Influence of switched-mode power supplies in an arbitrary waveform magnetic particle spectroscope

Abstract

At Fraunhofer IMTE an arbitrary waveform Magnetic Particle Spectroscope (MPS) is developed to gain further insight into particle behavior. To enable these arbitrary fields, no transmit filters, resonant circuits or receive filters are used, as both the send and the receive signal are broadband. To power the auxiliary components of the system in an initial setup Switched-Mode Power Supplies (SMPS) were used. SMPS are commonly used in modern electronic equipment as they are energy efficient and cost-effective. The downside of these converters is their output ripple and EMI due to the switching nature. The Low Noise Amplifier (LNA) used in the system was supplied with an SMPS. The developed four-stage LNA consists of a J-FET stage followed by two low noise, low distortion operational amplifiers, with a final differential amplifier stage. While the latter stages offer power supply rejection, the first stage of the LNA offers near to none. As the signal disturbance caused by the SMPS within the first stage is amplified in further stages a linear power supply with a very low output noise and high supply voltage rejection is a promising measure to reduce overall noise in the system. To evaluate the influence of different power supplies, the spectra of the receive signals of background measurements of the RedPitaya IO boards are compared. A comparison was made between a SMPS, a commercially available linear power supply and a specific developed low noise linear power supply.