JP2001010108A - Driver ic for light emitting diode array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control gradation such that the optical output is varied for each raster without lowering the speed by providing individual light emitting diodes in a light emitting diode array with a plurality of different latch circuits which can hold a plurality of current control data simultaneously. SOLUTION: The driver IC for light emitting diode array comprises a bi- directional shift register generating an internal clock, a data FLIP-FLOP for holding data temporarily, a current control latch for holding pixel data, a decoder generating a signal for selecting a current control latch in which the data is held, an AND circuit for selecting a transistor based on the content of the latch and a driver strobe signal, and transistors having different drive currents. Terminals Q1-Q64 are connected with the cathode of light emitting diodes, terminal VDD is connected with a + power supply, and terminals VSS0, VSS1 and VSS1-VSS8 are connected with GND.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode array driver I used for a recording head of an optical printer.
It concerns C.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram of a conventional driver IC for a light emitting diode array. A conventional light emitting diode array driver IC has an 8-bit parallel input (D
1 to D8), and the data input by 8 bits is
The data is read into the data FLIP-FLOP at the edge of the internal clock generated in synchronization with the clock input terminal (CLK). The internal clock is generated by a bidirectional shift register. The data is read eight times, and the 64-bit data is read from the data FLIP-FLOP1 to FLIP-FL.
Read in OP8.

A pixel data latch strobe input (LST)
When B) is set to the “L” level, the 64-bit pixel data latch L0 reads the 64-bit data read into the data FLIP-FLOP1 to FLIP-FLOP8 8 bits at a time, and sets the data when the LSTB is set to the “H” level. Hold.

When the current control data latch enable input (G) is set to the "L" level, the 64-bit data read into the data FLIP-FLOP1 to FLIP-FLOP8 8 bits at a time becomes 64-bit current control data latches L1 to L4. , And when G is set to the “H” level, the data is held.

Which of the current control data latches L1 to L4 is read is determined by a combination of the selection signals I1 and I2. Then, the current control data latch L1
L4 are connected to selection means for selecting transistors having different drive currents.

[0006]

The conventional driver IC for a light emitting diode array has the following problems.

[0007] Since only one current control data can be held for one light emitting diode, the driving current is always constant and the light output is also constant. Therefore, it is not possible to perform gradation control for changing the light output for each raster.

If the purpose of gradation control is to be performed, the current control data must be input and held again for each raster, so that the time for current control data transfer increases and the speed decreases.

In the conventional example shown in FIG. 3, since the current control data holding latch has four bits and the current control data transfer operation is performed four times, the data transfer time is five times as long as the pixel data transfer time. Will be required.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a driver IC for a light-emitting diode array having a gradation control function of changing the light output for each raster without reducing the speed while solving the above-mentioned drawbacks of the prior art. It is in.

[0011]

According to the present invention, in order to realize the above-mentioned object, when driving each driver of a light emitting diode in accordance with blinking data, a plurality of driving transistors having different output currents are connected in parallel to each driver. And selecting means for determining an arbitrary combination of driving transistors from the driving transistors connected in parallel is provided in each of the drivers, and the selecting means is operated by current control data held in a latch circuit. And a light emitting diode array driver IC configured to correct the light output of the light emitting diode connected to each of the drivers, wherein a plurality of different current control data can be simultaneously held for the light emitting diode. Are provided.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a first embodiment of a light emitting diode array driver IC according to the present invention. The light emitting diode array driver IC shown in FIG. 1 includes a bidirectional shift register that generates an internal clock, a data FLIP-FLOP that temporarily holds data, a pixel data latch that holds pixel data, and a current control data. A current control latch, a decoder for generating a selection signal for selecting which current control latch holds data, an AND circuit for selecting a transistor based on the contents of the latch and a driver strobe signal (DSTB), each having a different drive current The terminals Q1 to Q64 are connected to the cathode of a light emitting diode, the terminal VDD is connected to a positive power supply, and the terminals VSS0 and VSS1 to VSS8 are connected to GND.

The 8-bit parallel data input from the data input terminals (D1 to D8) is supplied to the clock input terminal (C
LK) is read into the data FLIP-FLOP at the edge of the internal clock generated in synchronization with the clock input to the clock. The internal clock uses two I / O terminals (EI / O
1, EI / O2). This data reading operation is performed eight times, and 64
FLIP-FLOP1 to FLI for bit data
Read into P-FLOP8. The shift direction of the bidirectional shift register is determined by a signal input to the L / R terminal. When L / R = “H” level, the shift direction is Q
1 → Q64 direction, EI / O1 is enable input,
EI / O2 is an output. When L / R = “L” level, the shift direction is Q64 → Q1 and the EI / O
2 is an enable input and EI / O1 is an output.

