JP3300033B2 - Light emitting element print head drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element print head driving circuit for driving a print head using a light emitting element such as a light emitting diode (hereinafter, referred to as an LED) in gradation.

[0002]

2. Description of the Related Art Conventionally, electrophotographic printers such as laser printers, LED printers, liquid crystal (hereinafter referred to as LCD) printers and the like have been developed and put into practical use (for example, Japanese Patent Application Laid-Open Nos. 60-140297 and 60-140297). 1963-3
No. 19167). Above all, the light-emitting element printer has a small and simple structure in which the printer head has only an LED array chip in which many light-emitting elements (for example, LEDs) are linearly arranged and a converging rod lens array. It is noted that the alignment of the optical system is simple.

FIG. 2 is a schematic configuration diagram of a conventional LED printer described in the above-mentioned Japanese Patent Application Laid-Open No. 63-319167. In this LED printer, when print data (for example, a video image signal for each pixel) DA is supplied to the drive circuit 10 in time sequence, the drive circuit 10 performs serial / parallel conversion (hereinafter, referred to as S / P conversion). To the LED array light source unit 30. The LED array light source unit 30
A plurality of LED arrays constituted by a plurality of LEDs are arranged in a straight line, and each LED has print data D.
A blinking operation is performed by the output of the drive circuit 10 according to A. The light of the emitted LED in the LED array light source unit 30 is irradiated to the surface of the recording medium, for example, the surface of the photosensitive drum 41 rotated in the direction of the arrow in FIG. 2 and charged by the charger 42 via the convergent rod lens array 40. Thus, an electrostatic latent image is formed. The electrostatic latent image formed on the photosensitive drum 41 is sent to the developing device 43 by the rotation of the photosensitive drum 41, toner is adhered to the electrostatic latent image portion, developed, and transferred to the paper 45 by the transfer device 44. Printing is performed.

FIG. 3 shows the LED array light source unit 30 shown in FIG.
FIG. The LED array light source unit 30 includes a plurality of LED arrays 31 arranged in a straight line. Each LED array 31 has approximately 32 to 128 monolithically integrated LEDs 32, and their respective LEs
A power supply electrode 33 is attached to D32, and is connected to an output terminal of the drive circuit 10 by wire bonding or the like. FIG. 4 is a block diagram illustrating a configuration example of the drive circuit 10 and the LED array light source unit 30 in FIG. Drive circuit 1
0 is an input terminal 11 for inputting print data DA of a pixel,
The integrated circuit includes a clock terminal 12 for inputting a clock signal CK, a strobe terminal 13 for inputting a strobe signal SB, a power supply terminal 14 for inputting a power supply voltage VDD, and a reference voltage terminal 15 for inputting a reference voltage _Vref. (Hereinafter referred to as IC) n driver ICs 20
-1 to 20-n. Each driver IC 20
-1 to 20-n convert the serial print data DA into parallel pixel data based on the clock signal CK.
/ P conversion shift register 21 and a latch circuit 2 for latching the strobe signal SB for controlling the light emission time of the LED 32 and the pixel data and outputting the pixel data at a predetermined timing.
2 and a driver circuit 23 connected to the output side of the latch circuit 22. Each driver circuit 23 operates by applying the power supply voltage VDD, amplifies the control signal generated based on the reference voltage _Vref and the output of the latch circuit 22, and outputs the output current to the LED array 31.
-1 to 31-n. These LED arrays 31-1 to 31-n enable the LE shown in FIG.
The D array light source unit 30 is configured.

FIG. 5 is a schematic circuit diagram of each driver circuit 23 in FIG. The driver circuit 23 has a number of current amplifying transistors 23a corresponding to the plurality of LEDs 32 in each of the LED arrays 31-1 to 31-n, and the collectors of the transistors 23a are connected to the power supply terminal 14; Is connected to the control terminal 16 for inputting the control signal S22, and the emitter is connected to the LED 32 through the electrode 33.
It is connected to the. When a control signal S22 generated by, for example, ANDing the output of the latch circuit 22 of FIG. 4 and the strobe signal SB is input to the control terminal 16, the voltage of the control signal S22 is current-amplified by the transistor 23a. , A constant current I (for example,
6 mA) is supplied to the LED 32 via the electrode 33,
The ED 32 emits light.

