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9180 Series Gradient Amplifiers These power amplifiers are designed specifically for use as high performance, high bandwidth, low noise gradient amplifiers in NMR and MRI applications. Performance and design are tailored to the unique output waveform and load impedances seen in these applications. The output stage is a linear amplifier bridge using mosfets. The power supply to the output stage is switched between two voltage levels depending on the load and output demand. This configuration gives some advantages over a switch-mode design in research applications – lower output noise levels, wider bandwidth, superior transient response, and freedom from uncertainty in the start point of a rising edge – while the 2 stage power supply gives the design competitive power efficiency. Power supply voltage levels can be changed to match a specific load resistance, inductance, and rise time requirements. The amplifier has a comprehensive fault protection system using a floating point DSP. Output
Control
AC power and Mechanical
Advantages in NMR/MRI applications
Performance These plots show the measured performance in a benchtop MRI application.
Flat top pulse response
Showing the rising edge of a 100A flat topped pulse. 25us per division. CH1: Output current 20A/Div CH2: Output voltage 50V/Div Showing the under-shoot at the end of a 100us fall to 0A from 100A 10us per division. CH1: Output current 1A/Div CH2: Output Voltage 50V/Div Current undershoot is less than 0.5% of peak current. Small signal frequency response Showing the gain (in black) and phase (in red) response. 3dB bandwidth is 40kHz. Gain plot is 10db per division.
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