TELEDYNE JUDSON TECHNOLOGIESA Teledyne Technologies Company 1/4

TELEDYNE JUDSON TECHNOLOGIESA Teledyne Technologies Company

221 COMMERCE DRIVEMONTGOMERYVILLE, PA 18936-9641PHONE: 215-368-6901FAX: 215-362-6107www.teledynejudson.com

PB 211August, 2000

J10D SERIESINSB DETECTORSOperating Instructions

TYPICAL OPERATINGCIRCUITS

High Detectivity Circuit

J10D series InSb detectors arephotovoltaic and generate a currentproportional to the intensity of thephotons absorbed. For maximumdetectivity these detectors areoperated at zero volt bias. Figure 1shows the recommended operatingcircuit, using a low-noise FET opamp in a negative feedback, currentmode configuration. The signalcurrent (Is) times the feedbackresistor (RF) results in the outputvoltage (VO). The properties of theop amp ensure that the detectorremains near zero volt bias.

Vout = Isignal x RFeedback

Selection of the feedback resistanceRF is determined by the systemrequirements as follows:

Op Amp Saturation

Photovoltaic detectors generate aDC short circuit current due tobackground radiation. To avoid opamp saturation, the product ISC timesRFmust be less than the maximumDC output capability of the op amp.Recommended level is less than 5volts.

Frequency Response

The feedback resistance RF ,combined with the detector capaci-tance and dynamic impedance,determines the frequency responseof the system. Capacitance andimpedance values are provided onthe data sheet supplied with eachdetector.

Recommended Preamplifiers

Recommended preamplifiers are theTeledyne Judson models PA-9 and PA-7. The PA-9 is an ultra-low noise preamp with a fixed RF matched to the detector for optimum detectivity,gain and bandwidth. The PA-7 hasadjustable gain and lower bandwidth.Refer to preamplifier productbulletin #216 (PA-7) or #218 (PA-9)for more information on the frequencyresponse of a particulardetector/preamplifier combination.

Fig. 1: Recommended Operating Circuit

High Speed Circuit

Frequency response can beimproved by using the circuit shownin Figure 2, where the load resistanceRL is small compared to the detectordynamic impedance. However, thesmall load resistor generatesJohnson Thermal Noise, which maybe larger than the detector noise, sothat overall detectivity is reduced.

Vo= Is x RL x Gain

Fig 2: High Speed Operating Circuit

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J10D SERIESINSB DETECTORSOperating Instructions

TELEDYNE JUDSON DETECTOR TESTS

Test Conditions

All Teledyne Judson detectorsundergo stringent quality controltesting before shipment. The testsetup of Figure 3 is used to checkJ10D series detectors forresponsivity (R) and detectivity(D*).

Fig 3: Detector Test Setup

A copy of the test data isprovided with each detector andincludes the following test condi-tion information:

Blackbody TemperatureAbsolute temperature in °K ofthe blackbody source used forresponse test.

Background TemperatureRoom temperature in °K.

Detector TemperatureOperating temperature of thedetector during the test.

Flux Density (H)Actual rms total power in watts/cm2 irradiating the detectorsurface. Equal to F� T4

BB As/ � d2

where F is the rms constant ofthe chopper (� 0.36), s is theStefan-Boltzman constant, TBBis the blackbody temperature,As is the aperture area and d isthe source-to-detector distance.

Chopping FrequencyFrequency of chopper formodulating the blackbodysource signal.

Field of ViewEqual to 60° unless otherwisespecified by the customer.Defined as two times the halfangle �� /2 from the edge of thedetector as in Figure 4. Objectsat larger angles are obscured.This cold field stop reducesbackground radiation on thedetector and may give im-proved detectivity. Theoreticaldependence is:

FilterThe center wavelength andbandpass of the cold filter (ifany) mounted in the dewar.Must be specified by customerwhen ordering. Cold filtersimprove D* by reducing thebackground radiation reachingthe detector.

D*(� ) =D* (180°) /SIN (� /2)

Fig 4: Field of View Definition

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TELEDYNE JUDSON TECHNOLOGIESA Teledyne Technologies Company

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J10D SERIESINSB DETECTORSOperating Instructions

Electrical Test MeasurementsThe following parameters aremeasured to verify proper detectorperformance:

Open Circuit Voltage (VOC)DC voltage generated by thedetector at operating tempera-ture into a high impedance load.Measured with a digitalvoltmeter.

Short Circuit Current (ISC)Current generated by thedetector into a shorted loadwhile viewing backgroundradiation only.

NoiseRms noise current at 1 KHznormalized to a 1 Hz bandwidth.InSb detector noise is domi-nated by shot noise; currentgenerated by the detectorlooking at a 300°K background.

i2 = 2qI� f

where I is the total current, q isthe electric charge and � f isnoise bandwidth.