Next, referring to FIG. 4 and FIG.
The light emitting operation of No. 32 will be described. In FIG. 4, when the print data DA is supplied to the input terminal 11, the print data DA
Is synchronized with the clock signal CK and each driver IC 20-1
20-n are sequentially taken into the shift register 21,
It is stored as pixel data corresponding to each LED 32 in the LED arrays 31-1 to 31-n. The pixel data stored in each shift register 21 is stored in each latch circuit 2 together with a strobe signal SB for controlling the light emission time of the LED 32.
2 and each of the latch circuits 22
2 is output to each driver circuit 23 for a certain period of time as a light emission or extinction state.

In each driver circuit 23, as shown in FIG. 5, the control signal S22 generated from the logical product of the strobe signal SB and the output of the latch circuit 22 is supplied to the base of each transistor 23a. The signal S22 is current-amplified by the transistor 23a, a constant current I is supplied to the LED 32, and the LED 32 emits light. FIG.
Is a circuit for performing binarized printing. However, when performing gradation printing corresponding to an image image such as photographic data or graphic data or colorization, it is desired to provide the LED array light source unit 30 with a gradation function instead of the above-described binarization printing method. It is rare.
As a method, print data DA composed of a video image signal is used.
In addition, a printing method has been proposed in which a pixel signal having a gradation is added to provide gradation. The gradation method includes a dither method and an area gradation method. When printing is performed using the LED 32, the resolution per pixel is reduced by the dither method, and the LED array 31-1 is reduced by the area gradation method. ~ 3
Since it is necessary to increase the density of 1-n, practical application is difficult from a technical viewpoint.

In order to solve these problems, according to the technique of the above-mentioned document (Japanese Patent Laid-Open No. 63-319167), the driving circuit 10 shown in FIG. 4 is configured as follows. That is, the density value of each pixel read from a subject such as a manuscript is converted into a density value of a plurality of bits, and the density value of each pixel is converted into a current value of a size corresponding to all or a predetermined number of pixels. The LED corresponding to each pixel is driven by the light emission power corresponding to each current value. Thus, a driving circuit excellent in gradation printing can be provided.

[0009]

However, the driving circuit disclosed in the above-mentioned document (Japanese Patent Laid-Open Publication No. 63-319167) has a problem that the circuit configuration becomes complicated, and is relatively simple as shown in FIG. Performing gradation printing using the binarization driver ICs 20-1 to 20-n having a simple circuit configuration is desired from the viewpoint of simplification of the circuit configuration and cost reduction. It was difficult.

The present invention solves the problem of the prior art, in that it is difficult to perform gradation printing using a conventional binary driver IC having a relatively simple circuit configuration. A print head drive circuit is provided.

[0011]

To solve the previous SL problems SUMMARY OF THE INVENTION The first aspect of the present invention sequentially inputs the print data inputted from the input terminal, the input data and the light emitting element A light emitting element print head driving circuit for driving the light emitting element by a strobe signal for controlling the light emitting time of the light emitting element corresponds to the voltage value based on the voltage value of the reference voltage .
A driver circuit for supplying an output current to the light emitting element,
Duplicate reference voltage values for each of the different output currents
A voltage value selected from among the plurality of voltage values.
And a selector circuit for supplying a voltage to the driver circuit, the driver circuit, the output current generated based on the voltage value and the pixel data of the reference voltage supplied from the selector circuit, said output current It is configured to supply the light to the light emitting element. The second invention is the first invention.
In the light emitting element print head drive circuit, the select
The selector circuit sequentially selects the plurality of reference voltages line by line.
And a configuration supplied to the driver circuits Te. Third
The invention provides a light emitting element print head drive circuit according to the second invention.
, The clock signal for one line is counted,
A counter circuit that generates a counter output for each line,
Input the counter output of the counter circuit, and
Output a selection signal for sequentially selecting the reference voltage based on the
And a selector circuit, the selector circuit comprising:
Signal, and the reference signal is supplied for each line by the selection signal.
The pressure is switched and supplied to the driver circuit.
You.

[0012]

In accordance with the first to third invention, since the configuration of the light emitting element print head driving circuit as described above, the selector
The circuit has a plurality of reference voltages for different output currents,
The reference voltage selected from the plurality of reference voltages is
Supply to Iva circuit. The driver circuit is based on the supplied reference
Voltage, and outputs corresponding to this reference voltage and pixel data.
A force current is supplied to the light emitting device.

As a result, the light emitting element emits light, and gradation printing is performed.
Is performed.

