JP2002267752A - Time measuring device and distance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a time (distance) measuring device capable of setting a measurable time resolution higher than the time (distance) resolution determined by an operating clock frequency without increasing the operating clock frequency. SOLUTION: This spectrum diffused type distance measuring device comprises a shift clock generation part 20 for generating an 8-phase shift clock having the same period as a reference clock MCK used for emitting a range finding laser beam according to a PN code. The generated 8-phase shift clock is inputted to a latch part 22, whereby the received pulse Pbr of the reflected light from a target is latched at a timing synchronized to each clock. The thus- latched 8 kinds of binary data are inputted to 8 correlators 30, respectively, to calculate the correlation value of the received pulse line with the PN code, whereby the reciprocation time of the range finding laser beam between the device and the target is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time measuring device for measuring a time from a measurement start time to an input time of a pulse train generated based on a pseudo-random noise code using a reference clock having a constant period, and The present invention relates to a distance measuring device that measures a distance to a measurement target using the device.

[0002]

2. Description of the Related Art Conventionally, in a car, for example, a pseudorandom noise code (M-sequence code (maximum period code sequence)) or the like has been used as a distance measuring device for measuring the distance to an object (for example, a preceding vehicle) ahead in the traveling direction. 2. Description of the Related Art A spread-spectrum (hereinafter, also referred to as SS) distance measuring device that performs distance measurement using a PN code is known.

In this type of distance measuring device, first, an electromagnetic wave for transmission is amplitude-modulated by a PN code having a predetermined bit length,
This is transmitted toward the target, and the reflected wave is reflected by the transmitted electromagnetic wave hitting the target, and the binary signal corresponding to the PN code used for transmitting the electromagnetic wave is demodulated. Then, a correlation value between the demodulated binary signal and the PN code used for transmitting the electromagnetic wave is obtained by using a time measurement device (circuit) incorporated in the distance measurement device, and the time at which the correlation value becomes maximum is determined. By detecting, the time required for the electromagnetic wave to travel back and forth between the distance measuring device and the object is measured, and finally, the distance from the time and the speed of the electromagnetic wave (300,000 km / s) to the object is measured. Is calculated.

[0004]

However, such S
In the S type distance measuring device, the time resolution when measuring the round trip time of the electromagnetic wave using the time measuring device is determined by the frequency of the clock (that is, the reference clock) used to demodulate the binary signal corresponding to the PN code. There is a problem that the measurable distance resolution is limited by the frequency of the reference clock.

For example, when the frequency of the reference clock is 20 MHz
z, the measurable time resolution is 50 nsec.
(= 1 [sec.] / 20 × 10 ⁶ ), and the distance resolution that can be measured is 7.5 m (= 3 × 10 ⁸ [m / sec]).
c. ^{] × 50 × 10- 9 [sec} . / 2)).

Therefore, in the above-mentioned conventional distance measuring device, it is necessary to increase the frequency of the reference clock in order to increase the measurable distance resolution. For this purpose, a time measuring device incorporated in the distance measuring device is required. However, there is a problem that the device must be constituted by a circuit element capable of operating at high speed, which results in an increase in size and cost of the device. In addition, since there is a limit in increasing the speed of circuit elements, there is a limit in increasing the measurable time resolution even with the fastest circuit element that can be used at present.

On the other hand, as a technique for solving such a problem, the present applicant transmits and receives an electromagnetic wave modulated by a PN code, and measures the time required for transmitting and receiving the electromagnetic wave with a time resolution determined by the frequency of a reference clock. ,
By transmitting and receiving one pulse of electromagnetic waves, the error of the previously measured measurement time is measured using the gate delay time of the gate circuit, and the previously measured time is corrected using the measurement result. Then, the measurement target time (the distance to the measurement target) until the transmitted electromagnetic wave hits the obstacle and is reflected is determined by the gate delay time (several ns).
c. It has been proposed that measurement can be performed at a high resolution determined by the following (see JP-A-2000-121726).

[0008] However, the proposed device performs two types of time measurement, a low-resolution time measurement using a reference clock and a high-resolution time measurement using a gate delay time. Two types of devices must be incorporated in the distance measuring device, and the time measurement is performed in two stages, so that there is a problem that time measurement (and hence distance measurement) takes time.

In a distance measuring device, a laser beam is generally used as an electromagnetic wave for distance measurement. However, since the number of driving of a signal source (generally, a laser diode) for transmitting the electromagnetic wave is increased, There is also a problem that the signal source for transmitting electromagnetic waves is easily deteriorated due to heat generation or the like. In order to prevent this problem, it is only necessary to take measures to dissipate heat such as enlarging the heat sink for heat dissipation. However, in this case, the size of the apparatus is increased and the cost is increased.

[0010] The present invention has been made in view of such a problem, and in the above-described SS type time measuring apparatus,
A time measuring device capable of increasing the measurable time resolution to be higher than the time resolution determined by the frequency without increasing the frequency of a clock used for time measurement, and
An object of the present invention is to provide a distance measuring device for performing distance measurement using this device.

[0011]

According to a first aspect of the present invention, there is provided a time measuring apparatus, comprising: a plurality of shift clocks having the same period as a reference clock and different phases from each other; And a plurality of signal input means sequentially takes in, as binary data, an input signal including a pulse train generated according to the pseudo random code, using each of the plurality of generated shift clocks.

Then, the plurality of correlation means respectively calculate the correlation between the data sequence of the binary data fetched by each signal input means and the pseudo-random code used for generating the pulse train,
The detecting means detects the time at which the correlation between the data string of binary data and the pseudo-random code is maximum as the input time of the pulse train based on the calculation results of the correlation calculating means.

For this reason, the time resolution of the input time of the pulse train detected by the detecting means corresponds to the phase difference between the plurality of shift clocks, and the time resolution is synchronized with the period of the pulse train to be measured. It is higher than a conventional time measuring device (a time measuring device incorporated in the above-described SS type distance measuring device) that detects the input time of a pulse train using the reference clock thus set.

Therefore, according to the time measuring device of the present invention,
The time from the measurement start time to the input time of the pulse train generated according to the pseudo random code can be measured with a time resolution higher than the time resolution determined by the cycle of the reference clock (shift clock). If an SS type distance measuring device is configured using a time measuring device,
By increasing the measurable distance resolution, the distance to the object can be measured with high accuracy.

Further, in the time measuring device of the present invention, the time resolution that can be measured is determined by the phase difference between the shift clocks generated by the shift clock generating means, so that as the number of shift clocks increases, the number of shift clocks increases. Time resolution can be increased. Therefore, according to the time measuring device of the present invention, the measurable time resolution can be arbitrarily set according to the number of shift clocks.

Further, if the number of shift clocks is increased, the number of signal input means and correlation calculation means which operate corresponding to each shift clock is also increased. However, since the cycle of each shift clock is the same as the reference clock, the signal The operating speeds of the input means and the correlation operation means may be the same as in the case where time is measured using one reference clock. Therefore, it is not necessary to increase the operation speed of these signal input means and correlation calculation means in order to increase the measurable time resolution. Can be prevented from increasing costs.

By the way, the time measuring device of the present invention measures time using a phase difference between a plurality of shift clocks generated by the shift clock generating means as a time resolution. Although time can be measured with higher resolution than a conventional time measuring device that does not use a shift clock, variations occur in the minimum unit of time that can be obtained.

For this reason, in order to be able to always measure time with a stable time resolution, the shift clock generating means is required to set the shift clock generating means so that the phase is shifted by 1 / n of one cycle of the reference clock. It is preferable to generate n different shift clocks, and to provide n signal input units and n correlation operation units corresponding to the number of shift clocks generated by the shift clock generation unit. .

On the other hand, since the pulse train included in the input signal is generated at the same fixed period as the reference clock based on the pseudo random noise code, if no noise or the like is superimposed on the input signal, Is inverted in units of time corresponding to one cycle of the shift clock, and the same binary data is sequentially output from each signal input means starting from one of the signal input means. The calculated correlation value sequentially changes to the same value starting from one of the correlation calculation means.

