JPH03216073A - Picture signal processor - Google Patents

Abstract

PURPOSE:To output an accurate pulse width modulation signal without being effected by a level of a just preceding picture signal by selecting a changing area of a triangle wave signal to be a level smaller than a lower limit level of a change level of a picture signal. CONSTITUTION:The unit is provided with a Miller integration device 26 receiving a picture element synchronizing signal S1 being a square signal and outputting a triangle wave signal S2, a picture signal output device 28 receiving a digital picture data SD and generating a picture signal S3 and a comparator circuit 30 receiving the triangle wave signal S2 and the picture signal S3 and outputting a pulse width modulation signal Sp. In this case, the picture signal is a signal taking a level as its changing region between a 1st DC level V1 and a 2nd DC level V2 in excess of the 1st DC level V1 and the triangle wave signal S2 takes a level as its changing region between a 3rd DC level V3 less than the 1st DC level V1 and the 2nd DC level V2. Thus, the pulse width is not affected by a level of a just preceding picture signal and an accurate pulse width modulation signal is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image signal output device that can input an image signal and a triangular wave signal and accurately output a pulse width variation 1 signal.

[Prior Art] An image signal processing device 2 shown in FIG. 4 can be cited as a conventional technique for inputting an image signal and a triangular wave signal and outputting a pulse width modulated signal. This image signal processing device 2 operates according to the waveform shown in FIG. 5, and includes a comparator 6, and further outputs an integral signal B, which is a triangular wave, to the comparator 6 in synchronization with the pixel synchronization signal 8. An integrator 4 introduced into one input terminal, and an image signal generator 8 which outputs an image signal C in synchronization with the pixel synchronization signal 8 and introduces this image signal C into the other input terminal of the comparator 6. Be prepared.

A pulse width modulated signal D shown in FIG. 5 is output from the comparator 6 of the image signal processing device 2 configured as described above. As understood from FIG. 5, this pulse width modulation signal D is
This signal has a pulse width proportional to the level of the image signal C.

Incidentally, in fields where the image signal processing device 2 is used, there is a demand for faster signal processing. This is to increase the added value of devices that use the image signal processing device 2 by increasing the speed of processing.

[Problems to be Solved by the Invention] However, when trying to process a high-speed image signal in the conventional image signal processing device 2, when the image signal C falls and rises, the problems shown in FIGS. 7F, 6 and 6 occur. A signal delay as shown in FIG. 7 occurs.

In this case, as can be understood from the diagram, the pulse widths Pa, Pb, and Pc of the pulse width modulated signal D corresponding to the image signal having the same level There is a problem that it changes depending on (1), (2), and (2).

The present invention has been made in order to solve the above-mentioned problems, and by devising the changing area of the triangular wave signal with respect to the changing area of the image signal, it is possible to An object of the present invention is to provide an image signal processing device that can accurately output pulse width modulated signals having the same pulse width.

[Means for Solving the Problems] In order to solve the problems described in item 7, the present invention provides a first direct current level and a second direct current exceeding the first direct current level in synchronization with a pixel synchronization signal. a third DC level lower than the first DC level in synchronization with a pixel synchronization signal, and a third DC level that is lower than the first DC level; a triangular wave signal generator that outputs a triangular wave signal whose changing region is between the image signal and the triangular wave signal; and a comparator that receives the image signal and the triangular wave signal and outputs a pulse width modulated signal. It is characterized by having the following.

In the image signal processing device of the present invention configured as described above, the changing area of the triangular wave signal output from the triangular wave signal generator is set to the lower limit level of the changing area of the image signal (the first DC level), it is possible to avoid pulse width fluctuations caused by the signal delay of the image signal, and therefore, it is possible to avoid fluctuations in the pulse width caused by the signal delay of the image signal, and therefore to avoid being affected by the level of the image signal immediately before the image signal. Therefore, an accurate pulse width modulation signal for the image signal can be output from the comparator.

[Embodiment] Next, an image signal processing device according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings, citing preferred embodiments in relation to a device incorporating the same.

In FIG. 1, reference numeral 20 indicates a circuit block diagram of an exposure apparatus incorporating an image signal processing apparatus 22 according to this embodiment.

This exposure device 20 has a film l. A laser diode LD that exposes and records F with the emitted light I4, and a pixel synchronization signal Sl
an image signal processing device 22 that outputs a pulse width modulation signal Sp based on the digital image data SD and the digital image data SD;
A laser diode driver 24 (
(hereinafter referred to as the LD drive unit).

The image signal processing device 22 includes a mirror integrator (triangular wave signal generator) 26 that inputs a pixel synchronization signal S1, which is a square wave signal, and outputs a triangular wave signal S2, and inputs the digital image data SD. The image signal output device 28 generates an image signal S3, and a comparator 30 receives the triangular wave signal S2 and the image signal S3 and outputs a pulse width modulated signal Sp.

Here, as shown in FIG. 2, the image signal S3 has a level x between a first DC level V1 and a second DC level V2 exceeding the first DC level Vt. The triangular wave signal S2 has a variation region at a level VY between the third DC level v3, which is lower than the first DC level v1, and the second DC level (2).

