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JP2001245187

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DESCRIPTION JP2001245187
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
video camera with a microphone, and more particularly to a video camera with a microphone
capable of performing audio focusing in synchronization with image focusing.
[0002]
2. Description of the Related Art FIG. 10 is an external view showing a schematic configuration of
a conventional video camera 200 with a microphone. A lens 202 for inputting an image from a
subject and a microphone 203 for inputting a sound emitted from the subject are attached to the
camera body 201. Conventionally, stereo microphones and monaural microphones have been
used as the microphones 203 mounted on such video cameras. Microphones mounted on such
video cameras are switched to unidirectionality or switched to omnidirectionality according to
the improvement for preventing the generation of noise due to wind pressure when used
outdoors, or according to the condition of the subject. Devices such as were made.
[0003]
On the other hand, the video camera performs focusing on the subject by adjusting the lens 202
in accordance with the distance of the subject, and is operated to obtain an optimal image signal.
In addition, when a zoom lens is used, it is possible to obtain an image of an object at a long
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distance by zooming (zooming up) to a short distance or reducing an image of an object at a
short distance to a long distance (zooming down). On the other hand, the microphone 203
performs an operation separate from the operation of the lens 202 and collects surrounding
sound with a one-point microphone or a stereo microphone regardless of enlargement or
reduction of an image captured from the zoom lens. Further, in recent years, an optical
microphone element has been attracting attention as a small microphone element, and in
particular, a device using a vertical cavity surface emitting laser (hereinafter referred to as a
VCSEL) as a light emitting element can realize further miniaturization.
[0004]
As described above, in the conventional video camera with a microphone, even if the subject
image is enlarged or reduced by the zoom, the sound recorded from the subject is not linked to
this, but is merely the surroundings. Only voice could be caught. Therefore, a phenomenon
occurs in which the sound from the subject can be heard from a distance even when the camera
zooms and captures an enlarged image. This is because the microphone attached to the video
camera was a unidirectional or omnidirectional microphone, and therefore it was not possible to
switch the audio sensitivity in conjunction with the zooming of the image.
[0005]
Therefore, in a video camera with a microphone, a microphone is required which is captured as
an audio from a short distance when the image is enlarged and as an audio from a far distance
when the image is reduced. The inventors arrived at the invention of the present application
focusing on the fact that the optical microphone element using the VCSEL is not only suitable for
the microminiaturization, but also the directivity adjustment can be easily realized. Therefore, an
object of the present invention is to provide a video camera with a microphone using an optical
microphone element capable of zooming the sound of the microphone in conjunction with the
zooming of the image.
[0006]
In order to achieve the above object, the video camera with a microphone of the present
invention of the present invention comprises a microphone capable of controlling the directional
characteristic, and the directional characteristic is synchronized with the focusing on the subject
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of the video camera. In a video camera with a microphone for focusing on a subject, a vertical
cavity surface emitting laser light emitting element having a substantially uniform light emission
intensity distribution is disposed as the microphone, and a light receiving element for receiving
emitted light of the light emitting element is provided. A disposed substrate, and a diaphragm
which is disposed substantially in parallel and close to a position facing the substrate, vibrates
due to sound pressure, reflects light from the light emitting element, and emits the light to the
light receiving element; A light source drive circuit for supplying a drive current to the light
emitting element, and a part of the signal output from the light receiving element is negative The
light is changed by changing the magnitude of the negative feedback signal according to a
zooming signal indicating a zooming amount to a subject of the video camera, using an optical
microphone provided with a negative feedback circuit supplying the light source drive circuit as
a feedback signal. Controlling the directivity of the microphone; Further, in the video camera with
a microphone of the present invention, the zooming signal may be a zoom amount change signal
indicating a change amount of a zoom lens of the video camera.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION In the video camera with a microphone
according to the present invention, the voice recorded from the microphone is also synchronized
and scaled in accordance with the scaling of the zoomed image, thereby changing the directivity
and reducing it. The sound from the image projected at a distance can be heard from a distance,
and the sound corresponding to the image magnified and projected at a large size can be heard
from a distance. Furthermore, an optical microphone using a VCSEL is used as a microphone
used for such purpose. First, prior to describing the embodiment of the video camera with a
microphone of the present invention, the basic operation and configuration of an optical
microphone using a VCSEL used in the present invention will be described.