However, like the distance measuring device described above,
If the input signal is a signal that receives an electromagnetic wave reflected from the object to be measured, noise is superimposed on the input signal. When the noise is superimposed on the input signal in this manner, the binary data input from each signal input unit to each correlation operation unit is affected by the noise and fluctuates, and the calculation results by the correlation operation unit also vary. Will be. This problem becomes a serious problem when, for example, the distance to the object is long and the signal level of the input signal is low.

If there is a variation in the calculation results of the correlation calculation means, the detection means cannot accurately detect the input time of the pulse train, and the time measurement accuracy (and hence the distance measurement accuracy) decreases. I do. Therefore, in order to prevent such a problem, each of the plurality of correlation calculation units may be configured as described in claim 3.

That is, in the time measuring device according to the third aspect, each of the correlation calculation means is a correlation calculation corresponding to the signal input means operated by the shift clock whose phase is the most different from the shift clock used by the corresponding signal input means. An averaging means is provided for averaging the operation result by adding the operation result of the means and its own operation result, and outputs the operation result averaged by the averaging means to the detection means.

As a result, the calculation results of the respective correlation calculation means are averaged using the calculation results of the other correlation calculation means, and the calculation result input to the detection means is calculated based on the noise superimposed on the input signal. Fluctuation due to the influence can be suppressed.
In order to maximize the phase difference between two clocks that change at a constant period, the phase difference may be set to 180 degrees. The most different shift clock may be a shift clock having a phase difference of 180 degrees or the closest to 180 degrees with respect to the shift clock used by the signal input means.

In the third aspect, the other averaging means sets another correlation operation means used for averaging as described above, because the specific correlation operation means is affected by noise superimposed on the input signal. This is because the correlation operation means which is not most affected by the noise when it is used is a correlation operation means corresponding to a shift clock whose phase is the most different from the shift clock corresponding to the specific correlation operation means.

Next, in the present invention, by providing a plurality of signal input means for taking in input signals with a plurality of shift clocks having different phases, sampling of binary data input from each signal input means to each correlation operation means is provided. The timing is shifted by the phase difference of each shift clock, and the time at which the correlation between the data sequence and the pseudo-random noise code becomes maximum can be detected with high time resolution by this shift. The correlation operation means for performing the correlation operation upon receiving the binary data does not need to operate in synchronization with each shift clock, and may operate on a common reference clock having the same cycle as each shift clock.

That is, the output from each signal input means 2
Even if the value data is latched by a common reference clock having the same cycle as each shift clock and input to each correlation operation means, each correlation operation means is operated by a common reference clock. The operation results obtained by the means are the same.

Further, if each correlation operation means is operated simultaneously with a common clock, the output timing of the operation result from each correlation operation means to the detection means becomes the same. Should be synchronized. Therefore, when actually configuring the time measuring device of the present invention, the binary data taken in by each signal input means is sampled by a common reference clock and sent to each correlation calculating means. An input signal synchronizing means may be provided so that each correlation calculating means and detecting means operate on the common reference clock.

With this arrangement, it is not necessary to supply the same shift clock to each of the correlation operation means as the corresponding signal input means, so that the wiring when the time measuring device is actually assembled on a printed circuit board or the like is reduced. Thus, the size of the device can be reduced. On the other hand, the detection means may detect the peak time at which the correlation between the data sequence and the pseudo random noise code becomes maximum from the calculation results of the plurality of correlation calculation means as the input time of the pulse sequence. In order to actually detect the peak time, the calculation result of each correlation calculation unit is sampled as time series data,
Since the timing at which the correlation value becomes maximum must be detected from among them, the detection timing is delayed.

Therefore, when the time measuring device of the present invention is actually mounted on a vehicle to measure the distance from a preceding vehicle or to detect an obstacle, the time can be detected earlier. To achieve this, the detecting means may be configured as described in claim 5. That is, in the time measuring device according to claim 5, the detecting means includes a time when one of the calculation results of each correlation calculating means exceeds a predetermined threshold value, and a calculation result when the calculation result exceeds the threshold value. The input time of the pulse train is detected based on the shift of the shift clock from the reference clock corresponding to the correlation calculating means that outputs the pulse signal.

Therefore, in the apparatus according to the fifth aspect, the input time of the pulse train is quickly increased at a timing when one of the calculation results of the correlation calculation means exceeds the threshold value (in other words, the peak time). , And the detection timing can be prevented from being delayed.

In this case, a plurality of calculation results among the calculation results of the correlation calculation means may exceed the threshold value at the same time. As described in claim 6, when a plurality of input times of the pulse train are simultaneously detected by the detecting means, a selecting means for selecting the earliest input time among the plurality of input times may be provided.

That is, according to this configuration, of the plurality of input times detected by the detecting means at the same operation timing,
Since the earliest input time is the input time of the pulse train,
It is possible to improve safety when the time measuring device is applied to a vehicle distance measuring device.

On the other hand, the invention according to claim 7 is a pulse train generating means for generating a pulse train corresponding to a pseudo-random noise code having a predetermined bit length in synchronization with a reference clock, and modulating by a pulse train generated by the pulse generating means. Transmitting means for transmitting the reflected electromagnetic wave, receiving means for receiving a reflected wave of the electromagnetic wave transmitted from the transmitting means and being reflected by the object to be measured, and restoring a pulse train; and a pulse train and a pulse train generating means restored by the receiving means. Based on the pseudo random noise code used to generate the pulse train, the time measuring means for measuring the time from when the transmitting means starts transmitting the electromagnetic wave to when the reflected wave is received, and the time measuring means for measuring the time. And a distance calculating means for calculating a distance to an object to be measured based on a measured time, and a distance measuring apparatus of a spread spectrum method (SS method). A.

In this distance measuring device, since the time measuring device according to any one of claims 1 to 6 is used as the time measuring means, the frequency of the reference clock used for distance measurement is increased. In other words, the time required for transmitting and receiving the electromagnetic waves for distance measurement (and hence the distance to the object to be measured) can be measured with high resolution.

Therefore, according to this distance measuring device, if it is mounted on a moving object such as an automobile and used as a radar device for detecting an obstacle requiring accuracy and speed of distance measurement or for automatically tracking a preceding vehicle. , Can exert excellent effects. That is, the time measuring device of the present invention (claims 1 to 6) does not need to increase the frequency of the reference clock in order to increase the measurable time resolution. According to the device, it is possible to realize a distance measuring device capable of measuring distance with high resolution without increasing the size of the device, and it can be a distance measuring device suitable for an in-vehicle radar device requiring miniaturization. .

As described above, according to the present invention (claim 1)
When the time measuring device of the present invention is applied to a distance measuring device, the distance calculating means generates a pulse train only once from the pulse train generating means for each distance measurement, and an electromagnetic wave modulated by the pulse train is used. By measuring the time until the light hits the object to be reflected by the time measuring device, the distance to the object to be measured may be measured, but more preferably, as described in claim 8 It is good to configure.

That is, in the distance measuring device according to claim 8, the distance calculating means generates a pulse train a plurality of times from the pulse train generating means for each distance measurement, and measures the time by the time measuring means with the generation of the pulse train. A plurality of pieces of time data are sequentially fetched, and a distance to the object to be measured is calculated from an average value of the plurality of fetched time data.

For this reason, according to the distance measuring device of the present invention, the time (distance) measured by generating a pulse train once from the pulse train generating means is deviated from the true value due to the influence of noise or the like. Also, by averaging the measurement results of a plurality of times, the accuracy of time (distance) measurement can be increased, and the resolution of the measurement results can be further increased by averaging. The distance can be measured with higher accuracy.

In the case where the distance measuring device is configured as described in claim 8, if the measurement result by the time measuring device deviates greatly from other measurement results, the measurement result is affected by noise. Therefore, it is more preferable that the distance calculation means is configured as described in claim 9.

