JPH02309393A - Optical element driving device - Google Patents

Abstract

PURPOSE:To obtain a brightness modulation of a good contrast by adjusting light emission time to the integer times the unit light emission time and a brightness level to >=1 or 2 times the reference brightness according to the digital value of a video signal, then driving an optical element. CONSTITUTION:The input video signal is digitized by an A/D converter 2 and the control signal of a light quantity is formed according to this digital value. Namely, a light quantity adjusting means A consisting of a coincidence detecting circuit 12, a counter 13, a reference current source 15, and an adder 16 forms the signal constituted of the unit brightness level at which the light emission time is integer times the unit light emission time and the brightness level is >=1 or 2 times of the stable light output. Since the optical element 18 is driven according to this signal, the emitted light quantity proportional to the video signal is obtd. regardless of the current to light output characteristics. The brightness modulation of the good contrast and rectilinearity is thus possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical element driving device for driving an optical element used as a light emitting source in a drawing device or the like, and particularly relates to a brightness modulation technique for an optical element.

[Summary of the Invention] The present invention provides a video converter that is provided with a light amount adjustment means that can adjust the luminance time by an integral multiple of the unit luminescence time and the luminance level by one or more reference luminance levels, and which is converted by an A/D converter. By controlling the light emission time and brightness level according to the digital value of the signal and driving the optical element according to this control signal, it is possible to obtain a light emission amount proportional to the video signal regardless of the current vs. output characteristics. Therefore, brightness modulation with good contrast and linearity can be performed.

[Prior art and problems to be solved by the invention] Conventionally,
2. Description of the Related Art Optical element driving apparatuses used in drawing apparatuses are known to perform brightness modulation by controlling the amount of current applied to an optical element.

However, the optical output characteristic of an optical element with respect to current does not change linearly; for example, a laser diode, which is an optical element, has an optical output characteristic as shown in FIG. As shown in Figure 4, the optical output of a laser diode is divided into the LED mode and laser mode regions, and because the slope in the circular region is different, it is difficult to perform brightness modulation with good contrast and linearity using current control. It has the disadvantage of being.

Even if only the laser mode region were used, proper current control would be difficult because the slope of the laser mode region is steep.Furthermore, the linearity of the slope is not guaranteed, making current control difficult. It has the same disadvantages as mentioned above.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical element driving device that is capable of brightness modulation with good contrast and linearity by emitting a light amount proportional to a video signal regardless of the current vs. output characteristics of the optical element. .

[Means for Solving the Problems] To achieve the above object, an optical device driving device of the present invention includes an A/D converter that digitizes a video signal at a constant sampling frequency, and an A/D converter that digitizes a video signal at a constant sampling frequency. A light quantity configured such that the luminance time can be adjusted at one or more basic luminance levels, and a control signal for the luminance time and luminance level is output according to the digital value of the output signal of the A/D converter. and adjustment means;
The drive of the optical element is controlled according to the control signal of this light ffl adjustment means.

[Operation] The input video signal is digitized by an A/D converter, and a control signal for controlling the light emission time and brightness level is generated according to this digital value.

The light emitting time is an integral multiple of the unit light emitting time, the brightness level is purchased at 1 or 2 or more unit brightness levels with stable light output, and the light emitting time and brightness level are combined as much as possible to obtain the light emitting m that corresponds to the digital value. In order to generate a control signal using the same method, brightness modulation with good contrast and linearity is performed.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

Embodiments of the present invention are shown in FIGS. 1 to 3(b).

In FIG. 1, a video signal is input to an input terminal, and this input video signal is guided to a buffer amplifier/clamp circuit l. Buffer amplifier/clamp circuit
A/D amplifies and clamps the video signal
Output to converter 2 and synchronous separation/burst gate circuit 3. The sync separation/burst gate circuit 3 separates the sync signal from the video signal, extracts a burst signal based on this sync signal, sends the separated sync signal to a blanking control circuit 4, and sends the extracted burst signal to f.
ll and generator 5, respectively.

