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Abstract very low level current measurement (1 2 -13A) requires a high input impeadance amplifier,generally using an unprotected MOSFET and a high value resistor (=lE12 ohm ). An irnl!roved integrated current to frequency converter (CFC) fully in NMOS technology is presented in this thesis. This converter uses the switched capacitor technique. This version is characterized by better topology of devices, wider uynamic range of frequency and the incooperation of circuitry that detects the saturation of the 1fF characteristics and then enforces a range change which effectively moves the current measurement points towards the linear portion of the characteristics. In CHAPTER 1, we recall the MaS processing (ma ter ia l, oxidation, diffusion, masking, etching, scrihing and fabrication), structure and characteristics. We also intoduce a formulation of the MOSFET capacitor in its different modes of operation. We present also in this chapter the methods of very low level current measurements, the different sources of leakage currents in MaS devices and the precautions to be considered for the compensation or the minimization of this leakage which enables the very low level current measurements at a very good resolution accuracy and linearity. In CHAPTER 2, we explain a new accurate, sensitive and linear current to frequency converter (CFC) and present a detailed study of the analysis and design considerations for the different blocks constructing it. We have proposed models for predicting the performance and characterizing these building blocks. These models take into account alJ restrictions and limitations associated with the MOSFET VLSI circuits. These models are very important for the study and the treatment of some nonlinearity problems revealed from comparing the theory and experimental results. However, our simulation results show that the CFC which we have presented properly functions at very good linearity and accuracy. In CHAPTER 3, we introduce the different precautions to be considered when preparing the test samples,to guarantee the lowest possible level of leakage current during discussmeasurements. We present our results of simulation, and compare it with experimental results performed on an old version of CFC. Our results revealed that: a) Lower limit of current measurement is related to the uncompensated leakage current created at the input of the current controlled oscillator, b) The suplementary current is related to the proximity effect, c) The related frequency jump in the CFC transfer function is not to the OPAMP oscillation due to instability as was beleived to be, but is related to the threshold voltage instability of the MOSFET’s used in the l/F resistance and, d) Frequency related to exponential saturation of the CFC characteristlcs is the deviation from the exponential c/c’s of current generator, but is related to relatively long delay of the double bistable multivibrator used in the current controlled oscillator. We finally propose a) Using low leakage MOSFET techniques, b) Using deposied and diffused guard rings channel of the first MOSFET and the source of MOSFET used in the R(F) resistance, not the the between the the second ~) New techniques to compensate Eor the carrier heating in the R(F) resistance and, J)L1w use of more advanced technology (CMOS, CMOS/SOS) . MOS/SOS or |