JP2006135904A - Device and method for loaded driving - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for loaded driving that reduces an output offset voltage of the whole system and make respective element sizes small. <P>SOLUTION: The loaded driving device has: an input amplifier which inputs a driving signal and a reference signal and differentially amplifies them; a triangular wave generation section; a pulse-width modulation section which modules the output signal of the input amplifier into a modulated signal; a driving output circuit based upon the pulse-width modulated signal; and a feedback amplifier which amplifies and feeds the driving output circuit signal back to the input amplifier. The device further includes: an offset adjustment signal addition section which adds an offset correction voltage and outputs the result to an input terminal of the input amplifier; an input amplifier input signal setting section for substantially holding the two driving signal and reference signal at substantially the same potential with a specified signal; and an input amplifier offset decision section which decides whether the output signal of the input amplifier is nearly zero with a specified signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a load driving device and a load driving method having an offset adjustment function for reducing an output offset voltage.

  In order to drive a focus coil, a tracking coil, and the like of an actuator for an optical pick amplifier, a load driving device having a pulse width modulation output suitable for low power consumption is used.

  A conventional load driving apparatus will be described with reference to FIGS. 14 and 15. FIG. 14 is a block diagram of a conventional load driving apparatus. In FIG. 14, the conventional load driving apparatus includes a load driving circuit 100. The load driving circuit 100 includes an input amplifier 3, an absolute value circuit 4, a pulse width modulation unit 5, a polarity determination unit 6, a triangular wave generation unit 7, a drive output circuit 8, a feedback amplifier 10, a filter 22, and an input resistor 23. In the input amplifier 3, the first input terminal V 1 is connected to the drive signal input terminal 1 via the input resistor 23, and the second input terminal V 2 is connected to the reference signal input terminal 2. In the pulse width modulation unit 5, one input terminal V 4 is connected to the output terminal V 3 of the input amplifier 3 via the absolute value circuit 4, and the other input terminal V 5 is connected to the triangular wave generation unit 7. The polarity determination unit 6 has one input terminal connected to the drive signal input terminal 1 and the other input terminal connected to the reference signal input terminal 2. In the drive output circuit 8, one input terminal V 6 is connected to the output terminal of the pulse width modulation unit 5, and the other input terminal V 7 is connected to the output terminal of the polarity determination unit 6. The two output terminals of the drive output circuit 8 are connected to the load 9 and the input terminal of the feedback amplifier 10, respectively. The output terminal of the feedback amplifier 10 is connected to the first input terminal V 1 of the input amplifier 3 through the filter 22.

  The operation of the load driving circuit 100 configured as described above will be described with reference to FIGS. FIG. 15 is a waveform diagram of signals at various parts in a conventional load driving apparatus. In FIG. 15A, A1 is a drive signal input via the drive signal input terminal 1, and B1 is a waveform diagram of the reference signal input via the reference signal input terminal 2. In FIG. 15 (2), C represents a signal input to the input terminal V 4 of the pulse width modulation unit 5, and D represents a waveform diagram of the triangular wave signal input to the input terminal V 5 of the pulse width modulation unit 5. E in FIG. 15 (3) shows a waveform diagram of a signal input to the input terminal V 6 of the drive output circuit 8.

  First, the drive signal A1 is applied to the drive signal input terminal 1 of the load driving circuit 100, and the reference signal B1 is applied to the reference signal input terminal 2 (FIG. 15 (1)). The drive signal A1 is input to the first input terminal V1 of the input amplifier 3 via the input resistor 23, and the reference signal B1 is input to the second input terminal V2 of the input amplifier 3. The input amplifier 3 receives the drive signal A 1 and the reference signal B 1, differentially amplifies them, and outputs a signal C to the input terminal V 4 of the pulse width modulator 5 via the absolute value circuit 4. The triangular wave generation unit 7 outputs the triangular wave signal D to the input terminal V5 of the pulse width modulation unit 5 (FIG. 15 (2)). The pulse width modulation unit 5 compares the signal C with the triangular wave signal D, and outputs a pulse width modulated signal E to the input terminal V6 of the drive output circuit 8 ((3) in FIG. 15). The polarity determination unit 6 receives the drive signal A1 and the reference signal B1, and outputs a signal for switching the drive direction based on the polarity of the difference voltage to the input terminal V7 of the drive output circuit 8. The drive output circuit 8 creates a signal for driving the load 9 according to the output signal E of the pulse width modulation unit 5 and the output signal of the polarity determination unit 6, and outputs the signal to the load 9 and the feedback amplifier 10. The feedback amplifier 10 differentially amplifies the difference between the output signals of the drive output circuit 8, smooths the difference through the filter 22, and negatively feeds back to the first input terminal V 1 of the input amplifier 3.

The frequency characteristics of the load driving circuit 100 configured as described above can be set flat or arbitrarily by adjusting the value of the filter 22.
JP-A-10-135802

  In recent years, with the increase in data recording density in the field of optical discs, for example, a circuit that drives a load such as an actuator is required to have good linear input / output characteristics. Further, from the viewpoint of reducing current consumption, it is required to reduce the output offset voltage of the entire system that is generated due to mismatching of element characteristics in each block when the differential input voltage is zero.

The relationship between the offset voltage of each block of the conventional load driving apparatus and the output offset voltage of the entire system will be described with reference to FIG.
In FIG. 14, the amplification factor of the input amplifier 3 is A, the amplification factor obtained by combining the amplification factors of the absolute value circuit 4, the pulse width modulation unit 5, and the drive output circuit 8 is D, and the amplification factor of the feedback amplifier 10 is the input resistance. Assuming that B multiplied by the resistance value of 23 is B, the amplification factor G of the entire system is expressed by the following equation (1).
G = (A × D) / (1−A × B × D) (1)
Usually, in order to suppress variations, the value of A is increased, and the value of B is sufficiently smaller than the value of A.

In FIG. 14, the input offset voltage of the input amplifier 3 is a, the input offset voltage obtained by synthesizing the input offset voltages of the absolute value circuit 4, the pulse width modulation unit 5, and the drive output circuit 8 is d, and the input offset of the feedback amplifier 10. When the voltage is b, the output offset voltage Vofs of the entire system is expressed by the following equation (2).
Vofs = [{(b × B + a) × A + d} × D] / (1−A × B × D) (2)
From equation (2), a and b are multiplied by A, which is a large value, and are therefore dominant over the output offset voltage of the entire system. In other words, in an apparatus such as an analog MOS amplifier having a large mismatch in element characteristics, the output offset voltage of the entire system becomes large. Therefore, in order to suppress the output offset voltage of the entire system, the size of each element must be increased, resulting in an increase in cost.

  Further, in order to correct the output offset voltage of the entire system to be small with respect to the pulse width modulation output of the load driving device of the conventional example, the output after passing through the low offset voltage LPF must be detected. However, it is difficult to accurately detect the offset voltage value due to switching noise. Therefore, it has been difficult to correct the value of the output offset voltage of the entire system to be small.

