JPH04257464A - Driver of led array - Google Patents

Abstract

PURPOSE:To reduce the scale of an LED array driving circuit. CONSTITUTION:A luminance data ROM 22 stores luminance data for correcting the luminance of LED elements. A luminance correction table 24 receives the luminance data from the luminance data ROM 22 and gradation data sent from outside, and outputs data that are corrected for luminance. After the luminance-corrected data for a line are sent to a shift register 28, the data are held in a latch 30 and enable signals EN 1-EN 14 are selected by the data to control pulse signals that light the LED elements.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device for driving an LED array used in a scanner, printer, copying machine, etc., and more particularly to a drive device equipped with a brightness correction means for correcting the brightness of each LED element. .

0002

2. Description of the Related Art In order to correct the brightness of each LED element in an LED array driving device, a ROM having brightness correction data for each LED element is provided. A conventional LED array driving device is shown in FIG. 12 is a brightness data ROM having brightness data of the LED elements, and the brightness data of each LED element is expressed and held in m bits. Data for lighting the LED element is externally given as grayscale data in n bits. 14 is a shift register and latch into which gradation data is input, and 16 is a shift register and latch into which luminance data is input. N-bit gradation data is input to the shift register of the shift register and latch 14 using a clock (DCLK) and is shifted.
The shift register and the shift register of latch 16 have m
Bit luminance data is input and shifted using a clock (DCLK), and when one line worth of data is input, the data is held in a latch by a set signal (SET). 18 is a driver transistor that drives the LED element according to latched (m+n) bit data.

0003

[Problem to be Solved by the Invention] When (m+n) bits of data are input to the shift register and latch as shown in Figure 4, (m+n) bits of shift register and latch are required for each LED element. , the scale of the drive circuit becomes larger and larger, leading to higher costs. The present invention is an LED
The purpose of this invention is to reduce the circuit scale of the LED array drive circuit by reducing the number of bits of data input to the shift register of the array drive circuit.

0004

[Means for Solving the Problems] The LED array driving device of the present invention, which has a reduced circuit scale, includes a storage device that stores brightness correction values for each LED element of an LED array unit, and a brightness correction value from this storage device. A brightness correction table that inputs values and input data and outputs brightness-corrected data, a shift register that converts this brightness-corrected serial data into parallel data, and a shift register that converts the brightness-corrected serial data into parallel data. The device includes a latch that holds data in the shift register, and a multiplexer that selects a pulse signal for lighting an LED element according to the data held in the latch.

The present invention also provides a storage device storing brightness correction values for each LED element of an LED array unit, inputting the brightness correction values and input data from this storage device,
a brightness correction table that outputs brightness-corrected data;
The device includes a shift register that converts the brightness-corrected serial data into parallel data, and a selection circuit that selects the size of the LED drive transistor according to the brightness-corrected data.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows one embodiment, and shows a driving circuit for one LED element of an LED array unit. 22 is a brightness data ROM that holds brightness data for correcting the brightness of each LED element. The brightness of the bright LED element is set to 100%, and each LED
4 levels depending on the brightness of the element, e.g. 100%, 9
Levels are set such as 0%, 80%, 70%,
Brightness data RO is data indicating the brightness of each LED element.
It is stored in M22. 24 is a brightness correction table which inputs the brightness data from the brightness data ROM 22 and gradation data sent as data from the outside, and outputs brightness-corrected data.

A circuit 26 surrounded by a chain line is a driver circuit for one LED element. Driver circuit 2
6 includes a shift register 28 to which 4-bit data per LED element whose brightness has been corrected output from the brightness correction table 24 is sent at the timing of the clock signal DCLK, and a shift register 28 to which data for one line is sent to the shift register 28. After that, a latch 30 holds the data in the shift register 28, a multiplexer 32 selects enable signals EN1 to EN4 with a pulse width corresponding to each bit of data in accordance with the data in the latch 30, and a multiplexer 3
A gate circuit 3 that turns on the driver transistor 36 for the pulse time of the pulse signal determined in step 2 and energizes it.
4 are provided.

A current mirror circuit 38 is provided in the driver transistor 36 so that a constant current flows therethrough. 40 is a contact to which the LED element is connected. These driver circuits 26 are arranged in the same number as the LED elements, and these driver circuits 26 share brightness data RO.
M22, brightness correction table 24, current mirror circuit 3
8, enable signal terminals EN1 to EN4, a set signal terminal SET, and a clock signal terminal DCLK are provided. As the enable signals EN1 to EN4, pulse signals having a pulse width corresponding to 4-bit data are used as shown in FIG. 2.

In the embodiment shown in FIG. 1, the gradation of each LED element is expressed using 4 bits, so up to 16 gradations can be expressed. The gradation data input to the brightness correction table 24 has 12 gradations, and the brightness data has 4 gradations, representing 16 gradations corrected for the brightness of each LED element. Brightness correction table 2
An example of No. 4 is as shown in the following table.

