DC-coupled Doppler radar sensor with software-configured fine-tuning architectures for precise monitoring of complex motion patterns

In most of the traditional miniature Doppler radar systems, AC coupling is used between the RF front-end and baseband amplifier. However, the AC coupling can lose very low frequency and DC information, which represent the stationary moment when detecting the movement of the object under test. Although a larger coupling capacitor can alleviate the problem to some extent, it will slow down the system response by increasing the settling time. DC-coupled radar sensors using fine-tuning architectures are proposed in this paper to preserve the DC information. This solution is realized for both on-chip design and board-level design. In the on-chip design, a two-stage variable gain amplifier (VGA) with software-configured DC tuning is proposed. In the board-level design, the AC coupling capacitors are removed and an adaptive feedback loop is used to perform DC offset calibration. Simulations and experiments show that the proposed DC-tuning architectures can completely relieve the radar sensor from circuit saturation and allow it to accurately monitor motions with stationary moments.