JP2003063046A - Driving arrangement of printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and inexpensively provide a driving arrangement of a printer having stable print quality and minimal failure. SOLUTION: The driving arrangement of the printer which prints characters and images consisting of a plurality of dots based on control signals and data from a control device is provided with a plurality of latch circuits storing data, a plurality of gate circuits outputting the output from a plurality of respective latch circuits based on control signals, and a plurality of output transistors driving respective resistor elements for formation of a plurality of dots in accordance with the output from the gate circuits. In the plurality of gate circuits, the driving capabilities of MOS transistors operating based on the control signals in the MOS transistors composing of the gate circuits are formed smaller than driving capabilities of MOS transistors being operated based on data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer drive device, and more particularly to a circuit configuration thereof.

[0002]

2. Description of the Related Art FIG. 3 shows a driving device 200 and its application circuit which have been conventionally used as a driving device for a thermal printer. In FIG. 3, R1 to Rn are resistors as heating elements, E1 is an external power supply for flowing a current through each resistor, DO1 to DOn are output terminals connected to each resistor, SI is an input terminal for serial data, and CK is a clock signal. , EN is a control signal input terminal, L1 to Ln are serial data latch circuits, and NG1 to NGn.
Is a NOR gate circuit, T1 to Tn are N-channel type M
An output transistor including an OS transistor (hereinafter abbreviated as “NMOS”) is shown. Capacitors C1 to Cn, which are connected by dotted lines, represent parasitic capacitances such as the diffusion capacitance of the output of each gate circuit NGn, the input gate capacitance of each output transistor Tn, and the wiring capacitance. It should be noted that the dot unit circuits each including a latch circuit (L), a gate circuit (NG), and an output transistor (T) are BL1 to B.
It is surrounded by a dotted line as Ln.

The clock signal CK is connected to the clock input C of each latch circuit L, the serial data input SI is connected to the data input D of the latch circuit L1, and the latch circuit Lm (m is a natural number of n or less). The data output Q is connected to the data input D of the latch circuit L (m + 1) and to one input of each gate circuit NGm, and the control signal input terminal EN is connected to the other input of each gate circuit NGm. The output of each gate circuit NGm is connected to the gate input of each output transistor Tm, and the source of each output transistor Tm has a reference potential (GN
D), and its drain is connected to each output terminal DOm.

With such a configuration, each latch circuit Ln
The required resistance Rn based on the serial data stored in
Printing is performed by causing a predetermined current to flow to generate heat. Since operations such as serial data transfer and gradation display are not directly related to the present invention, heating element energization control used in a similar printer device shown in FIG. 9 of JP-A-5-57945 is used. The description of the circuit is omitted by referring to the description of the circuit.

[0005]

By the way, in the above-described drive device for the thermal printer, the voltage (about 24 V) applied by the external power source E1 is higher than the power supply voltage (VDD = about 5 V) applied to the drive device 200. Since it is a high voltage, it is impossible to provide a protection circuit such as a protection diode between each output terminal DOn and the power supply voltage VDD. Therefore, by making a large number of output transistors conductive (ON state) and setting their output terminals DOn to a low level and then making the control signal EN high level, all output terminals are made non-conductive (OFF state) at the same time. When the terminal voltage is set to a high level, the currents flowing through the resistors are simultaneously and rapidly cut off, so that the voltage at each output terminal DOn rises to a voltage (about 35V) significantly higher than the power source E1. It may happen. As a result, the characteristics of the output transistor Tn may be deteriorated or the current may not be controlled, which may result in uneven printing and deteriorate the printing quality. Further, in the worst case, the output transistor may be destroyed and normal printing may not be performed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve these problems, and to provide a printer driving device with stable printing quality and less troubles easily and at low cost.

[0007]

In order to solve the above-mentioned problems, a driving device for a printer according to a first aspect of the present invention comprises:
A drive device for a printer for printing a character or an image composed of a plurality of dots based on a control signal and data from a control device, wherein the drive device for the printer comprises a plurality of latch circuits for storing the data, A plurality of gate circuits that respectively output the outputs of the plurality of latch circuits to the output transistors based on the control signal, and a plurality of outputs that respectively drive the plurality of dot forming elements according to the outputs from the gate circuits. A plurality of gate circuits, the drive capability of a MOS transistor that operates based on the control signal among the MOS transistors that form the gate circuit, and the drive capability of a MOS transistor that operates based on the data. It is characterized by being smaller than. A printer driving device according to a second aspect of the present invention is the printer driving device according to the first aspect, wherein the MOS transistor that operates based on the control signal has a small driving capability that is commonly provided to a plurality of gate circuits. It is characterized by including a common transistor.