[0008]
FIG. 2 is a view showing the basic structure of the optical microphone element. FIG. 2A shows a
cross-sectional shape, in which the electronic circuit board 12 is placed on the bottom surface 8
of the container 1 and the board 9 on which the light emitting element and the light receiving
element are arranged is attached. The attachment can also be performed by electrically
connecting the substrate 9 and the substrate 12 by, for example, flip chip bonding. If the bottom
surface 8 is formed of a semiconductor substrate such as silicon, the electronic circuit substrate
12 can be omitted because an electronic circuit can be formed thereon. In the example shown in
FIG. 2, a vertical cavity surface emitting laser diode LD is used as a light emitting element, and a
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photodiode PD is used as a light receiving element. A circular surface emitting laser diode LD is
disposed at the center of the substrate 9, and the light receiving elements PD are disposed
concentrically so as to surround the surface emitting laser diode LD.
[0009]
FIG. 2B is an enlarged plan view of the light emitting and receiving part of the substrate 9 on
which the light emitting and receiving element shown by a dotted line in FIG. 2A is mounted. As
shown in the figure, a circular light emitting element LD is disposed at the central portion, and
light receiving elements PD1, PD2,... PDn are disposed concentrically so as to surround this. A
vertical cavity surface emitting laser can be used as the light emitting element LD used here. The
light emitting element LD and the light receiving element PD can be simultaneously
manufactured on a gallium arsenide wafer by a semiconductor manufacturing process.
Accordingly, since the alignment accuracy between the light emitting element LD and the light
receiving element PD is determined by the accuracy of the mask used in the semiconductor
manufacturing process, the alignment accuracy can be made 1 μm or less. It can be realized
with a high accuracy of one-hundredth or less compared to the alignment accuracy.
[0010]
In general, the vertical cavity surface light emitting element has a concentrically uniform light
emission intensity distribution. Therefore, the radiation light emitted toward the diaphragm 2 at
a predetermined angle from the light emitting element LD disposed at the central portion is
concentrically reflected with the same intensity, and the diaphragm 2 vibrates due to the
reception of the sound wave 7 As a result, the reflection angle changes and reaches the light
receiving element PD concentrically. Therefore, the vibration displacement of the diaphragm 2
can be detected by detecting the change in the amount of light received by the light receiving
elements PD1 to PDn arranged concentrically. Since the strength of the incident sound wave 7
can be detected by this, it can be used as an optical microphone element. An electrode 11 is
formed to drive the light emitting element LD and the light receiving element PD or to detect the
amount of incident light.
[0011]
Next, a vertical cavity surface emitting laser (hereinafter referred to as a VCSEL) which is a light
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emitting element used in the present invention will be described. FIG. 3 shows the light emission
intensity distribution of the VCSEL, and as shown in the figure, the radiation intensity distribution
is given as a Gaussian distribution with respect to the nucleus. The light emission intensity
distribution P0 (θ) is expressed by equation (1). Po (θ) = exp (−α 2 θ 2) (1) θ: Angular
displacement (in radians) from the vertical line on the light emitting surface α: A coefficient
defining the light emission spread angle (essentially “1 / α 2” in calculation Simplification)
[0012]
When the calculation of the light emission distribution coefficient α is calculated for a onedimensional case, it is expressed as equation (2). [alpha] 2 =-[ln (h)] / (FAHM / 2) 2 (2) h: Relative
intensity given by measuring the light emission distribution of the laser: 1. Half value = 0.5.
1/e=0.3183。 1 / e2 = 0.135335 FAHM: The manufacturer usually provides a full width half
maximum (FAHM) value. If h = 0.5, FAHM = 9 degrees (angle included) rad (9/2) = 0.07854 α2
=-[(ln (0.5)) / (0.07554) 2 = 112.369 and use this to specify the emission intensity distribution
The distribution as shown in FIG. 3 can be obtained by calculating for the designated orientation.
