A High Dynamic Range Vibration Radar Sensor With Automatic DC Voltage Extraction

One challenge of using a homodyne receiver to obtain accurate vibration information is the undesired DC voltage in a continuous wave radar. It reduces the output dynamic range and even saturates the signal path. In this paper, an adaptive DC extraction method with flexible clocks is proposed in a 5.8 GHz Doppler radar to separate the DC component from the input signal. Rather than simply eliminating the DC component, the proposed method digitizes the DC component as well as the input AC signal with a large dynamic range. It is accomplished by a mixed-signal feedback loop and features an excellent accommodation to large input DC variations and flexible settling time. In the loop, a closed-loop amplifier is used as the input stage and an ADC is followed to digitize the amplified quadrature signals from the radar. Afterward, a simplified digital filter is cascaded to extract the digital version of the DC component and feedback to the input stage. In this way, both the DC component and AC component in the input signal are separated and digitized without saturation. For verification, several simulations and experiments were conducted. The results show that a wide DC range can be tolerated and extracted. What's more, the target motion with sub-millimeter amplitude can be successfully captured based on the proposed DC extraction loop.