Currently, magnetic fluxgate circuits used for magnetic field measurements mostly adopt parallel excitation second harmonic generation. The magnetic fluxgate developed by this method cannot possess both low noise and high bandwidth at the same time. The orthogonal fundamental mode fluxgate is used in this paper: the excitation magnetic field is orthogonal to the magnetic field to be measured, and the external magnetic field is detected by measuring the voltage signal in the pick-up coil. The excitation magnetic field changes with the parallel excitation second harmonic method while the direction of the excitation magnetic field does not change in the orthogonal fundamental mode scheme, which can effectively reduce the influence of Barkhausen noise. The magnetic fluxgate circuit is designed based on the orthogonal fundamental mode scheme and its performance indexes are tested. The range of the magnetic fluxgate is ±100000 nT, the sensitivity is 100 μV/nT, the output noise is 8.9 pT/rt(Hz)@1 Hz, and the bandwidth is DC-15 kHz. The orthogonal fundamental mode fluxgate improves the bandwidth performance while enabling low-noise magnetic field measurements in practical applications.
A wideband RF logarithmic power detector with large dynamic range is presented in this work. The power detector fabricated in 180-nm SiGe process employs the successive approximation technique over a 6stage cascaded amplifier chain. A cross-coupled cascode amplifier architecture is proposed to expand bandwidth up to 8GHz. With a temperature compensation circuit and a DC offset compensation loop, the detector provides consistent logarithmic performance at different temperatures in band, which can be applied in highly reliable RF systems. The measured input dynamic range is larger than 50dB in 1MHz~8GHz with less than ±1dB error and 55dB at 8GHz with less than ±3dB error. The measured temperature drift is less than ±1.0dB at 5GHz over the temperature range from -40 to 85℃.
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