[0014]

FIG. 1 is a schematic block diagram of an LED print head drive circuit according to an embodiment of the present invention. Elements common to those shown in FIGS. Have been. This LED print head drive circuit is provided in the conventional drive circuit 10 of FIG. 2, and includes a plurality of driver ICs 20-1,.
Further, a parallel / serial converter (hereinafter, referred to as a P / S converter) 100 and a counter circuit 10 are provided on the input side.
1. Flip-flop circuit (hereinafter referred to as F / F circuit)
102 and a selector circuit 103 are added. P /
The S converter 100 is, for example, to reproduce the gradation from 1 to 0 to 15.
When 6 gradations are set, 4-bit gradation print data DA1
To DA4, and the grayscale data DA1 to DA4 in synchronization with the clock signal CK input from the clock terminal 12.
Is converted into a serial signal and supplied to the input terminal 11 of the driver ICs 20-1,. Here, the 4-bit gradation print data DA1 to DA4 are signals each having a meaning of weight. For example, DA1 means the least significant bit of the 4-bit gradation data, that is, 1, and DA2 is 4 bits.
Bit next to the least significant bit of the bit gradation data, ie, 2
DA3 means the bit next to the most significant bit of the 4-bit grayscale data, that is, 4, and DA4 means the most significant bit of the 4-bit grayscale data, that is, 8.

The counter circuit 101 has a clock terminal 12
This circuit counts one line of the clock signal CK input from the CPU and generates a counter output for each line. An F / F circuit 102 is connected to the output side.
The F / F circuit 102 is a circuit that holds a counter output and supplies a selection signal , which is the output S102a to S102d , to the selector circuit 103. The selector circuit 103
/ F circuit 102 outputs S102a to S102d
4 different levels of reference voltage V _ref based on the select signal
1 to V _ref 4 and select one from the driver IC 20
-1,... Are supplied to the reference voltage terminals 15. The four reference voltages V _ref 1 to V _ref 4 correspond to each driver IC 20
The voltages are different so that the ratio of the output currents of the driver circuits 23 in -1,... Is, for example, 1: 2: 4: 8. For example, the reference voltage V _ref 1 is 0.6 V, the output current i 1 at that time is 0.4 mA, V _ref 2 is 0.8 V, the output current i 2 is 0.8 mA, and V _ref 3 is 1. At 2 V, the output current i3 at that time is 3.2 mA.

FIG. 6 is a timing chart showing the operation of the drive circuit shown in FIG. 1. The light emitting operation of the LED will be described with reference to FIG. In FIG. 1, when 4-bit gradation print data DA1 to DA4 are supplied, they are input to the P / S converter 100 in synchronization with the clock signal CK,
As shown in FIG. 6, the gradation print data DA1, DA2, DA
3 and DA4 in that order. First, the grayscale print data DA1 for one line and the clock signal C
It is input to the shift register 21 in the driver IC 20-1 in synchronization with K. The pixel data input to the shift register 21 is input to the latch circuit 22 together with the strobe signal SB for controlling the light emission time of the LED 32, whereby the pixel data is output to the driver circuit 23 for a fixed time as the light emission or extinction state of the LED 32. You. At this time, the counter circuit 101 counts the number of input clock signals CK and counts the number of input clock signals CK for one line, and provides an output as shown in FIG. 6 to the F / F circuit 102. In the F / F circuit 102, the F / F circuits output S corresponding to four reference voltages V _ref 1 to V _ref 4
102a to 102d turn on sequentially as shown in FIG.
It is provided to the selector circuit 103. The selector circuit 103, the reference voltage V _ref 1 to V _ref 4 of the F / F circuit output S102a~S102d is on is output,
The signal is sent to the reference voltage terminal 15 of the driver IC 20-1, and is input to the driver circuit 23 in the driver IC 20-1,.

In the driver ICs 20-1,..., When the grayscale print data DA1 is stored in the shift register 21, the reference voltage V _ref 1 is supplied to the driver circuit 23, which is supplied by the transistor 23a in FIG. The current is amplified and a constant output current i1 is output. This output current i1 is supplied to the LED 32 via the electrodes 33 in the LED arrays 31-1,..., And the LED 32 emits light.
Similarly, when the gradation print data DA2 is stored in the shift register 21, the reference voltage V _ref is supplied to the driver circuit 23.
2 is supplied, a constant output current i2 is output, and when the grayscale print data DA3 is stored in the shift register 21, the reference voltage V _ref 3 is supplied to the driver circuit 23, and a constant output current i3 is output. When the gradation print data DA4 is further stored in the shift register 21, the reference voltage V _ref 4 is supplied to the driver circuit 23, and a constant output current i4 is output. Generally, LED32
Has a characteristic that the light emission output increases in proportion to the current supplied to the LED 32. Therefore, the LED array 31
Each of the LEDs 32 in -1,...
Output currents i1 to i4 each having a weight according to DA4.
The light is sequentially emitted by i4, and the photosensitive drum 41 is exposed to the gradation print data of 16 gradations via the convergent rod lens array 40 of FIG.