In other words, in the distance measuring device according to the ninth aspect, the distance calculating means selects a time out of a predetermined range which is largely deviated from the center of the plurality of time data from the plurality of time data fetched from the time measuring means. Exclude the data and calculate the average value of the time data.

Therefore, according to the distance measuring apparatus of the ninth aspect, the time required for the electromagnetic wave to hit the object to be measured and reflected can be measured with higher accuracy, and the accuracy of distance measurement can be further improved. It is possible to do.

[0042]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram illustrating an entire configuration of a spread spectrum type distance measuring apparatus according to an embodiment to which the present invention is applied.

As shown in FIG. 1, the distance measuring apparatus of this embodiment is, for example, for measuring the distance to another vehicle which is mounted on an automobile and runs ahead, and has a predetermined frequency (for example, 20 MHz). A) a reference clock generator 10 for generating a reference clock MCK, and a pulse train corresponding to a PN code having a predetermined bit length (for example, a 31-bit pseudo random code composed of an M-sequence code) in synchronization with the reference clock MCK. A pulse generator 12 for generating a pulse and a pulse generator 1
And a light emitting unit 14 that emits laser light, which is an electromagnetic wave for distance measurement, toward the front of the vehicle in accordance with a pulse train (hereinafter, referred to as a light emission pulse) generated by the light emitting unit 2.

The light emitting section 14 includes a laser diode LD as a light emitting element, and the energization / de-energization of the laser diode LD is switched by a drive circuit 15 which receives an output (emission pulse) from the pulse generation section 12. Thus, a laser beam corresponding to the PN code is emitted.

Further, the pulse generator 12 in synchronization with the reference clock MCK, the microcomputer (hereinafter, simply referred to as CPU) is input PN code 2, the pulse generator 12, a PN code in accordance with the PN code A corresponding light emission pulse is generated. On the other hand, the distance measuring device according to the present embodiment includes a light receiving unit 16 that receives reflected light of laser light emitted from the light emitting unit 14 hitting an object to be measured in front of the vehicle, and a light receiving signal from the light receiving unit 16. And a light receiving signal amplified by the amplifier 17 is compared with a predetermined reference voltage Vref. When the light receiving signal is higher than the reference voltage Vref, the light receiving signal goes to the high level, and the light receiving signal is lower than the reference voltage Vref. When is Lo
A comparator 18 that outputs a light receiving pulse PBr at w level is provided.

The light receiving section 16 includes a photodiode PD connected in a reverse bias state to a power supply line via a current detecting resistor or the like, and a laser beam (reflected light from an object to be measured) is applied to the photodiode PD. Is detected as a voltage value when the photocurrent flows due to the incident light.

In this embodiment, the pulse generator 12
The driving circuit 15 and the light-emitting unit 14 for receiving a light-emission pulse from the pulse generation unit 12 and emitting a laser beam for distance measurement correspond to the pulse train generation means according to the seventh invention. A light receiving unit 16, which corresponds to a transmitting unit and receives the reflected light of the emitted laser light to generate a light receiving pulse PBr;
The amplifier 17 and the comparator 18 correspond to a receiving unit described in claim 7.

Next, in the distance measuring apparatus of the present embodiment, eight kinds of clocks CKa and CKb synchronized with the reference clock MCK and having different phases are based on the reference clock MCK generated by the reference clock generator 10. , ... CKh
A shift clock generator 20 for generating a so-called eight-phase shift clock is provided.

As shown in FIG. 2, the shift clock generation unit 20 operates such that the phase difference between the clocks CKa to CKh is 1/8 of the cycle of the reference clock MCK.
Each clock CKa to CKh is generated. That is, in the shift clock generator 20, the clock CKa the reference clock MCK and phase match the clock CKb is delayed in phase by 45 degrees with respect to the reference clock MCK, clock CKc
Is 90 degrees out of phase with respect to the reference clock MCK, and the clock CKd is 135 degrees out of phase with the reference clock MCK.
The clock CKe is delayed by 180 degrees with respect to the reference clock MCK, and the clock CKf is
The clock CKg is generated such that the phase is delayed by 225 degrees with respect to the reference clock MCK, and the clock CKh is delayed by 315 degrees with respect to the reference clock MCK.

Here, in this embodiment, the eight-phase shift clock is generated by using the shift clock generator 20 for the following reason. That is, in the SS type distance measuring device, first, the light receiving pulse PBr is normally sampled sequentially using the reference clock MCK used to generate the light emitting pulse, and a predetermined bit length (PN code and PN code) obtained by the sampling is obtained. By calculating a correlation value between the data having the same bit length) and the PN code used to generate the light emission pulse, and detecting the time at which the correlation value becomes maximum as the light reception time of the reflected light, The time from the transmission start time of the laser light from 14 to the reception time of the reflected light is measured.

For this reason, in the conventional apparatus, the measurement target time required for the transmission and reception of the laser light is measured using one cycle of the reference clock MCK as the time resolution, and as shown in FIG. (See the conventional measurement results in FIG. 2).

FIG. 2 shows the reference clock MCK (= CK)
a) shows the case where the clock frequency is 20 MHz, and the conventional measurement result obtained using the reference clock MCK is 50 nsec. , 100 nsec. , 150 ns
c. , And the time resolution is 50 nsec. Becomes

Therefore, in this embodiment, the eight-phase shift clock CK is generated by using the shift clock generator 20 as described above.
By generating a to CKh, as shown in FIG. 2, the time to be measured is determined by the phase difference between the clocks CKa to CKh, and is 1/8 the conventional time resolution (6.25 nsec.).
(See the measurement results in the example of FIG. 2).

In order to realize such high-resolution time measurement (and distance measurement), eight types of clocks CKa to CKh generated by the shift clock generation unit 20 are used.
Are latch units 22 for latching the light receiving pulse PBr, respectively.
Is input to The latch unit 22 includes eight D flip-flops (hereinafter, referred to as DFFs) 22a, 22b,.
The clocks CKa to CKh are input to the DFFs 22a to 22h as operation clocks of the eight DFFs 22a to 22h, respectively.

As a result, in the latch section 22, each DF
F22a to 22h are clocks CKa to CKh, respectively.
, The light receiving pulse PBr is latched at the rising timing of, and as shown in FIG.
Eight types of binary data D1a, D1b,... D1h representing the signal level of the light receiving pulse PBr are output respectively. In this embodiment, 8 which constitutes the latch section 22 is used.
The DFFs 22a to 22h correspond to the signal input unit according to the first aspect.

Next, the eight types of binary data D1a to D1h output from the latch unit 22 are input to the synchronization unit 24. The synchronization unit 24 converts the eight types of binary data D1a to D1h output from the latch unit 22 into eight DFF2s, respectively.
4a, 24b,... 24h, the reference clock MCK is used.
By latching simultaneously at the rising timing of (= clock CKa), as shown in FIG. 3, the binary data D2a, D2b,
.. D2h, and corresponds to the signal synchronizing means according to the fourth aspect.

The eight types of binary data D2a to D2h synchronized by the synchronizing unit 24 are respectively transmitted through eight buffers 26a, 26b,. 30b,... 30h. Each of these correlators 30a-30h has a corresponding buffer 26a-2
6h, the binary data D2a to D2h are sequentially fetched in synchronization with the reference clock MCK, and the PN used by the pulse generator 12 to generate a light emission pulse out of the fetched binary data D2a to D2h. 2. The correlation calculating means according to claim 1, wherein a correlation value between a data string corresponding to the bit length of the code and a PN code actually used by the pulse generator 12 to generate a light emission pulse is calculated. Is equivalent to

The operation results of the correlators 30a to 30h are respectively converted into eight two-phase adders 40a and 40h.
.., 40h. Two-phase adders 40a to 40h
Are the operation results of the corresponding correlators 30a to 30h and the operation clock C of the corresponding DFFs 22a to 22h, respectively.
The correlators 30e corresponding to the DFFs 22e to 22h and 22a to 22d operated by the clocks CKe to CKh and CKa to CKd whose phases are the most different from Ka to CKh (in other words, the phases are different by 180 degrees, that is, delayed by a half clock cycle). To 30h and 30a to 30d,
Are added to each other, so that the corresponding correlators 30a to 30a to
30h, the calculation results are averaged, and each correlator 30a
This is for preventing the calculation result of 〜30h from greatly fluctuating due to the influence of noise, and corresponds to an averaging means according to claim 2.

