Modulated laser light detector with discrete fourier transform algorithm
AssigneeApache Technologies, Inc.
InventorsDuWain K. Ake, Ayman Hajmousa
Life of this patent
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Abstract
A modulated laser light detector that converts laser light energy into electrical signals which exhibit a frequency that is substantially the same as the laser light modulation frequency, in which these signals allow the detector unit to determine a position where the laser light is impacting upon a photodiode array. A superheterodyne receiver circuit is used to provide high gain at an improved signal-to-noise ratio to improve the range at which the modulated laser light signal can be reliably detected. Various types of signal detection circuits are available. Various processing algorithms are disclosed, including a Discrete Fourier Transform with a simplified computational algorithm for use with a low-power processor device.
Claims21
A method for detecting a modulated light beam, said method comprising:
- (a) receiving an electromagnetic laser signal having at least one predetermined range of wavelengths and at least one predetermined first modulation frequency, and converting said electromagnetic laser signal into a first electrical signal;
- (b) converting said first electrical signal from said at least one predetermined first modulation frequency to a second signal having at least one predetermined second, different frequency that is related to said at least one predetermined first modulation frequency;
- (c) sampling, over a sampling time interval, said second signal at a rate that is an integer multiple of said at least one second frequency, and determining a substantially instantaneous magnitude of said sampled second signal, thereby deriving multiple values A that each represent the substantially instantaneous magnitude of said sampled second signal;
- (d) determining a Discrete Fourier Transform (DFT) value for each said sampled second signal A over at least one complete period of said second frequency, thereby deriving multiple DFT values B;
- (e) after all samples are taken for a predetermined sample period, determining real and imaginary components of said multiple DFT values B, thereby deriving multiple values C;
- (f) determining a magnitude of a spectral component of said multiple values C, thereby deriving multiple values D;
- and
- (g) using one of said values D to substantially represent a steady state signal magnitude that is used as a representation of a signal strength of said second signal over the sampling time interval, and thereby determining a relative strength of said received modulated electromagnetic signal.
A modulated light detector, comprising:
- (a) at least one light photosensor, which generates at least one first electrical signal when receiving modulated light energy having at least one predetermined range of wavelengths and at least one predetermined range of modulation frequencies;
- (b) a first filter circuit having a predetermined frequency characteristic, which receives said at least one first electrical signal and outputs a filtered at least one second signal;
- (c) an intermediate frequency stage that (i) mixes said at least one second signal with a predetermined third signal to create a mixed signal, (ii) filters said mixed signal, and (iii) outputs at least one fourth signal, which has a substantially predetermined lower frequency component of said mixed signal;
- and
- (d) a processing circuit that is configured to:
- (i) receive said at least one fourth signal and sample it at a rate that is an integer multiple of said frequency of the substantially predetermined lower frequency component of said mixed signal;
- (ii) determine a substantially instantaneous magnitude of said sampled at least one fourth signal, thereby deriving multiple values A that each represent the substantially instantaneous magnitude of said sampled at least one fourth signal;
- (iii) determine a Discrete Fourier Transform (DFT) value for each said sampled second signal A over at least one complete period of said second frequency, thereby deriving multiple DFT values B;
- (iv) after all samples are taken for a predetermined sample period, determine real and imaginary components of said multiple DFT values B, thereby deriving multiple values C;
- (v) determine a magnitude of a spectral component of said multiple values C, thereby deriving multiple values D;
- and
- (vi) use one of said values D to represent a substantially steady state signal magnitude that is used as a representation of a signal strength of said at least one fourth signal, and thereby determine a relative strength of said received modulated light energy.
Dependencies are inferred from the claim text.