A 2–11 GHz 7-Bit High-Linearity Phase Rotator Based on Wideband Injection-Locking Multi-Phase Generation for High-Speed Serial Links in 28-nm CMOS FDSOI

Pushed by the ever-increasing demand of internet traffic, high-speed serial interfaces are expected to reach 400-Gb/s aggregate data rates in near future. At receiver (RX) side, phase rotators (PRs) are key blocks to align the phase of the local clock to the transitions of the incoming data and to sample the eye in the optimal position. Small phase step and high linearity are paramount in preserving the horizontal time margin, tightened by the reduced symbol duration at 25 Gb/s and beyond. Interpolation of π/4-spaced signals is a viable means of improving linearity at high resolution, provided multi-phase signals with low phase error are available. An injection-locked ring oscillator (ILRO) with a mixed analog and digital calibration loop is proposed for high accuracy multi-phase generation over a wide frequency range and against large voltage and temperature variations. A phase detector (PD) based on two passive mixers measures the quadrature error and continuously tunes the oscillator to achieve low phase error. Concurrently, a window comparator monitors the PD output and drives digital coarse calibration in background. Two test chips have been fabricated in 28-nm CMOS fully depleted silicon on insulator technology. The stand-alone ILRO demonstrates 0.2-11.7 GHz frequency range with better than 1.5° quadrature phase error over ±20% supply and -40 °C to +120 °C temperature variations. Power consumption is scalable from 3 to 15 mW. When the ILRO drives the 7-bit PR, it demonstrates differential and integral non-linearity within 0.5 and 1.1 LSB, respectively, across the 2-11 GHz frequency range with 18.6-mW maximum power dissipation. Measured performances compare favorably against the state of the art and meet the requirements of >25 Gb/s multi-standard I/O RXs.