Natalia Gudino1, Jeremiah A. Heilman2, Mark A. Griswold3
1Biomedical Engineering, Case Center for Imaging Research, Cleveland, OH, USA; 2Physics, Case Center for Imaging Research, Cleveland, OH, USA; 3Radiology, Case Center for Imaging Research, Cleveland, OH, USA
We present a novel, high efficiency system to modulate the amplitude of the RF output signal of a current mode class-D on-board amplifier (CMCD). The amplitude-modulating wave is used as the reference signal of a Pulse Width Modulated (PWM) controller that switches the gate of high frequency MOSFETs in a buck converter configuration. Current feedback is used to directly control the current in the transmit coil. We successfully showed the system can handle up to 20kHz AM signal and higher, and load insensitivity was significantly improved comparing with that of a tuned voltage-mode device.