In this embodiment, the two-phase adder 40a
The reason why the calculation results of the correlators 30a to 30h are averaged by using 40h is as follows. That is, in the distance measuring apparatus of the present embodiment, as described above, the received light pulse PBr is set to 8
By latching using the phase shift clocks CKa to CKh, respectively, the signals input to the correlators 30a to 30h
The latch timing of the value data (the latch timing of the DFFs 22a to 22h) is set to one cycle of the reference clock MCK.
/ 8, so that the time at which the correlation value between the pulse train of the light receiving pulse PBr and the PN code becomes the maximum can be detected as the time resolution of 1/8 of the cycle of the reference clock MCK. To

Then, as shown in FIG.
If Br completely corresponds to the light emission pulse, the latch unit 2
The binary data D1a to D1h output from the second DF are driven by a specific clock (clock CKe in FIG. 2) which rises first after the start timing of receiving the reflected light.
Starting from the output from F (the binary data D1e output from the DFF 22e in FIG. 2), the values sequentially change to the same value, and the calculation results in the correlators 30a to 30h also specify the values. Starting from the correlator corresponding to the clock (correlator 30e in the case of FIG. 2), they all change to the same value.

However, in practice, the light receiving signal photoelectrically converted by the light receiving section 16 fluctuates under the influence of noise, so that the light receiving pulse PBr also fluctuates under the influence of the noise, and the light emitting pulse PBr fluctuates. It does not become a beautiful waveform corresponding to. Therefore, the binary data D1a to D1h latched by the DFFs 22a to 22h of the latch unit 22 rarely change in sequence in synchronization with the reference clock MCK as shown in FIG. The result is
It will result in variations under the influence of the noise.

Therefore, the pulse train of the light receiving pulse PBr and the pulse train P are used by using the calculation results of the correlators 30a to 30h as they are.
If the time at which the correlation with the N code is maximized is detected, an error may occur in the detection time, and the time measurement accuracy (in other words, the distance measurement accuracy) may decrease.

The width of the noise superimposed on the received light signal is usually extremely short, and the same noise is not superimposed over one cycle of the reference clock MCK. And
For example, when the operation timing of the DFF 22a (in other words, the rising timing of the clock CKa) and the peak of the noise overlap, not only the DFF 22a but also the D which latches the light receiving pulse PBr at the operation timing before and after the DFF 22a.
It is conceivable that the FF 22h and the DFF 22b also latch erroneous binary data affected by noise, and the least affected by noise is that the phase difference from the clock CKa is the largest (in other words, the phase difference 180). Clock C)
The DFF 22e that operates at Ke.

Therefore, in the present embodiment, two clocks (CKa and CKE, CKb and CKf, Ck) having a phase difference of 180 degrees from each other among the eight-phase shift clocks CKa to CKh are used.
Kc and CKg, CKd and CKh) are paired, and the two-phase adders 40a to 40h calculate the results of the correlators corresponding to the paired clocks (the results of the operations of the correlators 30a and 30e, the correlators 30b and 30f). Calculation result, correlator 3
0c and 30g, and the correlation results of the correlators 30d and 30h).
Are averaged.

Hereinafter, specific examples of the correlators 30a to 30h and the two-phase adders 40a to 40h will be described with reference to FIG. FIG. 4 shows a correlator 30a and a two-phase adder 4 that perform correlation calculation and averaging based on the output from the DFF 22a that operates on the same clock CKa as the reference clock MCK.
0a.

As shown in FIG. 4, the correlator 30a has P
A shift register 32 including n (for example, 31) latch circuits 32a1, 32a2,... 32an corresponding to the bit length of the N code is provided. The CPU 2 presets binary data of each bit of the PN code to the latch circuits 32a1 to 32an before the distance measurement is started, and the latch circuits 32a1 to 32an store the reference data input after the distance measurement is started. In synchronization with the clock MCK, the preset binary data is sequentially shifted to the next-stage latch circuit.

Each of the latch circuits 32a1 to 32an is
Forming a closed loop, the final stage latch circuit 32an
(The initial value is the binary data used for generating the light emission pulse first) is output to the first-stage latch circuit 32a1.

The correlator 30a includes a latch circuit 32
The same number (n) of exclusive-OR circuits (hereinafter, referred to as EXOR) 34a1, 34a2,.
and EXORs 24a1 to 34an
The input data to each of the latch circuits 32a1 to 32an forming the shift register 32 is input to one input terminal of the shift register 32.

Specifically, the input to the first-stage latch circuit 32a1 (in other words, the output from the last-stage latch circuit 32an) is input to the EXOR 34a1.
The input to the second-stage latch circuit 32a2 (in other words, the output from the first-stage latch circuit 32a1) is input to a2, and so on to each of the EXORs 24a1 to 34an.
Input data to each of the latch circuits 32a1 to 32an is input.

On the other hand, binary data latched by the DFF 22a at the rising timing of the clock CKa is input to the other input terminals of the EXORs 34a1 to 34an via the DFF 24a constituting the synchronization unit 24. As a result, the outputs from the EXORs 34a1 to 34an are
Light receiving pulse PB input through F22a and F22a
r, the binary data representing the signal level of the
2 when the input data to the latch circuits 32a1 to 32an match, the signal goes to the low level, and when they do not match, the signal goes to the high level.

Then, each EXOR3 changing in this way
Outputs from 4a1 to 34an are respectively n (31)
Up / down counter (U / D counter) 36a1,
36a2,... 36an. Each of the up / down counters 36a1 to 36an operates in response to the reference clock MCK, and its count value is determined by the EXORs 34a1 to 34a3.
It increases as the output of 4an continuously goes to the low level.

Accordingly, the light reflected from the object to be measured is received by the light receiving section 16, and a light receiving pulse PBr obtained by binarizing the light receiving signal is transmitted to the correlator 30a via the DFFs 22a and 24a.
, 31 up-down counters 36a
One of 1 to 36 an continues to be counted up, and the reception time of the reflected light can be specified from the position of this counter.

However, as described above, since noise is superimposed on the received light signal, only the up / down counter corresponding to the received light time is counted up after the start of receiving the reflected light. The up-down counter may count up, or the up-down counter corresponding to the light receiving time may count down.

Therefore, in the two-phase adding section 40a, the correlator 3
In order to cancel the error due to the noise of the n (31) count values output from 0a, a correlator 30 as a pair is used.
, e, and the n adders 42a1, 42a2,... 42an are used to add the count values output from the correlator 30a to the correlator 30e.
Are added to the respective count values taken from.

The two-phase adder 40a includes the adder 4
The outputs from 2a1 to 42an are output to n output circuits 44a operating at the rising timing of the reference clock MCK.
, 44a2,... 44an, and outputs to the detection processing unit 46 at the subsequent stage. Although FIG. 4 shows the configuration of the correlator 30a and the two-phase adder 40a, the other correlators 30b
30h and the two-phase adding units 40b to 40h
a and the two-phase adder 40a.

In the two-phase adder 40a, each of the adders 42a1-42an applies a clock CKa and a clock CKa to the count value output from the correlator 30a.
Ke (180 degrees, in other words, the reference clock M
The count value is added at a timing delayed by an amount corresponding to １ ／ of the CK cycle).

That is, in the two-phase adding section 40a, the count value output from the first up / down counter 36a1 of the correlator 30a is incremented by 1 in the correlator 30e.
The count value output from the up-down counter 36e1 (not shown) is added, and the count value output from the n-th up-down counter 36an of the correlator 30a is added to the n-th count value of the correlator 30e. The count value output from the up / down counter 36en (not shown) is added.

