Patent ID: 7279996

Claim:
A method for testing functionality in a ring oscillator that comprises an odd number of inverters connected to form a closed loop, each inverter having an input and an output wherein the output of an inverter is connected to the input of the next inverter in proceeding around the loop, said method comprising the steps of: inserting a first test device between the input of a first inverter and the output of an adjacent second inverter; operating said first test device to apply first and second test bits as input test signals to said first inverter input; detecting the response to said applied first and second test bits at said output of said second inverter; using the detected response in evaluating the functionality of said ring oscillator; operating a second test device connected to said ring oscillator to provide further test bits for use in determining functionality of said first test device; and connecting a third test device to receive said response to said first and second test bit signals as a first input, and to receive the response to said further test bits as a second input, said first and second inputs to said third device collectively comprising a ring oscillator output for use in evaluating the functionality of said ring oscillator.