The latch strobe input (LSTB1, LS
When TB2) is set to the “L” level, the 64-bit data read into the data FLIP-FLOP1 to FLIP-FLOP8 by 8 bits at a time is stored in the pixel data latch (L1).
0, L20), and the data is held when the latch strobe input is set to “H” level. LSTB1
Is at "L" level, LSB is at L10, and LSTB2 is at "L" level.
In the case of a level, it is read into L20.

When the current control data latch enable input (G) is set to the "L" level, the 64-bit data read into the data FLIP-FLOP1 to FLIP-FLOP8 in units of 8 bits is converted into the current control data latch L11.
To G34, and when G is set to the "H" level, the data is held. Which of L11 to L34 is read is determined by a combination of the selection signals I1 to I4 as shown in Table 1.

[0017]

[Table 1]

When the driver strobe input (DSTB) is set at "L" level, the driver output transistor is turned on when the contents of the 64-bit latch are at "H" level.
, And turns off when the signal is at the “L” level, but the data of the current control data latch is selected as shown in Table 2 by the combination of the data of the pixel data latches L10 and L20.

[0019]

[Table 2]

As a result, it is possible to simultaneously store three levels of current setting values for one LED. For example, a current value that becomes a standard light output in a one-stage latch and a standard two-level current value in another two-stage latch are stored in advance. By storing current values that provide twice or 1/2 times the optical output, it becomes possible to select standard, 2 times, and 1/2 times of the optical output simply by inputting pixel data. It is possible to realize gradation control for changing the light output for each raster.

However, since it is necessary to input the pixel data twice, it takes twice as long pixel data input time as the conventional light emitting diode array driver IC without gradation control. If the driver IC dares to perform gradation control, it is necessary to re-input current control data every time. Therefore, in the case of 4-bit current control, it takes five times as long to input pixel data. In the case of 8 bits, nine times as long as pixel data input time is required. However, in the first embodiment of the light emitting diode array driver IC of the present invention, no matter how many bits the current control is, the pixel data input time is twice that of the conventional light emitting diode array driver IC which does not perform gradation control. Can be done.

Although the VG terminal is provided in the first embodiment, it is used to adjust the output currents of all the transistors in the same ratio in an analog manner.

FIG. 2 is a block diagram showing a second embodiment of the light emitting diode array driver IC of the present invention. The difference from the first embodiment is that only one stage of pixel data latch is provided, and two driver strobe signal lines DSTB1 and DSTB2 are provided for selecting a three-stage current control latch.

In the second embodiment, three-stage latch selection is selected by a combination of two pixel data.
This requires twice as long pixel data input time as a conventional light emitting diode array driver IC without gradation control. However, in the case of gradation control in which it is not necessary to change the light output for each dot, but only for each row, it is sufficient to provide a signal line for controlling the light output of the entire light emitting diode array without using a latch. In addition, the pixel data input time can be the same pixel data input time as that of a conventional light emitting diode array driver IC that does not perform gradation control.

By manufacturing an LED printer head using the light emitting diode array driver IC of the present invention and the light emitting diode array, and using this in a printer,
It is possible to realize a digital printer capable of printing characters and graphics that require smooth curves and diagonal lines and fine shades and graphics and graphic printing.

[0026]

According to the driver IC for a light emitting diode array of the present invention, a plurality of latch circuits capable of simultaneously holding a plurality of different current control data are provided for each light emitting diode in the light emitting diode array. The following effects can be exerted.

1. Gradation control that changes the light output for each raster becomes possible.

2. Gradation control can be performed without reducing the speed. (One or two times the pixel data input time is required as compared with a conventional light emitting diode array driver IC without gradation control.)

[Brief description of the drawings]

FIG. 1 is a light emitting diode array driver IC of the present invention.
FIG. 3 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a light emitting diode array driver IC of the present invention.
It is a block diagram which shows 2nd Example of this.

FIG. 3 is a block diagram of a conventional light emitting diode array driver IC.

Claims (1)

[Claims] When driving each driver of a light emitting diode in accordance with blinking data, each driver is constituted by connecting a plurality of driving transistors having different output current amounts in parallel, and the driving transistors among the driving transistors connected in parallel are provided. A selection means for determining an arbitrary combination of drive transistors from each of the drivers is provided, and the selection means is operated by current control data held in a latch circuit, and a light output of the light emitting diode connected to each of the drivers is provided. A driver IC for a light-emitting diode array configured to correct for the light-emitting diode, comprising a plurality of latch circuits capable of simultaneously holding a plurality of different current control data for the light-emitting diode. Driver IC.