JP2013038458A - Amplifier circuit, head drive circuit, and liquid injection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve power saving for power amplification.SOLUTION: The amplifier circuit, amplifying an input signal into an amplification signal, includes: a pulse density modulation section that outputs a density modulation pulse with a density modulated correspondingly to a difference between the input signal and the amplification signal; a delay circuit that delays an output of the pulse density modulation pulse correspondingly to the difference; a power supply section that supplies electric power for the amplification; and a switch section that switches a switch for power supply from the power supply section to output the amplification signal, correspondingly to the pulse output from the delay circuit.

Description

  The present invention relates to an amplifier circuit, a head drive circuit, and a liquid ejecting apparatus that realize power saving.

As a method of power amplification in accordance with an input signal, a method of amplifying by push-pull connection of bipolar transistors is known. Since the bipolar transistor generally consumes a large amount of power, a method of amplifying power using a class D amplifier has been considered in recent years.
Patent Document 1 discloses a method of power amplification using a class D amplifier.

JP 2010-114711 A

  In a class D amplifier that employs pulse density modulation, when the switching device is in an ideal state, the power consumed by the switching device is zero. However, there is a problem that power is consumed in an actual switching device, and power consumption increases as the switching frequency increases.

  The present invention has been made in view of such circumstances, and an object thereof is to save power when performing power amplification.

The main invention for achieving the above object is:
An amplifier circuit for amplifying an input signal into an amplified signal,
A pulse density modulation unit that outputs a density modulation pulse that is density-modulated according to a difference between the input signal and the amplified signal;
A delay circuit for delaying the output of the density modulation pulse in accordance with the input signal;
A power supply for supplying power for the amplification;
In accordance with the pulse output from the delay circuit, a switch unit that switches the power supply switch from the power supply unit and outputs the amplified signal;
Is an amplifier circuit.
Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a perspective view of an inkjet printer 1 in the present embodiment. It is an internal side view of the inkjet printer 1 in this embodiment. It is a figure explaining the structure of head HD. It is explanatory drawing of the amplifier circuit in this embodiment. It is explanatory drawing of pulse density modulation. It is explanatory drawing of the self-excitation transmission frequency of the amplifier circuit 100 when changing the delay time in the delay circuit 112. FIG. It is explanatory drawing of a drive waveform when delay time td is 20 ns. It is explanatory drawing of a drive waveform when delay time td is 40 ns. It is explanatory drawing of changing the self-excited transmission frequency f according to the input signal VDAC. It is explanatory drawing of the amplified signal improved in this embodiment.

At least the following matters will become clear from the description of the present specification and the accompanying drawings. That is,
An amplifier circuit for amplifying an input signal into an amplified signal,
A pulse density modulation unit that outputs a density modulation pulse that is density-modulated according to a difference between the input signal and the amplified signal;
A delay circuit for delaying the output of the density modulation pulse in accordance with the input signal;
A power supply for supplying power for the amplification;
In accordance with the pulse output from the delay circuit, a switch unit that switches on / off of power supply from the power supply unit and outputs the amplified signal;
Is an amplifier circuit.
By doing so, for example, in the case of an input signal corresponding to the vicinity of 50% duty having a high average frequency in pulse density modulation, the delay time can be increased, and the self-excited transmission frequency can be reduced. And a switching frequency can be lowered | hung and the power consumption in a switch part can be restrained low. That is, power saving can be achieved.

In this amplifier circuit, it is desirable that the delay circuit has a delay time at the intermediate voltage of the input signal larger than a delay time at the highest voltage of the input signal and a delay time at the lowest voltage of the input signal.
By doing so, self-excitation in pulse density modulation can suppress the frequency in the vicinity of the intermediate voltage where the new frequency tends to be high, thereby reducing the power consumption in the switch unit.

The switch unit preferably includes a MOSFET and a gate driver for driving the MOSFET.
By doing so, it is possible to drive the switch unit according to the output density modulation pulse and output an amplified signal.

Further, it is desirable that a low-pass filter is provided at the output of the switch unit, and the amplified signal is output from the low-pass filter.
In this way, only necessary components of the amplified signal can be output as the amplified signal.