[0013]
FIG. 4 is a diagram in the case where the emission intensity distribution is calculated in two
dimensions and illustrated. In this case, the two-dimensional light emission intensity distribution
P 0 (θ) is given by equation (3). Po (θ) = exp (−α2θ2) · exp (−β2ψ2) (3)
[0014]
Calculation is performed in the same manner as the distribution calculation coefficients α and β
in the θ direction and the ψ direction. The light emission distribution coefficient α is given by
equation (4), and the light emission distribution coefficient β is given by equation (5). α2 = −
[ln (h)] / (FAHM / 2) 2 (4) h = 0.5, FAHM = 9 degrees rad (9/2) = 0.0754α2 = − [(ln (0.5)] /
(0.07554) 2 = 112. 369
[0015]
β2 = − [ln (h)] / (FAHM / 2) 2 (5) h = 0.5, FAHM = 9 degrees rad (9/2) = 0.07854β2 = − [(ln
(0.5)] / (0.07554) 2 = 112.369
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[0016]
As apparent from the two-dimensional emission intensity distribution obtained in this manner, in
the vertical cavity surface emitting laser, the intensity distribution of the light emitting element is
substantially uniform concentrically.
From this, in order to efficiently receive the laser emission as the deflection (displacement) of the
diaphragm 2, it is optimal to arrange the light receiving elements concentrically. And the
differential signal of the signal which the light receiving element which belongs to the different
concentric circle arrange | positioned concentrically becomes a signal which gives a sound
pressure change.
[0017]
Here, in order to limit or sort the dynamic range of the received signal, this can be achieved by
providing two or more light receiving elements concentrically. Here, in the optical microphone
shown in FIG. 2, the noise reduction effect can not be expected so much. That is, the diaphragm 2
vibrates also by the noise reaching the diaphragm 2, and this is superimposed on the vibration of
the normal sound wave 7 as a noise signal. An optical microphone having a structure as shown in
FIG. 5 is known as an optical microphone in which the effect of noise is reduced to further reduce
noise.
[0018]
In the structure shown in FIG. 5, the diaphragm 2 vibrating by the sound wave 7 is stretched at a
substantially central portion of the container 1. Then, the first opening 15 and the second
opening 16 are provided on both sides of the container 1 so as to be at the target positions with
respect to the diaphragm 2. By this configuration, the sound wave 7 intrudes into the container 1
from any of the openings 15 and 16 to vibrate the diaphragm 2. Although FIG. 5 shows a
structure in which the light emitting element LD and the light receiving element PD are separated
for convenience of explanation, in fact, the light emitting element LD and the light receiving
element PD are integrally formed on the substrate 9 as shown in FIG. The one with the structure
shown in is used.
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[0019]
When the sound pressure of the sound wave invading from the first opening 15 and the sound
wave invading from the second opening 16 in the optical microphone element 50 shown in FIG.
5 is equal to each other, these two sound waves are on both sides 2 a of the diaphragm 2, The
diaphragm 2 is not vibrated by canceling each other in 2b. It is known that when two
microphone elements with equal reception sensitivity are arranged close to each other and sound
waves generated at a long distance are received, the two microphone elements detect incoming
sound waves equally. Generally, sound waves are generated from the mouth of a person at a
short distance from the microphone element. That is, sound is generated at a short distance from
this microphone element. The voice of this short-distance person has a spherical field
characteristic as shown by a circular curve.
[0020]
On the other hand, sound waves generated at a long distance, for example, noise and sound, have
the characteristics of a flat field. The acoustic intensity of a spherical wave is about the same
along its spherical or falling line and varies along the radius of the sphere, but in the case of a
plane wave, the acoustic intensity is about the same at all points in the plane. Therefore, the
optical microphone element as shown in FIG. 5 can be considered to be a combination of two
microphone elements, so when it is placed in the far-field, it can be seen approximately from the
first opening 15 and the second opening 16 Sound waves having the same intensity and phase
characteristics arrive at the diaphragm 2, and as described above, they cancel each other and
their influence is reduced. On the other hand, since the sound wave from the near field is
unevenly incident from the first opening 15 or the second opening 16, the diaphragm 2 is
vibrated and taken out as a signal from the light emitting element PD. Thus, an optical
microphone element capable of further reducing the influence of noise is obtained by the
structure of FIG.
