Long-Term Storage Circuit Using a Sampling Technique

A circuit is presented that exhibits stable long-term memory analogous to that provided by Coulomb friction in mechanical systems. The circuit stabilizes the voltage across a capacitor. The capacitor voltage controls the length of a delay whose beginning is synchronized with a stable oscillator. At the end of the delay, the oscillator output is sampled and fed as a current to the capacitor. Periodic repetition of this procedure produces an average capacitor current that is a periodic function of capacitor voltage. Over the voltage range where the peak value of this current exceeds the intrinsic leakage current, every other one of those voltages at which the net average current is zero is a stable voltage. The principles used in this circuit may be applied to cancel the drift of any viscous-type analog memory element. The stored values are discrete but may be made so numerous as to approximate true analog memory to virtually any desired degree.