Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Synchronizing
Reexamination Certificate
2002-03-05
2004-08-03
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Synchronizing
C327S269000, C327S270000
Reexamination Certificate
active
06771103
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a time measurement apparatus. In addition, this invention relates to a distance measurement apparatus. Furthermore, this invention relates to an apparatus for generating a clock signal or a set of different-phase clock signals (multi-phase clock signals) which can be used in, for example, a time measurement apparatus or a distance measurement apparatus.
2. Description of the Related Art
A prior-art distance measurement apparatus of a spread spectrum type which is mounted on an automotive vehicle measures the distance between the present vehicle and a preceding target object such as a preceding vehicle by using an electromagnetic wave modulated in accordance with a pseudo random noise code (for example, a maximum length code). Specifically, a beam of an electromagnetic wave whose amplitude is modulated in accordance with a pseudo random noise code of a predetermined bit length is emitted in a forward direction with respect to the body of the present vehicle. A moment of the transmission of the pseudo random noise 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 preceding target object. The received echo beam is converted into a binary echo electric signal. Calculation is made about the value of the correlation between the binary echo electric signal and the pseudo random noise 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 pseudo random noise code contained in the echo beam. The prior-art apparatus calculates the distance between the present vehicle and the preceding target object from the time interval between the moment of the transmission of the pseudo random noise code and the moment of the reception thereof, and also from the velocity of the electromagnetic wave.
In the prior-art apparatus, the pseudo random noise code has a sequence of bits, the number of which is predetermined. The correlation-value calculation is iterated at a period corresponding to one bit of the pseudo random noise code. Accordingly, the time interval between the moment of the transmission of the pseudo random noise code and the moment of the reception thereof is determined at a resolution corresponding to a 1-bit time interval (a 1-chip time interval). A resolution of the measured distance between the present vehicle and the preceding target depends on the resolution of the determination of the time interval. In the case where a clock frequency, the reciprocal of which corresponds to a 1-bit time interval, is equal to 20 MHz, the resolution of the measured distance between the present vehicle and the preceding target is equal to 7.5 m.
U.S. Pat. No. 6,218,982 B1 corresponding to Japanese patent application publication number 2000-121726 discloses a distance measurement apparatus in which a pseudo random noise code is generated synchronously with a reference clock signal. A first forward electromagnetic wave is transmitted in response to the pseudo random noise code. A first echo wave is received which is caused by reflection of the first forward electromagnetic wave at an object. The received first echo wave is converted into a binary signal. A value of a correlation between the binary signal and the pseudo random noise code is repetitively calculated at a predetermined period having a synchronous relation with the reference clock signal. A time interval taken by the first forward electromagnetic wave and the first echo wave to travel to and from the object is measured in response to a timing at which the calculated correlation value peaks. Then, a second forward electromagnetic wave is transmitted in response to a transmitted pulse signal. A second echo wave related to the second forward electromagnetic wave is received. The received second echo wave is converted into a received pulse signal. A delay circuit defers the transmitted pulse signal by a delay time corresponding to the measured time interval to generate a delayed transmitted pulse signal. A phase difference between the received pulse signal and the delayed transmitted pulse signal is measured at a resolution higher than a resolution corresponding to the predetermined period of the correlation-value calculation. A distance to the object is calculated on the basis of the measured time interval and the measured phase difference.
U.S. Pat. No. 5,477,196 corresponding to Japanese patent application publication number 7-183800 discloses a pulse signal device for encoding a pulse phase difference or controlling an oscillation frequency based on delayed signals sequentially outputted by a delay circuit. The encoding of a pulse phase difference or the oscillation frequency control can be simultaneously performed by using a single delay device. There is provided a frequency converter including a ring oscillator consisting of inverting circuits interconnected in the form of a ring, a pulse phase difference encoding circuit for encoding the cycle of a reference signal into a binary digital value based on a pulse outputted by the ring oscillator, an arithmetic circuit for multiplying or dividing the binary digital value by a predetermined value to generate control data, and a digitally controlled oscillation circuit for generating a pulse signal in a cycle in accordance with the control data. The ring oscillator is shared by the encoding circuit and the oscillation circuit. This makes constant the time resolutions of the encoding circuit and the oscillation circuit, thereby allowing accurate frequency conversion.
U.S. Pat. No. 4,559,606 corresponding to Japanese patent application publication number 60-51338 discloses an arrangement to provide an accurate time-of-arrival indication for a received signal. The arrangement comprises a plurality of correlation means coupled to the received signal. The received signal is clocked into each of the plurality of correlation means by a different one of a plurality of different phased clocks. The different phased clocks occur at a predetermined different time uniformly spaced over a given time interval. The arrangement further comprises integration means coupled to each of the plurality of correlation means to provide the indication of the time of arrival of the received signals. The plurality of correlation means includes a plurality of received-signal shift registers into which the received signals are shifted by a different one of the plurality of phased clocks, a common reference signal shift register and a plurality of comparison means each coupled to each stage of a different one of the plurality of received-signal shift registers and each stage of the common reference signal shift register to compare the contents of the associated stages of the plurality of received-signal shift registers and the common reference signal shift register and to produce an output signal indicative of the results of each of the comparisons.
Japanese patent application publication number 4-363687 discloses a distance measurement system having a transmitter side and a receiver side. In the transmitter side, a carrier signal outputted from a carrier oscillator is spread-spectrum-modulated in accordance with a PN (pseudo noise) code fed from a PN code generator. The transmitter side transmits the modulation-resultant spread spectrum signal as a forward radio wave. An echo radio wave caused by reflection of the forward radio wave at an object is received by the receiver side, being converted into a received spread spectrum signal thereby. The receiver side includes a variable delay circuit which variably shifts the phase of the PN code used in the transmitter side to get a phase-shifted PN code. The receiver side detects a correlation between the phase-shifted PN code and the received spread spectrum signal. The receiver side determines the quantity of the PN-code phase shift at which the detected correlation peaks
Isomura Hirohumi
Watanabe Takamoto
Denso Corporation
Lam Tuan T.
Posz & Bethards, PLC
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