Class D RF amplifier for 20 MHz NMR MOUSE sensor

A 20 MHz Class D RF amplifier has been developed to work with an NMR MOUSE sensor. The prototype has been built on a 4-layer PCB with an area of 50 cm² and weighs less than 120 g; it outputs 100 W into a 50Ω load using a single 24 V DC supply. Even with the high switching power losses at that frequency, the amplifier is able to achieve 73% efficiency. Test results from the MOUSE sensor show the class D amplifier is operating well at 20 MHz with fast turn on and turn off times, producing constant amplitude pulses as short as 2 μs. and is able to run long CPMG experiments with hundreds of echoes. The results confirm that the Class D amplifier is a worthy replacement for the existing, market available Class A amplifier, which is running at 19% efficiency and weighs 480 g with a PCB area of 160 cm².