  An object of the present invention is to provide a load driving device and a load driving method capable of reducing the output offset voltage of the entire system and reducing the size of each element.

In order to achieve the above object, the present invention has the following configuration.
A load driving device according to an aspect of the present invention includes an input amplifier that receives a drive signal and a reference signal, differentially amplifies and outputs the input signal, a triangular wave generation unit that outputs a triangular wave signal, and an output signal of the input amplifier that is a modulated signal. A pulse width modulation unit that inputs the triangular wave signal as a modulation signal and outputs a pulse width modulation signal, a drive output circuit that outputs a signal for driving a load based on the pulse width modulation signal, and an output of the drive output circuit A load driving device having a feedback amplifier for amplifying a signal and feeding back to the input amplifier, an offset adjustment signal adding unit for adding an offset correction voltage to an input terminal of the input amplifier and outputting the predetermined signal An input amplifier input signal setting unit for setting the drive signal and the reference signal to substantially the same potential, and two inputs of the feedback amplifier by a predetermined signal. Feedback amplifier input signal setting section for substantially the same potential of the signal, and further comprising an input amplifier offset determination unit determines whether or not the output signal of the input amplifier is substantially zero by a predetermined signal.

In the load driving device of the present invention, the differential input voltage of the input amplifier and the feedback amplifier is made zero by the input amplifier input signal setting unit and the feedback amplifier input signal setting unit. The input amplifier offset determination unit determines whether the input amplifier and the feedback amplifier have an offset voltage component, and detects an offset correction voltage that makes the offset voltage substantially zero in the input amplifier and the feedback amplifier. The offset adjustment voltage adding unit adds the offset correction voltage to drive the load driving device. As a result, when the differential input voltage is zero, it is possible to reduce the output offset voltage of the entire system that is generated due to inconsistency of element characteristics in each block. Therefore, each element size can also be reduced.
Since the load driving device of the present invention does not perform pulse width modulation driving during the operation of detecting the offset correction voltage (offset adjustment), it is possible to eliminate the intrusion of the offset correction error due to the pulse width modulation noise. Judgment accuracy can be improved. Further, since the offset correction voltage is added to the reference signal, the frequency characteristics of the entire system are not affected.

In the load driving device of the invention according to the one aspect, the offset control unit further outputs a control signal for causing the offset adjustment signal adding unit to create the offset correction voltage according to the output signal of the input amplifier offset determining unit. May be provided.
In the load driving device according to the one aspect of the present invention, the offset adjustment signal adding unit generates the offset correction voltage, and an output control signal is output according to the output signal of the input amplifier offset determination unit. And a selection circuit unit for outputting the control signal to the offset adjustment signal adding unit.

The load driving device of the invention according to the one aspect may further include a storage unit that stores the control signal.
According to the load driving device of the present invention, it is not necessary to perform the offset adjustment every time the power is turned on, so that the time required for the offset adjustment can be saved.

  In the load driving device of the invention according to the one aspect, the input amplifier includes a first input terminal to which the driving signal is input and a second input terminal to which the reference signal is input, and the offset correction voltage. May be added to either the first input terminal or the second input terminal.

In the load driving device of the invention according to the one aspect, the input amplifier amplifies a value obtained by subtracting the reference signal from the drive signal and outputs the amplified reference value to a predetermined reference value; and the reference signal A second amplification output unit that amplifies a value obtained by subtracting the drive signal from the output signal and outputs the amplified value to a predetermined reference value. The pulse width modulation unit outputs the output signal of the first amplification output unit and the triangular wave. A first pulse width modulator for inputting a signal and outputting a first pulse width modulation signal; a second pulse width modulation for inputting an output signal of the second amplification output section and the triangular wave signal; A second pulse width modulator for outputting a signal, and the drive output circuit includes a first drive signal for driving a load based on the first pulse width modulation signal, and the second pulse width. A second drive signal for driving a load based on the modulation signal. Is intended to, the feedback amplifier, the first driving signal and the second driving signal may be one that differential amplifier.
According to the load driving device of the present invention, by driving the output of the input amplifier at 50% duty, the linearity near the output voltage difference of 0 can be improved, and the pulse width waveform can be stably output.

In the load driving device of the invention according to the one aspect, the offset adjustment signal adding unit includes a first offset adjustment signal adder that adds a first offset correction voltage to the output signal of the first amplification output unit; A second offset adjustment signal adder for adding a second offset correction voltage to the output signal of the second amplification output unit, and instead of adding an offset correction voltage to the input terminal of the input amplifier, A first offset correction voltage may be added to the first pulse width modulation signal, and a second offset correction voltage may be added to the second pulse width modulation signal.
In the load driving device according to the one aspect of the present invention, the input amplifier offset determination unit is configured to determine whether or not a difference voltage of an output signal of the input amplifier is substantially zero, instead of determining whether or not the first offset is approximately zero. It may be determined whether the difference voltage between the output signal of the adjustment signal adder and the output signal of the second offset adjustment signal adder is substantially zero.
In the load driving device of the invention according to the one aspect, the input amplifier offset determination unit is configured to determine whether or not a difference voltage of an output signal of the input amplifier is substantially zero. The first offset determiner has a difference voltage between the output signal of the first offset adjustment signal adder and the output signal of the input amplifier that is substantially zero. The second offset determiner determines whether or not the difference voltage between the output signal of the second offset adjustment signal adder and the output signal of the input amplifier is substantially zero. It may be determined.
In the load driving device of the invention according to the one aspect, the predetermined reference value serving as a reference of the outputs of the first and second amplification output units may be a substantially average value of the triangular wave signal.
According to the load driving device of the present invention, when the voltage difference between the input signals of the first and second pulse width modulators is 0, the outputs of the first and second pulse width modulators are driven at 50% duty. As a result, the linearity of the difference voltage of the output signal of the drive output circuit near 0 can be improved. Furthermore, good linear characteristics can be maintained near the output dynamic range.

  In the load driving device of the invention according to the one aspect, the offset adjustment signal adding unit may include at least one constant current source, at least one resistor, and at least one switch. The substantial resistance value of the resistor or the substantial current value flowing through the resistor may be variable.

