Design of a dual OPAMP low offset integrator system for plasma reactor

Abstract

In a fusion reactor, where tokamaks are used to confine the plasma using toroidal and poloidal magnetic fields, highly accurate magnetic measurements are a necessity for automatic control. However, due to extremities in temperature, acquiring uncorrupted signals become a challenging task. Presented in this thesis is a design of a twin operational amplifier based low offset integrating system to eliminate any error in measurement due to temperature dependent DC offset. This integrator system comprises mainly three stages after the inductive sensor. The first stage consists of a dual integrator in which the output signal from the sensor was fed to one integrator and the input terminals of the other integrator were grounded. An instrumentation amplifier which has a very high common mode rejection ratio and large input impedance was implemented in the second stage to find the differential signal between the outputs of the two integrators. Any noise arising in the environment was eliminated in the next stage by a Digital Signal Processor based Finite Impulse Response Low-Pass Filter. The first two stages of the design were simulated by using Multisim Circuit Design Suite. The low-pass filtering stage was realized on a Texas Instruments TMS320C6713 starter kit using Kaiser Windowing technique to achieve a sharp cut-off at 780Hz. To obtain a full layout of the operational amplifier based design Cadence Electronic Design Automation UMC_180 nm tool was used. The primary objective of DC offset elimination was verified through the results.
KEY WORDS:
Inductive Sensor, Operational Amplifier, Integrator, Instrumentation Amplifier, Low-pass Filter