Digital time constant tracking technique and apparatus

A digital time constant tracking circuit for tuning out time constant variations of a resistor-capacitor (RC) network, comprising:

• a clock reference standard configured to generate digital time constant pulses having a pulse width correlated to the nominal time constant of the RC network;
• a resistor array and a capacitor array within the RC network configured to receive the digital time constant pulses from the clock reference standard and to output a charge/discharge waveform in time synchronism with the received digital time constant pulses;
• a comparator configured to receive the charge/discharge waveform from the RC network at a first input, and to receive a predetermined reference voltage at a second input, and to generate a tune signal when the voltage swing of the charge/discharge waveform does not equal or exceed the level of the predetermined reference voltage, and to generate a stop signal when the voltage swing of the charge/discharge waveform does equal or exceed the level of the predetermined reference voltage;
• and
• a control circuit configured to receive the tune and stop signals from the comparator, and to generate an output tuning signal corresponding to a received tune signal, wherein the output tuning signal is applied to the resistor and capacitor arrays in the RC network to adjust the time constant of the RC network so that the voltage swing of the charge/discharge waveform is substantially equal to the predetermined reference voltage.

A digital time constant tracking circuit for stabilizing the time constant and corresponding bandwidth of a filter network, comprising:

• a clock reference standard configured to generate digital time constant pulses having a pulse width correlated to the nominal time constant of the filter network;
• a component array within the filter network configured to receive the digital time constant pulses from the clock reference standard and to generate an output voltage waveform in time synchronism with the received digital time constant pulses;
• a comparator configured to receive the output voltage waveform from the filter network at a first input, and to receive a predetermined reference voltage at a second input, and to generate a tune signal when the voltage swing of the output voltage waveform does not equal or exceed the level of the predetermined reference voltage, and to generate a stop signal when the voltage swing of the output voltage waveform does equal or exceed the level of the predetermined reference voltage;
• and
• a control circuit configured to receive the tune and stop signals from the comparator, and to generate an output tuning signal corresponding to a received tune signal, wherein the output tuning signal is applied to the component array in the filter network to adjust the time constant of the filter network so that the voltage swing of the output voltage waveform is substantially equal to the predetermined reference voltage, thereby stabilizing the time constant and the corresponding bandwidth of the filter network.