Abstract: To improve noise rejection, a native (or undoped) NMOS transistor is used as a source follower in place of a conventional common source PMOS transistor in a voltage regulator circuit. The native transistor has a threshold voltage of approximately 0 volts which allows the maximum voltage output of the regulator to be higher by one threshold voltage of a conventional NMOS transistor than might be obtained from a voltage regulator that used a conventional NMOS transistor. Alternatively, a depletion transistor can be used to provide even higher output. In another illustrative embodiment, a conventional bandgap reference circuit is modified by replacing a common source transistor connected to the output of an op amp with a native MOS transistor connected as a source follower.

Abstract: Techniques are provided for monitoring the performance of circuits and replacing low performing circuits with higher performing circuits. A frequency detector compares the frequency of a first periodic signal to the frequency of a second periodic signal. The difference in the frequency between the first periodic signal and the second periodic signal indirectly indicates how much the threshold voltages of the transistors have shifted. The difference in frequency between the two periodic signals can be monitored to determine the speed and performance of circuits on the chip. The output of the frequency detector can also indicate when to replace low performing circuits with higher performing circuits. When the frequency of the second periodic signal differs from the frequency of the first periodic signal by a predefined percentage, a low performing circuit is replaced with a higher performing replica circuit.