Blackbody Responsivity (RBB)Defined as the current pro-duced by a detector in re-sponse to the radiant power onthe detector (amps/watt). Forthe test setup of Figure 3, RBBis equal to Vout / (HBB AD Gain)where HBB is the blackbodyirradiance in watts/cm2, AD isthe area of the detector in cm2,Vout is the rms signal voltage atthe output of the preamplifier involts, and Gain is the gain ofthe preamplifier in volts/amp.

Peak Responsivity (R� )Responsivity in amps/watt atthe wavelength of peakresponse. Related to blackbodyresponsivity by R� = RBB G,where the constant G is theratio of total blackbody powerto the power “utilized" by thedetector. For InSb detectorswithout filters, G�� 5.5 and isdetermined as follows:

where N(� ,TBB) is the irradianceat � in w/cm2/µ and WBB is thetotal blackbody irradiance in w/cm2.

Peak Detectivity (D� *)Detectivity at the wavelengthof peak response. Defined as:

Detector Shunt ImpedanceEffective dynamic impedance ofthe detector at operatingtemperature, measured nearzero bias. NOT measured with astandard ohmmeter.

Junction CapacitanceCapacitance of the detector atzero bias.

Additional InformationLN2boil-off rate is measuredwith a flow meter to determinethe rate at which coolantevaporates from the dewar. Theboil-off rate is used to calculatethe LN2 hold time of the dewar.

SUGGESTED METHODSFOR USER TESTING

Preliminary Inspection

• Read precaution instructions onpage 4 of this bulletin.

• Examine the detector for visiblesigns of damage.

• Carefully cool the detector tooperating temperature by filling withliquid nitrogen.

Measuring Voc

Measure the open circuitvoltage Voc using a digital voltmeter.Do not use an ohmmeter. Thecurrent generated by an ohmmetermay destroy the detector. Thedetector should be viewing a roomtemperature background (approxi-mately 295°K). Generally, if the VOCmeasured is within ±10 mV of thevalue specified on the data sheet,you can be confident that thedetector is operating properly.

G - 1 ��� 1 N(� , TBB) R(� ) d� WBB R(� p)

D� * = AD R� cm Hz(1/2)/W-1

Noise

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TELEDYNE JUDSON TECHNOLOGIESA Teledyne Technologies Company 4/4

TELEDYNE JUDSON TECHNOLOGIESA Teledyne Technologies Company

221 COMMERCE DRIVEMONTGOMERYVILLE, PA 18936-9641PHONE: 215-368-6901FAX: 215-362-6107www.teledynejudson.com

J10D SERIESINSB DETECTORSOperating Instructions

Further Testing

Further testing can be done ifproblems are suspected or if theuser wishes to verify the test datasupplied. Place the detector in viewof a modulated source of knownirradiation, ideally a 500°K blackbody.Assemble the circuitry shownin Figure 3. Recommended preampsare Teledyne Judson models PA-7 or PA-9.Turn power on only after all connections have been made.Measure the signal to computeresponsivity as described above.Measure the noise to compute D*.(Note that noise due to the userpreamp may differ from noise due tothe factory test set preamp.)

Malfunctioning Detector

If the detector is not cooling orthe data measured is not consistentwith the test data sheet provided,contact the factory for assistance.

PRECAUTIONS

• The detector dewar is fullyevacuated at time of shipping. Donot attempt to remove the window,or the plug in the pump-out port onthe side of the dewar. (Fordetectors packaged in glass dewarswith JTC cryostat systems, seeProduct Bulletin #219.)

• The detector should be cooled toits operating temperature (usually~77°K) before power is applied tothe system. Use the funnelprovided and avoid spilling coolantaround the pump-out port orwindow areas. When the detectorreaches 77°K, a spout of cold gaswill erupt from the fill port. Do notlook into the fill port until thiseruption is past.

• Make all circuit connectionsbefore applying power to the circuit.

• Power must be turned off beforedisconnecting the detector from thecircuit.

• Do not use an ohmmeter acrossthe detector. Standard ohmmetersmay apply excess current throughthe detector.

• Operation at 0 volt bias isrecommended (see Figure 1).Maximum reverse bias is -200 mV.Do not allow a current more than tentimes the short circuit current toflow through the junction.

• Ultraviolet and visible radiationcan convert the surface of anexposed n-type material to p-type,enlarging the junction area. Thiseffect, called “flashing”, willincrease the effective area of thedetector, lower the impedance,increase the signals, and causeexcessive crosstalk. To preventflashing, protect the detectorelement from direct UV or visiblelight, particularily fluorescent light.The flashing effect is mostpronounced if the detector isexposed while cooled, and cangenerally be reversed by warmingthe detector to room temperatureand recooling. Extended exposureor exposure to high intensity light,even at room temperature, mayresult in permanent damage.

• Do not drop the detector packageor subject the package to shock,vibrations or temperatures above70°C.

Information in this document is believed to be reliable. However, no responsibility is assumed for possible inaccuracies oromission. Specifications are subject to change without notice.