As described above, in this embodiment, the 4-bit gradation print data DA1 to DA4 are converted into serial data by the P / S converter 100, and the data is converted via the input terminal 11 into the driver IC 20-1. , ..., shift register 2
Supplies to 1, the reference voltage terminal 15 to one of the reference voltage V _ref 1 to V _ref 4 selected by the selector circuit 103
Is supplied to the driver circuit 23 via the.
Therefore, the conventional binarization driver ICs 20-1,.
Of each dot in the LED array 31-1,.
D32 can emit light with a multi-valued light emission output without causing a decrease in resolution.
The gradation reproduction can be obtained without increasing the density of 1,. Furthermore, the conventional driver ICs 20-1,.
Converter 100, counter circuit 101, F / F circuit 102
And only by adding a simple circuit that the selector circuit 103 enables gradation printing, moreover, the driver circuit 2
3 can generate different output currents.
It is necessary to provide a plurality of driver circuits 23 to generate current.
It is unnecessary, and the circuit configuration of the LED print head drive circuit can be simplified and the cost can be reduced with a small circuit scale .

The present invention is not limited to the above embodiment,
For example, the 4-bit gradation printing data DA1~DA4 and the reference voltage V _ref 1 to V _ref 4 of the other number of bits,
Other circuits may be added to the driver ICs 20-1,.
Alternatively, various modifications are possible, such as applying the present invention to a print head drive circuit of a light emitting element other than an LED.

[0020]

As described in detail above, the first to third embodiments
According to the invention of the present application, the reference voltages for different output currents are duplicated.
A reference voltage selected from among the plurality of reference voltages
And a selector circuit for outputting the signal to the driver circuit.
The receiver circuit accepts the selected reference voltage and
Supply output current corresponding to voltage and pixel data to light emitting element
Then, it is configured to perform gradation printing. This allows
Since different output currents can be generated from the
Provide multiple driver circuits to generate output current
This eliminates the need for a simple circuit configuration with a small circuit scale and enables gray-scale printing at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic configuration block diagram of an LED print head drive circuit showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional LED printer.

FIG. 3 is a configuration diagram of an LED array light source unit in FIG. 2;

FIG. 4 is a block diagram illustrating a configuration of a driving circuit and an LED array light source unit in FIG. 2;

FIG. 5 is a schematic circuit diagram of a driver circuit in FIG. 4;

FIG. 6 is a timing chart showing the operation of FIG.

[Explanation of symbols]

Reference Signs List 10 drive circuit 11 input terminal 12 clock terminal 13 strobe terminal 14 power supply terminal 15 reference voltage terminal 20-1 to 20-n driver IC 21 shift register 22 latch circuit 23 driver circuit 30 LED array light source section 31, 31-1 to 31-31 n LED array 32 LED 40 Convergent rod lens array 41 Photosensitive drum 42 Charger 43 Developing device 44 Transfer device 45 Paper 100 P / S converter 101 Counter circuit 102 F / F circuit 103 Selector circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B41J 2/44 B41J 2/45 B41J 2/455 B41J 2/36

Claims (3)

(57) [Claims] 1. A light emitting element print head drive circuit for sequentially inputting print data input from an input terminal and driving the light emitting element by the input data and a strobe signal for controlling a light emitting time of the light emitting element. Based on the voltage value of the reference voltage, the output voltage corresponding to the voltage value
A driver circuit for supplying a current to the light emitting element and a reference voltage value corresponding to each of the different output currents.
A voltage value selected from among the plurality of voltage values.
And a selector circuit for supplying a voltage to the driver circuit, the driver circuit, supplied from the selector circuit
Emitting element print head driving circuit, characterized in that the reference voltage the output current generated based on the voltage value and the pixel data of and the construction for supplying the output current to the light emitting element. 2. The light emitting element print head according to claim 1,
In the driving circuit, the selector circuit is configured to output the plurality of reference voltages for each line.
The configuration is such that the signals are sequentially selected and supplied to the driver circuit.
And a light emitting element print head driving circuit. 3. The light emitting element print head according to claim 2,
In the drive circuit, count the clock signal for one line, and for each line
A counter circuit for generating a counter output, enter the counter output of the counter circuit, said counter
A selection signal for sequentially selecting the reference voltage based on the output;
Means for outputting the selection signal, the selector circuit receiving the selection signal,
The reference voltage is switched for each line by
A light-emitting element characterized in that the light-emitting element is configured to be supplied to an inverter circuit.
Child print head drive circuit.