LTP IS FEE Sensing Channel: Front-End Modeling and Symmetry Adjustment Method

The inertial sensor (IS) front-end electronic (FEE) is one of the key subsystems in the laser interferometer space antenna (LISA) pathfinder (LPF) satellite. The front-end circuit of the IS FEE sensing channel, consisting of the transformer and transimpedance amplifiers (TIAs), is considered to be a critical part of the design. Asymmetry of this circuit would produce the sensing offset and provide wrong information to the control loop, which would incorrectly position the spacecraft. Also, the imbalance of this circuit could introduce multiplicative noise to the sensing output. In this paper, a detailed mathematical model of the transformer and TIAs is derived, and a new symmetry adjustment method is proposed based on the analysis of the model. The suggested adjustment method is verified on the prototype circuit designed at ETH Zürich, and the experimental results show that the suggested method can accurately adjust the circuit symmetry and greatly reduce the sensing offset.