Furthermore, it is desirable that the delay circuit delays the output of the density modulation pulse according to the difference.
In this way, for example, when there is no steep waveform change in the input signal, the self-excited transmission frequency can be lowered by increasing the delay time. On the other hand, when there is a steep waveform change in the input signal, the self-excited oscillation frequency can be increased by reducing the delay time. As a result, when there is a steep waveform change, the self-excited oscillation frequency can be kept high to ensure followability to the input signal. The power consumption in can be reduced. That is, it is possible to save power while improving the accuracy of the amplified waveform.

The delay circuit delays the output of the density modulation pulse by a first delay amount when the difference is the first difference, and the density modulation pulse when the difference is a second difference larger than the first difference. It is desirable to delay the output of the second delay amount smaller than the first delay amount.
By doing so, the difference becomes large when there is a steep waveform change in the input signal, so the self-excited oscillation frequency can be increased by reducing the delay time, while there is no steep waveform change. Sometimes the delay time can be increased to keep the self-excited oscillation frequency low.

In addition, at least the following matters will become clear from the description of the present specification and the accompanying drawings. That is,
A head drive circuit that amplifies an input signal into an amplified signal and drives a head that ejects liquid according to the amplified signal,
A pulse density modulation unit that outputs a density modulation pulse that is density-modulated according to a difference between the input signal and the amplified signal;
A delay circuit for delaying the output of the density modulation pulse in accordance with the input signal;
A power supply for supplying power for the amplification;
In accordance with the pulse output from the delay circuit, a switch unit that switches the power supply switch from the power supply unit and outputs the amplified signal;
A driving element that is driven in response to the amplified signal and ejects the liquid;
It is a head drive circuit provided with.
By doing so, for example, in the case of an input signal corresponding to the vicinity of 50% duty having a high average frequency in pulse density modulation, the delay time can be increased, and the self-excited transmission frequency can be reduced. And a switching frequency can be lowered | hung and the power consumption in a switch part can be restrained low. That is, power saving can be achieved.

In addition, at least the following matters will become clear from the description of the present specification and the accompanying drawings. That is,
A liquid ejecting apparatus that amplifies an input signal into an amplified signal, drives a head that ejects liquid according to the amplified signal, and ejects the liquid onto a medium,
A pulse density modulation unit that outputs a density modulation pulse that is density-modulated according to a difference between the input signal and the amplified signal;
A delay circuit for delaying the output of the density modulation pulse in accordance with the input signal;
A power supply for supplying power for the amplification;
In accordance with the pulse output from the delay circuit, a switch unit that switches the power supply switch from the power supply unit and outputs the amplified signal;
A head having a drive element driven in response to the amplified signal and a nozzle for ejecting the liquid;
A liquid ejecting apparatus.
By doing so, for example, in the case of an input signal corresponding to the vicinity of 50% duty having a high average frequency in pulse density modulation, the delay time can be increased, and the self-excited transmission frequency can be reduced. And a switching frequency can be lowered | hung and the power consumption in a switch part can be restrained low. That is, power saving can be achieved.

=== Embodiment ===
FIG. 1 is a perspective view of an ink jet printer 1 in the present embodiment. FIG. 2 is an internal side view of the inkjet printer 1 in the present embodiment. The ink jet printer 1 includes a recording unit 40 whose longitudinal direction is horizontally arranged.

  The recording unit 40 has its internal mechanism covered with a top cover 42 and a front cover 44. Inside the recording unit 40, a head unit HD including a head HD is arranged, and ink is ejected onto the medium drawn from the roll R of the loading unit 10 and fed to the recording unit 40, thereby forming an image. Is done. The medium on which the image is formed in the recording unit 40 is discharged to the outside from a discharge unit 60 formed below the recording unit 40.

  FIG. 3 is a diagram illustrating the structure of the head HD. In the figure, a nozzle Nz, a piezo element PZT, an ink supply path 402, a nozzle communication path 404, and an elastic plate 406 are shown.

  Ink is supplied to the ink supply path 402 from an ink tank (not shown). These inks and the like are supplied to the nozzle communication path 404. A drive signal described later (corresponding to an amplified signal of the input signal VDAC described later) is applied to the piezo element PZT. When a drive signal is applied, the piezo element PZT expands and contracts in accordance with the voltage, causing the elastic plate 406 to vibrate. An amount of ink droplets corresponding to the amplitude of the drive pulse is ejected from the nozzle Nz.

Incidentally, the total number of piezo elements PZT is several thousand. The drive signal is generated by amplifying the input signal. It is conceivable to use a bipolar transistor for power amplification, but in that case, the power loss is large and the efficiency is only about 30% to 40%. Therefore, 60 to 70% is consumed as heat. If it does so, a heat sink and a fan will be needed for heat dissipation, and it will enlarge and cost will also increase. Therefore, power saving of the amplifier circuit is desired. Particularly, in a large-sized ink jet printer as shown in FIG. 1 and FIG. 2, there are many piezo elements to be driven, and thus further power saving is required.
In the present embodiment, power saving is achieved by using the following amplifier circuit.

  FIG. 4 is an explanatory diagram of an amplifier circuit according to this embodiment. In the figure, an amplifier circuit 100 and a head unit HDU are shown. The amplifier circuit 100 according to the present embodiment reduces power consumption by introducing a delay circuit 112 described later while using the operation of the class D amplifier. In the class D amplifier used in this embodiment, a modulation frequency of 4 to 5 MHz is used.

  The amplifier circuit 100 includes a voltage comparator 110, a first branch point 111, a delay circuit 112, a gate driver 114, two power MOSFETs 116A and 116B, a second branch point 117, a low-pass filter LPF, and an attenuator 118. And a third branch point 119 and an adder 120.

  The digital-analog converted voltage signal is input to the amplifier circuit 100 as the input signal VDAC. The terminal of the input signal VDAC is branched into two systems at the third branch point 119, one connected to the delay circuit 112 and the other connected to the adder 120.

  The output terminal of the attenuator 118 is connected to the adder 120. Then, the adder 120 outputs a signal obtained by subtracting the input signal VDAC from the output signal from the attenuator 118. The output terminal of the adder 120 is connected to the first branch point 111.

  The first branch point 111 is branched into two systems, one connected to the voltage comparator 110 and the other connected to the delay circuit 112. The output terminal of the voltage comparator 110 is also connected to the delay circuit 112. The function of the voltage comparator 110 and the function 112 of the delay circuit will be described later.

  The output terminal of the delay circuit 112 is connected to the gate driver 114. Two power MOSFETs 116 </ b> A and 116 </ b> B are connected to the output terminal of the gate driver 114. The power MOSFET 116A is connected to a power supply PW and supplied with power used for power amplification. The gate driver 114 turns on one of the power MOSFETs 116A and 116B according to the output of the delay circuit 112.

  The output end 115 of the power MOSFET is connected to the low pass filter LPF. The low pass filter LPF includes an inductance L1 and a capacitance C1. One end of the inductance L1 and one end of the capacitance C1 are connected via a second branch point 117. The other end of the inductance L1 is connected to the output end 115 of the power MOSFET. The other end of the capacitance C1 is connected to ground. At the second branch point 117, the connection line is branched, one is connected to the head unit HDU, and the other is connected to the attenuator 118. The output terminal of the attenuator 118 is connected to the adder 120 as described above.

  The head unit HDU includes a flexible cable FC and a head HD. The flexible cable FC includes a parasitic inductance L2 and a resistor R2. An amplified signal from the amplifier circuit 100 is input to the head HD via the flexible cable. The head HD includes a resistor R3 and a piezo element PZT that is driven to eject ink.

  Next, the operation of each unit will be described. The adder 120 has a function of subtracting the signal of the input signal VDAC from the signal output from the attenuator 118 and outputting an error signal. The voltage comparator 110 compares the input voltage with a reference voltage (for example, DC 1.5V), and outputs a pulse voltage corresponding to the comparison result. The reference voltage is omitted in this figure.

  The delay circuit 112 delays the density modulation pulse according to the error signal input from the first branch point 111. The delay circuit 112 delays the density modulation pulse according to the input signal VDAC.

  The gate driver 114 drives the power MOSFETs 116A and 116B according to the delayed density modulation pulse. These power MOSFETs are supplied with a power supply voltage of 42 V from a power supply PW, and output an amplified signal corresponding to the density modulation pulse to the output terminal 115 by switching.

  The low pass filter LPF cuts the high frequency component of the amplified signal at the output end 115 (the high frequency component is discarded through the capacitor C1), and outputs a smooth amplified signal. The smooth amplified signal (driving signal) passes through the flexible cable FC and is applied to the piezo element PZT of the head HD.

  The attenuator 118 attenuates the voltage of the input amplified signal. The amplified signal is attenuated in order to adjust the voltage level to the voltage of the input signal VDAC. In this manner, the amplified signal is fed back to the adder 120, so that the amplifier circuit 100 oscillates by itself.

  FIG. 5 is an explanatory diagram of pulse density modulation. In the figure, a trapezoidal wave as an input signal is shown as a duty, and below that, a “sawtooth wave” used for modulation is shown, and further below that, pulses in pulse density modulation are shown. Yes. The horizontal axis is the time axis. Here, the pulse density modulation will be described with reference to FIG.

  In the illustrated trapezoidal wave, an intermediate voltage (that is, a duty of 50%) is input from time 0 and is kept flat. Thereafter, the duty increases to 90% and remains flat, and then the duty decreases to 6% and remains flat again. Then, it rises again to 50%, which is the duty of the intermediate voltage, and keeps flat.

  In pulse density modulation, the pulse frequency is highest when the duty is 50%. Therefore, when the duty is 50%, the sawtooth waves are also arranged with high density. Thereafter, when the duty increases, the average frequency of the pulse itself decreases, and the density of the sawtooth wave also decreases. On the other hand, the average time that the pulse is on is longer.

  Next, in the process of decreasing the duty from 90% to 50%, the density of the sawtooth wave gradually increases again, and in the process of decreasing the duty from 50% to 6%, the density of the sawtooth wave gradually decreases. . On the other hand, when the duty is reduced from 90% to 6%, the average time during which the pulse is on is shortened.

  Again, when the duty increases from 6% to 50%, the density of the sawtooth wave increases. The average time during which the pulse is on is 50%.

  As described above, when pulse density modulation is performed, the frequency of the pulse is reduced when the duty is high (for example, 90%) and when the duty is low (for example, 6%). On the other hand, the pulse frequency when the duty is close to 50% increases.

  FIG. 6 is an explanatory diagram of the self-excited transmission frequency of the amplifier circuit 100 when the delay time in the delay circuit 112 is changed. In the amplifier circuit of this embodiment shown in FIG. 4, the delay time is changed according to the signal (error signal, input signal VDAC) input to the delay circuit 112, but here the delay time is temporarily set to a predetermined delay time. A description will be given of what the self-excited oscillation frequency of the amplifier circuit 100 will be when fixed.

  In the figure, the horizontal axis represents the amplified voltage value VAMP in the amplifier circuit 100, and the vertical axis represents the self-excited transmission frequency f. Here, the self-excited transmission frequency when the delay time td is 10 ns, 20 ns, and 30 ns is shown. The minimum voltage of the amplified voltage value VAMP is 0V, and the maximum voltage is 42V.

  As a result, it can be said that the self-excited oscillation frequency is low when the amplified voltage value VAMP is the lowest voltage and the highest voltage, while the self-excited oscillation frequency is highest when the amplified voltage value VAMP is the intermediate voltage (21 V). It is a point. This is because the pulse density modulation is performed as already described, and is caused by the maximum when the average frequency of the pulse is 50%.

  As can be seen from FIG. 6, the self-oscillation frequency f increases as the delay time decreases, and the self-oscillation frequency decreases as the delay time td increases. In the power MOSFET described above, the switching operation is performed at a frequency related to the self-excited oscillation frequency.

In the MOSFET in the ideal state, the loss associated with switching is zero. However, in reality, there is a gate drive loss and a drain loss, so it does not become zero. The former is a power loss required for charging / discharging the FET gate parasitic capacitance, and the latter is a power loss due to an on-resistance (R _{DS (ON)} ) when the FET is on. In both cases, the amount of power loss is proportional to the switching frequency. Therefore, power consumption in MOSET increases as the switching frequency increases. And if the power consumption becomes too large, the advantage of power saving by adopting the MOSFET is impaired. In particular, when the amplified voltage value VAMP is in the vicinity of the intermediate voltage, the self-excited transmission frequency increases, so that the power consumption increases significantly.

