טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAdato Avi
SubjectDesign Methods to Reduce Radiation Effects on Electronic
Circuits
DepartmentDepartment of Electrical Engineering
Supervisor Professor Ran Ginosar
Full Thesis textFull thesis text - English Version


Abstract

All objects in space are exposed to extreme environments be it temperature, pressure or radiation. Absorbed dose (also known as total ionizing dose, TID) is a measure of the energy deposited in a medium by ionizing radiation per unit mass. It is equal to the energy deposited per unit mass of medium, which may be measured as joules per kilogram and represented by the equivalent SI unit, gray (Gy), or the CGS unit rad.

When VLSI circuits absorb TID, their behavior changes. Also, because the change is not uniform across the chip, it causes various offsets in the VLSI circuits. Charge trapped in the oxide may cause VT to change, leakage current may increase, etc.
It is important to compensate for these effects, or the VLSI circuits may stop functioning.

It is our goal to suggest a design for a self compensating amplifier, which will be able to calibrate itself as the TID changes over its lifetime. In this work we review current approaches to reduce offset in VLSI circuits, for both space and non-space applications.

Although common approaches to offset cancellation usually involve switched capacitor circuits or chopper amplifier, we decided to avoid these solutions as they introduce modulation to the output signal. Instead, we have chosen to implement one of the suggested non-space solutions, which entails a feedback amplifier with a very large low pass filter. In this fashion, the offset correction is only preformed at DC frequencies, as the TID effects accumulate slowly, and the circuit operated freely at standard, faster, operating frequencies.

Feasibility simulation performed validated this concept. However, when substituting ideal blocks with real element as suggested by the concept solution, the circuit could not achieve a sufficiently low band width. Failing to implement the solution as originally suggested, we went on to redesign the feedback amplifier. Through the use of this newly designed amplifier we managed to achieve a forty decibel offset reduction. Future work may include production and testing of this concept.