22.3 A 4-to-11GHz injection-locked quarter-rate clocking for an adaptive 153fJ/b optical receiver in 28nm FDSOI CMOS
Modern SoC systems impose stringent requirements on on-chip clock generation and distribution. Ring-oscillator (RO) based injection-locked (IL) clocking has been used in the past  to provide a low-power, low-area and low-jitter solution. Ring-based injection-locked oscillators (ILO) can also be used to generate quadrature phases from a reference clock  without frequency division, which is desirable for half-rate and quarter-rate CDR. However, ILO inherently has a small locking range  making it less suitable for wideband applications. In addition, drift in the free-running frequency due to PVT variations may lead to poor jitter performance and locking failures . Adding a PLL to an ILO provides frequency tracking. However, PLL-aided techniques have second-order characteristics that lead to jitter peaking. They also add design complexity and power consumption . We present a frequency-tracking method that exploits the dynamics of IL in a quadrature RO to increase the effective locking range. This quadrature locked loop (QLL) is used to generate accurate clock phases for a 4-channel optical receiver using a forwarded clock at quarter-rate (Fig. 22.3.1). The QLL drives an ILO at each channel without any repeaters for local quadrature clock generation. Each local ILO has deskew capability for phase alignment. The receiver maintains per-bit energy consumption across wide data-rates (16 to 32Gb/s) by adaptive body biasing (BB) in a 28nm FDSOI technology.
© 2015 IEEE. The authors thank M. Monge for technical discussions and ST Microelectronics for chip fabrication.