JP2001277584A - Led driver and led printer head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED driver and an LED printer head capable of preventing an erroneous operation due to a noise and being operated at a high speed. SOLUTION: Differential clock signal pair CLKP, CLKN having a complementary phase relation are input from an exterior into an IC via an input terminal, and waveform shaped by a differential receiver 31 to form an internal clock signal CLK. The clock signal CLK is applied to a shift register 2. Accordingly, an influence of the noise is difficult to be received. Thus, an erroneous operation of the shift register 2 can be prevented, and a frequency of the clock signal can be raised.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED (Light Emitting Diode) driver and an LED printer head, and more particularly to an LE driver for reducing noise superimposed on a clock signal supplied to a shift register incorporated in an LED driver circuit.
The present invention relates to a technology that enables high-speed display of D and high-speed printing by an LED printer.

[0002]

2. Description of the Related Art Generally, an LED driving device includes a shift register which shifts a print signal serially input from the outside and a correction signal for gradation control in synchronization with a clock signal. A circuit configuration is adopted in which an LED is driven by a drive circuit in accordance with parallel output data.

FIG. 4 is a schematic view of an LED printer head 50 incorporating the LED driving device. In the figure,
Reference numeral 51 denotes a mounting board such as a printed board, and 30 to 40 LED driving chips 52-1, 52-2,... Are arranged in the longitudinal direction on the mounting board 51. Also,
LED arrays 53-1 adjacent to each LED driving chip,
53-2 ... are arranged. Reference numeral 54 denotes an external connection terminal group to which various drive signals (clock signal, print signal), power supply voltage and the like are applied. Reference numeral 55 denotes a wiring cable connected to the external connection terminal.

Conventionally, a clock signal supplied to a shift register is supplied from a wiring cable 55 via an external connection terminal.
Each of the LED driving chips 52-
1, 52-2... As prior arts of LED driving circuits, Japanese Patent Application Laid-Open Nos. 58-78476, 5-265399, 8-3986.
No. 2, JP-A-8-197773, JP-A-8-197773
There are those disclosed in Japanese Patent No. 3288511, Japanese Patent Application Laid-Open No. 9-244570, and the like.

[0005]

The wiring cable 55 is L
It has a length of 60 cm to 1 m due to the structure of the ED printer. When the clock signal supplied to the above-described shift register is transmitted through the wiring cable 55, there is a problem that external noise is superimposed due to a large clock amplitude of, for example, 5 V, and the shift register is likely to malfunction. Also,
Since the wiring cable 55 is long, it is difficult to increase the frequency of the clock signal.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and prevents a malfunction of a shift register of an LED drive circuit, increases the speed of a clock signal,
An object is to provide an LED printer head that enables high-speed printing.

[0007]

An LED driving apparatus according to the present invention comprises a shift register for shifting a print signal in synchronization with a clock signal, and a plurality of shift registers for latching parallel output data of the shift register in synchronization with a latch signal. An LED driving apparatus comprising: a latch circuit; and a driving circuit for driving an LED according to output data of the latch circuit. An input terminal pair to which a differential clock signal pair is input from outside, and the differential clock signal And a differential receiver for shaping the waveform of the pair. The differential receiver outputs the clock signal and supplies the clock signal to the shift register.

An LED printer head according to the present invention includes a plurality of LED arrays and a plurality of LED driving circuits provided adjacent to the LED arrays and driving the LED arrays on a single mounting substrate. In the LED printer head, each of the LED drive circuits includes an input terminal pair to which a differential clock signal pair is input, a differential receiver for shaping the waveform of the differential clock signal pair, and an output of the differential receiver for outputting a clock signal. And a shift register that shifts a print signal input from the outside in synchronization with the clock signal, wherein the differential clock signal pair is adjacent to the plurality of LED drive circuits on the mounting board. Paired in the longitudinal direction of the mounting board, and input to each input terminal pair of the differential clock signal pair of each LED drive circuit. It is characterized in being.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic circuit diagram of an LED driving device according to an embodiment of the present invention.

In FIG. 1, 1 is 4-bit data DATAI.
Input terminals 3 to 0 are shift registers for shifting input data in synchronization with the clock CLK.
It is composed of 48 stages of DFFs. Where input data D
ATAIs 3 to 0 are a print signal and a correction signal input serially. 3 is a DFF of the 49th stage, and serial output data DATAO3-0 of the shift register 2 is DF.
It is output to the output terminal 4 via F3.

A feature of the present invention is that an LVDS system (Low Voltage Differential Signal) is used for transmitting a clock signal.
And a differential clock signal pair CLKP, CLKN having a complementary phase relationship is externally supplied to an input terminal pair (inverted input terminal-, non-inverted input terminal +) through an input terminal I
The internal clock signal CLK is created by inputting the signal into the C and shaping the waveform by the differential receiver 31.

The differential receiver 31 is composed of a differential amplifier, and its output is an E-NOR (Exclusive Nor) gate 3.
2 is applied to one input terminal. E-NOR gate 3
The SEL signal is applied to the other input terminal of 2.

The SEL signal is set to L level for odd-numbered LED driving chips and H level for even-numbered LED driving chips arranged in an LED printer head described later. Further, the differential clock signal pair CLK
P and CLKN are alternately input to the input terminal pair between adjacent LED driving chips, and as a result, the internal clock signal CLK is configured to have the same phase in all LED driving chips.

Reference numeral 33 denotes a load signal LOAD described later.
An E-NOR gate for creating -P. Also,
The LOADI signal is applied to the E-NOR gate 33 and inverted by the inverter 34, output as a / LOAD signal, and input to the next-stage LED drive chip. Reference numeral 5 denotes a 192-bit latch circuit that latches parallel output data output from the shift register 2 in synchronization with the rise of the load signal LOAD-P.