  A load driving method according to one aspect of the present invention includes an input amplifier that receives a drive signal and a reference signal, differentially amplifies and outputs the input signal, a triangular wave generator that outputs a triangular wave signal, an output signal of the input amplifier, and the triangular wave signal And a pulse width modulation unit that outputs a pulse width modulation signal, a drive output circuit that outputs a signal for driving a load based on the pulse width modulation signal, and an input amplifier that amplifies the output signal of the drive output circuit A feedback amplifier that feeds back to the input amplifier, an offset adjustment signal adder that outputs an offset correction voltage added to the input terminal of the input amplifier, and an input amplifier input that makes the drive signal and the reference signal substantially the same potential by a predetermined signal A signal setting unit, a feedback amplifier input signal setting unit for making the input signal of the feedback amplifier substantially the same potential by a predetermined signal, and the input by a predetermined signal In the load driving device including an input amplifier offset determining unit that determines whether or not the output signal of the amplifier is substantially zero, the load driving method of the load driving device adjusts an offset voltage between the input amplifier and the feedback amplifier. An offset adjustment step, wherein the input amplifier input signal setting unit sets the drive signal and the reference signal to substantially the same potential according to a predetermined signal, and the feedback amplifier input signal setting unit A setting step of setting the input signal of the feedback amplifier to substantially the same potential; a control step of sequentially variably controlling the offset correction voltage added to the input terminal of the input amplifier by the offset adjustment signal adding unit; and the input amplifier offset A detection step of detecting that the output signal of the input amplifier is substantially zero by the determination unit; Comprising a holding step of holding the control signal to generate the offset correction voltage when it is detected that the output signal of the fine said input amplifier is substantially zero.

  A load driving method according to another aspect of the present invention includes an input amplifier that inputs a drive signal and a reference signal, differentially amplifies and outputs a predetermined reference value, a triangular wave generation unit that outputs a triangular wave signal, and an output of the input amplifier A pulse width modulation unit for inputting a signal and the triangular wave signal and outputting a pulse width modulation signal, a drive output circuit for outputting a signal for driving a load based on the pulse width modulation signal, and amplifying the output signal of the drive output circuit A feedback amplifier that feeds back to the input amplifier, an offset adjustment signal adding unit that outputs an output signal of the input amplifier with an offset correction voltage added thereto, and the drive signal and the reference signal are substantially at the same potential by a predetermined signal. An input amplifier input signal setting unit, a feedback amplifier input signal setting unit that makes the input signal of the feedback amplifier substantially the same potential by a predetermined signal, and a predetermined signal In the load driving device including an input amplifier offset determining unit that determines whether or not the output signal of the offset adjustment signal adding unit is substantially zero, the load driving method of the load driving device includes the input amplifier and the feedback amplifier. An offset adjustment step for adjusting an offset voltage of the input amplifier, wherein the input amplifier input signal setting unit sets the drive signal and the reference signal to substantially the same potential according to a predetermined signal, and the feedback A setting step in which an amplifier input signal setting unit sets an input signal of the feedback amplifier to substantially the same potential; an output of the input amplifier in which the offset adjustment signal adding unit is output to the predetermined reference value by a predetermined signal; A control step for sequentially and variably controlling the offset correction voltage to be added to the signal, the input amplifier offset determination unit; Therefore, a detection step for detecting that the output signal of the offset adjustment signal adding unit is substantially zero, and a control for generating an offset correction voltage when it is detected that the output signal of the offset adjustment signal adding unit is substantially zero. A holding step for holding the signal is provided.

In the load driving method of the invention according to the one aspect and the other aspect, the load driving device further includes a storage unit that stores the control signal, and the offset adjustment step further includes the offset correction after the holding step. You may provide the step which memorize | stores a signal in a memory | storage part.
In the load driving method of the invention according to the one aspect and the another aspect, the control step may perform control so that the offset correction voltage monotonously increases or monotonously decreases.
In the load driving method of the invention according to one aspect and another aspect, the control step may control the offset correction voltage by a binary search method that searches for a target correction value while narrowing a search range by half.
In the load driving method of the invention according to the one aspect, the predetermined reference value of the control step may be a substantially average value of the triangular wave signal.

  According to the present invention, it is possible to provide a load driving method capable of reducing the output offset voltage of the entire system and reducing the size of each element.

  The load driving device according to the present invention has an advantageous effect of reducing the output offset voltage of the entire system and providing a load driving device and a load driving method capable of reducing the size of each element.

Embodiments 1 to 7 which are the best embodiments of the load driving device of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1
The load driving apparatus according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of the load driving apparatus according to the first embodiment. The load driving device according to the first embodiment further includes an offset adjustment circuit 200 than the load driving circuit 100 which is a conventional load driving device. Since it has the same structure in the other points, redundant description is omitted.

  In FIG. 1, the offset adjustment circuit 200 includes an input amplifier offset determination unit 12, a selection circuit unit 13, an offset control unit 14, an offset adjustment signal addition unit 15, an input amplifier input signal setting unit 17, a feedback amplifier input signal setting unit 18, and Switches 20 and 21 are provided. The input amplifier offset determination unit 12 has one input terminal V8 connected to the output terminal V3 of the input amplifier 3 via the switch 20, and the other input terminal V9 connected to the offset reference terminal 16 via the switch 21. . The selection circuit unit 13 has a predetermined number of gate circuits. The selection circuit unit 13 has one input terminal connected to the output terminal of the input amplifier offset determination unit 12 and the other input terminal connected to the output terminal of the offset control unit 14. The offset control unit 14 has its input terminal connected to the offset adjustment start signal input terminal 11, and its output terminal selected by the selection circuit unit 13, input amplifier input signal setting unit 17, feedback amplifier input signal setting unit 18, and switches 20, 21. Connected to each. The offset adjustment signal adding unit 15 has one input terminal connected to the reference signal input terminal 2 and the other input terminal connected to the selection circuit unit 13. The offset adjustment signal adding unit 15 has its output terminal connected to the second input terminal V <b> 2 of the input amplifier 3. The input amplifier input signal setting unit 17 has a switch 17a. The input amplifier input signal setting unit 17 is configured to be able to switch the connection between the drive signal input terminal 1 and the input resistor 23 to the connection between the reference signal input terminal 2 and the input resistor 23. The feedback amplifier input signal setting unit 18 includes switches 18 a and 18 b and is configured to be able to switch the connection between the drive output circuit 8 and the feedback amplifier 10 to the connection between the fixed voltage source 18 c and the feedback amplifier 10. The offset adjustment circuit 200 is configured as described above.

Here, the principle of offset adjustment for reducing the output offset voltage of the entire system in the load driving apparatus according to the first embodiment of the present invention will be described.
Two input signals of the feedback amplifier 10 are set to the same potential. Only b × B, which is the output offset voltage of the feedback amplifier 10, is output to the first input terminal V 1 of the input amplifier 3. Further, the drive signal and the reference signal are set to the same potential. The output terminal V3 of the input amplifier 3 outputs a voltage Vα that is A times the sum of the output offset voltage b × B of the feedback amplifier 10 and the input offset voltage a of the input amplifier 3. The voltage Vα is expressed by the following equation (3).
Vα = (b × B + a) × A (3)
Next, when the offset correction voltage Vβ is added to the potential of the reference signal (drive signal), the output offset voltage Vofs2 of the entire system is expressed by the following equation (4).

