Belgian research lab imec has shown a low power phase locked loop (PLL) design that can be used for short range industrial millimetre wave radar designs
The digitally calibrated charge-pump (CP) PLL can generate high-quality frequency-modulated continuous-wave (FMCW) signals for mmwave radars at low power consumption. The PLL is a critical building block for future short-range collaborative robot sensing radar applications and is built in a 28nm CMOS process.
FMCW mmwave radar sensors are becoming increasingly popular for multiple automotive, healthcare, and industrial applications. FMCW radars transmit a sinusoidal wave whose frequency increases linearly in time, a sweep referred to as ‘chirp.’
After being reflected by the object, the signal is picked up by the receiver and mixed with the original chirp signal, after which the object’s distance and speed can be extracted. The quality of the radar signal depends largely on the performance of the PLL used to generate the chirp signal.
The PLL generates highly linear, high-quality chirp signals centred around 16GHz with a chirp bandwidth of 1.5GHz. A key achievement is reaching chirp speeds down to 12µs, with as low as 41kHzrms error in frequency modulation (rms-FM-error) with a fast startup time below 1µs and minimal reset time between chirps of 1µs.
The chirp generator operates in duty-cycled mode – synthesizing N chirps in one burst before powering down – providing significant power savings. This means the PLL consumes only 9.2mW and 1.48mW when operating in a 50 percent and one percent duty-cycled mode, respectively. Even after power-down mode, the rms-FM-error of the first chirp remains below 41kHz.
“Our PLL opens doors to robotics radar applications – think of cobot radar sensors to enhance safety and efficiency of human-robot interaction in industrial environments – as well as to radar sensors mounted on small moving objects or vehicles such as drones,” said Ilja Ocket, programme manager at imec. The design is being shown at ISSCC 2023 in the US this week.
“At ISSCC, we are presenting a functional demo that integrates our CP-PLL with imec’s existing 140GHz radar receiver and transmitter blocks to showcase the potential of the technology for future automotive and industrial applications. The PLL can also be used for up-conversion to mmwave radar signals with other carrier frequencies, e.g., 80GHz.”
The design can also be used for short-range automotive radar applications ranging up to several tens of meters such as in-cabin radar sensors to monitor presence, movements and well-being of driver and passengers, as well as out-of-cabin sensors for parking assistance or vehicle detection.
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