Reference numeral 6 denotes a static memory (SRAM) for temporarily storing parallel output data output from the shift register 2. This static memory 6
Is composed of 6 words × 192 bits. A write control circuit 7 supplies a write signal to the static memory 6, and the write control circuit 7 is controlled by the inverted standby signal / STB and the load signal LOAD-P.

The parallel output data of the shift register 2 includes an inverted standby signal / STB and a load signal LOAD.
By -P, the data path is switched in time series such that the data signal is input to the latch circuit 5 at a predetermined timing as a print signal and then input to the static memory 6 as a correction signal.

As described above, the print signal temporarily stored in the latch circuit 5 and the correction signal temporarily stored in the static memory 6 are simultaneously supplied to the LED drive circuit 8 arranged in the next stage. The LED drive circuit 8 outputs a drive current for lighting the LED based on the print signal and the correction signal.

Reference numeral 9 denotes a reference current circuit for setting a reference level of an output drive current of the LED drive circuit 8.
One method of setting the reference current is performed by selecting one of 16 resistors described later using 4-bit serial output data DATAO3 to DATAO3.

Reference numeral 10 denotes an input terminal of a reference voltage VREF supplied to the reference current circuit 9, and 11 denotes an LED driving circuit 8.
And an input terminal of a power supply voltage VDDH supplied to the reference current circuit 9; 12 are 192 output terminals of the LED drive circuit;
3 is a test terminal of the LED drive circuit 8, and 14 is an input terminal of the inverted strobe signal / STB.

FIG. 2 shows a differential clock signal pair CLKP,
FIG. 3 is a waveform diagram of CLKN and a waveform diagram of an output of the differential receiver 31. The differential clock signal pair CLKP and CLKN are complementary clock signals having an amplitude of about 1.2 V, and the differential receiver 31 generates an internal clock signal CLK having an amplitude of 5 V.

As described above, according to the LED driving device having the above-described configuration, the differential clock signal pairs CLKP and CLKN having a complementary phase relationship are externally input into the IC via the input terminal pair, and the differential clock signal pair is input to the differential driver. Since the internal clock signal CLK is formed by shaping the waveform in the receiver 31 and applied to the shift register 2, the internal clock signal CLK is less likely to be affected by noise and malfunction of the shift register 2 can be prevented. It is possible to increase the frequency of the signal.

Next, an LED printer head 50 to which the above-configured LED driving device is applied will be described with reference to FIG. The same components as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

The differential clock signal pair is connected to the wiring cable 55
The cable is transmitted through the inside pair cable, and is input to the LED printer head 50 via the external connection terminal group 54. Are transmitted in the longitudinal direction on the mounting board 51 on the pair wires 60, 61 arranged adjacent to the LED driving devices 52-1, 52-2,.... This pair wiring 60,
Reference numeral 61 is branched and connected alternately to the input terminal pair of the differential receiver 31 of each LED driving device.

The LED printer head 5 having the above configuration
According to 0, high-speed transmission of the clock signal is possible, and the printing speed of the printer is improved.

[0025]

According to the LED driving apparatus of the present invention, an input terminal pair to which a differential clock signal pair is inputted from outside,
A differential receiver for shaping the waveform of the differential clock signal pair. Since the internal clock signal is output from the differential receiver, the differential clock signal pair is less susceptible to noise and malfunction of the shift register can be prevented. At the same time, high-speed operation is enabled by increasing the frequency of the clock signal.

Further, according to the LED printer head of the present invention, the differential clock signal pair is formed by a plurality of L on the mounting board.
Adjacent to the ED drive circuit and paired in the longitudinal direction, and input to each input terminal pair of the differential clock signal pair of each LED drive circuit, eliminating the influence of noise and enabling high-speed printing Becomes

In particular, the present invention is suitable as an LED driving device and an LED printer head for a color LED printer having a large print data amount.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an LED driving device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of a differential clock signal pair CLKP and CLKN and a waveform diagram of an output of a differential receiver 31.

FIG. 3 is a schematic view of an LED printer head according to an embodiment of the present invention.

FIG. 4 is a schematic view of an LED printer head according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 2 Shift register 3 DFF 4 Output terminal 5 Latch circuit 6 Static memory 7 Write control circuit 8 LED drive circuit 9 Reference current circuit 10 Input terminal of reference voltage VREF 11 Input terminal of power supply voltage VDDH 12 192 of LED drive circuit Output terminal 13 Test terminal of LED drive circuit 14 Input terminal of inverted strobe signal / STB 31 Differential receiver 32 E-NOR gate 33 E-NOR gate 34 Inverter 54 External connection terminal group 55 Wiring cable 60, 61 Pair wiring

Claims (2)

[Claims] A shift register for shifting a print signal in synchronization with a clock signal; a plurality of latch circuits for latching parallel output data of the shift register in synchronization with a latch signal; L
A driving circuit for driving the ED, comprising: an input terminal pair to which a differential clock signal pair is externally input; and a differential receiver for shaping the waveform of the differential clock signal pair. An LED driving device, wherein the clock signal is output from a differential receiver and supplied to the shift register. 2. A plurality of LED arrays and these LEDs
A plurality of LED drive circuits provided adjacent to the array and driving the LED array, on a single mounting substrate, wherein each LED drive circuit receives a differential clock signal pair Input terminal pair, a differential receiver for shaping the waveform of the differential clock signal pair, and an output of the differential receiver supplied as a clock signal, and a print / correction signal input from the outside in synchronization with the clock signal The differential clock signal pair is wired on the mounting board adjacent to the plurality of LED driving circuits in the longitudinal direction of the mounting board, and the respective LED driving circuits An LED printer head is inputted to each input terminal pair of the differential clock signal pair of (1).