Vofs2 = [{(b × B + a−Vβ) × A + d} × D] / (1−A × B × D) (4)
When the offset correction voltage Vβ in the equation (4) is Vβ = b × B + a, the output offset voltage Vofs2 of the entire system is expressed by the following equation (5).
Vofs2 = (d × D) / (1−A × B × D) (5)
Therefore, since a and b which are main offset factors can be removed, the output offset voltage of the entire system can be reduced regardless of the size of the element. That is, the output offset voltage of the entire system can be reduced and the element size can be reduced.

Based on the principle of the offset adjustment described above, an offset correction voltage appropriate for removing a and b which are main offset factors is detected.
The offset adjustment operation in the load driving apparatus of the first embodiment will be described with reference to FIGS. FIG. 2 is a flowchart of offset adjustment in the load driving apparatus according to Embodiment 1 of the present invention.

  First, an offset adjustment start signal is applied to the offset control unit 14 via the offset adjustment start signal input terminal 11 (step 1). Although not shown, the offset adjustment start signal may be a signal linked to a standby release signal for enabling the load driving device or a signal linked to application of a power supply voltage. Further, it may be a command signal from a system outside the apparatus. The offset control unit 14 switches the switch 17a to short-circuit the reference signal input terminal 2 and the input resistor 23 so that the drive signal input to the input amplifier 3 and the reference signal have the same potential. That is, the output signal of the input amplifier input signal setting unit 17 is set to the same potential. At the same time, the offset control unit 14 switches the switches 18a and 18b of the feedback amplifier input signal setting unit 18 to be connected to the fixed voltage source 18c in order to make the signals input to the two input terminals of the feedback amplifier 10 have the same potential. Then, a fixed voltage equal to each other is applied (step 2). Note that the value of this fixed voltage is preferably set to 1 / (1) of the average power supply voltage in consideration of the input voltage dependency of the feedback amplifier 10 because the drive output circuit 8 performs pulse width modulation driving from zero to the power supply voltage. The voltage is about 2.

  Next, the offset correction control unit 14 outputs a control signal that causes the offset adjustment signal adding unit 15 to create an offset correction voltage (hereinafter, the offset correction voltage during offset adjustment is referred to as an offset adjustment signal) via the selection circuit unit 13. To do. Based on the control signal, the offset adjustment signal adding unit 15 creates an initial signal of the offset adjustment signal (step 3). As a result, a signal obtained by adding the initial signal of the offset adjustment signal to the reference signal is input to the second input terminal V2 of the input amplifier 3. A reference signal is applied to the first input terminal V 1 of the input amplifier 3 through the input resistor 23. After the initial signal is input to the input amplifier 3, the offset correction control unit 14 switches the switch 20 to connect the output terminal V 3 of the input amplifier 3 and the input terminal V 8 of the input amplifier offset determination unit 12. At the same time, the offset correction control unit 14 switches the switch 21 to connect the offset reference terminal 16 and the input terminal V9 of the input amplifier offset determination unit 12 (step 4). The offset adjustment signal adding unit 15 uses the control signal of the offset correction control unit 14 to sweep the voltage range within the offset adjustment target, and the offset adjustment signal is stepped up from the negative minimum value or stepped down from the positive maximum value. Is created (step 5).

  The input amplifier 3 differentially amplifies the signal input to the first and second input terminals V1 and V2, and outputs the signal to the input terminal V8 of the input amplifier offset determination unit 12. An offset reference signal voltage is applied to the input terminal V 9 of the input amplifier offset determination unit 12 via the offset reference terminal 16. This offset reference signal is equal to the output signal of the input amplifier 3 when it is assumed that the output offset voltage of the input amplifier 3 is not generated. The input amplifier offset determination unit 12 detects the timing at which the polarity of the difference voltage between the input signals at the input terminals V8 and V9 changes (step 6). During the period in which the polarity does not change, the selection circuit unit 13 outputs the control signal from the offset control unit 14 to the offset adjustment signal adding unit 15 as it is. When the polarity changes, the selection circuit unit 13 holds the control signal at that time, and thereafter stops accepting the change of the control signal (step 7). At this time, the offset adjustment signal generated by the offset adjustment signal adding unit 15 based on the control signal held in the selection circuit unit 13 is set as an offset correction voltage. After detecting the offset correction voltage, the input amplifier input signal setting unit 17, the feedback amplifier input signal setting unit 18, and the switches 20 and 21 are returned to the original state (step 8). Thus, the offset adjustment operation is completed.

  By the offset adjustment described above, the load driving apparatus according to the first embodiment can reduce the offset voltage components of the input amplifier 3 and the feedback amplifier 10 and can reduce the output offset voltage of the entire system. In the load driving device according to the first embodiment, during offset adjustment, the absolute value circuit 4, the pulse width modulation unit 5, the polarity determination unit 6, the drive output circuit 8, and the feedback amplifier 10 have a small influence on the output offset voltage of the entire system. Do not use. For this reason, the generation of a correction error due to noise mixing can be suppressed by stopping the pulse width modulation signal. Moreover, since the amplification factor A of the input amplifier 3 is a large value as described above, the determination accuracy of the offset voltage is good. Furthermore, since the offset correction voltage is added to the reference signal, the frequency characteristics of the entire system are not affected.

  A case where the first to third gate circuits are used in the selection circuit unit 13 will be described with reference to FIG. FIG. 3 shows a waveform diagram of each signal of the offset adjustment circuit 200. FIGS. 3A to 3C are waveform diagrams of control signals 1 to 3 input from the offset control unit 14 to the first to third gate circuits, respectively. FIG. 3 (4) shows a waveform diagram of an input signal input from the input amplifier offset determination unit 12 to the first to third gate circuits. FIGS. 3 (5) to 3 (7) show waveform diagrams of output signals 1 to 3 output from the first to third gate circuits to the offset adjustment signal adding unit 15, respectively. FIG. 3 (8) shows a waveform diagram of the offset adjustment signal created by the offset adjustment signal adding unit 15.

In order to facilitate the explanation, conditions are set as follows.
Each signal of (1) to (3) in FIG. 3 is a signal for controlling the offset adjustment signal so that the voltage Vs is increased by one step when one signal becomes H. It is assumed that the offset correction voltage that makes the output offset voltage of the input amplifier 3 substantially zero is between 1 × Vs and 2 × Vs. The input amplifier offset determination unit 12 outputs L below the offset adjustment signal, and outputs H after the offset adjustment signal becomes larger than the offset adjustment signal.

