An Analog Phase Interpolation Based Fractional-N PLL

A novel phase-locked loop topology is presented. Compared to conventional designs, this architecture aims to increase frequency resolution and reduce quantization noise while maintaining the fractional-N benefits of high bandwidth and low phase noise up-conversion. This is achieved utilizing a feedforward mechanism for offset cancellation from the integer-N frequency. The design is implemented in a 0.13μm CMOS process technology. A frequency resolution of 1.16Hz is achieved on a 5GHz differential delay cell VCO with a 100MHz reference oscillator. A ping-pong swallow counter topology alleviates pipeline latency to achieve 1-64 divide ratios. A digital pulse generator and nested phase-frequency detector provide tunable offset cancellation. A 5-bit current-steering DAC capable of 200ps pulses reduces output spurs. Theoretical calculations and Simulink modeling provides insight to the effects of non idealities in the system. Test structures and loop configurability are programmed via SPI interface through a custom GUI and prototype PCB