A DC-Coupled High Dynamic Range Biomedical Radar Sensor With Fast-Settling Analog DC Offset Cancelation

One challenge of designing a dc-coupled biomedical radar sensor is dealing with the dc offset voltage presented in its receiver. The undesired dc offset is mainly caused by clutter reflection and hardware imperfection. It may saturate the baseband amplifier and limit the maximum dynamic range that a biomedical radar sensor can achieve. AC-coupling the signal can eliminate dc offset but it will also distort the signal, and thus may not be acceptable for high precision applications. In this paper, a dc-coupled biomedical radar sensor is proposed incorporating an analog dc offset cancellation circuit with fast start-up feature. It can automatically remove any dc offset in the baseband signal and emulates an ac-coupling system. It can also be easily reconfigured into a dc-tracking mode when application requires. When entering this mode, the initial dc offset will be removed, whereas future dc change can be recorded. The proposed solution only uses analog components without requiring any digital signal processing nor software programming. Therefore, compared with the existing digitized dc offset calibration techniques, the proposed method has the advantage of low cost, easy implementation, short delay, and high resolution. The experiment results demonstrated that a wide range of dc offset can be successfully removed from the biomedical radar sensor, and its dynamic range can be maximized. The reconfiguration of the dc-tracking mode has also been tested and verified. Furthermore, the proposed dc offset cancellation circuit has the potential to be easily adopted by other systems that also face the dc offset problem.