Area-efficient reconfigurable ring oscillator for device and circuit level characterization of static and dynamic variations

Abstract

Accurate characterization of transistor variation under dynamic switching condition has become important for reliable digital circuit design. This paper proposes a reconfigurable ring oscillator (RO) structure which enables measurement of transistor level variation. Each inverter stage in the RO can be configured into several delay modes. The delay of a particular inverting stage can be made dominant by configuring an inhomogeneous RO structure. By scanning the inhomogeneous stage, delay variation of each stage can be measured. Furthermore, pMOSFET and nMOSFET variation can be measured separately by making only rise or fall delay dominant. Specific transistor with random telegraph noise (RTN) in the inhomogeneous stage can be identified by reconfiguring the inhomogeneous stage. Thus, using a single RO, static delay variation as well as dynamic variation such as RTN can be measured. The area for a 127-staged reconfigurable RO including peripheral circuits is only 0.0085 mm2 thus area-efficient measurement becomes possible. Measurement results from a 65-nm test chip shows the validity of the proposed circuit structure.

Wide-Supply-Range All-Digital Leakage Variation Sensor for On-Chip Process and Temperature Monitoring

“…variation is measured by configuring the RO as inhomogeneous and then measuring the oscillation periods by swapping the inhomogeneous stage across the inverter chain [24]. Fig.…”

“…One example can be to take the delay ratio of two transistors to (5). Assuming variation in sub-threshold swing coefficient and DIBL coefficient to be negligible, delay ratio can be expressed as follows: (24) Here, and are oscillation periods for the th and th stage respectively. and need to be chosen such that gives us sufficient resolution of temperature monitoring.…”

“…and need to be chosen such that gives us sufficient resolution of temperature monitoring. Equation (24) does not have supply voltage related term and only depends on temperature. Thus, the proposed sensor provides opportunities to implement various methods by exploiting the capability of monitoring multiple transistors.…”

Wide-supply-range all-digital leakage variation sensor for on-chip process and temperature monitoring

“…The proposed sensor can monitor I leak variation as well as average I leak of nMOSFET and pMOSFET. I leak variation is measured by configuring the RO as inhomogeneous and then measuring the oscillation periods by swapping the inhomogeneous stage across the inverter chain [24]. output node will be driven by the footer nMOSFET I leak .…”

In-situ variability characterization of individual transistors using topology-reconfigurable ring oscillators

“…In order to overcome the above problems, a topologyreconfigurable RO structure is proposed where transistor-bytransistor variability becomes visible [10,11]. This paper develops an estimation and characterization methodology by which variability of each transistor in the RO can be characterized.…”