On-Chip Measurement of Rise/Fall Gate Delay Using Reconfigurable Ring Oscillator

In this brief, a new technique to measure the on-chip rise/fall delay of an individual gate is presented. In the proposed technique, the rise/fall gate delay is measured using the duty cycle of a reconfigurable ring oscillator (RRO). A set of linear equations is formed with the different configuration settings of the RRO, relating the rise/fall delay of all the gates in the path of the RRO to the positive/negative duty cycle of the undivided RRO. The high-frequency undivided RRO signal is needed for this type of measurement as it preserves the rise/fall delay of an individual gate. However, it is difficult to bring the high-frequency undivided RRO signal outside the chip due to the frequency limitation of the output pad. The high-frequency RRO signal is subsampled by a clock that is generated from an on-chip phase-locked loop to make it low frequency. The rise and fall delays of an individual gate can be calculated from the difference of the duty cycle of the subsampled RRO signal at two different configurations of the RRO. The proposed concept is validated in a test chip that is fabricated in an industrial 65-nm technology node.