Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-11-01
2003-02-11
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S2140AL
Reexamination Certificate
active
06518561
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a user detection circuit for a display apparatus that switches between the normal operation and the power-saving standby operation (hereinafter referred to as standby operation) of the display apparatus by detecting a user in front of the display screen.
Recently, a flat-panel display apparatus such as a liquid crystal display apparatus has been drawing attention as a display apparatus alternative to the CRT. In addition, energy conservation is required of OA equipment in general including this type of display apparatus. Therefore, a flat-panel display apparatus is required to save energy by suspending display and switching itself to standby operation to stand by when display is not necessary.
As a method for automatically switching between normal operation and standby operation in this type of display apparatus, there is a method conceivable in which a user in front of the display screen is detected by a sensor, and the apparatus is switched to standby operation if the user is absent for a certain period of time.
FIG. 7
is a circuit diagram showing a concrete example of such a user detection circuit as a prior art.
A sensor
10
for detecting a user (hereinafter referred to as a user sensor) is a reflection type infrared sensor having a light emitting unit
12
and a light receiving unit
14
.
The light emitting unit
12
has a resistance
12
A, an infrared diode
12
B, and a switch
12
C, and emits infrared rays from the infrared diode
12
B to the front of a display apparatus.
On the other hand, the light receiving unit
14
has a phototransistor
14
A and a resistance
14
B. The phototransistor
14
A receives the infrared rays which are emitted from the infrared diode
12
B of the light emitting unit
12
and reflected from the user, and then a detection signal in response to the quantity of light is outputted.
However, although in such a user sensor
10
, the phototransistor
14
A has frequency characteristics to detect infrared rays, it is difficult for the phototransistor
14
A to distinguish between the light reflected from the user and infrared rays included in the light in the environment that also enter the phototransistor
14
A. This may cause erroneous function.
As a measure to deal with this problem, the infrared diode
12
B is conventionally made to provide pulsed lighting by turning on and off the switch
12
C of the light emitting unit
12
, so that a lighting time period and the other time period are each detected by a sample hold circuit consisting of a switch
15
and hold circuits
16
and
18
. Then only a reflected component is extracted by subtracting an environmental light component.
Specifically, in
FIG. 7
, the switch
12
C in the light emitting unit
12
and the switch
15
on the side of the light receiving unit
14
open and close with pulse periods in sync with each other. That is, when the infrared diode
12
B in the light emitting unit
12
is turned on, the output of the phototransistor
14
A in the light receiving unit
14
is inputted to a first hold circuit
16
. When the infrared diode
12
B in the light emitting unit
12
is turned off, the output of the phototransistor
14
A in the light receiving unit
14
is inputted to a second hold circuit
18
.
The first hold circuit
16
has a capacitor
16
A and a buffer circuit
16
B. The capacitor
16
A accumulates detection voltage from the phototransistor
14
A during a time period when the infrared diode
12
B turns on, and then the level of the resulting voltage is outputted via the buffer circuit
16
B.
The second hold circuit
18
has a capacitor
18
A and a buffer circuit
18
B. The capacitor
18
A accumulates detection voltage from the phototransistor
14
A during a time period when the infrared diode
12
B is turned off, and then the level of the resulting voltage is outputted via the buffer circuit
18
B.
Therefore, sample hold output from the first hold circuit
16
corresponds to a quantity of infrared rays representing a total of infrared rays reflected from the user and infrared rays from environmental light. Sample hold output from the second hold circuit
18
corresponds to a quantity of infrared rays that does not include infrared rays reflected from the user but includes only infrared rays from environmental light.
Thus, the polarity of the sample hold output from the second hold circuit
18
is reversed by a reversing circuit
20
, and then the resulting sample hold output from the second hold circuit
18
is added to the sample hold output from the first hold circuit
16
by an adding circuit
22
. A resultant signal is outputted as a sensor output signal via an amplifier
24
.
This makes it possible to provide sensor output that corresponds only to a quantity of infrared rays emitted from the light emitting unit
12
and reflected from the user without being affected by increases or decreases in the quantity of environmental light. Then, presence or absence of the user in front of the display apparatus is detected by determining the level of the sensor output using a determination circuit.
In the conventional user detection circuit as described above, however, the operation of the switch
12
C in the user sensor
10
needs to be synchronized precisely with the operation of the switch
15
on the side of the light receiving unit
14
by a timing circuit (not shown in the figure) for controlling the switches.
In addition, switching noise should not be mixed into the capacitors
16
A and
18
B.
Thus, the conventional user detection circuit described above has a complex circuit configuration. Moreover, attention needs to be paid to the arrangement of components and further to the capacities and temperature characteristics of the capacitors
16
A and
18
B.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a user detection circuit for a display apparatus that makes it possible to perform highly accurate user detection with a simple configuration without using a highly accurate, complex timing circuit or sample hold circuit.
According to the present invention, in order to achieve the above object, there is provided a user detection circuit that detects absence of the user in front of the display screen and thereby switches the normal operation of the display apparatus to power-saving standby operation for allowing the display apparatus to suspend display and standby. The user detection circuit includes a user sensor for detecting a user in front of the display screen, an illumination sensor for detecting the brightness of the environment of the display screen; a correction means for correcting a detection signal of the user sensor based on a detection signal of the illumination sensor, and a determination means for determining whether the user is present based on the detection signal of the user sensor corrected by the correction means.
In the user detection circuit according to the present invention, the user sensor detects a user in front of the display screen, while the illumination sensor detects the brightness of the environment of the display screen.
The correction means corrects a detection signal of the user sensor based on a detection signal of the illumination sensor. The determination means determines whether the user is present based on the detection signal of the user sensor corrected by the correction means.
Thus, in the user detection circuit according to the present invention, conventional sample hold operation by time division is not required because detection signals are corrected by using a user sensor and an illumination sensor that are independent of each other. Hence a highly accurate, complex timing circuit or sample hold circuit for the above sample hold operation is not required.
It is thus possible to perform highly accurate user detection with a simple configuration, and therefore correctly switch between the normal operation and the standby operation of the display apparatus.
The above and other objects, features and advantages of the present invention wil
Kao Chih Cheng G
Kim Robert H.
Maioli Jay H.
Sony Corporation
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