Integrated tri-state PLL for the control of a switched injection-locked oscillator at 2.45 GHz

This paper presents a novel combination of two fully integrated phase-locked loops (PLLs) to control the oscillation frequency and modulation frequency of a switched injection-locked oscillator (SILO). The SILO is used as an active reflector transponder in a frequency-modulated continuous wave (FMCW) radar system. A fractional-N PLL (RF-PLL) with a tri-state phase-frequency detector (TSPFD) sets the oscillation frequency of the voltage controlled oscillator (VCO) to 2.45 GHz. Another integer-N PLL (modulation PLL) switches the tail current source of the VCO to achieve SILO behavior at the time when the RF-PLL is not controlling the VCO. The RF-PLL supports division ratios from 64 to 511 with a frequency resolution of 0.2 Hz. Reference spur levels are below −48 dBc while the out-of-band phase noise is −103 dBc/Hz at a 1MHz frequency offset. The modulation PLL is based on a Maneatis-cell ring-oscillator supporting modulation frequencies between 6MHz and 20 MHz. Furthermore, the duty cycle of the modulation signal can be set in steps of 0.8 %. Due to the novel TSPFD, the oscillation frequency of the SILO changes only by 36MHz within 10 minutes when the RF-PLL is inactive. The complete circuit is manufactured in a 180nm SiGe BiCMOS process and consumes a total power of 128mW.