JPH0466707B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a thermal head in which a plurality of heating elements and their driving circuits are mounted on the same substrate.

[Technical Background of the Invention and Problems Therewith] A thermal head is a recording device in a thermal recording type or thermal transfer type line printer that has recently become widely used in facsimile machines, various data terminal devices, and the like. A direct drive type is known as one type of thermal head.
This combines a driving element that individually drives a heating element consisting of a plurality of resistors as a recording element, and a signal distribution circuit that distributes image signals to be recorded from the outside to these driving elements on a single substrate together with the heating element. It is placed above.

However, in this direct drive type thermal head, all heating elements are driven at the same time, so there is a risk that the induced noise generated by switching large currents by the driving elements may affect the signal distribution circuit made up of logic circuits. be.
This type of recording method is becoming more dense and faster, and the induced noise itself also tends to increase accordingly, which poses a big problem in terms of the stability of the recording operation. In addition, when a CMOS-IC, which has advantages over bipolar types in terms of power consumption, transfer speed, and chip area, is used in the signal distribution circuit, the effect is significant due to the high input impedance, and there is a risk of malfunction. is high.

[Object of the Invention] An object of the present invention is to provide a thermal head that can effectively reduce the influence of noise generated by the switching operation of a driving element.

[Summary of the Invention] That is, the present invention includes a plurality of heating elements arranged in a line, driving elements that individually drive these heating elements, and image signals input from the outside to these driving elements. In a direct drive type thermal head in which a signal distribution circuit that operates these drive elements is arranged on the same board, the drive element is connected between the wiring pattern connected to the signal distribution circuit and the power supply wiring of the drive element. It is characterized in that a conductor pattern is provided to shield noise generated by switching, and a resistor is further inserted in the middle of the conductor pattern.

[Effects of the Invention] According to the present invention, the induced noise generated by switching a large current by the drive element is shielded from the wiring of the signal distribution circuit by the noise shielding conductor pattern, and is prevented from entering the signal distribution circuit. There isn't. Therefore, even if this noise is large and the signal distribution circuit is composed of a CMOS-IC or the like that is susceptible to noise, no malfunction will occur and stable recording operation can be achieved. Also,
By inserting a resistor in the middle of the noise-shielding conductor pattern, noise power is consumed by the resistor and noise is no longer re-radiated from the noise-shielding conductor pattern, making noise shielding more effective. be able to.

[Embodiment of the Invention] FIG. 1 shows a circuit configuration of a thermal head according to an embodiment of the invention. In the figure, 1 is a thermal head, which includes a plurality of heating elements 2 arranged in a line, drive elements 3 individually connected to these heating elements 2, and an external circuit 5.
A signal distribution circuit 4 comprising a shift register, a latch circuit, a gate circuit, etc., which transfers an image signal serially supplied together with various control signals from and distributes it to each drive element 3 in parallel.
are arranged on a single substrate such as a ceramic substrate.

The driving element 3 is selectively turned on in accordance with the image signal supplied from the signal distribution circuit 4, and supplies current from the external power supply 6 to the corresponding heating element 2. Due to this energization, the heating element 2 generates heat according to the image signal,
A visible image is recorded in the form of thermal transfer by causing color development on thermal paper that moves in opposition to this, or by melting the ink on the ink ribbon.

Here, assuming that the thermal head 1 has a width of 216 mm with a resolution of 16 lines/mm, and that the heating elements 2 are driven by shifting half the phase, the resistance value of the heating elements 2 is 400Ω, and the applied voltage is 15V. At this time, a large current of up to approximately 65A flows. If the noise generated by switching the six currents is left unchecked, it will cause large power ringing due to stray capacitance and inductance and crosstalk to the wiring of the signal distribution circuit 4, leading to malfunction of the signal distribution circuit 4 consisting of a logic circuit. . Therefore, in the present invention, such a problem is solved by providing a noise shielding conductor pattern as described below.

FIG. 2 is a plan view showing the mounting structure of the thermal head of FIG. 1. In the figure, 11 is a ceramic substrate, and each part of the thermal head 1 shown in FIG. 1 is formed on this substrate 1 by thin film etching technology used in semiconductor manufacturing processes or thick film printing technology used in printing. Ru.

That is, 12 is a heating element array, each one end of which is commonly connected to the hot side wiring 14 of the power supply record of the drive element 3 (hereinafter referred to as drive power supply wiring) via an individual wiring 13, and each The other end is connected via individual wiring 15 to an IC chip 16 incorporating several drive elements 3 and several signal distribution circuits 4. Terminals 17 of IC chip 16 are connected to column wiring 19 by bonding wires 18. The column wiring 19 is formed under the interlayer insulating film 20 as a lower layer wiring of the two-layer wiring.

