US Patent 7190213 Digital time constant tracking technique and apparatus

Methods and apparatus are provided for tuning out time constant deviations of a network (414) due to process, voltage, and temperature variations. The apparatus (400) comprises a clock reference (404) from which a digital time constant is correlated to the nominal time constant of the network (414). The correlated digital time constant is applied to the network (414), and the output charge/discharge waveform swing is compared to a predetermined reference voltage. If the charge/discharge waveform swing does not match the reference voltage, an offset signal is generated. The offset signal is applied to a control circuit (402) that generates a corresponding tuning signal. The tuning signal is applied to the network (414) to adjust the internal components incrementally until a match is achieved. The apparatus (400) can be configured as a built-in self-test digital time constant tracking circuit, and can be integrated with the network (414) on an IC chip.