The two-phase adder 40e, which is a pair of the two-phase adder 40a, takes in the n count values output from the correlator 30a and converts them into the n count values output from the correlator 30e. Each is added, but at the time of this addition,
A count value at a timing delayed by a phase difference between the clock CKa and the clock CKa is added to each count value output from the correlator 30a.

That is, in the two-phase adder 40e, the first up / down counter 36e1 of the correlator 30e is used.
(Not shown), the count value output from the second up-down counter 36e2 of the correlator 30a is added to the count value output from the correlator 30e.
The count value output from the first up / down counter 36a1 of the correlator 30a is added to the count value output from the up / down counter 36an (not shown).

The two-phase adders 40b to 40b other than those described above
d and 40f to 40h, the two-phase adder 40 corresponding to the clocks CKb to CKd rising in the first half of one cycle based on the rising timing of the reference clock MCK.
b to 40d operate in the same manner as the two-phase addition unit 40a,
Two-phase adders 40b-4 corresponding to clocks CKf-CKh rising in the latter half of one cycle of reference clock MCK
0d operates in the same manner as the two-phase addition unit 40e.

Accordingly, in this embodiment, two two-phase adders (40a) for averaging the operation results of the correlators forming a pair
And 40e, 40b and 40f, 40c and 40g, and 40d and 40h) do not match. Next, the detection processing unit 46 receiving the outputs (8 × n count values) from the two-phase addition units 40a to 40h outputs the n count values output from the two-phase addition units 40a to 40h. From among them, count values that first exceed a predetermined threshold value are detected, and data representing the position of the up / down counter corresponding to the count value (in other words, the reception time of the reflected light from the measurement object) is obtained. Is output to the near-field priority processing section 47 at the next stage.

That is, the n count values output from each of the two-phase adders 40a to 40h are calculated based on each clock CK.
Since the correlation value indicates the correlation between the light receiving pulse PBr and the PN code sampled at each rising timing of a to CKh, the detection processing unit 46 sets the correlation value when any of the count values exceeds the threshold value. Is determined to be the maximum, and data indicating the position of the up / down counter that outputs the count value (in other words, the light receiving time) is output.

Next, when a plurality of data are output from the detection processing unit 46 at the same time, the near field priority processing unit 47 receiving the output from the detection processing unit 46 selects the data having the earliest light receiving time from among them. (In other words, the reference clock MCK
(Data corresponding to a correlator corresponding to a clock having the smallest phase difference with the clock) is output to the distance measurement result output unit 48.

That is, in the present embodiment, the provision of the synchronization section 24 allows the correlators 30a to 30h and the two-phase addition section 4
0a to 40h are operated at the same timing synchronized with the reference clock MCK.
In some cases, the count values respectively output from the threshold values h may exceed the threshold value at the same time, and the detection processing unit 46 may output a plurality of data at the same time.

The data output from the detection processing unit 46 is the position of the up / down counter whose count value exceeds the threshold value among the up / down counters provided in the correlators 30a to 30h (in other words, Since this is for specifying the reflected light reception time), when a plurality of data are output from the detection processing unit 46, it becomes impossible to specify the reflected light reception time.

Therefore, in this embodiment, the near-field priority processing unit 4
In step 7, the data having the earliest reception time of the reflected light is selected from the plurality of data, and the distance measurement result output unit 4 is selected.
8 is output. When one data is output from the detection processing unit 46, the near field priority processing unit 47 outputs the data as it is to the distance measurement result output unit 48.

Then, in the distance measurement result output section 48,
The input data from the near-field priority processing unit 47 is converted into distance measurement data representing the time from the transmission start time of the laser beam from the light emitting unit 14 to the reception time of the reflected light and output to the CPU 2. Here, the input data from the near-field priority processing unit 47 is
Among all the up / down counters provided in the correlators 30a to 30h, the position of the up / down counter whose count value exceeds the threshold value earliest (in other words, the reception time of the reflected light) is indicated. Since the latch timing of the binary data input to each of the correlators 30a to 30h via the synchronizer 24 is shifted by 1/8 of the cycle of the reference clock MCK by the 8-phase shift clock, the distance measurement is performed. The time resolution of the distance measurement data output from the result output unit 48 to the CPU 2 is one time of the cycle of the reference clock MCK.
/ 8 time.

Therefore, the CPU 2 can measure the distance to the object to be measured with a resolution higher than the resolution determined by the cycle of the reference clock MCK by taking in the distance measurement data from the distance measurement result output unit 48. become,
Based on the measurement results, follow-up control that controls the vehicle's drive system and braking system to follow the vehicle in front, and obstacle detection control that detects an obstacle in front of the vehicle and generates an alarm It is possible to perform well.

In this embodiment, the detection processing unit 46
Corresponds to the detecting means of the present invention (claims 1 and 4), and the near-field priority processing unit 47 corresponds to the selecting means according to claim 6. On the other hand, when actually performing the distance measurement using the function as the time measuring means realized by the above-described time measuring measurement circuit, the CPU 2 horizontally (or horizontally and vertically) emits the laser light from the light emitting unit 14. ) Direction, and measures the distance to a measurement object (preceding vehicle or obstacle) existing within a predetermined angle range in front of the vehicle. Further, the CPU 2 improves the distance measurement accuracy by performing the distance measurement a plurality of times for each distance measurement point and averaging the measurement results during optical scanning with the laser light.

Next, the distance measurement processing performed by the CPU 2 for each distance measurement point will be described with reference to the flowchart shown in FIG. In the distance measurement processing described below, the function of the distance calculation means of the present invention (claims 7 to 9) is realized by the operation of the CPU 2.

As shown in FIG. 5, when the emission direction of the laser beam from the light emitting section 14 reaches a preset distance measuring point by an optical scanning control process (not shown), the CPU 2 firstly performs S100 (S represents a step). In step S110, an initialization process for initializing various parameters used in the process, such as counters i and j, which will be described later, is performed. 30
h and a detection processing unit 4 for measuring time.
6, a measurement circuit initial setting process for initializing the near field priority processing unit 47, the distance measurement result output unit 48, and the like.

Then, in S120, the generated PN code is output to the pulse generation unit 12 in synchronization with the reference clock MCK, so that the light emitting unit 14 emits a laser beam corresponding to the PN code. The light control process is activated, and in S130, a counter i for counting the number of times of distance measurement at the current distance measurement point is counted up.

Next, in S140, a laser beam is emitted from the light emitting section 14 by the light control processing started in S120, and the reflected light of the laser beam from the object to be measured is received by the light receiving section 1.
By receiving the light at step 6, it is determined whether or not distance measurement data indicating the time from the emission of the laser light until the reception of the reflected light is input from the distance measurement result output unit 48.

If the distance measurement data has not been input, the flow shifts to the subsequent S150, where the light control processing is started in S120 (in other words, after the current distance measurement is started), and then the previously set distance measurement data is obtained. Determine whether the distance setting time has elapsed,
If the set distance measurement time has not elapsed, the process returns to step S140, and the process waits for the input of the distance measurement data from the distance measurement result output unit 48 or the elapse of the set distance measurement time.

Next, in S140, the distance measurement result output unit 48
If it is determined that distance measurement data has been input from S160, S160
In step S170, the input distance measurement data is stored in a memory (RAM), and in step S170, a counter j for counting the number of distance measurement data obtained in the current distance measurement operation is counted up.

Then, if the process of S170 is executed as described above, or if it is determined in S150 that the set distance measurement time has elapsed, the value of the counter i representing the number of times of distance measurement is set in advance in S180. It is determined whether or not the set upper limit value imax has been reached. If the value of the counter i has not reached the upper limit value imax (i <imax), the process proceeds to S110,
The processing described above is executed again.

On the other hand, if it is determined in S180 that the value of the counter i has reached the upper limit value imax, that is, the laser light corresponding to the PN code is emitted from the light emitting unit 14 and the reflected light is received. If it is determined that the time measurement operation (in other words, the distance measurement operation) for measuring the time until the measurement has been performed a predetermined number of times determined by the upper limit value imax, the process proceeds to subsequent S190,
Now, in the distance measurement data of a plurality (j pieces) obtained in the distance measuring operation, improper bad data executes failure data existence determination processing determines whether or not present in the distance calculation.