  On the other hand, if the self-excited transmission frequency is lowered by increasing the delay time td, the power consumption due to the switching operation is reduced, but the number of feedbacks per unit time is reduced, so the followability of the amplified signal to the input signal VDAC is deteriorated. There is a problem of doing. In particular, as shown in FIG. 6, when the amplified voltage value VAMP is around the lowest voltage or around the highest voltage, the self-excited transmission frequency is lowered, and the follow-up deterioration becomes more remarkable.

  FIG. 7 is an explanatory diagram of the amplified signal when the delay time td is 20 ns. In this figure, the horizontal axis is the time axis, and the vertical axis is the voltage. Further, in the figure, a broken line waveform is shown as a waveform when the input signal is accurately amplified, and a simulation result of the amplified signal when the delay time td is 20 ns is shown by a solid line.

  As shown in the figure, the solid line almost overlaps the broken line, and it can be seen that the amplified signal appropriately follows the input signal. In particular, the ability to follow in the vicinity of 21 V, which is a high frequency, is high. However, since the self-excited transmission frequency is high as described above, power consumption is high.

  FIG. 8 is an explanatory diagram of the amplified signal when the delay time td is 40 ns. Also in this figure, a horizontal axis is a time axis and a vertical axis | shaft is a voltage. As shown in the figure, the degree of overlap between the solid line and the broken line is clearly worse as compared with the above-described FIG. In particular, it can be seen that in the portion close to the maximum voltage and the portion close to the minimum voltage, the width that swings up and down the solid line (amplified signal) has become unacceptable. This is presumably because the self-oscillation frequency is too low because the delay time td is too large, and as a result, the followability to the input signal deteriorates and the waveform becomes rough. On the other hand, since the self-excited oscillation frequency is lowered, the power consumed in the power MOSFET is reduced, and power saving is achieved.

<Adjust delay time according to error signal>
In this embodiment, in order to improve the followability of the amplified signal with respect to the input signal, the delay time td in the delay circuit 112 is flexibly changed according to an error (error signal) generated between the input signal and the amplified signal. It is carried out.

  Specifically, when the error generated between the input signal and the amplified signal is large (when the error signal at the first branch point 111 in FIG. 4 is large), the self-excited transmission is made to follow the input signal more quickly. It is preferable to increase the frequency. Therefore, the delay circuit 112 sets the delay time td small when the value of the error signal is large. On the other hand, the delay circuit 112 is set to increase the delay time td when the value of the error signal is small.

  By doing this, when the value of the input signal changes suddenly, the delay time td is reduced to increase the self-excited transmission frequency to improve the follow-up property, while when the change of the input signal value is small, the delay time td is set. The self-excited transmission frequency can be reduced by increasing the power to save power.

  In particular, in an ink jet printer that ejects ink by driving a piezo element, ink is ejected when the voltage changes rapidly, and the error that occurs between the input signal and the amplified signal tends to be the largest. It is a place. When ejecting ink, the shape of the amplified signal is important, and if the followability of the amplified signal with respect to the input signal is low, the size of the ejected ink may differ from the desired size, or the ejection timing may shift. Is produced. On the other hand, by performing the operation as in the present embodiment, it is possible to improve the followability of the input signal while saving power.

<Adjust delay time according to input signal VDAC>
FIG. 9 is an explanatory diagram of changing the self-excited transmission frequency f in accordance with the input signal VDAC. As described above, in pulse density modulation, since the transmission frequency is high near the intermediate voltage of the amplified voltage (or input voltage VDAC), power consumption in switching is high.

  In this embodiment, as shown in FIG. 9, the self-excited oscillation frequency is intentionally lowered as the input voltage VDAC approaches the intermediate voltage. Specifically, as the input voltage VDAC approaches the intermediate voltage, the delay time td of the delay circuit 112 is increased to reduce the self-excited transmission frequency. By doing so, the power consumption in the switching element can be reduced as a result without increasing the self-excited oscillation frequency more than required near the intermediate voltage.

  FIG. 10 is an explanatory diagram of an amplified signal improved in the present embodiment. In this figure, the horizontal axis is the time axis, and the vertical axis is the voltage. Also, in the figure, the amplified signal is displayed divided into the section A to the section I with respect to the time axis.

  In the section A, the section C, the section E, and the section G, as a result of the above operation, followability is appropriately secured. In the section B and the section H, the followability is good even though the voltage is far from the intermediate voltage.