The f me generator 5 generates a sub-gear r s of this burst signal from a burst signal that is intermittently inputted at regular intervals.
A continuous signal (frequency: fl) synchronized with c is output to the phase comparator 6.

This phase comparison 56, low pass filter (LPr') 7,
VCO8,1/2(r+-@*II frequency divider 9, square wave generator 10 and I/P frequency divider 11 constitute a PLL loop. When VCO8 is phase locked, f I15×2''-
The frequency signal of "°1" is output to the frequency divider 9 and the counter 3 as 1/2"-1°1). Here, n is the number of bits of the A/D converter 2, m is the number of unit brightness levels,
In this example, since ray is 6 and m is 3, 2 n-+s
The value of *+ is 16. l/2 f″---11 frequency divider outputs a frequency signal of f to the square wave generator 10,
This square wave generator IO generates a sine wave of f.

generates a square wave. This rectangular wave f is output to the A/D converter 2, the coincidence detection circuit 12, the counter 13, and the l/P frequency divider 11. The 1/P frequency divider II divides the frequency signal of f by I/P (P=f, /fme) and divides the frequency signal of f by I/P (P=f, /fme).
The frequency signal of e is sent to the phase comparator 6.

The A/D converter 2 samples the video signal from the buffer amplifier/clamp circuit 1 and the signal from the rectangular wave generator 10 at a sampling frequency f. Then, convert the video signal into a 6-bit digital value (64th floor?A)
2' to 23, the signal is sent to the coincidence detection circuit 12, 24. Switching circuit 14 for each bit signal of Q5
Output each.

The counter 13 counts the clock 16f and outputs a signal of each bit from 2° to 23 indicating this count value to the coincidence detection circuit 12. This counter 13 is cleared by the signal f from the rectangular wave generator 10.

The coincidence detection circuit 12 compares the digital value from the A/D converter 2 with the count value of the counter 13.
When the point where the count value of 3 matches the digital value is detected, the output is switched to the (signal) signal.Therefore, in this embodiment, the unit light emission time t is set to 1/16·f.And, It is reset at the rising edge of the signal f from the square wave generator 10, and when it is reset, I-I
The output of the coincidence detection circuit 12 is led to the switching circuit 14, which is in a signal output state.

This switching circuit 14 selectively switches each input signal to the reference current source 1.
This switching is controlled by a switching signal from the blanking control circuit 4. Based on the synchronization signal, the blanking control circuit 4 outputs a control signal to open the switching circuit 14 during the blanking period and to conduct the switching circuit 14 during the video period.

The reference current source 15 adjusts to the reference brightness level P as shown in FIG. A corresponding current is output during the H signal period. In addition, when the I signal is output from the 25-bit output terminal of the A/D converter 2, the current corresponding to the reference brightness level P, (Pt=2P,) is output as the H signal as shown in FIG. 3(b). Output during the interval. Therefore, in this embodiment, the number of reference brightness levels (m) consists of three in total, two of level P1 and one of level P.
I, P! selects a stable value in the laser mode section from the current vs. output characteristics. Each output of the reference current source 15 is added 7ii times in an adder 16 and then led to an automatic power control circuit (APC) 17. This automatic power control circuit 17 operates according to the output of the adder 16 to control a laser diode which is an optical element! Controls the drive of 8.

Therefore, the coincidence detection circuit! 2. The counter 13, the reference current source 15, and the adder 16 are light m adjustment means that generate control signals for the light emission time and brightness level based on the unit light emission time and the reference brightness level according to the output of the A/D converter 2. A
It consists of

Hereinafter, the operation of the above configuration will be explained based on FIGS. 1 and 2.

In Fig. 1, the video signal supplied from the input terminal t is synchronized and separated via the buffer amplifier/clamp circuit I.
The signal is guided to the burst gate circuit 3 and the A/D converter 2. f, generated based on the burst signal of the synchronous separation/burst gate circuit 3.

