Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-08-08
2003-07-01
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S237000, C359S238000
Reexamination Certificate
active
06587248
ABSTRACT:
TECHNICAL FIELD
The present invention relates to optical modulation apparatuses and, more specifically, to an optical modulation apparatus that uses a light source and a device for ON/OFF control of light outputted from the light source.
BACKGROUND ART
In one conventional optical modulation apparatus that uses a light source and a device for ON/OFF control of light outputted from the light source, by controlling the device for ON/OFF control of the output light to vary the density of ON time (typically, by carrying out pulse-width modulation or pulse-number modulation), light is outputted that has luminance according to a provided luminance signal. At this time, the apparatus is structured to operate by varying density during ON time in a unit of a clock signal (that is, to modulate the pulse width or pulse number of the output light from the light source within a unit of the clock signal).
Described below is the conventional optical modulation apparatus with reference to drawings.
FIG. 20
is a block diagram showing the structure of the conventional optical modulation apparatus. In
FIG. 20
, the conventional optical modulation apparatus includes a pulse-width modulation circuit
101
, a power supply.
102
, a light source
103
, and a light valve
104
.
The light source
103
is supplied with electric power by the power supply
102
for outputting light. The light valve
104
receives an output pulse (pulse-width modulating signal) from the pulse-width modulation circuit
101
and the output light from the light source
103
, and outputs pulse-width modulated light.
FIG. 21
is a block diagram showing one example of structure of the pulse-width modulation circuit
101
of FIG.
20
. In
FIG. 21
, the pulse-width modulation circuit
101
includes a down counter
1011
, a flip-flop circuit
1012
, and a D flip-flop circuit
1013
.
In
FIG. 21
when the pulse-width modulation circuit
101
is supplied with a synchronizing signal, the down-counter
1011
loads a value of a signal YS indicating a luminance of a specific pixel according to the synchronizing signal. Simultaneously, the flip-flop circuit
1012
is set to “1”.
The value loaded to the down-counter
1011
is down-counted in accordance with a clock signal. When the value becomes 0, the down-counter
1011
outputs a value of 0. This 0 output from the down-counter
1011
resets an output from the flip-flop circuit
1012
to “0”. The D flip-flop circuit
1013
takes in the output from the flip-flop circuit
1012
according to the clock signal, and then outputs the same.
If the reset operation has higher priority than any other operation in the flip-flop circuit
1012
, when YS is 0, the D flip-flop circuit
1013
does not output any pulse. On the other hand, if YS has a value other than 0, pulses spaced by a time-width in proportion to the value are outputted.
Again in
FIG. 20
, the pulse-width modulation circuit
101
receives the synchronizing signal, the clock signal, and the YS for carrying out the above operation, thereby outputting pulses spaced by the time-width in proportion to the value of the luminance signal YS. On the other hand, the light source
103
is supplied with electric power by the power supply
102
for outputting light having predetermined intensity. The output light of the light source
103
is supplied to the light valve
104
, and ON/OFF-controlled therein with the output pulses from the pulse-width modulation circuit
101
.
FIG. 22
is a diagram showing operating waveforms of the conventional optical modulation apparatus (the apparatus of FIG.
20
). Shown in
FIG. 22
are a waveform indicating output light intensity of the light source
103
and a waveform of the output pulses (pulse-width modulating signal) of the pulse-width modulation circuit
101
.
Note that shown in
FIG. 22
are the waveforms for four frame periods (from left on the drawing, a first to fourth frame periods; the same goes in the following). One frame period includes eight cycles of the clock signal (that is, one frame period is equal to eight clock periods).
The output light of the light source
103
having the intensity waveform as shown in FIG.
22
and the output pluses (pulse-width modulating signal) of the pulse-width modulation circuit
101
having the waveform as shown in
FIG. 22
are supplied to the light valve
104
. From the light valve
104
, light having the luminance “8” at maximum is outputted. This light has the luminance “8” during the first field period, the luminance “4” during the second field period, the luminance “2” during the third field period, and the luminance “1” during the fourth field period.
The luminance described herein is a value obtained by time-integrating the output light intensity of the light source
103
over one frame period. In the example of
FIG. 22
, the output light intensity of the light source is constant (=1), and the luminance of the light outputted from the light valve
104
is represented by a density, per one frame period (=eight clock periods), representing the number of clock periods during which the light valve
104
is ON.
Therefore, if the light valve
104
is OFF during one frame period, the output light luminance of the light valve
104
during that frame period is “0”.
Also, if the light valve
104
is ON at the density of one clock period per one frame period, the output light luminance is “1”, and this is minimum luminance for the light (that is, the darkest) outputted from the light valve
104
(the fourth frame). Similarly, the output light intensity for ONs for eight clock periods is “8”, and this is maximum luminance for the light (that is, the brightest) (the first frame).
In other words, the optical modulation apparatus of FIG. can output light of nine types of luminance including “0”.
Note that description has been made in the foregoing for a case where the light valve
104
has only one pixel. In this case, there needs only one pulse-width modulation circuit
101
. However, there exists a light valve having a plurality of pixels as shown in
FIG. 23
, and an optical modulation apparatus using such light valve has been made for practical use.
FIG. 23
is a diagram showing a light valve having a plurality of pixels and a relation between each pixel of the light valve and a video signal. In
FIG. 23
, each pixel included in the light valve is supplied with output light from a single light source.
A conventional optical modulation apparatus using the light valve of
FIG. 23
includes a plurality of pulse width modulation circuits
101
corresponding to each pixel. Each of the pulse-width modulation circuit
101
is supplied with a value of a luminance signal YS corresponding to each pixel. Then, outputted through the light valve
104
is a ray bundle having a plurality of lights each having a luminance corresponding to each pixel.
As is evident from the above description, in the conventional optical modulation apparatus using the light source
103
and the device (light valve
104
) for ON/OFF control of the output light of the light source, for the purpose of increasing the types of luminance (that is, the number of gradations) of light outputted from the light valve
104
, it is required to increase the frequency of the clock signal which serves as a unit for ON/OFF control. In other words, the operating speed of the light valve for ON/OFF control of the output light of the light source
103
(that is, the frequency of the clock signal) disadvantageously restricts the number of gradations of the light outputted from the light valve
104
.
DISCLOSURE OF THE INVENTION
Therefore, an object of the present invention is to provide an optical modulation apparatus that uses a light source and a device for ON/OFF control of an output light of the light source, the optical modulation apparatus capable of increasing the number of gradations (types of luminance) of light outputted from the device without increasing the frequency of a clock signal which serves as a unit of the ON/Off control of the output light from the light source.
To solve the above p
Schwartz Jordan M.
Stultz Jessica
Wenderoth , Lind & Ponack, L.L.P.
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