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Design & Implementation of Test circuit for an array of sensor Diodes in Low Temperature (77K)

Ghoreishizadeh, Sara | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40292 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Medi, Ali; Fardmanesh, Mahdi
  7. Abstract:
  8. A Focal Plane Array (FPA) consists of one or two dimensional array of sensor elements and is widely used in imaging systems. Generally an FPA can be divided into two main parts: Sensor array and read-out/test circuit. In this thesis we design and implement a test circuit for an FPA that works in 77K. The circuit will be attached to the sensor to detect and amplify its very low level current that is in the range of 10 pA to more than 10 nA. Reducing MOSFET temperature from room temperature (300K) down to liquid nitrogen (77K) will greatly changes its parameters and characteristics such as Threshold Voltage and carrier mobility. However MOSFET models in low temperature are either unavailable or inaccurate. So in this thesis, to investigate the effects of lowering temperature on MOSFET performance, the Characteristics of MOSFETs with various dimensions in the wide temperature range 77K-300K is measured. Consequently the changes in the behavior of MOSFETs in common Process of 0.18 um and 0.5 um are predicted. The first circuit prototype for revealing the current of a 2×2 array of sensors diodes is designed. It is based on current mirror structure. Thus, the current gain of it is almost temperature independent. The circuit is then fabricated in a common 0.18um process. Measurement results in 77 K match the theoretical expectations to a great extent. The final circuit prototype is designed for 4×4 array of sensors using 0.5um low temperature process and fabricated in 2 different layouts. The circuit is capable of amplifying very small currents from 10pA up to more than 10nA in 77K. To support such a wide range of input current, a technique is being used in which the gain and bias of the current amplifier could be changed in proportion with the input current.
  9. Keywords:
  10. Metal Semiconductor Field Effect Transistor (MESFET)Technology ; Finishing Temperature ; Variable Gain Amplifier ; Current Amplifier ; Current Mirror

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