In this processing, for example, distance measurement data representing a time distant from the center (average time) of a plurality of distance measurement data (time) by a predetermined time or more is searched, and the distance measurement data is regarded as defective data. Setting is performed.
In other words, even if the time measurement is performed at the same distance measurement point, each distance measurement data varies due to disturbance (noise) or the like. It is set as received bad data.

Then, in the following S200, the above S190
It is determined whether or not there is distance measurement data set as defective data by the above processing. If there is no defective data, the process directly proceeds to S220. Conversely, if there is defective data, the process proceeds to S220.
At 210, from the distance data stored in the memory,
After deleting the defective data and subtracting the number of deleted defective data from the counter j indicating the number of distance measurement data, the value of the counter j is updated, and the process proceeds to S220.

Next, in S220, the average value (average time) of the distance measurement data is calculated by reading out all the distance measurement data stored in the memory in the current distance measurement operation and dividing the sum by the value of the counter j. I do. Finally, in S230, the distance to the object to be measured at the current ranging point is calculated from the average value (average time) of the ranging data, and the calculated distance is stored in the memory. finish.

If there is no distance measurement data stored in the memory in the current distance measurement operation (that is, if there is no object to be measured at the current distance measurement point), in step S220, it indicates that there is no distance measurement data. A flag is set, and in S230, it is determined that there is no distance measurement data from the flag, and data representing that there is no measurement object is stored in the memory.

Since the above-described distance measurement processing is executed for each distance measurement point, it is repeatedly executed in the CPU 2 during laser light scanning. As described above, in the distance measuring device of the present embodiment, the eight DFFs 22a to
By inputting the eight-phase shift clocks CKa to CKh generated by the shift clock generation unit 20 to the reference clock MCr 22h, respectively,
It is sequentially latched at a time interval of 1/8 of the cycle of K, and a correlation value between the latched pulse train of the light receiving pulse PBr and the PN code is obtained by eight correlators 30a to 30h corresponding to the respective DFFs 22a to 22h. , These correlators 30a to 30
The time when the correlation value obtained in h first exceeds the threshold value is the time when the reflected light from the measurement object is received, and the time required for the laser light to reciprocate between the vehicle and the measurement object is measured. Have been to be.

Therefore, according to the present embodiment, the distance measurement time is measured with a time resolution of 1/8 of the cycle of the reference clock MCK without increasing the frequency of the reference clock MCK. As a result, distance measurement to the object to be measured can be performed with high accuracy. As described above, according to the present embodiment, it is not necessary to increase the frequency of the reference clock MCK in order to increase the measurable time resolution, and each time measurement circuit has the same cycle as the reference clock MCK. Therefore, it is not necessary to make the circuit elements constituting the measurement circuit capable of high-speed operation. Therefore, according to this embodiment, although the number of circuits for time measurement, such as a correlator, increases, each circuit can be realized at low cost, so that the measurable time resolution can be achieved without increasing the cost of the entire apparatus. Can be higher.

Also, in particular, in this embodiment, the latch 22
Instead of directly inputting the binary data latched by the DFFs 22a to 22h to the correlators 30a to 30h, these binary data are converted into the DFFs 24 constituting the synchronization unit 24.
a to 24h, the data is latched again in synchronization with the reference clock MCK, and the latched binary data is input to the corresponding correlators 30a to 30h.
The processing circuits (two-phase addition units 40a to 40h, the detection processing unit 46, the near field priority processing unit 47, and the distance measurement result output unit 48) subsequent to the 30h and the correlators 30a to 30h are all shared by the common reference clock MCK. It can be made to work with.

For this reason, the eight-phase shift clocks CKa to CKa
Kh constitute a latch portion 22 DFF22a～22h
To each of these clocks CKa to CK.
There is no need to transmit h to other processing circuits. Therefore, according to the present embodiment, it is possible to easily design a wiring pattern for assembling a circuit for time measurement on a printed circuit board, and furthermore, to simplify the wiring pattern, so that the printed circuit board has a large area. large there is no need to make, it can be prevented an increase in the size of the apparatus.

Further, in this embodiment, each correlator 30a
Instead of using the calculation results obtained by the calculation of 〜 to 30 h as they are, the reception time of the reflected light is specified, but the two-phase addition units 40 a to 40 h
Are used to add the two-phase results of the operations of the correlators 30a to 30h, and the reception time of the reflected light is specified using the results of the two-phase addition. Noise measurement can be improved and time measurement (and distance measurement) even under conditions where the S / N (signal-to-noise ratio) of the received light signal is poor
Can be performed well.

On the other hand, when measuring the distance at each ranging point, the CPU 2 emits a laser beam corresponding to the PN code from the light emitting unit 14 and measures the time until the reflected light is received. Distance operation is performed a plurality of times, and from the average value (average time) of the plurality of distance measurement data obtained by the distance measurement operation,
Calculate the distance to the measurement object. Also, the CPU 2
When calculating the average value of the plurality of distance measurement data, the distance measurement data greatly deviated from the center of the plurality of distance measurement data is deleted as defective data. Therefore, according to the present embodiment, the noise resistance can be improved and the distance measurement accuracy can be increased by the operation of the CPU 2.

[0108] In this case, 8-phase shift clock CKa~CK
The shift clock generation unit 20 that generates h can be configured using, for example, an analog PLL 50 and a shift register 56 as shown in FIG. 6, or from a gate circuit as shown in FIG. Many (k
) Of the delay units 80 (1) to 80 (k) in cascade.

Next, the configurations and operations of these two types of shift clock generators 20 will be described with reference to FIGS. The shift clock generation unit 20 shown in FIG. 6 generates an operation clock having a frequency eight times as high as the reference clock MCK by the analog PLL 50, and drives the shift register 56 with this operation clock, so that the shift register 56 The clocks CKa to CKh are output.

That is, the analog PLL 50 includes an oscillator (VCO) 51 capable of controlling the oscillation frequency by voltage and a VCO 51
A frequency divider 52 that divides the output from the by １ ／, an output from the frequency divider 52 (a signal having a frequency １ ／ of the oscillation frequency of the VCO 51) and a reference clock MCK are compared in phase.
Phase comparator 53 for generating a control signal corresponding to the phase difference
And a loop filter 54 that performs filter processing (integration processing) on the control signal from the phase comparator 53 and outputs the result as an oscillation frequency control voltage of the VCO 51. For this reason, the oscillation frequency of the VCO 51 is controlled to be eight times the frequency of the reference clock MCK.

On the other hand, the shift register 56 includes eight latch circuits 56a, 56b,.
It is composed of Each of the latch circuits 56a to 56h
Each of them can preset binary data from the outside, and receives a high-frequency signal (operation clock) output from the VCO 51 of the analog PLL 50 to sequentially shift the latched binary data.

The binary data preset in each of the latch circuits 56a to 56h is "000011111". The binary data having the value 0 is stored in the latch circuits 56a to 56d, and the binary data is stored in the latch circuits 56e to 56h. The binary data of the value 1 is preset respectively.

As a result, when the operation clock is input from the analog PLL 50 to the shift clock generation unit 20, the reference clock MCK is output from each of the latch circuits 56a to 56h.
And the cycle is the same, and the phase is shifted by 1/8 of that cycle.
The phase shift clocks CKa to CKh are output.

The shift clock generator 2 shown in FIG.
In order to make the clock CKa output from the latch circuit 56a the same phase as the reference clock MCK at 0, for example, after presetting binary data in each of the latch circuits 56a to 56h, the analog PLL 50 shifts the shift register 5
6 may be controlled based on the rise timing of the reference clock MCK.

