Diagnostic ring oscillator circuit for dc and transient characterization

Abstract

A ring oscillator (RO) circuit for capturing one or more characteristics relating to aging of CMOS circuitry in a CMOS device has been described. The RO circuit includes a plurality of stages coupled via an RO feedback signal line and forming an inverter chain. The plurality of stages include, for each stage, a respective CMOS inverter comprising a pair of pMOS and nMOS transistors followed by a pass gate, wherein an output of a pass gate for a stage is coupled to an input for the respective CMOS inverter of a next stage. The plurality of stages include an enable stage to enable the inverter chain to be put into a free oscillating mode or another mode in which the RO circuit does not freely oscillate. The plurality of stages include a Device Under Test (DUT) stage preceded by a pre-stage where respective supply rails of the DUT stage and pre-stage are isolated from one another.