  The operation will be described based on the above conditions. The offset adjustment start signal is input to the offset control unit 14 via the offset adjustment start signal input terminal 11. During the period from 0 [s] to t1 [s] after the offset adjustment start signal is input, the offset control unit 14 sets the control signal 1 to H. At this time, since the input signal is L, each gate circuit outputs the control signals 1 to 3 as output signals 1 to 3 as they are. That is, the output signal 1 is H, the output signal 2 is L, and the output signal 3 is L. Since only the output signal 1 is H, the offset adjustment signal adding unit 15 outputs 1 × Vs obtained by increasing the offset adjustment signal by one step. During the period from t1 [s] to t2 [s], the offset control unit 14 sets the control signal 2 to H. Also at this time, since the input signal is L, each gate circuit outputs the control signals 1 to 3 as they are. That is, the output signal 1 is H, the output signal 2 is H, and the output signal 3 is L. Since the output signals 1 and 2 are H, the offset adjustment signal adding unit 15 outputs the offset adjustment signal 2 × Vs. The input amplifier offset determination unit 12 detects that the polarity of the difference voltage between the signals input to the input terminals V1 and V2 has changed, and sets the input signal to H. During the period from t2 [s] to t3 [s], the offset control unit 14 sets the control signal 3 to H. At this time, since the input signal is H, the third gate circuit outputs L without switching to H. That is, the output signal 1 is H, the output signal 2 is H, and the output signal 3 is L. The first to third gate circuits hold the output signals 1 to 3 at this time. The offset adjustment signal adding unit 15 outputs the offset adjustment signal 2 × Vs because the output signal 1 and the output signal 2 are H. Thereafter, the offset adjustment signal adding unit 15 outputs 2 × Vs as an offset correction voltage.

As described above, the selection circuit unit 13 outputs in accordance with the control signals 1 to 3 from the offset control unit 14 during the interval in which the output signal of the input amplifier offset determination unit 12 does not change. When the output signal of the input amplifier offset determination unit 12 changes, the selection circuit unit 13 holds the output signals 1 to 3 of the offset control unit 14 at the time of change.
When the output signal of the input amplifier offset determination unit 12 changes when the offset adjustment start signal is input and the initial signal of the offset adjustment signal is added, that is, the output offset voltage of the input amplifier 3 is made substantially zero. When the offset correction voltage is smaller than 0, the selection circuit unit 13 holds the initial values of the output signals 1 to 3. In other words, the output signals 1 to 3 in FIG. Further, when the output signal of the input amplifier offset determination unit 12 does not change even when the maximum value of the offset adjustment signal is added, that is, when the offset correction voltage is larger than the maximum value of the offset adjustment signal, the selection circuit unit 13 holds the last output signals 1 to 3. That is, in FIG. 3, when the offset adjustment signal is larger than 3 × Vs, 3 × Vs is held as the offset correction voltage.

  Although the selection circuit unit 13 uses a predetermined number of gate circuits, a predetermined number of latch circuits may be used. When the latch circuit is used, the control signal of the offset control unit 14 is input to the data terminal, and the output signal of the input amplifier offset determination unit 12 is input to the clock terminal. Can be fulfilled.

Next, the offset adjustment signal adding unit 15 will be described with reference to FIGS. 4A to 4D are circuit diagrams of offset adjustment signal adding units 15a to 15d, which are examples of the offset adjustment signal adding unit 15, respectively.
In FIG. 4A, the offset adjustment signal adding unit 15a is connected in series between the reference signal input terminal 2 and the second input terminal V2 of the input amplifier 3. The offset adjustment signal adding unit 15a includes a resistor R, current sources I1 to I6, and switches S1 to S6. The resistor R is inserted in series between the reference signal input terminal 2 and the input terminal V5 of the input amplifier 3. Each of the current sources I1, I2, and I3 has one end connected to the power source and the other end connected between the resistor R and the second input terminal V2 of the input amplifier 3 via the switches S1, S2, and S3. . Each of the current sources I4, I5, and I6 has one end connected to the GND and the other end connected between the second input terminal V2 of the input amplifier 3 via the switches S4, S5, and S6.

The offset adjustment signal adding unit 15a configured as described above controls the total current of the current sources I1 to I3 by switching the switches S1 to S3. By flowing the total current through the resistor R, a positive offset adjustment signal (offset correction voltage) can be added to the reference signal applied from the reference signal input terminal 2. The offset adjustment signal adding unit 15a controls the switches S4 to S6 to control the total current of the current sources I4 to I6. By causing the total current to flow through the resistor R, a negative offset adjustment signal offset correction voltage) can be added to the reference signal.
Preferably, the current values of the current sources I1 to I6 are equal to each other and the current value for one step. If it does so, what is necessary is just to control the electric current amount of one current source for every step, and control of a total electric current amount does not become complicated. Alternatively, the current value is weighted to 2 to the nth power of 1 time, 2 times, and 4 times the current value for one step. By doing so, the amount of current can be changed in various ways by combining several current sources, so that the number of current sources and the number of switches can be reduced.

  The offset adjustment signal adding unit 15b will be described with reference to FIG. In FIG. 4 (2), the offset adjustment signal adding unit 15 b is connected in series between the reference signal input terminal 2 and the second input terminal V 2 of the input amplifier 3. The offset adjustment signal adding unit 15b includes resistors R1 to R3, current sources I7 and I8, and switches S7 to S8. The resistors R1 to R3 are connected in series between the reference signal input terminal 2 and the second input terminal V2 of the input amplifier 3, respectively. The switches S11 to S13 are connected in parallel with the resistors R1, R2, and R3, respectively. Each of the current sources I7 has one end connected to the power supply and the other end connected between the resistor R3 and the second input terminal V2 of the input amplifier 3 via the switch S7. One end of the current source I8 is connected to the GND, and the other end is connected between the resistor R3 and the second input terminal V2 of the input amplifier 3 via the switch S8.

The offset adjustment signal adding unit 15b configured as described above controls the combined resistance of the resistors R1 to R3 by switching the switches S11 to S13. A positive offset adjustment signal (offset correction voltage) can be added to the reference signal by passing a current from the current source I7 through the combined resistor. In addition, a negative offset adjustment signal (offset correction voltage) can be added to the reference signal by passing a current from the current source I8 through the combined resistor.
Preferably, the resistance values of the resistors R1 to R3 are equal to each other and have a resistance value for one step. If it does so, if one resistance value is short-circuited with a switch for every step, control of synthetic | combination resistance can be performed and control of total resistance will not become complicated. Alternatively, the resistance value is weighted to a power of 2 that is 1 times, 2 times, and 4 times the resistance value for one step. By doing so, the combined resistance can be varied in various ways by combining several resistors, so that the number of resistors and the number of switches can be reduced.

  The offset adjustment signal adding unit 15c will be described with reference to FIG. In FIG. 4 (3), the offset adjustment signal adding unit 15 c is connected in series between the reference signal input terminal 2 and the second input terminal V 2 of the input amplifier 3. The offset adjustment signal adding unit 15c includes resistors R4 to R9, current sources I9 and I10, switches S9 and S10, and switches S14 to S20. The current source I9 has one end connected to the power supply and the other end connected to the reference signal input terminal 2 via the switch S9 and resistors R4 to R6. The current source I10 has one end connected to the GND and the other end connected to the reference signal input terminal 2 via the switch S10 and resistors R7 to R9. The switches S14 to S20 are connected between the resistance ends of the resistors R4 to R9 and the second input terminal V2 of the input amplifier 3, respectively.

