A 3.5-mW 2.45-GHz frequency synthesizer in 0.18μm CMOS

A 3.5-mW, 2.45-GHz integer-N frequency synthesizer compliant to Zigbee standard is presented. Addressing the high-speed low-voltage challenges confronting prescaler design, a power-down circuit featuring zero voltage headroom with negligible loading is proposed, which enables full synthesizer functionality with reduced supply of 1.2 V. Realized in 0.18 μm CMOS, the synthesizer exhibits measured phase noise of -112 dBc/Hz at 1 MHz offset, reference spur below -60 dBc with 2.5 MHz reference. The synthesizer settles to within 40 ppm of the target frequency in less than 500 μS with 82.5 MHz frequency jump.