Note that the third DC level ■ applied to the triangular wave signal S2
3 can be changed by changing the value of the resistor R V 2 in the resistor voltage divider circuit 32 consisting of the resistor R1 and the resistor RV2 provided on the input side of the operational amplifier 27 constituting the Miller integrator 26. The slope of the triangular wave signal S2 can be determined by resistor R3 and capacitor C3. Further, level determination of the first DC level V1 and the second DC level V2 will be described later.

The image signal output device 28 includes a D/A converter 34, a resistive voltage divider circuit 36 including a resistor R4 and a resistor RV5 connected to a reference voltage input terminal Vref of the D/A converter 34, and a D/A converter 34. It consists of a resistive voltage divider circuit 38 which is connected between the output terminal Vout of the converter 34 and the input terminal of the comparator 30 and includes a resistor R6 and a resistor R7. Therefore, the first
The DC level v1 and the second DC level V2 can be determined by changing the resistor RV5 of the resistive voltage dividing circuit 36, or by changing the values of the resistors R6 and R7 that constitute the resistive voltage dividing circuit 38. Note that the D/A converter 34 is configured so that 10-bit digital image data SD is introduced into the data input terminal Da.

The exposure apparatus incorporating the image signal processing apparatus according to this embodiment is constructed as shown in 1- below, and its operation will be explained next.

FIG. 2 is a waveform diagram illustrating the operation of the exposure apparatus 20 shown in FIG. 1.

Therefore, pixel numbers n to n+5 (second
The pixel synchronization signal S1 (see figure) is input to the mirror integrator 26 and the synchronization signal input terminal CL of the D/Δ converter 34 that constitute the image signal processing device 22. In this case, the mirror integrator 26 integrates the pixel synchronization signal S1, and as shown in FIG. A shape wave signal S2 is obtained.

On the other hand, in synchronization with the pixel synchronization signal S1, the digital image data SD input to the D/A converter 34 constituting the image signal output device 28 is passed through the resistive voltage divider circuit 38 so that the DC level reaches the first level. DC level V1 and second DC level V2
The image signal S3 is converted into an image signal S3 having a change area between the two. Note that the DC level of the image signal S3 is here a first DC level ■1, a second DC level ■2, and a fourth DC level between the first DC level V1 and the second DC level V2. There are three levels including DC level v4.

Therefore, as the output signal of the comparator 30, a pulse width modulation signal Sp shown in FIG. 2 is obtained. In this case, as can be understood from the figure, by providing a so-called offset Voff between the first DC level V1 for the image signal S3 and the third DC level V3 for the triangular wave signal S2, Even if a signal delay occurs when the image signal S3 moves from pixel number n to pixel number n+1 as shown in FIG. Since the comparison process is completed at the signal level after the waveform has been stabilized, the pulse width modulated signal Sp output from the image signal processing device 22 for the image signal S3 having the same first DC level V1 The pulse widths PΔ, PB, and PC are exactly constant and do not fluctuate (see FIGS. 2 and 3).

This pulse width modulation signal Sp is transmitted to the L. Introduced into the D drive section 24, the laser diode L
is converted into a current signal sufficient to drive D. Therefore, the file l. While moving F in a direction perpendicular to the plane of the paper, the pulse width modulated signal Sp is output from the laser die L D.
An image corresponding to the digital image data SD is formed on the film F by irradiating the film F with the emitted light L corresponding to the above.

[Effects of the Invention] As described above, according to the present invention, an image whose changing region is a level between a first DC level and a second DC level exceeding this DC level in synchronization with a pixel synchronization signal is produced. an image signal output device that outputs a signal; and a triangular shape whose changing region is a level between a third DC level lower than the first DC level and the second DC level in synchronization with the pixel synchronization signal. It has a triangular wave signal generator that outputs a shape wave signal, and a comparator that receives the image signal and the triangular wave signal and outputs a pulse width modulation signal.

Therefore, the lower limit third DC level of the triangular wave signal can be set to a lower level than the lower limit first DC level of the image signal, thereby producing a pulse width modulated signal related to the image signal having a predetermined level. The effect is that the pulse width of the pulse width is not affected by the level of the image signal just before it, and a pulse width modulation signal with an accurate pulse width can be obtained.

4.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an exposure device incorporating an image signal processing device according to an embodiment of the present invention; FIGS. 2 and 3 illustrate the operation of the exposure device shown in FIG. 1. FIG. 4 is a circuit block diagram of an image signal processing device according to the prior art, and FIGS. 5 to 7 are waveform diagrams illustrating the operation of the image signal processing device shown in FIG. 4. 20...Exposure device 22...Image signal processing device 26...Miller integrator 28...Image signal output device 30...Comparators 32, 36...Resistance voltage divider circuit 34...D /Δ converter 38...Resistance voltage divider circuit F...Film L...Emission light LD...Laser diode 1...Pixel synchronization signal 2...Triangular wave signal 3...Image signal 1]...Digital image data p...Pulse width modulation signal 1 to V3...DC level

Claims (1)

[Claims] (1) A first DC level in synchronization with a pixel synchronization signal,
an image signal output device that outputs an image signal whose changing region is a level between the first DC level and a second DC level; a triangular wave signal generator that outputs a triangular wave signal whose changing region is a level between the third DC level and the second DC level; and the image signal and the triangular wave signal are inputted. An image signal processing device comprising: a comparator that outputs a pulse width modulated signal.