The offset adjustment signal adding unit 15c configured as described above controls the combined resistance of the resistors R4 to R6 and the resistors R7 to R9 by switching the switches S14 to S20. A positive offset adjustment signal (offset correction voltage) can be added to the reference signal by flowing a current from the current source I9 to the combined resistor. In addition, a negative offset adjustment signal (offset correction voltage) can be added to the reference signal by passing a current from the current source I10 through the combined resistor.
Note that, similarly to the offset adjustment adding unit 15b illustrated in FIG. 4B, preferably, the resistance values of the resistors R4 to R9 are equal to each other and have a resistance value for one step. If it does so, if one resistance value is short-circuited with a switch for every step, control of synthetic | combination resistance can be performed and control of total resistance will not become complicated. Alternatively, the resistance value is weighted to a power of 2 that is 1 times, 2 times, and 4 times the resistance value for one step. By doing so, the combined resistance can be varied in various ways by combining several resistors, so that the number of resistors and the number of switches can be reduced.

The offset adjustment signal adding unit 15d will be described with reference to FIG. 4 (4), the offset adjustment signal adding unit 15c further includes switches S14 ′ to S20 ′ in addition to the offset adjustment signal adding unit 15c shown in FIG. 4 (3). The switches S14 ′ to S20 ′ are respectively connected between the resistance ends of the resistors R4 to R9 and the second input terminal V2 ′ of the input amplifier 3.
The offset adjustment signal adding unit 15d configured as described above can obtain two outputs for operating two load driving circuits. Similarly, if a switch is connected between each resistance terminal of the resistors R4 to R9 and the input terminal of the input amplifier of each load driving circuit according to the desired number of outputs, a predetermined number of load driving circuits can be connected simultaneously. It can be operated.

Preferably, the numbers of resistors and current sources of the offset adjustment signal adding units 15a to 15d shown in FIGS. 4 (1) to 4 (4) are offset correction voltages derived from the principle of offset adjustment described above. The total number of currents that can be formed is (± (b × B + a)) or more.
Each switch of the offset adjustment signal adding units 15a to 15d may use a zener zap, a fuse, an antifuse, or a PROM as a trimming element. In this case, the offset adjustment is performed only once, and the offset correction voltage obtained thereby is permanently corrected. If such a trimming method is used, the offset adjustment time during driving of the load driving device can be omitted. Further, the offset adjustment for permanently correcting the offset correction voltage may be performed by the customer as a system including the load driving device, or may be corrected at the time of inspection using only the load driving device.

In the offset adjustment according to the first embodiment, the offset adjustment signal is added to the reference signal. However, the offset adjustment signal may be added to the drive signal. In that case, the offset adjustment signal added to the reference signal may be added to the drive signal with the sign reversed.
Note that the input amplifier input signal setting unit 17 is not limited to the above configuration, and may be any configuration as long as the drive signal input to the input amplifier 3 and the reference signal can have the same potential. The feedback amplifier input signal setting unit 18 is not limited to the above configuration, and may be any configuration that can make the input signal of the feedback amplifier 10 the same potential.
In the load driving device according to the first embodiment, the offset control unit 14 creates a control signal that causes the offset adjustment signal adding unit 15 to create an offset correction voltage. Further, the selection circuit 13 is used to hold the control signal according to the output signal of the input amplifier offset determination unit 12. However, the present invention is not limited to this, and although not shown, the offset adjustment signal adding unit 15 is configured to directly create and hold an offset correction voltage according to the output signal of the input amplifier offset determination unit 12. Also good. In this case, the offset adjustment signal adding unit 15, the input amplifier input signal setting unit 17, the feedback amplifier input signal setting unit 18, and the switches 20 and 21 may be configured to operate directly in conjunction with the offset adjustment start signal. .

<< Embodiment 2 >>
The load driving apparatus according to the second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a block diagram of the load driving apparatus according to the second embodiment. The load driving device according to the second embodiment is configured so that three load driving circuits 100 according to the first embodiment can be operated simultaneously.
In FIG. 5, the load driving device of the second embodiment includes a load driving circuit group 100A having three load driving circuits 100 and an offset adjusting circuit 200A. The offset adjustment circuit 200A is replaced with the input amplifier offset determination unit 12, the selection circuit unit 13, the offset adjustment signal addition unit 15, the feedback amplifier input signal setting unit 18, and the switches 20 and 21 of the offset adjustment circuit 200 according to the first embodiment. , An input amplifier offset determination unit group 12A, a selection circuit unit group 13A, an offset adjustment signal addition unit group 15A, a feedback amplifier input signal setting unit group 18A, and switch groups 20A and 21A. The input amplifier offset determination unit group 12A includes a selection circuit unit group 13A, an offset adjustment signal addition unit group 15A, a feedback amplifier input signal setting unit group 18A, and a switch group 20A and 21A. 12, a selection circuit unit 13, an offset adjustment signal addition unit 15, a feedback amplifier input signal setting unit 18, and switches 20 and 21. Each output signal of the offset control unit 14 and the input amplifier input signal setting unit 17 is used in common for each element of each group. Since the load driving apparatus of the second embodiment has the same configuration and operation as that of the load driving apparatus of the first embodiment shown in FIG.

  Even if the offset voltage value differs for each of the three load driving circuits 100, the load driving device of the second embodiment can be reduced by one offset adjustment. Similarly, the input amplifier offset determination unit 12, the selection circuit unit 13, the offset adjustment signal addition unit 15, the feedback amplifier input signal setting unit 18, and the switches 20 and 21 are provided by the number corresponding to the desired number of load driving circuits. With this configuration, the output offset voltage of the entire system of the plurality of load driving circuits can be reduced by a single offset adjustment. Furthermore, the time for offset adjustment can be shortened.

<< Embodiment 3 >>
A load driving apparatus according to a third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a block diagram of the load driving apparatus according to the third embodiment. In the load driving device of the third embodiment, the selection circuit unit 13 is built in the offset control unit 14 of the load driving circuit 100 of the first embodiment. In FIG. 6, the load driving device according to the third embodiment is different from the load driving device 100 according to the first embodiment in that an offset adjustment circuit 200 </ b> B is provided instead of the offset adjustment circuit 200. The other points have the same configuration as that of the load driving device of the first embodiment, and those having the same reference numerals have the same functions, and therefore redundant description is omitted.

