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.

A voltage converter includes a first N-channel MOSFET transistor, an inverter, a plurality of serially-connected diodes and a second N-channel MOSFET transistor. The inverter is coupled to the gate of the first N-channel MOSFET transistor to turn on/off the voltage converter. The anode of the diodes is coupled to the source of the first N-channel MOSFET transistor and the cathode of the diodes are coupled to the drain of the second N-channel MOSFET transistor. Since the source of the second N-channel MOSFET transistor is ground, the voltage clamped at the source of the first N-channel MOSFET transistor is not higher than 3.4V when a high voltage applied to the gate of the second N-channel MOSFET transistor turns it on.

Voltage regulator circuitry is provided that produces a stable programming-voltage on a programmable integrated circuit. The programmable integrated circuit has programming control circuitry that provides logic-level programming signals. A controllable voltage supply increases the strength of the logic-level programming signals to produce programming-voltage-level programming signals. The programming-voltage-level programming signals are used to program programmable elements such as flash transistors on the programmable integrated circuit. A temperature-insensitive diode-based voltage feedback circuit is connected to the output of the controllable voltage supply. The voltage feedback circuit provides a corresponding feedback voltage to the controllable voltage supply that the controllable voltage supply used to stabilize the magnitude of the programming-voltage-level programming signals.

Integrated circuit standby power consumption may be reduced using a reverse-bias transistor control arrangement that reduces transistor leakage current. Integrated circuit transistors may be turned off using a reverse bias voltage rather than a ground voltage. A charge pump circuit on the integrated circuit may be used to generate the reverse bias voltage. The reverse bias voltage may also be provided from an external source. The integrated circuit may be a programmable logic device in which logic is configured by providing programming data to configuration cells. The configuration cells may be used to apply either a positive power supply voltage to a given transistor to turn that transistor on or to provide the reverse bias voltage to that transistor to turn that transistor off.

Integrated circuits are stabilized by monitoring changes that affect circuit operation and by compensating for those changes using power supply adjustments. Changes in operating temperature and threshold voltage changes may be measured. Differential measurements may be made in which threshold voltages measured in continuously-biased monitoring circuits are compared to threshold voltages measured in intermittently-biased monitoring circuits. Temperature changes may be monitored using a temperature monitoring circuit based on an adjustable current source and a diode. Monitoring and compensation circuitry on the integrated circuits may use analog-to-digital and digital-to-analog converters controlled by a control unit to make temperature and threshold voltage measurements and corresponding compensating changes in power supply voltages.