Self-Powered Artificial Sensory Nervous System Using Ring Oscillator for Pulse Density Modulation

Unlike typical sensor electronics that always require a voltage source for sensors, amplifiers, and analog-digital converters, we use a mechano-electric transducer as a sensor and also in place of a power source to drive the rest of the electronics, thereby realizing an autonomous self-powered artificial sensory nervous system. A piezoelectric (lead zirconate titanate oxide) PZT is used as an inertia sensor that produces a voltage signal as a function of the acceleration of incoming vibrations. The PZT output current is rectified and stored in a capacitor to develop a time-varying dc voltage of typically upward of 1 V, which is used to drive a subsequent three-stage ring oscillator. The running frequency of the ring oscillator is voltage-controlled by three orders of magnitude from 2.1 kHz to 1.3 MHz within a single period of the sinusoidal waveform of acceleration that has the acceleration of 9 m/
$\text{s}^{2}$
at 160 Hz. By repeatedly counting the number of pulses in an every 6.3-ms time frame, the original waveform of the incoming acceleration is reproduced as a digital data. Dynamic range is defined by the frequency shift from 2.1 kHz to 3 MHz when the acceleration amplitude is changed from 6 to 12 m/
$\text{s}^{2}$
, thereby yielding a sensitivity of 240
$\text{s}^{2}$
/m.