Patent ID: 8921757
Filing Date: 2014-12-30
Classification: H03F

Abstract:
1. A preamplifier for generating a preamplifier output voltage proportional to current derived from an optical sensor, the preamplifier including an input voltage clamp that prevents an input voltage from exceeding an input voltage limit, the preamplifier comprising: a preamplifier input, the preamplifier input being configured to receive an input current from the optical sensor; an input transistor configured to generate a drain output voltage proportional to the input current, where the drain output voltage drops rapidly when the input voltage or current exceeds a maximum operating input voltage or current; and a clamping transistor configured to limit the input voltage, the clamping transistor being gated by the drain output voltage of the input transistor, so that when the input transistor drain output voltage is at a normal operating level the clamping transistor is turned off, but if the input voltage or current surpasses the maximum operating input voltage or current, and the input transistor drain output voltage drops, the clamping transistor is turned on and conducts sufficient current from the preamplifier input to ground to inhibit the input voltage from rising above the input voltage limit.