Analysis of 320X240 uncooled microbolometer focal plane array ...

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42switching circuit is a MOS step-down converter, which recycles the current produced byon-pulse during the off cycle of the pulses and converts the pulses to DC voltage to powerthe thermoelectric cooler.As shown in Figure 2.13 and 4.4, there are two temperature sensors inside thepackaging for the feedback to the thermoelectric cooler controller. The sensors are twonpn transistors, where the base to emitter junction is used as a diode with temperaturesensitivity of about -2.18 mV/°C. The diodes are connected in series to increase theoutput voltage of the diodes, where the sensitivity increases to -4.36 mV/°C. Thecontroller circuit is to be able to stabilize minimum change in temperature of about20mK. The temperature change translates to change in voltage of -4.36 mV/°C x 20mK=The operation of the control loop is as follows. If the temperature inside thepackaging increases, the diode sensors' voltage drop. The voltage drop is compensatedby the control amplifiers. The output of the controller circuit produces a negative pulsecausing the PWM to increase the pulse width allowing the power supply to draw morecurrent out of the TEC, which enables the TEC to pump more heat out from the arraypackaging. If the temperature decreases, the same procedure follows. Now, the output ofthe controller is a positive pulse, which decreases the pulse width of the PWM. Thedecrease in the pulse width causes the power supply to draw less current out, thus theTEC warms up.The first step in designing the controller was to determine the transfer function ofthe TEC/diode pair (refer to as "TEC pump" in the thesis). An experiment was
43performed at Inframetrics to determine the step response of the TEC pump. Thetemperature sensing diodes were connected as shown in Figure 4.6. The two diodes wereconnected in series and biased with 102K0 resistor from +5 volts with current of about40p.A. The output of the diodes were connected to an oscilloscope to measure the stepresponse of the TEC pump due to heating and cooling of the thermoelectric pump.Figure 4.6 The setup for determining the diode response.The thermoelectric cooler was connected to a power supply, and the step inputwas simulated by turning on the power supply. The oscilloscope was set to trigger on therising edge of the input pulse to record the response data. Figure 4.7 shows the resultingresponse curves of the TEC pump, where the vertical scale represents the output voltageof the temperature sensors (diodes) and the horizontal scale represents time. In Figure4.7 a), the TEC was cooled without a heat sink.
Page 1 and 2:
Copyright Warning & RestrictionsThe
Page 3 and 4: ABSTRACTANALYSIS OF 320X240 UNCOOLE
Page 6 and 7: APPROVAL PAGEANALYSIS OF 320X240 UN
Page 8 and 9: This thesis is dedicated tomy famil
Page 10 and 11: TABLE OF CONTENTSChapterPage1 INTRO
Page 13 and 14: CHAPTER 1INTRODUCTIONIn recent year
Page 17 and 18: 5radiation (LWIR) between 811m to 1
Page 19 and 20: Figure 2.1 Simplified bolometer str
Page 21 and 22: 9The first function of the right ha
Page 23 and 24: 11corresponding to T 1 . With radia
Page 25 and 26: 13then the transient term goes to z
Page 27 and 28: 15The signal voltage (Eauation 2.26
Page 29 and 30: 172.2.3 NoiseThe detection capabili
Page 31 and 32: 19F is the f/# of the optics, VN is
Page 33 and 34: 21To obtain the temperature fluctua
Page 35 and 36: 23provide protection against detect
Page 37 and 38: ZE1 L4t46LII C. 10 aft( IL.The UFPA
Page 39 and 40: 27reflection (AR) coated Ge window
Page 41 and 42: 29170 synchronization standard sign
Page 43 and 44: 31amplified and integrated detector
Page 45 and 46: 33processing module by a scan conve
Page 47 and 48: Figure 3.3 UFPA camera platform.35
Page 49 and 50: 37high mechanical strength as shown
Page 51 and 52: Unlike the photon sensors, the micr
Page 53: 414.2 The Controller DesignThe cont
Page 57 and 58: 45c) Heating of the TEC without hea
Page 59 and 60: 47[(RiR2C1)s + — (R1 + R2) 4.1( )
Page 61 and 62: 49The third amplifier stage has the
Page 63 and 64: t 1
Page 65 and 66: 53c) T showing the response time of
Page 67: REFERENCES1. R. A. Wood, "Uncooled
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Analysis of 320X240 uncooled microbolometer focal plane array ...

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