Apparatus and methods for transmitting electrical signals indicative of optical interactions between a light beam and a flowing suspension of particles
First Claim
1. Apparatus for detecting an optical signal representing optical interactions between a light beam and a flowing stream of particles and transmitting a low gain electronic output representative of the optical interactions, comprising:
- a first circuit board including a high gain amplifier having an input and an output;
a cable having a characteristic impedance, a first end and a second end, the first end being coupled to the high gain amplifier input; and
a second circuit board including;
a first amplifier having a current output;
a photodetector connected to said first amplifier current output, the photodetector having an optical input and an electrical signal output responsive to an optical signal intensity at the optical input;
a second amplifier coupled to said photodetector electrical signal output having a first amplified voltage output;
an RC filter having as an input the first amplified voltage output and having a filtered voltage output corresponding to the filtered first amplified voltage output; and
a third amplifier having as an input said filtered voltage output, and a second amplified output coupled to the second end of the cable, the second amplified output having a low impedance output to match substantially the characteristic impedance of the cable.
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Accused Products
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 Z0 =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.
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Citations
17 Claims
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1. Apparatus for detecting an optical signal representing optical interactions between a light beam and a flowing stream of particles and transmitting a low gain electronic output representative of the optical interactions, comprising:
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a first circuit board including a high gain amplifier having an input and an output; a cable having a characteristic impedance, a first end and a second end, the first end being coupled to the high gain amplifier input; and a second circuit board including; a first amplifier having a current output; a photodetector connected to said first amplifier current output, the photodetector having an optical input and an electrical signal output responsive to an optical signal intensity at the optical input; a second amplifier coupled to said photodetector electrical signal output having a first amplified voltage output; an RC filter having as an input the first amplified voltage output and having a filtered voltage output corresponding to the filtered first amplified voltage output; and a third amplifier having as an input said filtered voltage output, and a second amplified output coupled to the second end of the cable, the second amplified output having a low impedance output to match substantially the characteristic impedance of the cable. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of transmitting an electrical signal representative of an interaction between a light beam and a flowing stream of particles comprising:
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(a) sensing an optical signal having a variable intensity corresponding to the interaction of particles passing through the light beam with a photodetector having a capacitive effect and a sensed optical signal output; (b) minimizing the capacitive effect of the photodetector by bootstrapping and backbiasing the photodectector; (c) converting the sensed optical signal from the photodetector to an analog electrical signal; (d) low pass filtering the analog signal; (e) driving the filtered analog signal with a buffer amplifier having a low impedance output over a length of cable; (f) amplifying the low gain signal transmitted over the cable, thereby to provide a high gain signal; and (g) processing the high gain signal and determining therefrom a peak amplitude indicative of a peak intensity of the optical signal. - View Dependent Claims (12, 13, 14, 15, 16, 17)
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Specification