Next, the shift clock generation unit 20 shown in FIG. 7 inputs the reference clock MCK generated by the reference clock generation unit 10 to the delay line, thereby delay units 80 (1) to 80 (1) to form the delay line. 80 (k) is used to delay in order. Each of these delay units 80
(1) On the output side of ~ 80 (k), the reference clock MC
Seven switches SWb (1) to SWb (k), SWc for extracting clocks CKb to CKh out of phase with K
(1) to SWc (k),... SWh (1) to SWh (k) are connected. The switch groups SWb, SWc,... SWh for clock extraction are provided with decoders 90b to 90b.
0h is provided.

The decoders 90b to 90h are provided with switches SWb (?) To which clocks CKb to CKh are extracted from k switches constituting each of the switch groups SWb to SWh.
SWh (?) Position is set, and the set switch SW
The drive signal for turning on b (?) to SWh (?) is transmitted to the data line Lb.
To the switch groups SWb to SWh through the switches SWb (?) To SWh (?) To selectively turn on the switches SWb (?) To SWh (?).
Through (?), X / 8 of the cycle of the reference clock MCK
This is for extracting seven types of shift clocks CKb to CKh obtained by delaying the reference clock MCK by the time (x: 1, 2,..., 7).

That is, each of the decoders 90b to 90h has:
The delay time (specifically, the average delay time) of each of the delay units 80 (1) to 80 (k) is set as the time resolution, and the reference clock M
Cycle data CD which is obtained by digitizing one cycle of CK is input,
Each of the decoders 90b to 90h has its periodic data CD,
Each clock CKb to CKh with respect to the reference clock MCK
, SDh, which represents the delay ratio x / 8 (x: 1, 2,..., 7)
Switch SWb (?) Used to extract Kb to CKh
The position of SWh (?) Is calculated, and the switch SWb (?)
Turn on SWh (?).

For example, assuming that the cycle of the reference clock MCK is 80 times the delay time of the delay unit 80, each of the decoders 90b to 90h supplies the cycle data C
D, the decoders 90b to 90h use the preset delay data SDb to SDh to set the delay amount of the reference clock MCK (specifically, the number of connection stages of the delay unit 80) to “80/8”, “ 80x2 / 8 ", ..." 80x
7/8 ", and the operation results 10, 2
0,... 70 corresponding to the switches SWb (10), SWc (2
0),... SWh (70) is turned on.

As a result, from the switch groups SWb to SWh, seven types of clocks CKb to CKh in which the reference clock MCK is sequentially delayed by 1/8 of the cycle of the reference clock MCK are selectively output. Will be. still,
The delay unit 80 may be composed of two stages of inverters, or another gate circuit (AND gate, NAN
D gate) or the like. Further, the above numerical value “80” is illustrated for simplicity of explanation, and is different from an actual value. For example, if the delay time of the delay unit 80 is 1 nsec. And the frequency of the reference clock MCK is 20 MHz, one cycle of the reference clock MCK is 50 nsec. Becomes

The shift clock generator 2 shown in FIG.
The buffer 92a for improving the driving capability of the reference clock MCK input from the reference clock generator 10 and the seven types of clocks CKb to CKh selectively output from the switch groups SWb to SWh are respectively set to 0. 92b, ...
92h are provided. And the reference clock MCK
And the seven types of clocks CKb to CKh
After the driving capability is improved in 2a to 92h, the signals are output to the outside as eight-phase shift clocks CKa to CKh.

As described above, the shift clock generation unit 20
Is an eight-phase shift clock C having a desired phase difference even if it is configured using a delay line composed of a large number of delay units 80.
Ka to CKh can be generated. Then, according to the shift clock generation unit 20 of FIG.
Although it is necessary to generate the periodic data CD to be input to .about.90h, as in the shift clock generation unit 20 shown in FIG.
Since there is no need to generate a high-frequency signal (operation clock) obtained by multiplying the reference clock MCK by using the L50, the circuit configuration can be simplified, and unnecessary high-frequency noise is generated by operating the VCO 51. Since this does not occur, the reliability of time (distance) measurement can be improved.

In the shift clock generator 20 shown in FIG. 7, the cycle data CD input to each of the decoders 90b to 90h determines the cycle of the reference clock MCK by the delay unit constituting the delay line of the shift clock generator 20. Since the delay time of 80 is quantified as a time resolution, as a circuit for generating this cycle data CD, the cycle of the reference clock MCK is quantified using the same delay element as the delay unit 80 constituting the delay line. What is necessary is just to use a time A / D converter (for example, refer to the above-mentioned JP-A-2000-124726).

For example, the reference clock generator 10
Is constituted by a digital PLL as shown in FIG. 7, if the control data for generating the reference clock used in the reference clock generation unit 10 is directly input to the shift clock generation unit 20 as the periodic data CD. Since there is no need to separately provide a circuit for generating the periodic data CD, the device configuration can be simplified.

That is, the reference clock generator 1 shown in FIG.
Reference numeral 0 denotes a reference clock MCK generated by multiplying a clock (low-frequency clock) PREF having a lower frequency than the reference clock MCK input from the outside by digital processing. Is provided with a ring delay line (RGD) 60 in which the same delay units as the delay units 80 constituting the above are connected in a ring shape.

The RGD 60 circulates a start pulse inputted from the outside via delay units connected in a ring shape. The output from each delay unit is output not only to the delay unit at the next stage but also to the time A. / D converter (TA
D) 62 and a digitally controlled oscillator (DCO).

The TAD 62 has a counter for counting the number of times the pulse circulates in the RGD 60 and a low-frequency clock P
RG at rising edge (or falling edge) of REF
And an encoder for detecting the orbital position of the pulse in D60, and outputs digital data of predetermined bits with the count value of the counter as upper bit data and the orbital position obtained by the encoder as lower bit data.

That is, the TAD 62 uses the RGD 60 to sequentially measure the rising time (or the falling time) of the low-frequency clock PREF whose time resolution is the delay time of the delay unit constituting the RGD 60, and digitally represents the time. It outputs data (time data).

The time data sequentially output from the TAD 62 is input to the data processing unit 66,
The data processing unit 66 generates cycle data representing the cycle of the low-frequency clock PREF from the difference between the input time data. The time resolution of this cycle data, R
A delay unit configuring the GD60 (and a delay unit configuring a delay line in the shift clock generation unit 20)
Delay time.

The reference clock generator 10 has a register 68 in which multiplied value data necessary for generating the reference clock MCK from the low frequency clock PREF is stored in advance.
And the low-frequency clock PR obtained by the data processing unit 66
A divider 70 is provided for calculating the period of the reference clock MCK to be generated by dividing the period data representing the period of the EF by the multiplied value data stored in the register 68. The division result (specifically, the positive part of the division result) is output to the data latch circuit 72.

The data latch circuit 72 latches the cycle of the reference clock MCK obtained by the divider 70 as control data (= cycle data CD),
Output to O64. The DCO 64 monitors the number of times the pulse circulates in the RGD 60 and the circling position in the RGD 60 in the same manner as the TAD 62, so that the time corresponding to the control data (= periodic data CD) output from the data latch circuit 72 is represented by R
The delay time of the delay unit constituting the GD60 is timed (counted) as time resolution, and one time is counted per time measurement.
A reference signal MCK is generated by generating a pulse signal on a per-time basis.

Note that, of the results of division by the divider 70, values after the decimal point that cannot be divided by the multiplied value data (decimal part)
Is output to the frequency fine adjustment circuit 74 and the frequency fine adjustment circuit 7
4 is a data latch circuit 7 at a rate corresponding to the decimal part.
By adding the value 1 to the control data latched by 2, a small phase error of the reference clock MCK with respect to the low frequency clock PREF is accumulated, thereby preventing a large phase error.

