Photodetector circuit for an electronic sprayer
DCFirst Claim
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1. A method comprising:
- receiving radiation A of a first wavelength on a photodetector, the radiation A of the first wavelength being modulated with a modulation signal MA of a first frequency; and
coupling the photodetector to an active filter tuned to a frequency substantially equal to the first frequency such that the active filter outputs a signal of the first frequency, the frequency to which the active filter is tuned being substantially independent of whether ambient radiation impinges upon the photodetector.
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Abstract
An agricultural implement for spraying herbicide on weeds in a field without spraying herbicide on bare soil includes a photodetector circuit. The photodetector circuit includes a photodetector and an active filter. The photodetector is not AC coupled in parallel with an inductor/capacitor resonant circuit which tunes the active filter. As a result, changes in photodetector capacitance due to changes in ambient lighting conditions are not impressed across the resonant inductor/capacitor circuit and therefore do not adversely change the frequency and phase characteristics of the photodetector circuit.
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Citations
15 Claims
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1. A method comprising:
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receiving radiation A of a first wavelength on a photodetector, the radiation A of the first wavelength being modulated with a modulation signal MA of a first frequency; and coupling the photodetector to an active filter tuned to a frequency substantially equal to the first frequency such that the active filter outputs a signal of the first frequency, the frequency to which the active filter is tuned being substantially independent of whether ambient radiation impinges upon the photodetector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An agricultural implement comprising:
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a first light source emitting light modulated with a first modulation signal of a first frequency, the first modulation signal having a first phase; a second light source emitting light modulated with a second modulation signal, the second modulation signal having a second phase different from the first phase; a photodetector configured to receive light emitted from the first and second light sources, the light having scattered off an object in a field; and an active filter having an input terminal connected to the photodetector and an inductor coupled in parallel with a capacitor such that the active filter is tuned to the first frequency; wherein the photodetector is not AC coupled in parallel with the inductor. - View Dependent Claims (10, 11)
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12. A system comprising:
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a photodetector having first and second terminals, the photodetector configured to receive light and to provide an output signal on the first terminal; an amplifier including; an input terminal connected to the first terminal of the photodetector, the amplifier configured to receive the output signal from the photodetector; and a resonant circuit tuned to a selected frequency, the resonant circuit including a capacitance having first and second nodes; wherein at least one of the first and second terminals of the photodetector is electrically isolated from the first and second nodes of the capacitance of the resonant circuit. - View Dependent Claims (13, 14, 15)
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Specification