Patent Application
20080042596
The presently disclosed subject matter will now be described in detail based on certain exemplary embodiments shown in the above-referenced figures. The block diagram shown in
Recently, the market has been introduced to personal computers that also serve as TV receivers and comprise an LCD display 11 as large as a 37-inch LCD display, for example, which naturally includes a large number of fluorescent discharge tubes 10. The personal computer often includes an infrared remote control (not shown). Therefore, the LCD display 11 as shown in
Turning to a description of the configuration of the backlight device 1, the backlight device 1 can be provided with an oscillator 2 as a first circuit that oscillates at 55-100 kHz for lighting the fluorescent discharge tube 10.
The oscillator 2 can be connected to a phase modulator 4 that modulates the phase of a high frequency voltage that is oscillated as a sine wave of 55 kHz, for example, based on a signal from a phase-modulation data generator 3.
As described above, the high-frequency voltage that is oscillated at the oscillator 2 and phase-modulated at the phase modulator 4 is fed to a PWM circuit 6 with a PWM (Pulse Width Modulation) controller 5 attached thereto and converted to have a duty width that achieves viewer-preferred brightness. Finally, the voltage is boosted at a booster 7 that can be configured as an inverter, up to a sufficient voltage to light the fluorescent discharge tube 10. A current controller 8 can be connected between the output of the booster 7 and the oscillator 2 to monitor the current flowing in the fluorescent discharge tube 10 and handle the fluctuation of the input voltage.
In this case, the phase-modulation data generator 3 is designed to provide an “irregular modulation code” with less regularity and can be programmed to generate a pseudo noise (PN) that prevents concentration of energy at a specific frequency. On pre-production, no commercially available items were uncovered that include phase modulators that works at a low frequency corresponding to the lighting frequency of the fluorescent discharge tube 10. Therefore, an integrated chip (IC) that is capable of providing a phase shifter function can be used for phase modulation. (An example of such a device is part number AD 8333 available from ANALOG DEVICES, Inc.)
The thus modulated high-frequency drive voltage can be used to light the fluorescent discharge tube 10. In this case, the infrared frequency components that are modulated are obviously lower than those that are not phase-modulated and do not affect the remote control operation. This is because, when the PWM modulation signal is ON, the phase of the high-frequency drive voltage is not always constant, and the energy components at infrared frequencies from the fluorescent discharge tube 10 are spread near the noise level.
If the variations in phase of the high-frequency drive voltage when the PWM modulation signal is ON are repeated equally for every PWM modulation signal, energy concentrates at a specific frequency and a desired effect may not be achieved. Therefore, random variations in phase should be caused when the PWM modulation signal is ON.
The output from the phase modulator 4, denoted with the reference symbol B, is shown as output signal S2 that is phase-modulated in accordance with the output from the phase-modulation data generator 3. In this case, variations in phase can be achieved through modulation by use of an irregular modulation code with less regularity to provide an output having a so-called random phase characteristic.
The output from the phase modulator 4 is fed to the PWM circuit 6, which is controlled with a signal S3 received from the PWM controller 5 that is used by the viewer to set the screen brightness as a duty ratio. The PWM circuit converts the output into an intermittent signal S4 in accordance with the duty ratio. The intermittent signal is then fed to the booster 7 and boosted up to a sufficient voltage to light the fluorescent discharge tube 10. In this case, the booster 7 exerts little or no influence on the signal shape and allows the fluorescent discharge tube 10 to be lit in response to the phase state of the signal S4 as it is.
The signal S2 output from the phase modulator 4 is encoded and shown as a signal S5. For convenience of description, in this example, a waveform that is not phase-modulated is indicated with “0” and a waveform that is phase-modulated is indicated with “1”. In addition, the following description is given on the assumption that an on-region in one duty cycle includes 4 cycles.
In the above condition, one on-region can be configured in 16 combinations of [0, 0, 0, 0] through [1, 1, 1, 1]. In addition, the sorting of the 16 combinations can yield further variegated combinations. Accordingly, the phase-modulation data generator 3 selects an arrangement order for achieving a wider infrared spread among the above combinations and supplies it to the phase modulator 4 to obtain the so-called PN (Pseudo Noise).
After the phase modulation, the intensity level of infrared radiation from the fluorescent discharge tube 10 present in the remote control frequency band obviously lowers as shown in the graph in
In contrast, the graph shown in
The graph of
The block diagram shown in
In
The oscillator 22 sends a 50 kHz signal in response to the input of 0 V; 75 kHz in response to the input of 2.5 V; and 100 kHz in response to the input of 5 V from the frequency hopping data generator 23 as shown on a curve S22 in
The oscillator 22 varies the sending frequency in response to the signal from the frequency hopping data generator 23 while it executes continuous sending. Accordingly, the fluorescent discharge tube 10 lights at the maximum brightness and the LCD display 11 also illuminates at the maximum brightness.
Therefore, the consumer uses a PWM controller 26 to adjust the duty ratio to achieve a preferred brightness as shown on curve S23 in
The reference numeral 27 denotes a booster that boosts the output from the PWM circuit 25, which may not have sufficient power in practice to light the fluorescent discharge tube 10, up to a voltage capable of lighting it. Also in the embodiment of
As described above, the phase conversion or random frequency variation per cycle of the sine wave that is produced at the oscillator 2 can be set such that the combination of phases or frequencies is randomized to provide a lighting power source for the fluorescent discharge tube 10. The fluorescent discharge tube 10 can be used with the LCD display 11, which is contained in the backlight device 1 for a TV receiver, computer screen, or the like. In this case, infrared radiation radiated from the fluorescent discharge tube 10 spreads over a wider frequency band and lowers the level to the extent that exerts little or no influence on the remote control frequencies, thereby preventing an erroneous operation even if the infrared radiation overlaps the frequency band used for infrared remote controls.
Thus, the backlight device 1 can prevent infrared remote controls using the same infrared radiation from erroneously operating. The infrared radiation from the fluorescent discharge tube 10 is subjected to phase modulation not for the purpose of communications as phase modulation is used in mobile phones, for example. Accordingly, there is no need after modulation for receiving the infrared again for demodulation. Therefore, a quite random modulation may be sufficient if it can lower the level of focused infrared radiation.
While there has been described what are at present considered to be exemplary embodiments of the present invention, it will be understood that various modifications may be made thereto, and that other embodiments of the invention exist, and that it is intended that the appended claims cover such modifications as fall within the true spirit and scope of the presently disclosed invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-221958 | Aug 2006 | JP | national |
| 2007-104705 | Apr 2007 | JP | national |
