Backlight modulation circuit

Abstract

An exemplary backlight modulation circuit (200) includes a pulse generator circuit (210) configured for generating a first square pulse; a voltage division circuit (230) configured for receiving the first square pulse and generating a second square pulse according to the first square pulse; an oscillator circuit (240) configured for generating a reference voltage; and an amplifier (200) comprising a negative input configured for receiving the second square pulse from the voltage division circuit, and a positive input configured for receiving the reference voltage from the oscillator circuit as a reference pulse signal, the amplifier being configured for generating a backlight adjusting signal according to the reference pulse signal and the second square pulse.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a backlight modulation circuit according to an exemplary embodiment of the present invention, the backlight modulation circuit including a pulse generator, a voltage division circuit, and an oscillator circuit.

FIG. 2 is a graph of voltage versus time, showing a square pulse provided from the pulse generator of the backlight modulation circuit of FIG. 1.

FIG. 3 is a corresponding graph of voltage versus time, showing the square pulse as provided from the voltage division circuit of the backlight modulation circuit of FIG. 1.

FIG. 4 is a corresponding graph of voltage versus time, showing a 1.2V DC voltage provided from the oscillator circuit of the backlight modulation circuit of FIG. 1.

FIG. 5 is a diagram of a conventional backlight modulation circuit used in a backlight control circuit of an LCD, the backlight modulation circuit including a pulse generator, a voltage division circuit, and a oscillator circuit.

FIG. 6 is a graph of voltage versus time, showing a square pulse provided from the pulse generator of the backlight modulation circuit of FIG. 5.

FIG. 7 is a corresponding graph of voltage versus time, showing a corresponding 1.5V DC voltage provided from the voltage division circuit of the backlight modulation circuit of FIG. 5.

FIG. 8 is a corresponding graph of voltage versus time, showing a triangular pulse provided from the oscillator circuit of the backlight modulation circuit of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe various embodiments of the present invention in detail.

FIG. 1 is a diagram of a backlight modulation circuit according to an exemplary embodiment of the present invention, the backlight modulation circuit being typically used in an LCD. The LCD typically also includes an LCD panel and a backlight. The backlight can include one or more lamps, such as cold cathode fluorescent lamps. The backlight is driven by an inverter according to a backlight adjusting signal generated by the backlight modulation circuit, and the lamps thereby illuminate the LCD panel. The backlight modulation circuit 200 includes a pulse generator 210, a voltage division circuit 230, an oscillator circuit 240, and an amplifier 251.

The amplifier 251 includes a negative input, a positive input, and an output.

The oscillator circuit 240 includes a low frequency oscillator 243, a capacitor 241, and a resistor 242. The capacitor 241 and the resistor 242 are connected in parallel between the low frequency oscillator 243 and ground. An electrical connecting node between the low frequency oscillator 243 and the resistor 242 is connected to the positive input of the amplifier 150. A capacitance of the capacitor 241 is approximately 4.7 nF. A resistance of the resistor 242 is approximately 604 KΩ.

The pulse generator 210 includes a scaler 211, an NMOSFET 212, a bias resistor 213, and a 5V DC power supply 214. The NMOSFET 212 includes a source electrode “S” connected to ground, a drain electrode “D” connected to the power supply 214 via the bias resistor 213, and a gate electrode “G” connected to an output of the scaler 111 for receiving a pulse signal therefrom.

The voltage division circuit 230 includes two voltage division resistors 231, 232. The drain electrode “D” of the NMOSFET 212 is connected to ground via the voltage division resistor 231 and the voltage division resistor 232 in series. An electrical connecting node between the two voltage division resistors 231, 232 is connected to the negative input of the amplifier 251. A resistance of the voltage division resistor 231 is approximately 22 KΩ. A resistance of the voltage division resistor 232 is approximately 10 KΩ.

The pulse generator 210 outputs a first square pulse at the drain electrode “D” of the NMOSFET 212. This first square pulse is shown in FIG. 2. An amplitude of the first square pulse is approximately 5V. Then the voltage division circuit 230 reduces the amplitude of the first square pulse to 1.2V, thereby forming a second square pulse. This second square pulse is shown in FIG. 3. The voltage division circuit 230 then provides the second square pulse to the negative input of the amplifier circuit 251.

The oscillator circuit 240 generates a 0.7V DC voltage (as shown in FIG. 4), and provides the 0.7V DC voltage to the positive input of the amplifier 251 as a reference pulse signal. The amplifier 251 outputs a backlight adjusting signal according to the signals received by the positive input and the negative input, and provides the backlight adjusting signal to an inverter circuit (not shown) for adjusting a brightness of the backlight.

Because the backlight modulation circuit 200 does not include an integrating circuit or a regulation circuit, the backlight modulation circuit 200 is relatively simple. Furthermore, the 5V square pulse outputted from the pulse generator circuit 210 is provided to the positive input of the amplifier 251 only via the voltage division circuit 230. Thus any interference generated when the 5V square pulse is transmitted to the amplifier 251 is reduced.

