Apparatus and methods for transmitting electrical signals indicative of optical interactions between a light beam and a flowing suspension of particles

Abstract

A system and methods for transmitting analog signals, particularly analog signals derived from an optical signal intensity, in a noisy environment over a length of cable. The optical signal is sensed by a photodetector, which is bootstrapped and backbiased to minimize the capacitive effect of the photodetector, and converted to a voltage by a transconductance stage. The voltage signal is then driven over a length of cable by a buffer amplifier having a low impedance output substantially matched to the characteristic impedance of the cable (e.g., twin lead wires having a Z.sub.0 =120), to a second circuit board. The cable length may be, e.g, less than a meter. The second circuit board contains a high gain amplifier stage and circuits for processing the high gain amplifier signal to derive, e.g, a peak pulse amplitude corresponding to the peak intensity of the optical signal sensed at the first circuit board. The processing circuit also may include circuits to discriminate valid pulses from invalid pulses so that only valid pulse data is retained. The processing circuitry also may include automatic gain control, attenuation and DC signal restoration, and a test pulse generator for injecting calibrated test pulses into the first circuit board (or the second circuit board) to test the quality of or to calibrate the signal processing function and noise immunity.

Dependencies are inferred from the claim text.