Abstract: An optical sensor circuit for improved background signal cancellation in a musical instrument pickup. An operational amplifier is configured as a transimpedance amplifier (TIA). The TIA is electrically coupled to a first photodetector and a second photodetector in a series connection wherein the anode of the first photodetector and the cathode of the second photodetector are electrically coupled to define a connection node that is electrically coupled to an input of the TIA. In this configuration, symmetric in-band and out-of-band background optical signals and symmetric DC signals received by the pickup are negated. Asymmetric non-DC signals that are output from the photodetectors are passed to the input of the TIA as a signal of interest generated at the connection node.

Abstract: A device and method for an amplitude modulated optical pickup for a stringed instrument are disclosed. A first optical source comprising a first output signal comprising a first carrier frequency is provided and a first photodetector is in optical communication with the first optical source. A vibrating element such as a string on a musical instrument is disposed in an optical path between the first optical source and the first photodetector whereby a vibration of the element varies and modulates an amplitude of the first output signal received by the photodetector that is proportional to an element vibration amplitude and is at the same frequency as the element vibration frequency. An amplitude modulated (AM) photodetector signal output is generated from the first photodetector. The resultant signal is then demodulated with appropriate circuitry to produce a substantially noise free electronic signal representative of the element vibration frequency.