The PLL loop operates with the frequency signal f, and the rectangular wave signal f is input to the A/D converter 2, the coincidence detection circuit 12, and the counter 13, and the counter 13 receives the rectangular wave signal f,
The clock is manually operated. The A/D converter 2 samples the video signal fl, converts it into a 6-bit digital signal, and outputs it. Of these 6 bits, the upper 2 bits (2', 25) are sent to the switching circuit 14, and the lower 4 bits (2', 25) are sent to the switching circuit 14.
°~23) are respectively output to the coincidence detection circuit 12, and the coincidence detection circuit 12 outputs the r4 signal to the switching circuit 14 until a signal of the same value is sent from the counter 13.

Here, as shown in FIG. 2, the output of the video signal is 63
In the case of gradation, the outputs 25 and 24 of the A/D converter 2 are the tI signals, and the 2° to 2
The output of 3 becomes the f signal for I5/I6·[1, time. Then, the reference current source 15 outputs a current corresponding to P for the 2S to I signal, and a current corresponding to Pl for the 2' and 2° to 23 H signals, and these currents The currents are added up by an adder 16 and sent to the automatic power control circuit I7. Therefore, the laser diode 18 outputs a laser beam with an amount of light corresponding to 63/64.

In addition, when the output of the video signal is 25 gradations, the output of 25 of the A/D converter 2 is an L signal, and the output of 24 is a 1 (signal), and the output of 2° to 23 of the coincidence detection circuit 12 is a 9 The signal becomes H for a time of /16·f1, and as shown in FIG. 2, the laser diode 18 outputs a laser beam with an amount of light corresponding to 25/64.

Furthermore, when the output of the video signal is one gradation, the outputs of 24 and 21' of the A/D converter 2 are output signals, and the outputs of 2Q to 23 of the coincidence detection circuit 12 are 1/16·f.
, the signal becomes H for only the time, and as shown in FIG. 2, the laser diode 18 outputs a laser beam with an amount of light corresponding to 1/64.

In this example, a unit block with a unit light emission time t and a reference luminance level P shown in FIG. 3(a) and a unit block as shown in FIG. 3(b) are used.
A block with a light emission time of 16t=f at the basic brightness level Pl shown in FIG. 3(c) is combined with a block shown in FIG. Although the configuration is configured to perform ff1H adjustment, for example, it is also possible to adjust the light emission amount in 64 ways using the unit light emission time t as a unit block at the reference brightness level P, and various means can be considered. However, when the unit light emission time is used as a unit block at the reference brightness level P1, it is necessary to use a clock frequency of 64f, but in the above embodiment, the clock frequency can be set to 16f, which has the advantage of being lower than the maximum frequency. has.

[Effects of the Invention] As described above, according to the present invention, the luminescence time is an integral multiple of the unit luminescence time! Alternatively, a light amount adjustment means is provided so that the brightness level can be adjusted at two or more Motonashi brightness levels, and A/
The light emitting time and brightness level are controlled according to the digital value of the video signal converted by the D converter, and the optical element is driven according to this control signal, so it is proportional to the video signal regardless of the current vs. light output characteristics. Since the light emission m can be obtained, it is possible to perform brightness modulation with good contrast and linearity.

[Brief explanation of drawings]

5 to 4 show embodiments of the present invention, FIG. 1 is a circuit block diagram of an optical element driving device, FIG. 2 is a time chart, and FIG. 3(a) is an output of 2° to 23. Fig. 3(b) is a diagram showing the luminous quantity of output 24, Fig. 3(c) is a diagram showing the luminous quantity of output 25, and Fig. 4 is the current vs. previous output. It is a characteristic line diagram. 2... A/D converter, 18... Optical element (L/
- the diode), A... light amount adjustment means. Figure 3 (0) Optical likelihood of 24 outputs Figure 8 (b) Brightness Figure 3 (C)

Claims (1)

[Claims] (1) An A/D converter that digitizes a video signal at a constant sampling frequency, and an A/D converter configured to be able to adjust the light emission time by an integral multiple of the unit light emission time and the brightness level by one or more reference brightness levels, and a light amount adjusting means for outputting control signals for light emission time and brightness level according to the digital value of the output signal of the A/D converter, and driving of the optical element was controlled according to the control signal of the light amount adjusting means. An optical element driving device characterized by: