JPH0345575B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a high-voltage pulse generation circuit, and in particular generates high-wave, high-value pulses with fast rises and falls, thereby speeding up and stabilizing output pulses. The present invention relates to a high voltage pulse generation circuit that can reduce power consumption and eliminate the need for high resistance at the same time.

(Prior art) In general, device elements that apply piezoelectric elements are
It is often driven by a pulsed voltage. For example, in an ink jet printer using a piezoelectric element, the piezoelectric element is driven by applying a pulse voltage.

When driving these piezoelectric elements, a stable pulse voltage with quick rise and fall is required, and a high voltage pulse generation circuit is required to obtain high output from the piezoelectric element.

FIG. 1 shows an example of a conventionally used high voltage, high speed pulse generation circuit.

In this figure, 1 is a switching transistor, 2 and 3 are buffer transistors, 4 is a base current limiting resistor of transistor 1, 5 is a load resistor of transistor 1, 6 is an input control terminal for generating high-speed pulses, and 7 is a transistor for switching. 8 is a high-speed pulse output terminal, 8 is a power supply voltage, and 9 is a load circuit.

The figure also shows an example in which the input control terminal 6 can be controlled at the TTL level. That is, if the input control terminal 6 is currently at the "1" level, the transistor 1 is conductive and its collector becomes 0.
level. As a result, the buffer transistor 2 becomes non-conductive and the buffer transistor 3 becomes conductive, so that the pulse output terminal 7 becomes 0 level.

Here, when a "0" level signal is applied to the input control terminal 6, the transistor 1 is cut off,
That collector becomes level 1. As a result, the buffer transistors 2 and 3 become conductive and non-conductive, respectively, and a pulse voltage rising from the 0 level to the amplitude value of the power supply voltage 8 is generated at the pulse output terminal 7.

(Problems to be Solved by the Invention) The pulse voltage generation circuit according to the prior art described above has the following problems.

(1) In order to obtain high-voltage pulses, a high-voltage power supply must be used, but in this case, in order to reduce power consumption, the resistance value of the load resistor 5 of the switching transistor 1 must be increased. It is necessary to reduce the current flowing through the switching transistor. However, the load resistance 5
If the resistance value of is increased, the time constant due to the stray capacitance C and the load resistance will also be increased, and on the other hand, the rise speed of the pulse voltage is determined by the time constant, making it difficult to obtain high-speed pulses. . Therefore, it is not possible to simultaneously increase the voltage and speed of pulses and reduce power consumption.

(2) Due to the base accumulation effect of the switching transistor 1, its turn-off time varies with the variation of its collector current, that is, the power supply voltage, so in particular, the fall time of the output pulse, and therefore the output pulse width, vary. This will impede speeding up.

(3) If an attempt is made to increase the resistance value of the load resistor 5 in order to reduce power consumption, the area occupied by the load resistor will increase when a high voltage pulse generation circuit is integrated, which will hinder the improvement of the degree of integration. .

In view of the above-mentioned problems, the purpose of the present invention is to
It is possible to obtain stable output pulses at high speed, high voltage, and duration without using a particularly high value resistor for switching. An object of the present invention is to provide a high voltage pulse generation circuit that can be easily integrated.

(Means for Solving the Problems) A feature of the present invention is that a pair of first and a second current source circuit;
control means for controlling the pair of first and second current source circuits so that they operate alternately;
an output terminal connected to a connection point of the pair of first and second current source circuits, and generates a high voltage pulse determined according to a high potential difference between the first and second potential points. In the high voltage pulse generation circuit, the control means controls the operation of at least a first current source circuit connected to a first potential point of the pair of first and second current source circuits. The third current source circuit is a constant current circuit, and is connected to a first main terminal that controls the operation of the first current source circuit and a second potential point. a switch element having a second main terminal that is connected to the switch element and a control terminal that is supplied with an input signal; and means for maintaining a constant voltage between the control terminal of the switch element and the second potential point. At the point.

(Function) In the present invention, the on/off control of the first current source circuit connected to the first potential point is performed by the constant current of the constant current circuit, which is the third current source circuit.

Therefore, by setting the constant current value of the constant current circuit (third current source circuit) small, power consumption can be suppressed. In addition, in order to obtain high voltage pulses with high peak values, the power supply voltage is increased,
Even if the power supply voltage fluctuates, the current does not increase or fluctuate, so power consumption does not increase.
In addition, since the base accumulation effect of the transistors constituting the constant current circuit is held constant, the off time of the transistors in the constant current circuit is stabilized, and the output pulse width due to switching/fluctuation of the power supply voltage is stabilized. fluctuations will disappear.

Furthermore, the current limiting resistor required when the power supply voltage is increased is no longer required, and a resistor with a high resistance value is no longer required, making it easy to improve the degree of circuit integration.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing the basic configuration of a high voltage pulse generating circuit according to the present invention. In FIG. 2, 20 and 30 indicate constant current circuits as first and second current sources, and 40 and 50 indicate switching control circuits for driving the constant current circuits 20 and 30 on/off. The switching control circuit 4
0 is also composed of a constant current circuit.

The constant current circuit 20 operates when the switching control circuit 40 is conductive, and the constant current circuit 30 operates when the switching control circuit 50 conducts. 10 is an input control terminal, and the switching control circuits 40 and 50 are operated by an input control signal C supplied thereto.

11 is a logic circuit that inverts the input control signal C, and when the switching control circuit 40 is made conductive by the input control signal C, the switching control circuit 5 is inverted.
0 is opened and, conversely, when the switching control circuit 40 is opened, the switching control circuit 50 is controlled to be conductive.

Further, 12 is an output terminal for obtaining the output pulse V _p , 13 and 14 are first and second potential points, and the first power supply voltage V is used to set the high level of the output pulse V _p . _SS terminal and second power supply voltage V _DD terminal for setting the low level.

During operation, when a "1" level control signal C is applied to the input control terminal 10, the switching control circuit 40 becomes conductive and the constant current circuit 20 is driven.
At this time, since the switching control circuit 50 is in an open state, the constant current circuit 30 is in a cutoff state. Therefore, the current of the constant current circuit 20 is
When the voltage begins to flow and reaches a saturated state, the output voltage V _p of the output terminal 12 becomes approximately the power supply voltage V _SS .

On the other hand, when the control signal C at the "0" level is applied to the input control terminal 10, the switching control circuit 5
0 becomes conductive, and the constant current circuit 30 is driven. At this time, the switching control circuit 40 is in an open state, so the constant current circuit 20 is cut off. Therefore, the output voltage V _p of the output terminal 12 is reduced to a high level voltage V _SS by the drawing current of the constant current circuit 30.
to a low level voltage V _DD .

As is clear, when trying to obtain a voltage pulse whose level changes from the ground potential to the positive potential V _SS as the output voltage V _p , it is sufficient to configure the output voltage V _DD to be zero volts (ground).

Through the above-described operation, high-speed, high-voltage pulses can be generated according to the input control signal C.

When driving a piezoelectric element, the load of the high voltage pulse generation circuit becomes equivalently capacitive. Therefore, the output voltage, that is, the rising speed of the pulse signal V _p depends on the current value i of the constant current circuit 20 and the load capacitance C _p .

In other words, the rise time t (time required to rise from V _DD to V _SS ) of the output pulse signal V _p is
It is expressed by equation (1).

t=(V _SS −V _DD )·C _p /i (1) As can be seen from equation (1), the rise time t can be shortened by increasing the value of the constant current i.
That is, by increasing the constant current i,
The rise speed of the output pulse can be increased.

In the pulse generating circuit shown in FIG. 2, the period during which the constant current i flows is only the rise time t of the pulse voltage, so that an instantaneous large current can flow. For this, a faster output pulse signal
Can generate V _p .

Further, the fall time of the output pulse signal V _p is similarly determined by the current value of the constant current circuit 30, and can be easily increased in speed.

For this reason, especially in high-voltage pulse generation circuits that are connected to capacitive loads such as piezoelectric elements that drive inkjet nozzles, the circuit configuration shown in Figure 2 can achieve even higher speeds. A high voltage pulse with a sharp rise can be obtained.

FIG. 3 shows a specific circuit of the first embodiment of the present invention. In this figure, parts with the same reference numerals as those in FIG. 2 correspond to the same parts.

A pair of positive and negative current source circuits 20 and 30 connected in series between the terminal 13 of the first potential point V _SS and the second potential point (ground) generate a constant current using transistors 21 and 31. It consists of a circuit. 22, 32 are transistors 21, 3
1 is an emitter resistance, 23 and 33 are diodes used as reference voltage elements, and 24 and 34 are parallel resistances of the diodes 23 and 33.

When operating as a constant current circuit, the diode 23 (or 33)
1 (or 31) base and emitter resistor 22
A reference voltage is applied between (or 32) to generate a constant current I _S at its collector.

The constant current _IS in this case is approximately expressed by equation (2).

I _S = (2V _DS − V _BE )/R _E ......(2) In equation (2), V _DS is the diode 23
(or 33), V _BE is the base-emitter voltage of the transistor 21 (or 31), and R _E is the resistance value of the emitter resistor 22 (or 32).

A switching control circuit 40 for controlling on/off of the constant current circuit 20 is configured as a constant current circuit using a transistor 41.

In this way, when a constant current circuit is used for switching control of a constant current circuit connected to a high voltage, the second
As in the case of the constant current circuit 20 described above with reference to the figure, a load resistor with a high resistance value is not required.

Therefore, it is easy to increase the switching speed, and especially when trying to integrate the circuit, the area for forming the load resistor is not required, which improves the degree of integration. Since the power consumed is reduced, power consumption can be reduced.

In Fig. 3, 42 is the emitter resistance of the transistor 41, 43 is a diode used as a reference voltage element to keep the potential between the base and ground of the transistor 41 constant, 44 is a parallel resistance of the diode 43, and 45 is a current limiter. It is a resistance to

Now, when a "1" level is input as the input control signal C to the input control terminal 10, a current flows through the resistor 45 and into the diode 43. the result,
The forward voltage of diode 43 is applied between the base and emitter resistor 42 of transistor 41 as a constant reference voltage.

Therefore, the transistor 41 performs constant current operation,
A constant current flows through the collector-emitter circuit, that is, the switching control circuit 40. This constant current determines the base-emitter voltage V _BE of the transistor 21, and becomes a drive signal for causing a constant current to flow through the constant current circuit 20 according to equation (2).

On the other hand, the switching control circuit 50 for operating the constant current circuit 30 is composed of the switching control circuit 50 and the inverter logic circuit 1 shown in FIG.
1, a transistor 51 and a resistor 5
2 and 53.

It goes without saying that this switching control circuit 50 may be constructed from a constant current circuit like the above-described switching control circuit 40. However, since the constant current circuit 30 to be controlled by the switching control circuit 50 is grounded, that is, on the low potential side, the power supply voltage supplied via the resistor 52
A low voltage power supply (for example, +5V system) can be used for _VL .

Therefore, since the switching control circuit 50 does not originally require a high-resistance load resistor, it is desirable that the switching control circuit 50 be a voltage control circuit with a simple circuit configuration as shown in the figure.

During operation, when the input control signal C of "1" level is input to the input control terminal 10, the transistor 5
1 becomes conductive and short-circuits the reference voltage element diode 33 of the constant current circuit 30. Therefore, the constant current circuit 30 is cut off, and no constant current flows through the transistor 31.

On the other hand, when the input control signal C reaches the "0" level, the transistor 51 is cut off, so that current flows to the reference voltage element diode 33 through the resistor 52. As a result, a reference voltage is generated at the base of the transistor 31, and the transistor 31 operates as a constant current circuit.

That is, when the input control signal C is at the "1" level, the constant current circuit 20 operates, and the constant current circuit 30
doesn't work. On the other hand, input control signal C is “0”
When the current level is reached, the constant current circuit 20 becomes inactive and the constant current circuit 30 operates.

In FIG. 3, a buffer circuit 60 is for increasing the current capacity of the output pulse signal _Vp , and is composed of transistors 61 and 62. 63 and 64 are protective resistors.

According to the embodiment of FIG. 3, the transistor 21 of the first constant current circuit 20 connected to the terminal 13 to which the high voltage V _SS is applied, that is, the first potential point, is connected to the switching control circuit which is a constant current circuit. 40, the switching control circuit 40 includes a first main terminal (collector) for controlling the operation of the constant current circuit 20, and a second main terminal connected to a second potential point. 2 main terminal (emitter),
and the control terminal (base) supplied with the input signal.
a switch element (transistor) having a switch element, and a means (diode) for maintaining a constant voltage between a control terminal of the switch element and the second potential point.
Since it is equipped with this, the following effects can be achieved.

(1) Since the current between the main terminals of the switch element of the constant current circuit 40 is held constant, there is no need for a current limiting resistor, which not only reduces power consumption but also reduces the voltage applied to each resistor. Since it can be made at low voltage (about several volts), when integrating the circuit, it can be configured with only low resistance (several kilohms or less), which improves the reliability of the circuit, increases the degree of integration,
Cost reduction is achieved.

(2) Since the current between the main terminals of the switch element constituting the constant current circuit 40 is held constant, the base accumulation effect of the switch element (transistor 41) is held constant. Therefore, fluctuations in the collector current, that is, the rise and fall times of the output pulse, caused by changes in the base accumulation effect are eliminated, and high-speed pulses can be stably generated.
In particular, it is possible to obtain highly accurate pulses without fluctuations in output pulse width caused by fluctuations in fall time.

Inkjet printers using piezoelectric elements require a purge operation in which a high voltage pulse with a peak value approximately twice that of normal use is applied to the drive piezoelectric element to initialize the nozzle. It is particularly suitable for this purpose.

(3) A high-voltage pulse generation circuit with the same circuit constant (resistance value) can easily meet a wide range of pulse peak value ratings, that is, power supply voltage requirements, and together with the aforementioned high integration, the cost can be reduced due to the mass production effect. A reduction can also be expected.

(4) Even when the peak value of the output pulse voltage is varied over a wide range and output, since the switching control circuit 40 is a constant current circuit, the current flowing through the resistance of the constant current circuit remains unchanged, reducing power consumption. The increase is only proportional to the supply voltage.

In the above explanation, in FIG.
Although the second current sources 20 and 30 are both constant current circuits, if particularly high accuracy is not required, the reference voltage elements 23 and 33 may be omitted and a simple current source may be used. In this way, the circuit can be simplified. Furthermore, the protective resistors 63 and 64 of the buffer circuit 60 can also be omitted.

FIG. 4 shows another specific example of the buffer circuit 60. That is, the output pulse signal V _p
The transistor 61 is made conductive to generate a constant current at the output terminal 12 when the voltage rises, and the current is drawn out from the output terminal 12 through the diode 65 when the voltage falls.

As is clear, almost the same characteristics can be obtained even if such a simplified buffer circuit is used.
Very effective.

FIG. 5 is a block diagram of a second embodiment of the invention.

The circuit configuration shown in the figure is such that the load circuit 130 can operate in a floating state, and is particularly effective when high voltage pulses are required. suitable for application.

Block 110 in FIG. 5 is a circuit for generating a positive pulse signal, and specifically, it can be constructed according to the embodiment shown in FIG. That is, input control terminal 1
A positive pulse signal V _p1 is obtained from the output terminal 111 in response to the input control signal C applied to the output terminal 111 .

On the other hand, block 120 is a circuit that generates a negative pulse signal, and specifically, it can be constructed by reversing the polarity of each circuit element used in the embodiment shown in FIG. can.

That is, for example, in Figure 3, NPN
PNP transistors are used for parts that use transistors, and PNP transistors are used for parts that use PNP transistors.
By using each NPN transistor,
A negative pulse signal V _p2 can be generated at the output terminal 121 .

Note that 112 is a supply terminal for the power supply voltage +V _SS of the circuit 110 that generates the positive pulse signal V _p1 ;
Further, 122 is a supply terminal for the power supply voltage -V _SS of the circuit 120 that generates the negative pulse signal V _p2 .

Therefore, when the input control signal C is applied from the input control terminal 10, the output terminal 111 outputs a positive pulse signal V _p1 with a voltage value of +V _SS , and the output terminal 121 outputs a negative pulse signal with a voltage value of -V _SS . A signal V _p2 is output. Therefore, a pulse signal with a pulse amplitude of 2V _SS is applied to the load circuit 130 (for example, a piezoelectric element, etc.) connected between the pair of output terminals 111 and 121.

This circuit configuration not only doubles the output pulse voltage value, but also doubles the rise and fall speeds of the pulse signal, making it possible to obtain a pulse signal with a stable duration at high speed and high voltage. It is effective because it can be done.

In this embodiment as well, the same effects as described above with respect to FIG. 3, such as lower power consumption, easier application to a wide range of pulse voltage outputs, higher integration, and higher reliability, can be obtained. It will be easily understood.

(Effects of the Invention) As is clear from the above description, according to the present invention, not only can high-speed and high-voltage pulse signals be obtained with low power consumption, but also the integration density can be reduced when integrating. can be improved.

By setting the constant current value of the switching control circuit, which is a constant current circuit, to a small value, power consumption can be suppressed. Further, even if the power supply voltage is increased to increase the peak value of the output pulse or the power supply voltage fluctuates, the constant current of the switching control circuit does not increase or fluctuate, so power consumption does not increase.

In addition, since the base accumulation effect of the transistors constituting the constant current circuit is held constant regardless of switching/fluctuations in the power supply voltage, the off time of the transistors in the constant current circuit is stabilized, and the power supply voltage This eliminates fluctuations in the output pulse width due to switching/fluctuations. Furthermore, since a resistor with a high resistance value is not required, it is easy to further improve the degree of integration.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional pulse voltage generation circuit, FIG. 2 is a block diagram showing an example of the basic configuration of a high voltage pulse generation circuit according to the present invention, and FIG. A circuit diagram showing one embodiment,
FIG. 4 is a circuit diagram showing another specific example of the buffer circuit section of FIG. 3, and FIG. 5 is a block diagram showing a second embodiment of the present invention. 10...Input control terminal, 12...Output terminal, 2
0, 30... Constant current circuit, 40, 50... Switching control circuit, 60... Buffer circuit.

Claims (1)

[Claims] 1: a pair of first and second current source circuits connected in series between a first potential point and a second potential point having a lower potential than the first potential point; the first of the pair
and a control means for controlling the second current source circuits so that they operate alternately;
and an output terminal connected to the connection point of the second current source circuit, and generates a high voltage pulse determined according to the high potential difference between the first and second potential points. In this case, the control means includes a third current source for controlling the operation of the first current source circuit connected to at least the first potential point of the pair of first and second current source circuits. the third current source circuit is a constant current circuit,
a switch element having a first main terminal for controlling the operation of the first current source circuit, a second main terminal connected to the second potential point, and a control terminal supplied with an input signal; 1. A high voltage pulse generation circuit comprising means for maintaining a constant voltage between a control terminal of a switch element and the second potential point.