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Low power PLL for short-range mmwave industrial radar
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
www.eenewseurope.com, Feb. 21, 2023 –
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.
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