A 1V, 1mW, 4GHz Injection-Locked Oscillator for High-Performance Clocking

Abstract

Abstract-Injection-locked clocking (ILC) has been proposed [1] to improve the skew and jitter performance while reducing the power consumption in multi-gigahertz clock distribution networks. This paper presents a new design of the injectionlocked oscillator (ILO) suitable for ILC applications. It uses a transformer to generate differential signals and then directly inject them into the ILO core. It also incorporates a switchedcapacitor array for frequency tuning and hence digital deskew in ILC. A 4GHz test chip was designed and fabricated in a 0.18um standard digital CMOS. It consists of four ILOs driven by a balanced H-tree. Each ILO consumes less than 1mW from a 1V power supply. 5-bit digital deskew achieves 55ps delay tuning range and 1.8ps resolution. Measurement shows that only 30fs cycle-to-cycle jitter degradation was introduced and no phase noise degradation at frequency offset up to 600kHz.

Active deskew in injection-locked clocking

“…This phase tuning characteristics of an ILO is plotted in Fig. 2b, which shows the phase shift with respect to frequency tuning at different injection ratios [15]. It can be seen that the phase shift tuning characteristics is pretty linear in the middle of the tuning range for all injection ratios, which is good for linear deskew implementation.…”

“…The key for such an active deskew scheme is the phase tuning capability of ILOs, which has been demonstrated in our previous work [1], [14], [15]. As shown in Fig.…”

“…Each ILO drives a 2pF clock load, which models the local clock load in real processors, ). The ILOs use a newly developed transformer-direct-injection topology [15], as shown in the blow-up of Fig. 4.…”

“…Frequency tuning of an ILO can be implemented like in a generic voltage controlled oscillator by varactors [1] or switched capacitor array [15] in its resonator. The switched capacitor array approach is more suitable for digital deskew control.…”

“…Therefore, we propose a new active deskew scheme that utilizes the phase tuning capability of ILOs to compensate the skew [1], [15]. This deskew scheme does not require the additional deskew delay lines and hence does not suffer in clock latency and jitter while consuming minimal extra power.…”