0010

Next, the operation of the embodiment shown in FIG. 1 will be explained. Twelve gradation data is input to the brightness correction table 24 from the data input terminal, and brightness data indicating the level of the LED element at the position corresponding to the data is input from the brightness data ROM 22 to the brightness correction table 24. Based on these two pieces of data, brightness-corrected data is output from the brightness correction table 24. For example, if the brightness level is 8
Assuming that luminance data of gradation 5 (0101) is input to the luminance correction table 24 for the LED element at the 0% position, from the table, the LED driver circuit 26 receives gradation 6 (0110) as luminance-corrected data. is input. This brightness-corrected data is sent to the shift register 28 using the clock signal DCLK, and when one line has been input, the data in the shift register 28 is sent to the latch 3 using the set signal SET.
It is held at 0. Enable signals EN1 to EN4 shown in FIG. 2 are selected by the multiplexer 32 based on the data held in the latch 30, and the ON time of the LED element is determined. The LED element lights up using the 16-gradation data whose brightness has been corrected in this manner.

FIG. 3 represents a second embodiment. As an example, it is assumed that data D whose brightness is corrected by the brightness correction table 24 from the brightness data ROM 22 and gradation data as shown in FIG. 1 is sent as 3-bit data for one LED element.

This driver circuit consists of a data register section and a driver section, and the data register section is provided with a shift register 42 that sends data in response to a clock signal CK. The driver section includes driver transistors DT1 to DT3 that control the current flowing to the LED element 44.
are installed in parallel. These driver transistors DT1 to DT3 have different transistor sizes, and if the current value when all are turned on is 100, driver transistor DT1 has a current value of 70%, driver transistor DT2 has a current value of 20%, and driver transistor DT3 has a current value of 10%. It is assumed that the size is set to allow a current to flow.

In order to select and turn on the driver transistors DT1 to DT3 based on the data in the shift register 42, a NAND gate 46 which receives the data in the shift register 42 and an enable signal EN, and their NA
A gate circuit 48 is provided which is opened and closed by the output of the ND gate 46.

Next, the operation of the embodiment shown in FIG. 3 will be explained. When the enable signal EN is at a high level, the corresponding driver transistors DT1 to DT3 are turned on by the on bit of data in the data register section, and the LEDs are turned on.
Element 44 lights up. For example, the brightness is 70% when only driver transistor DT1 is on, the brightness is 80% when driver transistors D1 and D3 are on, the brightness is 90% when driver transistors D1 and D2 are on, and the brightness is 90% when driver transistors D1 and D3 are on. Transistor DT1~
The brightness is 100% when all DT3 are turned on. In this way, the brightness of the LED element of each bit is set by the data in the data register section.

Although only three driver transistors are provided in the circuit shown in FIG. 3, by increasing the number of driver transistors per one LED element, even finer luminance correction can be performed. Figure 3
In the embodiment, brightness correction is performed by changing the transistor size of the driver transistor and changing the current value, and the circuit is simpler than the pulse modulation method because a pulse generation circuit is not required.

[0017]

[Effects of the Invention] In the present invention, the brightness data checked in advance for each LED element is stored in the brightness data ROM, and the brightness data and gradation data are input into a brightness correction table to adjust the brightness of the LED elements with different brightness. However, when the same gradation data is input, it is input to the LED driver circuit as corrected gradation data such that the LED elements emit light at the same gradation, so the brightness-corrected data is input to the LED driver circuit. As a result, conventionally a shift register and a latch were required to input data for brightness correction, but according to the present invention, only one brightness correction table is required for one LED array driving device, and L
The ED array driving device becomes simpler, and the chip area of the semiconductor integrated circuit device that implements it becomes smaller.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment.

FIG. 2 is a waveform diagram showing four types of enable signals in the same embodiment.

FIG. 3 is a circuit diagram showing another embodiment.

FIG. 4 is a block diagram showing a conventional LED array driving device.

[Explanation of symbols]

22 Brightness data ROM24
Brightness correction table 26
FIG. 3 is a circuit diagram showing a drive circuit for one LED element. 28, 42 Shift register 30 Latch 32 Multiplexer 34, 48
Gate circuit 36, DT1 to DT3 driver transistor 44
LED element

Claims (2)

[Claims] 1. A storage device that stores brightness correction values for each LED element of an LED array unit, and a brightness device that inputs the brightness correction values and input data from the storage device and outputs brightness-corrected data. A correction table, a shift register that converts the brightness-corrected serial data into parallel data, a latch that holds the data in the shift register when one line of serial data is input, and the data held in this latch. A multiplexer that selects a pulse signal for lighting an LED element according to the following. 2. A storage device that stores the brightness correction value of each LED element of the LED array unit, and a brightness device that inputs the brightness correction value and input data from the storage device and outputs the brightness-corrected data. An LED array drive device comprising a correction table, a shift register that converts the brightness-corrected serial data into parallel data, and a selection circuit that selects the size of an LED drive transistor according to the brightness-corrected data.