when considering the channel amplifier require- ments. With the individual stages developed i t was possible to obtain input impedances up to 400,000 ohms, noise figures of 2 db, stable voltage gains over 20 d b with a power dissipation of less than 10 pw. These stages have been used to obtain the channel amplifiers, dc amplifiers, Schmitt triggers, flip-flops, and other spe- cial purpose ac amplifiers.

This IR subsystem has two primary modes of opera- tion: a course track mode, which includes acquisition, and a fine track mode. When a target is detected on any element but the center four, the system performs similar to bang-bang servo in that error signals generated by the guidance logic in the diode matrix are one-sided and tend to drive the target to the center of the mosaic. The de- tection of the target on any one of the four center mosaic elements initiates the fine tracking mode, and differential error signals are obtained which are driven to a null.

During both modes, infrared radiation is collected by the optics and nutated on the detector. This nutation is accomplished by wobulating the folded secondary mirror which is mounted on the end of a resonant beam and provides nutation without rotation at a rate equivalent to 50,000 rpm. The electrode pattern of the

dissipation of 1 watt. The diode matrix a t the output of the channel am-

plifiers performs a number of functions. I t is used to es- tablish a threshold for the amplified detector noise to ob- tain sensitivity enhancement; i t provides polarity to the - tracking error signal; i t provides a separate output from each channel for the AGC circuit; and the center four ele- ments have additional diodes to provide a switching signal.

The same diodes are used for sensitivity enhancement and to provide the tracking error signals. Four summing points are used to obtain up and down elevation and left and right azimuth tracking error signals. These tracking error signals are demodulated and amplified by the differential dc amplifiers shown in Fig. 3. A typical dc amplifier has an open-loop gain of 230,000, a closed- loop gain of 400, an input impedance approximately 1 megohm, an output impedance less than 100 ohms, and dissipates no more than 200 mw. The outputs of these dc amplifiers were used in a simulated electronic servo system (not shown) to provide tracking guidance.

Separate outputs from each channel, provided for the AGC circuit, are summed a t a common point, demodu- lated and amplified by a dc amplifier similar to the unit shown in Fig. 3. The output of the AGC dc amplifier is applied to a transistor which controls the mosaic de- tector bias current. Thus i t is possible to reduce the de- tection sensitivity on strong signals and thereby maintain the outputs of the channel amplifiers relatively constant. This permits better tracking accuracy.

When an IR signal is detected on any one of the center four elements and the fine tracking mode com- mences, an additional signal is obtained from separate diodes associated with those channels.

This signal is used to operate a switching circuit shown in Fig. 4 which includes an additional dc ampli-

1963 Hofman and Higby: Appl icat ion of Xolecular Engineering Techniques to Infrared Systems 1733

Fig. 1-Functional block diagram of molecular subsystem.

Fig. 2-Molecular IR channel amplifier. Fig. 3-Differential dc amplifier.

L---,-,--------- -&J

Fig. 4-Molecular switching circuit.

1734 PROCEEDINGS O F THE IEEE December

AMPLITUDE B Fig. 5-Nutation driver circuit.

1964 Hofman and Higby: Application of Molecular Engineering Techniques to Infrared Systems 1735

fer, a Schmitt trigger, and a switching transistor. Signals from the center four elements are amplified until the threshold of the Schmitt trigger is exceeded which then operates and controls the switching transistor. This transistor removes B+ from all the channel amplifiers but the center four and thereby reduces the field-of-view during the fine track mode. If the target is lost for any reason, the system automatically reverts back to the ful l acquisition or course track mode.

One of the more complex circuits used in the sub- system is the nutation driver circuit shown in Fig. 5 that is used to form a closed-loop oscillator with the resonant beam of the nutation transducer to which the secondary mirror is mounted. The circuit consists of a high-gain ac amplifier, an AGC circuit, phase shifting circuits to ob- tain quadrature outputs, and the driver stage. High ac gain is used to obtain amplified noise pulses to overcome the initial inertia of the resonant beam and make the complete oscillator self-starting. X strain gage mounted on the beam senses the motion and provides a signal to the input of the driver unit, thereby closing the loop. This signal is amplified and continues to drive the beam to resonance. As the beam approaches resonance, the feedback increases and an AGC circuit begins to reduce the ac gain to prevent the drive from becoming excessive. The nutation transducer has four electromagnets spaced 90 degrees apart to which the quadrature drive signals are applied. These attract and repel permanent magnets mounted on the secondary mirror which causes the mirror to nutate.

The output stages operate similarly to synchronous switches with one energized while the other is off. This circuit is very efficient, approximately 93 per cent, as the only lossesare in the transistors, battery, and leads. Total power dissipation of the nutation driver is 3 watts. When operated over a -2OOC to +70°C temperature range, the output power varies only 3 per cent.

The completed engineering model IR subsystem is shown in Fig. 6. All of the molecular electronics are mounted on the back of the optics housing and are de- signed to be removed as one unit. The detector assembly including the dewar is included as an integral part of the electronics assembly. The complete assembly provides the equivalent of 6250 electrical components and it is laid out to permit access to every major component or functional electronic block for evaluation.

The molecular circuits have been tested and maintain performance over a temperature range of a t least - 20°C to +70°C. Several of the channel amplifiers have been operated in a 100°C ambient since June 15, 1963 with no appreciable change in characteristics. A number of the basic stages exhibiting current gains of 20 a t collector currents of 1 pa have been soaked a t 2 O O O C for over 1000 hours with no change in gain. A breadboard version of the subsystem was operated almost daily for nine months without a single failure in the molecular circuits.

Fig. &Engineering model of molecular IR subsystem.

The performance of the subsystems has been evalu- ated in laboratory tests and have demonstrated tracking accuracies better than 1 milliradian and noise equivalent detection sensitivities better than 1 X watts/cm2.

CoXCLCsIoNs

When using the breadboard and engineering model IR subsystems, the advantages of the molecular electronics, as applied to a mosaic detector concept, have been dem- onstrated. Environmental and operational tests over ex- tended periods have demonstrated the reliability of the molecular circuits. The results obtained with the channel amplifiers demonstrate how size, weight, and power con- sumption can be reduced when redundant elelctronics are required.

These techniques developed to obtain small, low- power circuits are applicable to other linear system concepts and can be used to reduce power, weight, and size with no loss in performance. I R subsystems using the mosaic concept could be developed for surveillance,

rendezvous, and intercept applications. The use of mo- lecular techniques makes it possible to obtain complex amplifier channels, signal sorters, computers, and telem- etry equipment for use in aerospace applications.

ACKNOWLEDGMEKT

The authors wish to thank 14. Guiliano for his assist- ance on the molecular fabrication; E. E. McCoy, S. Bandy, and J. Fawcett for assistance on the molecular circuit and system development; and F. Kaisler for his assistance on the optics and nutation transducer. In addition, the authors thank J. Bagrowski and J. Case a t Westinghouse and F. Bennet at Eastman Kodak for their work on the detector, and F. Doell and J. Pniewski for much of the assembly and wiring.