Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2002-05-30
2003-12-02
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C342S135000, C342S145000, C356S005010, C356S005100
Reexamination Certificate
active
06657704
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a distance measurement apparatus using an electromagnetic wave modulated in accordance with a pseudo random noise code.
2. Description of the Related Art
A prior-art distance measurement apparatus of a spread spectrum type measures the distance between the apparatus and a target object by using an electromagnetic wave modulated in accordance with a pseudo random noise code (a PN code). Specifically, a beam of an electromagnetic wave whose amplitude is modulated in accordance with a PN code of a predetermined bit length (a predetermined chip length) is emitted in a forward direction with respect to the body of the apparatus. A moment of the transmission of the PN code with the electromagnetic wave is memorized. The prior-art apparatus receives an echo beam caused by reflection of the forward electromagnetic-wave beam at a target object. The received echo beam is converted into a corresponding electric signal. The echo-beam-corresponding electric signal is binarized into a bi-level echo electric signal. Calculation is made about the value of the correlation between the bi-level echo electric signal and the PN code used for the modulation of the transmitted electromagnetic wave. A moment at which the calculated correlation value peaks is detected as a moment of the reception of the PN code contained in the echo beam. The prior-art apparatus calculates the distance between the apparatus and the target object from the time interval between the moment of the transmission of the PN code and the moment of the reception thereof.
An example of the electromagnetic wave is light emitted from a laser diode. In this case, the prior-art apparatus uses a photodiode or a phototransistor as a photodetector (a photoelectric conversion device) for converting a received echo beam into a corresponding electric signal. The photodetector outputs the electric signal. The voltage of the electric signal outputted from the photodetector varies only in a positive side or a negative side of a circuit reference potential generally equal to a circuit ground potential. In the prior-art apparatus, binarizing the output signal of the photodetector is implemented by comparing the voltage of the output signal of the photodetector with a threshold voltage (a decision reference voltage). To accurately binarize the output signal of the photodetector, it is necessary to properly set the threshold voltage with respect to a range in which the voltage of the output signal of the photodetector varies. Inaccurately binarizing the output signal of the photodetector reduces the accuracy of the calculated distance to a target object.
Japanese patent application publication number 5-264724 discloses a distance measurement apparatus using a radio SS (spread spectrum) signal. The apparatus in Japanese application 5-264724 is divided into a transmitter and a receiver. The transmitter includes a PN generator, a carrier generator, a multiplier, and an RF (radio frequency) portion. The PN generator outputs a PN code to the multiplier. The carrier generator outputs a carrier to the multiplier. The multiplier executes multiplication between the PN code and the carrier, thereby subjecting the carrier with phase modulation responsive to the PN code. The multiplier outputs the modulation-resultant signal to the RF portion. The RF portion converts the output signal of the multiplier into a radio SS signal. The RF portion feeds the radio SS signal to a transmission antenna. The transmission antenna radiates the radio SS signal as a forward signal. The receiver includes an RF portion, a correlator, a detection and wave-shaping portion, a time calculator, and a distance calculator. The PN generator in the transmitter outputs a reference bit signal in the PN code to the time calculator, thereby starting the time calculator counting pulses of a clock signal. A reception antenna receives an echo radio SS signal. The received echo radio SS signal is fed from the reception antenna to the receiver RF portion. The receiver RF portion derives an echo PN code from the received echo radio SS signal. The receiver RF portion outputs the echo PN code to the correlator. The correlator calculates the correlation between the echo PN code and a reference PN code which is the same as the PN code outputted from the PN generator in the transmitter. The correlator generates an autocorrelation waveform signal in response to the calculated correlation. The autocorrelation waveform signal has an amplitude which is maximized when the echo PN code comes into agreement with the reference PN code. The correlator outputs the autocorrelation waveform signal to the detection and wave-shaping portion. The detection and wave-shaping portion subjects the autocorrelation waveform signal to a detection process. The detection and wave-shaping portion outputs the detection-process-resultant signal to the time calculator. The time calculator suspends counting pulses of the clock signal in response to the output signal of the detection and wave-shaping portion. Specifically, the time calculator suspends counting when the echo PN code comes into agreement with the reference PN code. The number of pulses counted by the time calculator indicates the time interval from the transmission of the PN code to the reception of the PN code. The time calculator informs the distance calculator of the time interval. The distance calculator computes, from the time interval, the distance to a measured object reflecting the forward radio SS signal and causing the echo radio SS signal.
Japanese patent application publication number P2000-338243A discloses a coherent laser radar apparatus including a CW laser device and a first optical coupler. The CW laser device outputs a source laser beam to the first optical coupler. The first optical coupler divides the source laser beam into a first sub light beam and a second sub light beam. The first sub light beam propagates from the first optical coupler to an optical modulator. The optical modulator modulates the first sub light beam in accordance with a pseudo random signal (a PN code signal) outputted from a PN-code generator. The modulation-resultant light beam propagates from the optical modulator to an optical antenna before being emitted from the optical antenna as a forward light beam. The forward light beam reaches a target, being scattered and reflected thereby and forming an echo light beam. The echo light beam reaches the antenna. The echo light beam travels from the antenna to a second optical coupler. The second sub light beam propagates from the first optical coupler to a frequency shifter. The frequency shifter changes the frequency of the second sub light beam to generate a local light beam. The local light beam propagates from the frequency shifter to the second optical coupler. The second optical coupler mixes the echo light beam and the local light beam. The second optical coupler outputs the mixing-resultant light beam to an optical detector. The optical detector subjects the mixing-resultant light beam to optical heterodyne detection, thereby generating a beat signal between the echo light beam and the local light beam. The optical detector outputs the beat signal to a correlator. A variable delay device receive the pseudo random signal from the PN-code generator. The variable delay device defers the pseudo random signal by a variable time to generate a delayed pseudo random signal. The variable delay device outputs the delayed pseudo random signal to the correlator. The correlator calculates the correlation between the beat signal and the delayed pseudo random signal. The correlator outputs a correlation-representing signal to a signal processor. The PN-code generator feeds the signal processor with information about the pseudo random signal. The variable delay device informs the signal processor of the signal delay time provided thereby. The signal processor analyzes the strength and frequency of the correlation-resultant signal in response to the infor
Morikawa Katsuhiro
Shirai Noriaki
Buczinski Stephen C.
Denso Corporation
Posz & Bethards, PLC
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