Patent Application
20070252806
The above features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Exemplary embodiments of the present invention will be described in detail herein below with reference to the accompanying drawings.
Display devices using light sources of red, green and blue have been proposed due to easy modulation of image signals, color reproduction improvement, and brightness improvement. In particular, when a semiconductor laser is used for a display light source, the light intensity is varied due to a variation in an ambient temperature or operating temperature, such that color quality of a display device may be deteriorated. Thus, a device for maintaining the light intensity of a light source substantially constant is required.
As illustrated in
In the drive structure 200 for a sequential RGB display in accordance with the exemplary embodiment of the present invention, a light source outputs light in the front and rear directions. In a TO-CAN structure in which multiple light source units are arranged, RGB laser diodes (LDs) 240, 250, and 260 form a light source array. Further, the LDs 240, 250, and 260 emit laser light in proportion to the magnitude of an applied operating current, respectively.
The light receiving means is configured with one monitor photodiode (MPD) 270 for detecting part of light output from the RGB LDs 240, 250, and 260
The LDs 240, 250, and 260 are driven by forward bias, whereas the MPD 270 is driven by reverse bias. LD drivers 210, 220, 230 are connected to cathodes of the LDs 240, 250, and 260, respectively, and an anode of the MPD 270, and are commonly connected to a resistor circuit 300. In this structure, a feedback current detected from the MPD 270 is provided to a light source driver.
The light source driver is provided with the LD drivers 210, 220, and 230 for controlling operating currents for sequentially emitting light from the RGB LDs 240, 250, and 260 in response to RGB modulation signals input via input terminals 280 from an external image processor (not illustrated).
The LD drivers 210, 220, and 230 are different from one another in that types of light sources for outputting light in response to the input RGB modulation signals are different. Further, operating currents of the LDs differ according to the magnitudes of resistors Rmod.
For example, a red LD driver 210 will be described below. As illustrated in
Further, the red LD driver 210 includes a resistor circuit 300 for dropping a voltage according to a feedback current Impd output from an MPD 270 for receiving part of light output from a red LD 240 and performing conversion to a current signal. In the red LD driver 210, an automatic power controller 320 includes a comparator 310 for comparing a preset reference voltage VREF with a voltage vb generated by an electric current flowing to the resistor circuit 300 when a constant current Imod output from the current mirror 290 is added to the current output Impd from the MPD 270. On the other hand, the automatic power controller 320 further includes a current source 330 for adjusting an amount of current to be supplied to the red LD 240 in response to a signal output from the comparator 310.
Herein, the resistor circuit 300 is provided with a load resistor for protecting the red LD 240 from static electricity or a variable resistor Rbias for adjusting light power of the red LD 240 in response to the feedback current Impd output from the MPD 270.
The automatic power controller 320 performs a control operation for maintaining laser light power of the red LD 240 substantially constant by varying the operating current to be applied to the red LD 240 according to the magnitude of the feedback current provided from the MPD as in an automatic power control (APC) scheme. Further, the feedback current Impd is obtained by converting light detected by the MPD 270 to an electric current with respect to laser light output from the red LD 240.
In particular, the resistor circuit 300 includes a variable resistor Rbias for variably adjusting light power, such that an initial light-quantity state of the LD can be adjusted when a laser display device is manufactured. As a result, when an amount of feedback current to be output from one MPD 270 is adjusted through the variable resistor Rbias, an amount of current flowing to the LD is varied and therefore an amount of operating current is varied in the drive structure 200 for a sequential RGB display.
Direct current (DC) characteristics of the LD determine the output current Impd of the MPD 270 for receiving part of light output from the red LD 240 and performing conversion to a current signal, i.e., the feedback current. In other words, an operating current of the laser for obtaining the desired light intensity is defined by the DC characteristics of the LD. When the operating current flows to the laser, the output current Impd of the MPD 270 is defined. When the feedback current Impd is output from the MPD 270, a voltage drop is caused by the resistor circuit 300 and the comparator 310 compares the associated voltage with the preset reference voltage VREF. The resistance value is defined as shown in Equation (1), and is input to the automatic power controller 320 for adjusting the light intensity of the red LD 240.
R
bias
=V
REF
/I
mpd(or a given value in a laser DC characteristic curve) [1]
When a red modulation signal (of an amplitude voltage Va) is input to the input terminal 280 in the red LD driver 210, the bias voltage Vbias is supplied to the emitters of the transistors TR1 and TR2 of the current mirror 290. The constant current Imod is output from the collector of the output transistor TR2 as shown in Equation (2).
I
mod(Vm−Va)/Rmpd [2]
The output current Imod can increase until it is equal to the output current Impd of the MPD 270. In this case, the generated light is not output.
On the other hand, when the constant current Imod output from the output transistor TR2 of the current mirror 290 is added to the feedback current Impd output from the MPD 270 in the automatic power controller 320, the voltage drop is caused by the resistor circuit 300. The comparator 310 compares the dropped voltage with the preset reference voltage VREF. As the amount of electric current increases, an output voltage of the comparator 310 has a negative value. The negative value output from the comparator 310 decreases an amount of electric current flowing to the current source 330 and decreases the light intensity of the red LD 240. As the light intensity of the red LD 240 decreases, the operating current flowing to the red LD 240 decreases. When the voltage magnitude is adjusted at the input terminal 280 of the modulation signal, a pulse-shaped light output can be adjusted and a continuous waveform can be output.
Although the principles of the invention have been described with regard to a red LD, it would be recognized by those skilled in the art that similar processing and operation would be applicable to green and blue (or an other color) LD utilized.
At least three LD drivers corresponding to the drive structure 200 for a sequential RGB display are connected in parallel. When the red, green, or blue modulation signal is input to the input terminal 280 in each of the RGB LD drivers 210, 220, and 230, the bias voltage vbias is supplied to the current mirror 290. When the constant current Imod output from the current mirror 290 is added to the feedback current output Impd from one MPD 270 in the LD drive 210, 220, or 230, the comparator 310 compares the voltage vb of the resistor 300 with the preset reference voltage VREF.
According to a comparison result, the current source 300 adjusts an amount of electric current to be supplied to the LD 240, 250, or 260, such that a control operation is performed to maintain the light power of the red, green or blue LD 240, 250, or 260. Light is sequentially emitted from the RGB LDs 240, 250, and 260 in response to R, G, and B modulation signals input to the input terminals 280.
As illustrated in
For example, when the number of pixels is (L×M), one field displays (L×M) pixels. Each light source driver sequentially displays one color of RED, GREEN or BLUE from the 1st pixel to the (L×M)th pixel.
A drive structure and method for a sequential RGB display can be implemented in accordance with the exemplary embodiments of the present invention.
Although the exemplary embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope of the present invention. Therefore, the present invention is not limited to the above-described embodiments, but is defined by the following claims, along with their full scope of equivalents.
In the present invention, one light receiving means receives partial light output from ROB light sources and performs conversion to a current signal, and each light source driver performs a control operation for maintaining the light intensity of each light source substantially constant by adjusting an amount of operating current applied thereto according to the magnitude of a feedback current provided from the light receiving means. Light is sequentially emitted and received from light sources in response to input RGB modulation signals. According to a simplified structure, a small-sized or cost-effective light source display device can be implemented.
| Number | Date | Country | Kind |
|---|---|---|---|
| 37691/2006 | Apr 2006 | KR | national |