  In the section D and the section F, the followability is not so much needed (high followability is required at a portion where the voltage change is large from the viewpoint of ink ejection). For this reason, as a result of the operation as described above, ripples are generated to some extent, but power saving is achieved accordingly.

  As described above, since power saving can be achieved while ensuring followability, there is an advantage that a heat sink can be reduced, a size can be reduced, and a cost can be reduced.

=== Other Embodiments ===
In the above-described embodiment, the liquid ejecting apparatus has been described as being applied to the ink jet printer 1. However, the present invention is not limited to this, and fluid other than ink (liquid or functional material particles are dispersed). The present invention can also be embodied in a liquid ejecting apparatus that ejects or discharges a liquid or a fluid such as a gel. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, gas vaporizer, organic EL manufacturing apparatus (especially polymer EL manufacturing apparatus), display manufacturing apparatus, film formation You may apply the technique similar to the above-mentioned embodiment to the various apparatuses which applied inkjet technology, such as an apparatus and a DNA chip manufacturing apparatus. These methods and manufacturing methods are also within the scope of application. The amplifier circuit can be used not only for the liquid ejecting apparatus but also for other apparatuses.

  The above-described embodiments are for facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof.

1 Inkjet printer,
40 recording section, 42 top cover, 44 front cover,
60 discharge section,
100 amplifier circuit, 110 voltage comparator,
111 first branch point, 112 delay circuit,
114 gate driver, 115 output end,
116A power MOSFET, 116B power MOSFET,
117 second branch point, 118 attenuator,
119 Third branch point, 120 adder,
402, ink supply path, 404 nozzle communication path, 406 elastic plate,
HD head, HDU head unit,
LPF low pass filter,
Nz nozzle,
PZT Piezo element

Claims (8)

An amplifier circuit for amplifying an input signal into an amplified signal,
A pulse density modulation unit that outputs a density modulation pulse that is density-modulated according to a difference between the input signal and the amplified signal;
A delay circuit for delaying the output of the density modulation pulse in accordance with the input signal;
A power supply for supplying power for the amplification;
In accordance with the pulse output from the delay circuit, a switch unit that switches the power supply switch from the power supply unit and outputs the amplified signal;
An amplifier circuit comprising:   2. The amplifier circuit according to claim 1, wherein the delay circuit makes a delay time at an intermediate voltage of the input signal larger than a delay time at the highest voltage of the input signal and a delay time at the lowest voltage of the input signal.   The amplifier circuit according to claim 1, wherein the switch unit includes a MOSFET and a gate driver that drives the MOSFET.   The amplification circuit according to claim 1, wherein a low-pass filter is provided at an output of the switch unit, and the amplified signal is output from the low-pass filter.   Furthermore, the said delay circuit is an amplifier circuit in any one of Claims 1-4 which delays the output of the said density modulation pulse according to the said difference. The delay circuit is
When the difference is the first difference, the output of the density modulation pulse is delayed by a first delay amount,
The amplifier circuit according to claim 5, wherein the output of the density modulation pulse is delayed by a second delay amount smaller than the first delay amount when the difference is a second difference larger than the first difference. A head drive circuit that amplifies an input signal into an amplified signal and drives a head that ejects liquid according to the amplified signal,
A pulse density modulation unit that outputs a density modulation pulse that is density-modulated according to a difference between the input signal and the amplified signal;
A delay circuit for delaying the output of the density modulation pulse in accordance with the input signal;
A power supply for supplying power for the amplification;
In accordance with the pulse output from the delay circuit, a switch unit that switches the power supply switch from the power supply unit and outputs the amplified signal;
A driving element that is driven in response to the amplified signal and ejects the liquid;
A head drive circuit comprising: A liquid ejecting apparatus that amplifies an input signal into an amplified signal, drives a head that ejects liquid according to the amplified signal, and ejects the liquid onto a medium,
A pulse density modulation unit that outputs a density modulation pulse that is density-modulated according to a difference between the input signal and the amplified signal;
A delay circuit for delaying the output of the density modulation pulse in accordance with the input signal;
A power supply for supplying power for the amplification;
In accordance with the pulse output from the delay circuit, a switch unit that switches the power supply switch from the power supply unit and outputs the amplified signal;
A head having a drive element driven in response to the amplified signal and a nozzle for ejecting the liquid;
A liquid ejecting apparatus comprising:

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