Then, as described above, RGD60, TAD6
2. The digital PLL constituted by using the DCO 64 or the like is disclosed in Japanese Patent Application Laid-Open No. 7-183800 or the like, and has been well known in the related art. As described above, in the reference clock generator 10 shown in FIG.
Is a value obtained by digitizing the cycle of the reference clock MCK using the delay time of the delay unit 80 as the time resolution. For this reason, when the reference clock generator 10 is constituted by the digital PLL shown in FIG. 7, the control data generated in the reference clock generator 10 is used as the periodic data CD, and the shift clock generator 20 is used as it is.
You just have to enter

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.
Various embodiments can be adopted. For example, in the above embodiment, the shift clock generation unit 20 generates the eight-phase shift clocks CKa to CKh, and the DFFs 22a to 22h and the correlators 30a to 30h constituting the latch unit 22 correspond to the number of clocks. In the distance measuring device, the measurable time resolution (and hence the distance resolution) is determined by the phase difference between the shift clocks. In order to further increase the distance resolution), the number of shift clocks generated by the shift clock generation unit 20, the DFFs 22a to 22h provided corresponding to the clocks, and the correlator 3
What is necessary is just to increase the number of 0a-30h. When the number of shift clocks is increased, the DFFs 22a to 22h and the correlator 30
Since the number of a to 30h also increases, the number of shift clocks may be reduced when miniaturization of the device is required.

Also in this case, the measurable time (distance) resolution can be increased as compared with the case where the time (distance) measurement is performed by one reference clock.
The effects of the present invention can be exhibited. Further, as in the above embodiment, if the distance measurement operation is performed a plurality of times at one distance measurement point and the obtained distance measurement data (time) is averaged, measurement can be performed by averaging. Time (distance)
Since the resolution can be increased, the number of shift clocks may be reduced and the number of distance measurement operations (time measurement) performed per one distance measurement may be increased.

However, the number of distance measuring points required for safely and reliably detecting a preceding vehicle or an obstacle, and the time required for performing distance measurement at all the distance measuring points are provided by a distance measuring device. Determined by the size of the vehicle, athletic ability, etc.
Since there is an upper limit on the measurement time that can be assigned to one ranging point, the number of ranging operations performed at each ranging point is limited by the measuring time.

In the following control in which the vehicle follows the preceding vehicle, the measuring time that can be assigned to each ranging point is 5 μsec. To 50 μsec. Measurement)
It may be set appropriately based on this measurement time and the time required for one distance measurement operation (time measurement). To improve the accuracy of distance measurement, the maximum number of distance measurement operations that can be completed within the measurement time May be set.

In the above embodiment, the case where the time measuring device of the present invention is applied to a distance measuring device for an automobile has been described. However, the time measuring device of the present invention can be used for applications other than the distance measuring device. It is. For example, when an object to be measured is detected by the sensor, a detection signal (radio wave) generated by the spread spectrum method is transmitted from the transmitter on the sensor side, the detection signal is received on the receiver side, and a predetermined measurement is started. In a system that measures the time from the time to the reception time of the detection signal, or a system that measures the time interval of the detection signal transmitted from the sensor-side transmitter at the receiver, If the time measuring device of the present invention is provided, the time to be measured can be measured with high resolution as in the above embodiment.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a configuration of an entire distance measuring apparatus according to an embodiment.

FIG. 2 is an explanatory diagram illustrating a time measuring operation in the distance measuring device according to the embodiment.

FIG. 3 is a time chart illustrating operations of a latch unit and a synchronization unit according to the embodiment.

FIG. 4 is a configuration diagram illustrating a configuration of a correlator and a two-phase addition unit according to the embodiment.

FIG. 5 is a flowchart illustrating a distance measurement process executed by a CPU (microcomputer) according to the embodiment.

FIG. 6 is a configuration diagram illustrating a shift clock generation unit configured using an analog PLL.

FIG. 7 is a configuration diagram illustrating a shift clock generation unit and a reference clock generation unit configured by a digital processing circuit.

[Explanation of symbols]

2 CPU (microcomputer), 10 reference clock generator, 12 pulse generator, 14 light emitting unit, 15
... Drive circuit, 16 ... Light receiving section, 17 ... Amplifier, 18 ... Comparator, 20 ... Shift clock generating section, 22 ... Latch section, 24 ... Synchronizing section, 26a-26h ... Buffer, 30a
~ 30h ... correlator, 40a ~ 40h ... two-phase addition unit, 46
... Detection processing unit, 47 ... Near field priority processing unit, 48 ... Distance measurement result output unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F085 AA05 CC10 GG19 GG24 GG25 GG27 5J070 AB01 AC02 AD02 AH04 AK22 5J084 AA05 AB01 AC02 AD01 CA03 CA26 CA31 CA44 CA45 CA50 CA52 CA54 CA68 EA04

Claims (9)

[Claims] An input signal including a pulse train generated at a constant cycle using a pseudo random noise code is sequentially taken in as binary data in synchronization with a reference clock having the same cycle as the pulse train, and the data of the binary data is read. A time measuring device for measuring a time from a predetermined measurement start time to an input time of the pulse train by detecting an input time of the pulse train from a correlation between a train and a pseudo-random code, the same as the reference clock. A plurality of shift clocks that generate a plurality of shift clocks having different phases in a cycle; Signal input means; a data string of binary data captured by the plurality of signal input means; A plurality of correlation operation means for respectively calculating the correlations of the pulse data, based on the operation results of the plurality of correlation operation means, the time at which the correlation between the data sequence of the binary data and the pseudo-random code is maximized. A time measuring device, comprising: detecting means for detecting an input time. 2. The shift clock generating means generates n shift clocks whose phases are different from each other by 1 / n of one cycle of the reference clock, and wherein the signal input means and the correlation operation means comprise the shift clock. 2. The time measuring device according to claim 1, wherein n devices are provided for each of the numbers. 3. The correlation calculation means according to claim 1, wherein each of the plurality of correlation calculation means includes a calculation result of the correlation calculation means corresponding to the signal input means operated by the shift clock having the phase different from the phase of the shift clock used by the corresponding signal input means. 3. The time measuring device according to claim 1, further comprising: averaging means for averaging the calculation result by adding the calculation result to the detection result and outputting the result to the detection means. 4. A signal synchronization means for sampling binary data taken in by each of said signal input means with a common reference clock and inputting the sampled data to each of said correlation operation means, wherein said plurality of correlation operation means and said detection means are provided. 4. The time measuring device according to claim 1, wherein each of the plurality of clocks operates on the common reference clock. 5. The method according to claim 1, wherein the detecting means outputs a time at which one of the calculation results of the correlation calculation means exceeds a predetermined threshold value and a calculation result at which the calculation result exceeds the threshold value. 5. The time measuring apparatus according to claim 4, wherein an input time of the pulse train is detected based on a shift of a shift clock corresponding to an arithmetic unit from the reference clock. 6. The apparatus according to claim 1, further comprising: a selection unit that selects an earliest input time among the plurality of input times when the detection unit detects a plurality of input times of the pulse train simultaneously. 5. The time measuring device according to 5. 7. A pulse train generating means for generating a pulse train corresponding to a pseudo random noise code having a predetermined bit length in synchronization with a reference clock, and a transmitting means for transmitting an electromagnetic wave modulated by the pulse train generated by the pulse generating means. Receiving means for receiving a reflected wave from which the electromagnetic wave transmitted by the transmitting means hits the object to be measured and for restoring the pulse train, based on the pulse train restored by the receiving means and the pseudo random noise code; A time measuring means for measuring a time from when the transmitting means starts transmitting the electromagnetic wave to when the reflected wave is received, and a distance to the object to be measured based on the time measured by the time measuring means. a distance measuring apparatus of a spread spectrum scheme and a distance calculating means for calculating a, as the time measuring means, said claims 1 to 6 Izu A distance measuring device comprising the time measuring device according to any one of the preceding claims. 8. The distance calculating means generates the pulse train from the pulse train generating means a plurality of times per one distance measurement, and calculates the time data measured by the time measuring means with the generation of the pulse train. 8. The distance measuring device according to claim 7, wherein the distance to the object to be measured is calculated from an average value of the plurality of time data taken in sequentially. 9. The distance calculating means excludes time data outside a predetermined range greatly deviating from the center of the plurality of time data from the plurality of time data taken in from the time measuring means, and 9. The distance measuring device according to claim 8, wherein a value is calculated.