[0021]
FIG. 6 is a diagram showing the directivity pattern of the optical microphone element shown in
FIGS. 2 and 5. (A) shows the directivity pattern of the optical microphone element shown in FIG.
2, and the substantially circular directivity having the maximum sensitivity in the direction
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perpendicular to the diaphragm 2 toward the opening (left direction in the drawing) Have a
pattern. (B) shows the directivity pattern of the optical microphone element shown in FIG. 5 and
has an approximately 8-shaped directivity pattern having maximum sensitivity in both directions
of the openings 15 and 16. Here, as shown in FIGS. 7 and 8, the directional beam pattern of the
optical microphone element shown in FIGS. 2 and 5 is expanded in the axial direction showing
the maximum sensitivity, and is changed so as to narrow in the direction orthogonal to the axis. It
can be done.
[0022]
In order to change the directional beam pattern in this manner, a part of the detection output
from the light receiving element PD may be fed back to the light source drive circuit that drives
the light emitting element LD using a negative feedback circuit. FIG. 9 is a view showing a
schematic configuration of an optical microphone device using a feedback circuit 100 for
changing the beam pattern as shown in FIG. 7 or FIG. The output from the light receiving element
PD is taken out through the filter circuit 18 and amplified by the amplifier 19 to be a microphone
output. The filter circuit 18 is used to extract only signal components in the desired frequency
range. Here, in the optical microphone device shown in FIG. 9, a predetermined current is
supplied to the light emitting element LD through the negative feedback (negative feedback dot
NFB) circuit 100 for a part of the output signal taken out from the light receiving element PD.
Are supplied as a negative feedback signal to the light source drive circuit 13 which is driving the
light source.
[0023]
The negative feedback circuit 100 comprises a small signal amplification circuit 10, a filter
circuit 14 for taking out only a signal component in a desired frequency range from the output
thereof, and a comparator 20. The non-inverting input terminal of the comparator 20 is
connected to a reference power supply 14 serving as a reference voltage. The signal extracted via
the filter circuit 17 is supplied to the inverting input terminal of the comparator 20. The small
signal amplifier circuit 10 amplifies only the signal below a predetermined level. With such a
configuration, the comparator 20 outputs a smaller output level as the output of the filter circuit
17 is larger, whereby the light source drive circuit 13 operates to reduce the current supplied to
the light emitting element LD.
[0024]
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Here, the small signal amplifier circuit 10 amplifies the signal only when the input signal level is
lower than a predetermined level, and does not amplify a signal higher than a certain level.
Therefore, when the input signal level is equal to or higher than a certain level, the output signal
level does not change and becomes amplification (gain) 0. In addition, when the input signal is
lower than a predetermined signal level, amplification is performed so as to increase as the signal
level decreases. Furthermore, the rate of increase of the output signal relative to the input signal
is higher as the input signal level is smaller.
[0025]
Here, since the output from the light receiving element PD is proportional to the received sound
volume, the output of the small signal amplifier circuit 10 is amplified and output as it is smaller
the smaller volume. Since this is input to the inverting input terminal of the comparator 20 via
the filter circuit 17, the output of the comparator 20 decreases its output level as the volume
decreases. As a result, the current supplied to the light emitting element LD operates so as to
lower the light output of the light emitting element LD as the volume becomes smaller. That is,
the sensitivity of the microphone decreases as the volume decreases. Also, since the signal above
the predetermined level is not amplified, the light output is not limited at that signal level.
Therefore, the sensitivity of the microphone does not decrease either.
[0026]
With respect to a sound of a size that does not cause a drop in sensitivity of the microphone due
to a sound coming from an axial direction orthogonal to the diaphragm, if the sound is shifted
from the axial direction, the sensitivity gradually decreases due to the original directivity curve.
