Distance measurement apparatus and distance measuring method

Details Distance measurement apparatus and distance measuring method Distance measurement apparatus and distance measuring method

2001-03-09

2002-05-28

Tarcza, Thomas H. (Department: 3662)

Optics: measuring and testing

Range or remote distance finding

With photodetection

Reexamination Certificate

active

06396570

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a distance measurement apparatus and a distance measuring method. More particularly, it relates to a distance measurement apparatus and a distance measuring method in which a light flight time is detected and a distance from an object is detected, so that precision of distance measurement is enhanced.
Known is a conventional distance measuring technique by a time-of-flight system for detecting a timing of a reflected light which is reflected and returned by an object, detecting a time difference from a light emitting timing, and obtaining a light flight time to detect a distance to the object.
Moreover, another distance measuring method is usually a triangular survey system. As compared with the triangular survey system, in the time-of-flight system, there are advantages that the distance can be detected from one observation point and the apparatus can therefore be miniaturized, and that any occlusion as a problem of triangular survey does not occur and the distances to all object points from the observation point can therefore be detected.
Moreover, there are some methods for measuring a delay of the light reflected by the object. For example, in a method in which a charge distributing detector is utilized as disclosed in “Integration-Time Based Computational Image Sensors”, 1995 IEEE Workshop on Charge-Coupled Devices and Advanced Image Sensors, Apr. 20 to 22, 1995, Dana Point, Calif., USA, a distance extraction processing can be simplified. Additionally, since a semiconductor manufacturing technique is used, the method is suitable for miniaturizing the apparatus.
A constitution of the charge distributing detector disclosed in “Integration-Time Based Computational Image Sensors”, 1995 IEEE Workshop on Charge-Coupled Devices and Advanced Image Sensors, Apr. 20 to 22, 1995, Dana Point, Calif., USA, and the distance measuring method utilizing the charge distributing detector will next be described.
FIGS. 8A
,
8
B show a basic constitution of the charge distributing detector and a principle of a charge distributing operation by the detector.
First, the constitution of the charge distributing detector will be described.
That is to say, as shown in
FIG. 8A
, the charge distributing detector is constituted of an MOS light receiver
101
formed on a P-type semiconductor substrate
100
, a first transfer gate
103
disposed in the vicinity of the MOS light receiver
101
and between the MOS light receiver and a first charge accumulation area
102
, and a second transfer gate
105
disposed in the vicinity of the MOS light receiver
101
and between the MOS light receiver and a second charge accumulation area
104
.
The MOS light receiver
101
is provided with a gate electrode having a good light transmittance, and a voltage is applied to the gate electrode to form a depletion layer on the surface of the P-type semiconductor substrate
100
.
On the other hand, an electric potential is applied to the first and second charge accumulation areas
102
and
104
to form a potential well deeper than the semiconductor surface potential of the MOS light receiver
101
.
Moreover, transfer pulses &PHgr;WG
1
and &PHgr;WG
2
can individually be applied to the first and second transfer gates
103
and
105
.
A charge distributing operation by the charge distributing detector constituted as described above will next be described.
First, while the second transfer gate
105
is closed, a transfer pulse is applied to &PHgr;WG
1
to turn ON the first transfer gate
103
. Then, as shown by a solid-state line in
FIG. 8B
, electrons photo-generated in the MOS light receiver
101
flow into the first charge accumulation area
102
via the first transfer gate
103
, and are accumulated as an electric charge Q
1
in the first charge accumulation area
102
.
Conversely, while the first transfer gate
103
is closed, the transfer pulse is applied to &PHgr;WG
2
to turn ON the second transfer gate
105
. Then, as shown by a broken line in
FIG. 8B
, the electron photo-generated in the MOS light receiver
101
flows into the second charge accumulation area
104
via the second transfer gate
105
, and is accumulated as an electric charge Q
2
in the second charge accumulation area
104
.
When the transfer pulses &PHgr;WG
1
and &PHgr;WG
2
applied to the first and second transfer gates
103
and
105
are alternately turned ON in this manner, it is possible to control a transfer direction of the electron photo-generated in the first and second charge accumulation areas
102
and
104
.
The distance measuring principle using the charge distributing detector will next be described with reference to
FIGS. 9 and 10A
to
10
D.
As shown in
FIG. 9
, a measurement system is constituted of a pulse generating light source
110
, charge distributing detector
111
and timing controller
112
.
Here, the timing controller
112
establishes synchronization in the pulse generating light source
110
and charge distributing detector
111
, and further controls an operation timing.
It is assumed that a distance to the object
113
from the measurement system is R. For convenience of description, it is assumed that the distance to the object
113
from the pulse generating light source
110
is the same as the distance to the object
113
from the charge distributing detector
111
.
Moreover, as shown in
FIGS. 10A
to
10
D, first, the object
113
is irradiated with a pulse light with a light emitting time T from the pulse generating light source
110
.
The light reflected by the object
113
reciprocates by the distance R, that is, flies by a distance 2R, and is incident upon the charge distributing detector
111
with a delay of &Dgr;t=2R/c (here, c indicates light speed) behind the pulse light emitting timing.
In this case, the transfer pulse &PHgr;WG
1
is applied to the first transfer gate
103
of the charge distributing detector
111
at the same timing as that of the light emitting pulse, and the transfer pulse &PHgr;WG
2
is applied to the second transfer gate
105
at a timing at which the light emitting pulse turns off. During this, the photo-generated electron generated by the reflected light is detected.
Here, it is supposed that there is no cross talk in an electric charge transfer operation and that electric charge transfer is switched at a sufficiently high speed. Then, the electric charge Q
1
accumulated in the first charge accumulation area
102
and electric charge Q
2
accumulated in the second charge accumulation area
104
are represented by the following equations (1) and (2), respectively.
Q
1
=−Qt
×(
T−&Dgr;t
)/
T
  (1)
Q
2
=−Qt×&Dgr;t/T
  (2)
Therefore, the distance R to the object can be obtained by the following equation (3).
R
=(
cT/
4)×{(
Q
1
−Q
2
)/(
Qt−
1)}  (3)
As described above, in the distance measuring method in which the charge distributing detector is used as described above, the distance to the object can be measured with a very simple processing. As compared with the distance measuring method which is based on the triangular survey method, the distance to the object can be detected only by observation from one point. Therefore, it is possible to miniaturize the apparatus and to realize a very superior distance measurement apparatus in which no occlusion occurs.
Moreover, the charge distributing detector can be prepared by applying a technique of a charge transfer device (CCD) frequently used in a solid-state image pickup device, and is advantageous for integration of the apparatus.
Additionally, a shot noise by light quantum fluctuation exists in the signal charges Q
1
and Q
2
.
A standard deviation amount of the shot noise is generally a square root of the number of incident photons. However, since the photon having an energy of a visible light area usually generates a single electron-hole pair in a semiconductor, it is unnecessary to consider an amplification fluctuation. Additionally, a process

Affiliated with

Also associated with

Rating

Distance measurement apparatus and distance measuring method does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Distance measurement apparatus and distance measuring method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Distance measurement apparatus and distance measuring method will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2862546