[0008]

With the configuration of the present invention, when a large number of output states are changed all at once by a control signal, the output driving capability of each gate circuit is changed based on the serial data. The output driving power becomes smaller than the output driving capacity at that time, the time constant between the ON resistance of each gate circuit NGn and each parasitic capacitance Cn becomes large, and each output transistor T
n is gradually turned off. That is, when the output states of a large number of output terminals are changed all at once by the control signal, the output states are changed more slowly than when the output states are individually changed based on the latched serial data. The rise of the power supply voltage can be suppressed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a driving device 100 for a thermal printer and its application circuit as an embodiment of the present invention, and FIG. 2 shows a timing chart of each signal in FIG. In FIG. 1, 100 is a driving device using the configuration of the present invention, R1 to Rn are resistors for printing dots by individually flowing current and generating heat,
E1 indicates an external power supply that applies a high voltage (E1 (V)) to one end of each resistor. Further, the configuration of the driving device 100 is
DO1 to DOn are output terminals connected to one ends of the resistors R1 to Rn, SI is a data input terminal for receiving serial data from a control device (not shown), and CK
Is an input terminal for a clock signal that serves as a timing signal for transferring the serial data SI, EN is a control input terminal for collectively turning on / off the output of each data, and L1 to L
n is a latch circuit that stores and holds serial data, G1
To Gn are gate circuits that output the data of each latch circuit Ln according to the control input EN, and T1 to Tn are conductive according to the output of each gate circuit Gn, so that each output terminal D
The output transistor which consists of NMOS which sends a current to the resistance connected to On is shown. It should be noted that the unit circuits for each dot, which are composed of the latch circuit L, the gate circuit G, and the output transistor T, are shown by dotted lines as B1 to Bn, and may be several tens to several hundreds depending on the configuration of the printer.

Further, each gate circuit Gn includes a PMOS 12 and an NMOS to which the output from each latch circuit Ln is connected.
13 and the PMOS 11 and N to which the control signal EN is connected
The MOS 14 is connected like a NOR circuit. In other words, it is NOR except that the source side of the NMOS 14 of each gate circuit Gn is connected to the reference potential (GND) via the common transistor GT made of NMOS.
Type gate circuit configuration. In this respect, the drive device 100 of FIG. 1 is different from the conventional drive device 200 of FIG.

Each of the MOS transistors 11 to 14 has a size having a driving capability similar to or larger than that of a transistor forming another logic circuit, for example, channel width (W) / channel length (L) = 4 μm / 2 μm ( (Hereinafter abbreviated as "W / L"), but the common transistor GT
Has a very small driving capability (high on-resistance of output) (W / L = 4 μm / 190 μm).

The signal line from the clock input terminal CK is connected to the clock input C of each latch circuit Ln, and the signal line from the data input terminal SI is connected to the latch circuit Ln.
1 is connected to the data input D of the latch circuit Lm (1 ≦ m
The data output Q of a natural number of ≦ n) is the latch circuit L of the next stage.
The gate circuit Gm is connected to the data input D of (m + 1) and is also connected to one input of each gate circuit Gm.
Is connected to the gate input of each output transistor Tm, the source of each output transistor Tm is connected to the reference potential, and its drain is connected to each output terminal DOm. A signal from the control input terminal EN is input to the other input of each gate circuit Gm and the gate of the common transistor GT.

With this configuration, in normal operation,
After storing the serial data SI in each latch circuit in synchronization with the clock signal CK, each gate circuit Gn turns on the output transistor Tn according to the output data of each latch circuit Ln based on the signal from the control input terminal EN. By doing so, the current is passed only through the resistor Rn corresponding to the serial data SI to generate heat.

