Self-biasing low power adaptive photoreceptor

This report describes a self-biased 5-transistor, 2-capacitor, adaptive logarithmic photoreceptor circuit. The photoreceptor uses its photocurrent, multiplied by a constant factor, to bias its forward amplifier. As a result, power consumption scales with illumination and takes on low values under typical illumination levels. This scaling enables solar powered operation, because power consumption scales with available power. As in earlier circuits, the photoreceptor has an adaptive logarithmic response: it has a bandpass characteristic with low gain for DC (including mismatch) and a higher gain for transient changes in contrast. The gain-bandwidth product is higher than for a passive architecture by a desired multiple. Stability criteria, sharing the bias among many photoreceptors, and measurements from a fabricated chip are shown.