Ultra-High Range Resolution Doppler Radar Front End With Quadrature-Less Coherent Demodulation

Abstract

Researchers at the University of California, Davis have developed a Doppler radar front end to overcome detection nulls without quadrature demodulation.

Full Description

Doppler radars can determine the distance and speed of an object by sending a signal of a certain tone and observing the phase difference between the transmitted signal and its reflection off of an object. If the object’s distance from the radar is a multiple of the signal wavelength divided by 4, detection nulls occur, and the gain of the radar becomes unusable. To overcome detection nulls, quadrature demodulation is commonly used to extract phase information received by the radar. However, quadrature demodulation requires highly precise matching circuitry and intensive digital signal processing. Such signal processing necessitates powerful onboard computers and negatively impacts the system’s power efficiency. A Doppler radar that can overcome detection nulls without using quadrature demodulation would greatly improve performance and power efficiency.

Researchers at the University of California Davis have developed Doppler radar designs that simultaneously achieve ultra-low power consumption, ultra-low phase noise, free of detection nulls, and ultra-high displacement-sensing resolutions without using quadrature demodulation. The radar design uses low-noise sub-sampling phase-locked loops (SSPLLs) with the same reference (REF) signal to generate single-tone transmitted/radiated signal and a local oscillator (LO) signal. As a result, no quadrature demodulation is required, and the elimination thereof enables use of circuit design and hardware that are greatly simplified compared to conventional systems. A reflected signal (derived from an object) is downconverted into a time domain square wave, allowing for a simplified demodulation process and signal processing. A phase demodulator (PDM) is used to extract displacement-induced phase information from the square-wave signal and a PDM output is filtered to provide a signal proportional to vibration displacement of the object causing the reflected signal. With less computationally intensive digital signal processing, the power efficiency is improved compared to existing products. This radar is suitable for applications that require immense precision realized through its ultra-high-resolution capabilities.

Applications

• Doppler radar to determine an object’s distance and speed 
• Replacement of laser Doppler vibrometers used in MEMS devices to measure vibration in extreme detail

Features/Benefits

• Compact hardware design due to the removal of quadrature demodulation circuitry 
• Enhanced power efficiency and signal resolution compared to existing continuous wave Doppler radars

Patent Status

Additional Patent Pending