System and method for measuring negative bias thermal instability with a ring oscillator
View Patent ↗An integrated circuit, in accordance with one embodiment of the present invention, includes a first device under test (DUT), a first ring oscillator, a second DUT and a second ring oscillator. The first DUT is biased such that interface traps are generated during a first mode. The generated interface traps result in a decrease in a first drive current of the first DUT. The second device under test is biased to maintain a reference drive current during the first mode. The operating frequency of the first ring oscillator, during a second mode, is a function of the first drive current. The operating frequency of the second ring oscillator, during the second mode, is a function of the reference drive current. The integrated circuit may also include a comparator for generating an output signal as a function of a difference between the operating frequency of the first and second ring oscillator.
1. A method of measuring negative bias thermal instability, said method comprising:
generating a first drive current at a first device under test;
generating a reference drive current at a second device under test;
generating a first oscillator signal responsive to said first drive current during a second mode of operation of said first device under test;
generating a second oscillator signal responsive to said reference drive current during said second mode of operation of said second device under test; and
comparing said first oscillator signal and said second oscillator signal.
2. The method as described in claim 1 further comprising:
disabling said first oscillator signal when said first device under test is operating in a first mode of operation; and
disabling said second oscillator signal when said second device under test is operating in said first mode of operation.
3. The method as described in claim 1 further comprising:
generating interface traps operable to decrease said first drive current when said first device under test is operating in a first mode.
4. The method as described in claim 1 further comprising:
substantially maintaining said reference drive current when said second device under test is operating in a first mode of operation.
5. The method as described in claim 1 , wherein said comparing further comprises:
generating an output signal that is a function of a difference between said operating frequency of said first oscillator signal and said second oscillator signal.
6. The method as described in claim 1 , wherein said first device under test and said second device under test comprise at least one transistor.