Ring oscillator and test method and apparatus employing a ring oscillator for verifying fabrication of transistors in an integrated circuit

摘要

A ring oscillator for a test apparatus and method for verifying fabrication of transistors in an integrated circuit on a die under test is implemented. The ring oscillator is fabricated on the die and includes a positive feedback loop between a circuit output terminal and a feedback input terminal. The feedback loop includes a plurality of delaying stages connected in cascade. A transfer gate is coupled to each delaying stage. Each of the transfer gates includes a pair of transistors of the first and second conductivity types connected in parallel. The ring oscillator is operable to provide a first oscillator output signal during a first test mode when the transistors of the first conductivity type are ON and the transistors of the second conductivity type are OFF. The ring oscillator is operable to provide a second oscillator output signal during a second test mode when the transistors of the first conductivity type are OFF and the transistors of the second conductivity type are ON. The ring oscillator is operable to provide a second oscillator output signal during a second test mode when the transistors of the first conductivity type are ON and the transistors of the second conductivity type are ON.