Date of Graduation
5-2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Engineering (PhD)
Degree Level
Graduate
Department
Electrical Engineering
Advisor/Mentor
Alan Mantooth
Committee Member
Jia Di
Second Committee Member
Babak Parkhideh
Third Committee Member
Jeff Dix
Keywords
amplifier; current sensors; Integrated circuit design; power applications; readout interface; signal processing
Abstract
High-density and power-efficient circuits have become realizable with the advent of wide bandgap semiconductor devices due to their high switching speed and lower conduction/switching losses. The operation of these circuits requires current information for protection, monitoring, and control. For the realization and a further boost in the efficiency of such power circuits, small size, non-invasive, high bandwidth current sensors with noise immunity, accuracy, and linearity are required. Various hybrid sensors have been reported to meet the requirements of emerging power circuits. A combination of a magneto resistor or Hall sensor and a coil is used to cover a wide frequency band. The lower cutoff frequency of the coil is matched to the 3 dB bandwidth of the used MR/Hall sensor. The achieved flat band response is then limited by the bandwidth of the readout interface. The amplifiers are the major component of the interface circuit, and their design has a significant impact on the overall performance of the hybrid sensor. In the presented work, the readout interface of a hybrid sensor based on an Anisotropic Magneto resistor (AMR) sensor and a PCB-embedded Rogowski coil is designed on an Application Specific Integrated Circuit (ASIC). The readout interface is implemented using 350 nm length devices. A folded cascode input stage is designed with a dual pair for VDD to ground input common-mode range (ICMR). The consistent AC performance over the ICMR is achieved by using devices across all the input devices with fixed gate voltage applied. The push-pull stage is used for rail-to-rail output swing. Meeting the bandwidth requirement of the readout interface was challenging with the desired high resistances in the closed-loop configuration for sensor integration. The amplifiers are optimized for the desired gain and bandwidth and connected in the desired configuration on-chip. The readout interface offers a 5 kΩ load to the AMR sensor and a 13.3 kΩ load to the Rogowski coil. The sensor is non-invasive and does not cause any loss in the power circuit. The bandwidth of 48 MHz is measured with a 50 V/V gain for the AMR signal amplification and a 3 V/V gain for the Rogowski coil signal amplification. The readout interface consumes 4 mA current from a 3.3 V supply and has consistent AC performance over the complete input common-mode range. The output swing is measured to be rail-to-rail. The performance of ASIC with sensors is determined by applying a step input current to the trace and measuring the output voltage. The rise time of 9 ns and fall time of 10 ns is measured for 1 V amplitude with a 10 ns delay in response. The sensitivity of the hybrid sensor is 100 mV/A. A buck converter is used for testing performance in the targeted applications. Two triangular waveforms at 100 kHz and 1 MHz frequency are generated. The 100 kHz frequency signal has a 1.1 A peak current amplitude, and the 1 MHz frequency signal has a 9 A peak current amplitude. The output of the hybrid sensor is observed to follow the current waveform accurately in both test cases. Testing at high temperatures up to 100°C is performed and a temperature drift of 0.197%/°C is measured.
Citation
Mahar, A. (2024). High Bandwidth Hybrid Current Sensor Readout Interface for Power Applications. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/5353