To go. When the level becomes lower than a certain level, the small signal amplifier circuit 10
comes to have an amplification degree, the supply current control of the light source drive circuit
13 works, and the sensitivity of the microphone further decreases. As a result, in the optical
microphone device having the negative feedback circuit 100, as shown in FIG. 7 or FIG. 8, the
width of the directional beam of the directional pattern of sensitivity is narrowed.
[0027]
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FIG. 7 and FIG. 8 show the pattern change of directivity due to the change of the amount of
negative feedback. (A) shows the directivity pattern when negative feedback is not applied, and in
this case, it becomes a substantially circular directivity pattern. Next, directivity patterns when
negative feedback is applied are shown in (B) and (C). In the case of (B), the amount of negative
feedback is small, and in the case of (C), the amount of negative feedback is large. In this way, the
amount of negative feedback is changed by varying the amplification degree of the small signal
amplification circuit 10 to expand the directivity pattern of sensitivity in the axial direction of the
maximum sensitivity and change it so as to narrow it in the direction orthogonal to the axis. Can.
Thus, the directivity characteristic of the sensitivity of the optical microphone can be changed.
[0028]
In the sound pickup apparatus according to the present invention, the directivity characteristic of
the selected microphone is changed using an optical microphone element capable of changing
such a directional beam pattern. FIG. 1 is a block diagram showing an embodiment of a video
camera with a microphone according to the present invention. Instead of the microphone 203 in
the conventional camera shown in FIG. 10, an optical microphone 300 comprising an optical
microphone element 50, a light source drive circuit 13 and a negative feedback circuit 100 is
used. The configuration of the camera unit is such that the signal from the zoom amount
adjustment means 28 for adjusting the zoom amount of the lens 202 for inputting the input
image 27 is taken out by the zoom amount conversion means 31 via the image detection element
29 such as CCD and the amplification circuit 30. . That is, when the zoom amount adjustment
means 31 zooms in or out on a subject, the zoom amount conversion signal indicating the extent
of enlargement or reduction by detecting the image from the subject is the zoom amount
conversion circuit Obtained at the output of 31.
[0029]
This zoom amount change signal is used as a control signal for changing the negative feedback
amount of the negative feedback circuit 100. That is, when the image is enlarged by zooming up,
the negative feedback amount of the negative feedback circuit 100 is increased in response to
the zoom amount change signal which is the output signal from the zoom amount conversion
circuit 31, and the directivity of the optical microphone element 50 is increased. Sharpen the
beam width to reduce the influence of surrounding sound, and pick up and record only the signal
from the subject. On the contrary, when the image is reduced by zooming down, the amount of
negative feedback is reduced or the operation of the negative feedback circuit is stopped to make
it unidirectional, and sound collection is performed in consideration of the influence of
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surrounding sound.
[0030]
In the embodiment shown in FIG. 1, the zooming amount to the subject of the video camera is
obtained by the output of the zooming amount adjustment means 28 based on the image signal
from the imaging device, but the method of detecting the zooming amount is limited to this. It is
not something to be done. That is, it is also possible to directly detect the mechanical change of
the zoom amount adjustment means 18 and convert it to electrically detect it as a zoom amount
change signal and use it as a control signal of the negative feedback circuit 100. In addition, as
the optical microphone element 50 of the optical microphone 300 used in the present invention,
in principle either one having the structure shown in FIG. 2 or one having the structure shown in
FIG. 5 can be used. It is preferable to use one having a structure shown in 5.
[0031]
As described above in detail based on the embodiments, in the present invention, as a
microphone mounted on a video camera, an optical microphone using a VCSEL capable of
changing the directivity characteristic to a sound wave is used. The directivity of the microphone
is changed by changing the amount of negative feedback of the negative feedback circuit in
response to the amount of zooming to the subject of the camera, and the recording status of
voice is changed in response to the scaling of the image. Therefore, it is possible to record the
image and the sound as if the sound was emitted far from the reduced image, that is, the sound is
close to natural as the sound is emitted close to the corresponding to the enlarged image. .
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