It is to be understood, however, that even though numerous characteristics and advantages of the preferred embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in matters of arrangement of parts within the principles of present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

1. A backlight modulation circuit comprising: a pulse generator circuit configured for generating a first square pulse;a voltage division circuit configured for receiving the first square pulse and generating a second square pulse according to the first square pulse;an oscillator circuit configured for generating a reference voltage; andan amplifier comprising a negative input configured for receiving the second square pulse from the voltage division circuit, and a positive input configured for receiving the reference voltage from the oscillator circuit as a reference pulse signal, the amplifier being configured for generating a backlight adjusting signal according to the reference pulse signal and the second square pulse.

2. The backlight modulation circuit as claimed in claim 1, wherein an amplitude of the first square pulse is approximately 5V.

3. The backlight modulation circuit as claimed in claim 1, wherein an amplitude of the second square pulse is approximately 1.2V.

4. The backlight modulation circuit as claimed in claim 1, wherein the voltage division circuit comprises two voltage division resistors, a resistance of one of the voltage division resistors is approximately 22 KΩ, and a resistance of the other voltage division resistor is approximately 10 K.

5. The backlight modulation circuit as claimed in claim 1, wherein the oscillator circuit comprises a low frequency oscillator, a capacitor, and a resistor, the capacitor and the resistor are connected in parallel between the low frequency oscillator and ground, and an electrical connecting node between the low frequency oscillator and the resistor is connected to the positive input of the amplifier.

6. The backlight modulation circuit as claimed in claim 5, wherein a capacitance of the capacitor is approximately 4.7 nF.

7. The backlight modulation circuit as claimed in claim 5, wherein a resistance of the resistor is approximately 604 KΩ.

8. The backlight modulation circuit as claimed in claim 1, wherein the reference voltage is approximately 0.7V.

9. The backlight modulation circuit as claimed in claim 1, wherein the pulse generator comprises an n-channel metal-oxide-semiconductor field-effect transistor (NMOSFET), a bias resistor, and a 5V DC power supply, and the NMOSFET comprises a source electrode connected to ground, a drain electrode connected to the power supply via the bias resistor, and a gate electrode configured for receiving a pulse signal.

10. The backlight modulation circuit as claimed in claim 9, wherein the pulse generator further comprises a scaler, the scaler comprises an output connected to the gate electrode of the NMOSFET, and the scaler is configured for providing the pulse signal to the gate electrode of the NMOSFET.

11. A backlight modulation circuit comprising: a pulse generator circuit configured for generating a square pulse;a voltage division circuit configured for reduce an amplitude of the square pulse;an oscillator circuit configured for generating a reference voltage; andan amplifier comprising a negative input configured for receiving the reduced amplitude square pulse from the voltage division circuit, and a positive input configured for receiving the reference voltage from the oscillator circuit as a reference pulse signal, the amplifier being configured for generating a backlight adjusting signal according to the reference pulse signal and the reduced amplitude square pulse.

12. The backlight modulation circuit as claimed in claim 11, wherein the amplitude of the square pulse generated by the pulse generator circuit is approximately 5V.

13. The backlight modulation circuit as claimed in claim 11, wherein an amplitude of the reduced amplitude square pulse is approximately 1.2V.

14. The backlight modulation circuit as claimed in claim 11, wherein the voltage division circuit comprises two voltage division resistors, a resistance of one of the voltage division resistors is approximately 22 KΩ, and a resistance of the other voltage division resistor is approximately 10KΩ.

15. The backlight modulation circuit as claimed in claim 11, wherein the oscillator circuit comprises a low frequency oscillator, a capacitor, and a resistor, the capacitor and the resistor are connected in parallel between the low frequency oscillator and ground, and an electrical connecting node between the low frequency oscillator and the resistor is connected to the positive input of the amplifier.

16. The backlight modulation circuit as claimed in claim 15, wherein a capacitance of the capacitor is approximately 4.7 nF.

17. The backlight modulation circuit as claimed in claim 15, wherein a resistance of the resistor is approximately 604 KΩ.

18. The backlight modulation circuit as claimed in claim 11, wherein the reference voltage is approximately 0.7V.

19. The backlight modulation circuit as claimed in claim 11, wherein the pulse generator comprises an n-channel metal-oxide-semiconductor field-effect transistor (NMOSFET), a bias resistor, and a 5V DC power supply, and the NMOSFET comprises a source electrode connected to ground, a drain electrode connected to the power supply via the bias resistor, and a gate electrode configured for receiving a pulse signal.

20. The backlight modulation circuit as claimed in claim 19, wherein the pulse generator further comprises a scaler, the scaler comprises an output connected to the gate electrode of the NMOSFET, and the scaler is configured for providing the pulse signal to the gate electrode of the NMOSFET.