On the interlayer insulating film 20, image signal input lines 21, transfer clock input lines 22, latch pulse input lines 23, gate signal input lines 24 and
A hot-side wiring 25 and a ground-side wiring 26 are formed as logic power wiring for supplying power to the logic circuit section (signal distribution circuit 4) in the IC chip 16, and a through hole 28 connects the lower layer vertical wiring 19. are connected to each other. Further, on the interlayer insulating film 20, a ground side wiring 27 of the drive power supply wiring is formed adjacent to the ground side wiring 26 of the logic power supply wiring, and is also connected to the lower layer column wiring 19 via a through hole 28. There is.

Here, noise generated by switching of the drive element 3 usually appears on the hot side wiring 14 and the ground side wiring 27 of the driving power supply wiring, and these wirings 14 and 27 become secondary noise sources. In this case, since the hot side wiring 14 is located away from the logic wiring, the noise appearing on this wiring 14 has relatively little influence on the signal distribution circuit 4, but the ground side wiring 27 is separated from the logic wiring. Because they are close to each other, noise appearing on this wiring 27 due to coupling with logic wiring tends to enter the signal distribution circuit 4. Therefore, in this embodiment, a noise shielding conductor pattern 29 is formed between the ground side wiring 27 of the drive power supply wiring and the ground side wiring 26 of the logic power supply wiring.

Ground side wiring 2 in the power supply wiring of the drive element 4
In general, inductive coupling is predominant in the coupling between 7 and the logic wiring. Therefore, it is preferable that the noise-shielding conductor pattern 29 is electrically floating with both ends open as shown in the figure. in this case,
When the number of noise shielding conductor patterns 29 is an odd number (one in the figure), the directions of the noise current flowing through this conductor pattern 29 and the noise current flowing through the ground wiring 27 are opposite, and the electric fields due to the noise currents flowing through each cancel each other out. Therefore, the noise shielding effect can be further improved. Furthermore, a resistor R is inserted in the middle of the noise shielding conductor pattern 29 as shown in FIG. 4, which will be described later. As a result, the noise power induced in the noise shielding conductor pattern 29 is consumed as heat by the resistor and is not re-radiated. Therefore, noise can be more effectively shielded by inserting the resistor.

FIG. 3 is a waveform diagram showing experimental results for explaining the effects of this embodiment, in which a is the current waveform on the ground side wiring 27 of the drive power supply when the drive element 4 is off, and b is the current waveform on the noise shielding conductor. The voltage waveform of the induced noise to other adjacent wiring (for example, the ground side wiring 26 of the logic power supply wiring) when the pattern 29 is not present, and c is the noise shielding conductor pattern 29.
This is a voltage waveform of induced noise to the wiring 26 in the case where there is. As is clear from this figure, by providing the noise shielding conductor pattern 29, the induction of noise into the logic wiring is effectively suppressed.
It will be understood that the introduction of noise into the signal distribution circuit 4 can be significantly reduced.

As described above, according to the present invention, by simply forming a simple noise shielding conductor pattern, noise caused by large current switching in a direct drive type thermal head can be prevented from entering the signal distribution circuit. It is possible to stabilize the recording operation.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a thermal head according to an embodiment of the present invention, FIG. 2 is a plan view showing its mounting structure, and FIG. 3 is a waveform diagram for explaining the noise shielding effect of the embodiment. FIG. 4 is a diagram showing the configuration of main parts of the same embodiment. 1...Thermal head, 2...Heating element, 3...
...Drive element, 4...Signal distribution circuit, 5...External circuit, 6...External power supply, 11...Substrate, 12...Heating element array, 13...Individual wiring, 14...Hot side of drive power supply wiring Wiring, 15...Individual wiring, 16...
... IC chip, 19 ... Column wiring, 20 ... Interlayer insulating film, 21 ... Image signal input line, 22 ... Transfer clock input line, 23 ... Latch pulse input line,
24... Gate signal input line, 25, 26... Hot side wiring and ground side wiring of logic power supply wiring, 27... Earth side wiring of drive power supply wiring, 28
...Through hole, 29...Conductor pattern for noise shielding.

Claims (1)

[Claims] A plurality of heating elements arranged in one line, driving elements that individually drive these heating elements, and image signals input from the outside to these driving elements are distributed to drive these heating elements. In a thermal head in which a signal distribution circuit for operating a drive element is disposed on the same substrate, a problem occurs between the wiring pattern connected to the signal distribution circuit and the power supply wiring of the drive element due to switching of the drive element. 1. A thermal head comprising a conductor pattern for shielding noise, and a resistor inserted in the middle of the conductor pattern. 2. The noise shielding conductor pattern according to claim 1, wherein the noise shielding conductor pattern is connected between the ground side wiring of the power supply wiring of the driving element and the wiring pattern connected to the signal distribution circuit. thermal head. 3. The thermal head according to claim 1 or 2, wherein the noise shielding conductor pattern is in an electrically floating state. 4. The thermal head according to claim 1, wherein at least one end of the noise shielding conductor pattern is grounded directly or via impedance.