  The offset adjustment circuit 200B includes an input amplifier offset determination unit 12, an offset control unit 14B, an offset adjustment signal addition unit 15, and switches 20 and 21. The offset control unit 14B includes a selection circuit 13B, an up counter 25, a clock generation unit 26, and a start signal generation unit 27. The start signal creation unit 27 receives the offset adjustment signal via the offset adjustment start signal input terminal 11 and outputs a signal for controlling the switches 20 and 21 and a signal for causing the clock creation unit 26 to create a clock signal. The clock generation unit 26 generates a clock signal that is a step interval of the offset adjustment signal generated by the offset adjustment signal addition unit 15. The selection circuit unit 13B is configured by a latch circuit. The selection circuit unit 13B inputs the output signal of the input amplifier offset determination unit 12 and the clock signal of the clock generation unit 26, and selects whether to output or stop the clock signal according to the output signal. The up counter 25 outputs, to the offset adjustment signal adding unit 15, a signal whose number of bits increases for each clock signal based on the clock signal input via the selection circuit unit 13 </ b> B.

  In the offset adjustment circuit 200 </ b> B configured as described above, the selection circuit unit 13 </ b> B outputs the clock signal of the clock generation unit 26 to the up counter 25 as it is during a period in which the output signal of the input amplifier offset determination unit 12 does not change. The up counter 25 outputs a control signal that counts up at a timing corresponding to the clock signal, and sequentially increases the offset adjustment signal created by the offset adjustment signal adding unit 15 in steps. When the output signal of the input amplifier offset determination unit 12 changes, the selection circuit unit 13B stops the output of the clock signal to the up counter 25. Since the clock signal is stopped, the count-up of the up counter 25 is also stopped. The offset adjustment signal at this time is held, and thereafter used as an offset correction voltage.

  When the latch circuit is used for the selection circuit unit 13 of the load driving device according to the first embodiment, the number determined by the number of steps is necessary. However, the load driving device according to the third embodiment has the latch circuit of the selection circuit unit 13B. Can be reduced to one.

<< Embodiment 4 >>
A load driving apparatus according to Embodiment 4 of the present invention will be described with reference to FIGS. FIG. 7 is a block diagram of the load driving device of the fourth embodiment. The load driving device according to the fourth embodiment is configured to be able to detect the offset correction voltage using a binary search method that narrows the search range by half. In FIG. 7, the load driving device of the fourth embodiment is different from the load driving device of the third embodiment in that an offset control unit 14C is provided instead of the offset control unit 14B. Other points have the same configuration as that of the load driving device of the third embodiment, and those having the same reference numerals have the same functions, and therefore redundant description is omitted.

  When the offset adjustment start signal is applied, the offset control unit 14C outputs a control signal so that the offset adjustment signal addition unit 15 adds a voltage that is half the maximum value of the search range of the offset correction voltage. When the output signal of the input amplifier offset determination unit 12 changes, the offset control unit 14C outputs a control signal to add an intermediate voltage from the previous clock. During a period in which the output signal of the input amplifier offset determination unit 12 does not change, the offset control unit 14C outputs a control signal so as to add an intermediate voltage from two clocks before. The offset control unit 14C outputs the control signal until the step difference from the previous clock becomes one step interval.

  The operation when the binary search method is used will be described with reference to FIG. FIG. 8 is a waveform diagram of an offset adjustment signal in the load driving device of the fourth embodiment. For ease of explanation, the search range of the offset correction voltage is 0 to 8 × Vs [V], and the time of one step of the offset adjustment signal is ts [s]. Further, it is assumed that the offset correction voltage Ve to be searched is between 6 × Vs and 7 × Vs.

  This will be described based on the above conditions. First, during the period from 0 [s] to ts1 [s], the offset control unit 14 causes the offset adjustment signal adding unit 15 to create 0 [V] as an initial value. At this time, the input amplifier offset determination unit 12 outputs L because it is smaller than the offset correction voltage Ve. During the period from ts1 [s] to ts2 [s], the offset control unit 14 causes the offset adjustment signal adding unit 15 to create 8 × Vs [V] that is the maximum value of the search range. At this time, the input amplifier offset determination unit 12 outputs H because it is greater than the offset correction voltage Ve. During the period from ts2 [s] to ts3 [s], the offset control unit 14 creates 4 × Vs [V], which is a midpoint voltage between 0 [V] and 8 × Vs [V], in the offset adjustment signal adding unit 15. Let At this time, the input amplifier offset determination unit 12 outputs L. Since the output signal of the input amplifier offset determination unit 12 has changed, during the period from ts3 [s] to ts4 [s], the offset control unit 14 supplies the offset adjustment signal addition unit 15 with 4 × Vs [V] and 8 × Vs [ 6 × Vs [V], which is a midpoint voltage with respect to V], is generated. At this time, the input amplifier offset determination unit 12 outputs L. Since the output signal of the input amplifier offset determination unit 12 is the same, 7 × which is the midpoint voltage between 6 × Vs [V] and 8 × Vs [V] in the period from ts4 [s] to ts5 [s]. Vs [V] is created. At this time, the input amplifier offset determination unit 12 outputs H. Therefore, it can be seen that the offset correction voltage Ve is between 6 × Vs [V] and 7 × Vs [V]. Since the step interval is searched up to one step interval, the last created 7 × Vs [V] is the offset correction voltage.

  The detection method based on the binary search method described above is slightly more complicated in control method than the detection method in which the offset adjustment signal is sequentially increased or decreased as in the load driving device of the first embodiment, but the offset adjustment time is shortened. can do.

<< Embodiment 5 >>
A load driving apparatus according to Embodiment 5 of the present invention will be described with reference to FIGS. FIG. 9 is a block diagram of the load driving device of the fifth embodiment. The load driving device of the fifth embodiment is configured to drive the outputs of each other at 50% duty in order to improve the linearity of the input amplifier near the output voltage difference of zero. The load driving device according to the fifth embodiment is different from the load driving device according to the first embodiment in that a load driving circuit 100B is provided instead of the load driving circuit 100. The other points have the same configuration as that of the load driving device of the first embodiment, and those having the same reference numerals have the same functions, and therefore redundant description is omitted.

  In FIG. 9, the load driving circuit 100B includes an input amplifier 3B, a pulse width modulation unit 5B, a triangular wave generation unit 7, a drive output circuit 8A, a feedback amplifier 10, a filter 22, and an input resistor 23. The input amplifier 3B includes first and second amplification output units 3a and 3b. In the input amplifier 3B, the first input terminal V1A is connected to the drive signal input terminal 1 via the input resistor 23, and the second input terminal V2A is connected to the reference signal input terminal 2 via the offset adjustment signal adding unit 15. Connected. The input amplifier 3B includes first and second amplification output units 3a and 3b. In the first amplification output unit 3a, the first input terminal V1a is connected to the first input terminal V1A, and the second input terminal V2a is connected to the second input terminal V2B. The second amplification output unit 3b has a function similar to that of the first amplification output unit 3a. In the second amplification output unit 3b, the first input terminal V1b is connected to the second input terminal V2B, and the second input terminal V2b is connected to the second input terminal V2B. That is, the signal input to the second amplification output unit 3b is connected to be input to the input terminal opposite to the first amplification output unit 3a. The output terminal V3a of the first amplification output unit 3a is connected to the input terminal V8 of the input amplifier offset determination unit 12 via the switch 21. The output terminal V3b of the second amplification output unit 3b is connected to the input terminal V9 of the input amplifier offset determination unit 12 via the switch 20. The first and second amplification output units 3a and 3b differentially amplify the two input signals with reference to the midpoint voltage of the triangular wave signal output from the triangular wave generation unit 7 and output the resultant signal.

