JPS6312386Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a matrix display device, and more particularly, to a matrix display device that is composed of a group of elements such as LEDs exhibiting linear photoelectric characteristics as light emitting elements constituting picture elements. The purpose is to correct the linearity of the characteristics.

When displaying video signals using a so-called matrix panel, a pulse width modulation (hereinafter referred to as PWM) signal whose pulse width is proportional to the gradation of the picture element is applied to the light emitting element that displays the brightness of each picture element. An application method is used. In order to ensure sufficient brightness, the scanning method of the matrix panel is to simultaneously apply the corresponding PWM signal to each light emitting element that forms one line (one horizontal scanning line), one line at a time. A method of sequentially scanning in the vertical direction is adopted. To explain this point a little more, for example, in a TV video signal, the number of gradations for the signal from the black level to the highest brightness (white level) is set to 16, and the video signal is AD converted in 4-bit units, and the AD conversion output is (4 bits) is added to the PWM circuit as a modulation input to obtain a PWM signal with a pulse width approximately proportional to the gradation of the original signal.The number of units corresponds to the number of light emitting elements in one line. , PWM corresponding to each gradation of the original signal
Signals are simultaneously applied to the corresponding light emitting elements of one line, and the lights are sequentially emitted in the vertical direction.

Next, an example of the PWM modulation circuit used in the device of the present invention will be explained with reference to the circuit diagram of FIG.
This circuit is roughly divided into down counter DC and RS
The PWM output from the flip-flop F is set by setting the flip-flop F with a preset pulse P at the leading edge of the vertical scanning pulse and resetting it with the BORROW output of the down counter Dc. It is configured to take out. That is, the down counter Dc has a configuration in which the 4-bit AD conversion output of the video signal to be displayed on the matrix panel is used as a preset input, the preset pulse P is used as a reset or start signal, and the clock pulse CP is down counted. .

By the way, as mentioned above, the light emitting elements corresponding to each picture element constituting the matrix panel have linear input-to-light output characteristics, and therefore, γ( If the gamma-corrected signal is directly converted into a PWM signal as described above and applied to each light emitting element to perform matrix display, the disadvantage is that the linearity of the reproduced (displayed) image will be extremely poor. be forced to.

That is, if the clock pulses CP input to the down counter Dc in FIG. 1 are set at regular intervals and the relationship between the optical input and the optical output when displaying a television video signal in a matrix is normalized, the relationship is as shown in FIG. 2. , in order to correct this and reproduce images with good linearity, the PWM signal that should be applied to each light emitting element is:
Signal voltage (relative value) vs. original signal shown in Figure 3
It is necessary to follow the PWM pulse width (relative value) curve.

Therefore, in view of this point, the present invention is based on the above-mentioned
The period of the clock pulse input to the PWM modulation circuit is not set at equal intervals, and the curve is used to correct the aforementioned non-linearity of the gradation of the original signal to be displayed.
The PWM pulse width is changed non-linearly and continuously so that the electrical input versus optical output characteristics of a matrix panel composed of LEDs, etc. are approximated to that of a CRT (cathode ray tube), and linearity is improved. It is designed to reproduce a good image.

Hereinafter, the present invention will be further explained in detail with reference to FIGS. 4 and 5.

Figure 4 changes along the curve of Figure 3.
An example of a circuit for generating a clock pulse that changes non-linearly and continuously in order to obtain a PWM signal is shown, and FIG. 5 shows the operating waveforms of the main parts thereof.

In the circuit of FIG. 4, D is a variable capacitance diode, which is a coupling capacitor whose capacitance is much larger than that and the capacitance of the feedback capacitor _C1 of the clock oscillator, which will be described later.
C ₂ is connected to the input terminal of N1, one of the two NAND gates N ₁ and _{N 2} that constitute the clock oscillator OC, so that the oscillation frequency of the oscillator OC changes depending on the capacitance change of the variable capacitance diode D. It is configured to change accordingly. SO is a sweep signal generation circuit that is generated in synchronization with the preset pulse P explained in FIG. The voltage is applied to diode D. Therefore, in the initial state of the sweep signal, the voltage applied across the variable capacitance diode D is large, and the oscillator OC is oscillating at a relatively high frequency due to its small capacitance. As the sweep progresses and the voltage applied to the variable capacitance diode D decreases, the oscillation frequency of the oscillator CO decreases in accordance with the increase in its capacitance.
As a result, a clock pulse CP whose frequency changes continuously is obtained at the output terminal of the NAND gate _N2 at the subsequent stage of the oscillator, as shown in FIG.
At that time, although the sweep signal S is illustrated as a sawtooth wave in FIG. 5, the oscillation frequency of the oscillator CO is determined by the capacitance of the variable capacitance diode D and the feedback capacitor.
The capacitance of the capacitor C ₁ is determined by the capacitance of the capacitor C ₁ so that the frequency change of the clock pulse CP gives a pulse width change along the curve shown in FIG.
It is only necessary to appropriately select the value of and the curve of the sweep signal S.

According to the present invention as described above, the frequency of the clock pulse to be input to the PWM modulation circuit is non-linearly and continuously changed, and the signal voltage of a matrix panel composed of light emitting elements such as LEDs is adjusted by PWM.
Since the pulse width characteristics can be corrected to approximate the photoelectric characteristics of a CRT, the linearity of the gradation (brightness change) of the image displayed on the matrix panel is improved, and images that are close to natural brightness changes can be reproduced. I can do it.

In addition, in order to obtain a PWM signal with linearly corrected gamma characteristics, a variable capacitance diode whose capacitance value changes continuously according to a sweep signal with a vertical period is provided, and the clock pulse period is changed by changing this capacitance value. , the circuit configuration is extremely simple and can be realized at low cost.

[Brief explanation of drawings]

The drawings are all related to the present invention; Fig. 1 shows an example of a PWM modulation circuit, and Fig. 2 shows a normal matrix panel driven by a PWM signal using clock pulses of a constant period to display a video signal. FIG. 3 is a signal voltage vs. pulse width characteristic diagram necessary for linearity correction, and FIG. 4 is a diagram showing an embodiment of a clock pulse generation circuit.
FIG. 5 is an operational waveform diagram of the clock pulse generation circuit. Dc...Down counter, F...Flip-flop, OC...Clock oscillator, SO...Sweep signal generation circuit, D...Variable capacitance diode, Tr...
Transistor for voltage amplification.

Claims (1)

[Scope of utility model registration request] In a matrix display device that displays information by converting a luminance signal into a PWM signal corresponding to its gradation and synchronously applying this signal to a group of light emitting elements that constitute a picture element and exhibit linear photoelectric characteristics. , a sweep signal generation circuit that generates a sweep signal with a vertical period; a variable capacitance diode whose capacitance value changes continuously when this sweep signal is applied; 1. A matrix display device comprising a clock oscillator that generates changing clock pulses, and correcting linearity of optical input/output characteristics by performing PWM modulation using the clock pulses.