Monitor-Based In-Field Wearout Mitigation for CMOS LC Oscillators

Failure due to aging mechanisms is an important concern for RF circuits. In-field aging results in continuous degradation of circuit performances before they cause catastrophic failures. In this regard, the lifetime of RF/analog circuits, which is defined as the point where at least one specification fails, is determined not only by aging at the device level but also by the slack in the specifications, process variations, and the stress conditions on each of the devices. In this paper, we present a methodology for analyzing, monitoring, and recovering performance degradation in cross-coupled LC oscillators caused by aging mechanisms in MOSFET devices. At design time, we identify reliability hot spots and concentrate our efforts on improving these components. We also identify the circuit variable that is easy to measure but highly correlated to the performance of the primary circuit and codesign the monitoring and reconfiguration mechanism along with the primary circuit. Experimental results with a fabricated oscillator chip show that the phase noise of the oscillator degraded by 1.5 dB over ten days (240 h) of accelerated stress conditions, and this loss can be recovered by the proposed mitigation scheme.