A fully integrated CMOS DCS-1800 frequency synthesizer

A prototype frequency synthesizer for the DCS-1800 system has been integrated in a standard 0.4 μm CMOS process without any external components. A completely monolithic design has been made feasible by using an optimized hollow-coil inductor low-phase-noise voltage-controlled oscillator (VCO). The frequency divider is an eight-modulus phase-switching prescaler that achieves the same speed as asynchronous dividers. The die area was minimized by using a dual-path active loop filter. An indirect linearization technique was implemented for the VCO gain. The resulting architecture is a fourth-order, type-2 charge-pump phase-locked loop. The measured settling time is 300 μs, and the phase noise is up to -123 dBc/Hz at 600 kHz and -138 dBc/Hz at 3 MHz offset