Next, when all the output transistors are made non-conductive (OFF state = high impedance output) all together based on the control signal from the control input terminal EN, the output ON resistance of each gate circuit Gn is common. Since the on-resistance of the transistor GT is included, the output on-resistance greatly increases, and the time constant with each parasitic capacitance (C1 to Cn) increases. Therefore, as shown in FIG. 2 showing the waveforms of the control signal EN, the Q output of each latch circuit Ln, and each part of each output DOn, the waveform of each output DOn is a waveform when the output changes based on the serial data (dotted line). Compared with, the voltage rises significantly more slowly, and the maximum value of the rising voltage becomes low. Specifically, the common transistor GT has W / L = 4 μm / 190
Since it has a size of about μm, it has an on-resistance of several MΩ, and the value of each parasitic capacitance Cn is several tens of pF to several hundreds.
Even with a small pF, the time constant becomes a relatively large time constant, and a sufficient delay time td can be obtained.

Further, as described above, the common transistor G
Size of each transistor for logic other than T (W /
If L) is the same as the size of the transistor used in another logic circuit, the size of the large number of gate circuits Gn hardly increases, and the area can be increased by the amount of the common transistor GT. The chip size will be almost unchanged. On the contrary, if it is acceptable to increase the chip size, an NMOS corresponding to the driving capability of the common transistor GT is used as N in each gate circuit Gn.
A NOR circuit configuration integrated with the MOS 14 may be used. In other words, the NMOS 14 having a size of W / L = 4 μm / 190 μm and a source connected to the reference potential
Are required for the number of gate circuits, and the size of each gate circuit Gn is significantly increased, resulting in an increase in the chip size of the driving device 100. Further, in the case of this configuration, variations in the on-resistance value of each NMOS 14 and each parasitic capacitance Cn
The above-mentioned embodiment is more preferable because the above-mentioned variation in time constant (delay time) also increases.

The above is an NMOS as an output transistor.
Although only the case where a transistor is used is shown, even when a PMOS transistor or a bipolar transistor is used as an output transistor, only the driving capability of the transistor that operates based on the control signal in the gate circuit that similarly drives the output transistor is reduced. Then, the same effect can be obtained. Although only one driving device 100 has been described in the present description, the driving circuit of the printer is actually configured using a large number of driving devices 100. In addition, circuits other than the illustrated circuits may be included in the driving device 100, or serial data may be sent to each latch circuit Ln at once using a shift register. In this case, not only the signal from the control input terminal EN but also the serial data may be turned off all at once. In this case, the effect of the common transistor GT cannot be obtained. In the program, it is necessary to limit the number of serial data to be changed at one time to a certain number or less. Further, in the present description, only the case of the driving device of the thermal printer has been described, but it can be used as a driving device of an inkjet printer, a bubble jet (registered trademark) printer, or the like.

[0018]

As described above, according to the present invention, in the printer driving device according to the first aspect, when a large number of output states change all at once by a signal from the control signal input terminal EN, Since the output change of each output transistor becomes gradual, the voltage change of the power supply E1 becomes gradual, and the rise of the voltage value becomes small, so that there is an effect that the drive device is not deteriorated or damaged and the characteristics are stable. Further, the printer driving device according to claim 2 is
Since the MOS transistor that operates based on the control signal is provided in common to the plurality of gate circuits, the above-mentioned effects are hardly delayed in the chip size and variation in the resistance value and the parasitic capacitance is suppressed. There is an effect that the time variation can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention,

FIG. 2 is an explanatory diagram showing operation timing,

FIG. 3 is a circuit diagram showing a conventional thermal printhead.

[Explanation of symbols]

Gn: Gate circuit Ln: Latch circuit Tn: Output transistor GT: Common transistor Bn: Drive circuit (dot unit) SI: Serial data input CK: Clock input EN: Control input 100: Driving device (semiconductor integrated device) Rn: dot forming element (heating element) E1: Power source (for heating element)

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Claims (2)

[Claims] 1. A drive device of a printer for printing a character or an image composed of a plurality of dots based on a control signal and data from a control device, wherein the drive device of the printer comprises a plurality of latches for storing the data. Circuit, a plurality of gate circuits that respectively output the outputs of the plurality of latch circuits based on the control signal, and a plurality of output transistors that respectively drive the plurality of dot forming elements according to the outputs from the gate circuits. The plurality of gate circuits has a driving capability of a MOS transistor that operates based on the control signal among the MOS transistors that form the gate circuit, and a driving capability of a MOS transistor that operates based on the data. A driving device for a printer, which is also small. 2. A MOS that operates based on the control signal.
The driving device for a printer according to claim 1, wherein the transistor includes a common transistor having a small driving capability, which is commonly provided to the plurality of gate circuits.