  The pulse width modulation unit 5B includes first and second pulse width modulators 5a and 5b. In the first pulse width modulator 5 a, the input terminal V 4 a is connected to the output terminal V 3 a of the first amplification output unit 3 a, and the input terminal V 5 a is connected to the triangular wave generation unit 7. In the second pulse width modulator 5b, the input terminal V4b is connected to the output terminal V3b of the second amplification output unit 3b, and the input terminal V5b is connected to the triangular wave generator 7. The drive output circuit 8A has an input terminal V6A connected to the output terminal of the first pulse width modulator 5a, and an input terminal V7A connected to the output terminal of the second pulse width modulator 5b. The drive output circuit 8A has two output terminals connected to the input terminal of the feedback amplifier 10 via the load 9 and the feedback amplifier input signal setting unit 18, respectively. The output terminal of the feedback amplifier 10 is connected to the first input terminal V1A of the input amplifier 3B through the filter 22. As described above, the load driving circuit 100B is configured.

  Next, the operation of the load driving circuit 100B will be described with reference to FIG. FIG. 10 is a waveform diagram of signals at various parts of the load driving device according to the fifth embodiment. In FIG. 10A, A is a drive signal, and B is a waveform diagram of a reference signal. F, G, and H in FIG. 10B are waveform diagrams of signals input from the pulse width modulators 5a and 5b and the triangular wave generator 7, respectively. In FIG. 10 (3), I and J show waveform diagrams of signals input to the input terminals V6 and V7 of the drive output circuit 8, respectively.

  First, the drive signal A is applied to the drive signal input terminal 1, and the reference signal B is applied to the reference signal input terminal 2 (FIG. 10 (1)). The drive signal A is input to the first input terminal V1A of the input amplifier 3B via the input resistor 23. The reference signal B is added with an offset correction voltage by the offset adjustment signal adding unit 15 and input to the second input terminal V2B of the input amplifier 3B. The triangular wave generator 7 outputs a triangular wave signal H. The first and second amplification output units 3a and 3b of the input amplifier 3B differentially amplify the drive signal A and the reference signal B with reference to the midpoint voltage of the triangular wave signal H and output signals G and F, respectively. At this time, the signal F output to the output terminal V3b of the second amplification output unit 3b is based on the signal G output to the output terminal V3a of the first amplification output unit 3a with reference to the midpoint voltage of the triangular wave signal H. The signal is inverted. (FIG. 10 (2)). The first pulse width modulator 5a receives the signal F and the triangular wave signal H, and outputs a first pulse width modulation signal I subjected to pulse width modulation. The second pulse width modulator 5b receives the signal G and the triangular wave signal H and outputs a second pulse width modulated signal J that has been subjected to pulse width modulation ((3) in FIG. 10). First and second drive signals for driving the load 9 are created in response to the first and second pulse width modulation signals I and J of the pulse width modulators 5a and 5b, respectively. The feedback amplifier 10 differentially amplifies the difference between the output signals of the drive output circuit 8A, smoothes the difference through the filter 22, and negatively feeds back to the first input terminal V1A of the input amplifier 3B.

  The offset adjustment in the load driving device according to the fifth embodiment will be described. The load driving device of the first embodiment described above detects the offset correction voltage by determining the polarity of the difference voltage between the output signal of the input amplifier 3 and the offset reference signal applied from the offset reference terminal 16. Instead of this, the load driving device of the fifth embodiment detects the offset correction voltage by determining the polarity of the difference voltage between the output signals of the first amplification output unit 3a and the second amplification output unit 3b. Since it is the same about other points, the overlapping description is omitted.

The load driving apparatus according to the fifth embodiment reduces the offset voltage component of the feedback amplifier 10 and the input amplifier 3B by determining and adding an offset correction voltage at which the differential voltage of the output signal of the input amplifier 3B becomes zero. Can do.
The load driving device of the fifth embodiment can drive the output of the input amplifier 3B with 50% duty, thereby improving the linearity near the output voltage difference of 0 and stably outputting the pulse width waveform.

<< Embodiment 6 >>
A load driving apparatus according to a sixth embodiment of the present invention will be described with reference to FIG. FIG. 11 is a block diagram of the load driving device according to the sixth embodiment. The load driving device of the sixth embodiment is different from the load driving device of the fifth embodiment in that an offset adjustment circuit 200D is provided instead of the offset adjustment circuit 200. The other points have the same configuration as that of the load driving device of the fifth embodiment, and those having the same reference numerals have the same functions, and therefore redundant description is omitted.

  The offset adjustment circuit 200D includes an input amplifier offset determination unit 12D, a selection circuit unit 13D, an offset control unit 14D, an offset adjustment signal addition unit 15D, an input amplifier input signal setting unit 17, a feedback amplifier input signal setting unit 18, and switches 20a and 20b. , 21a, 21b. The input amplifier offset determination unit 12D includes first and second offset determination units 12a and 12b. In the first offset determination unit 12a, one input terminal is connected to an output terminal V15e of a first offset adjustment signal adder 15e described later via a switch 20a, and the other input terminal is offset via a switch 21a. Connected to the reference terminal 16. In the second offset determination unit 12b, one input terminal is connected to an output terminal V15f of a second offset adjustment signal adder 15f described later via a switch 20b, and the other input terminal is connected to an offset reference via a switch 21b. Connected to terminal 16. The selection circuit unit 13D includes first and second selection circuits 13a and 13b. The first selection circuit 13a has one input terminal connected to the output terminal of the first offset determination unit 12a and the other input terminal connected to the output terminal of the offset control unit 14D. The second selection circuit 13b has one input terminal connected to the output terminal of the second offset determination unit 12b and the other input terminal connected to the output terminal of the offset control unit 14D.

  The offset control unit 14D has its input terminal connected to the offset adjustment start signal input terminal 11. The offset control unit 14D controls the switch 17a of the input amplifier input signal setting unit 17, the switches 18a and 18b and the switches 20a, 20b, 21a and 21b of the feedback amplifier input signal setting unit 18. The offset adjustment signal adder 15D includes first and second offset adjustment signal adders 15e and 15f. The first offset adjustment signal adder 15e has one input terminal connected to the output terminal V3a of the first amplification output unit 3a and the other input terminal connected to the output terminal of the first selection circuit 13a. The output terminal of the first offset adjustment signal adder 15e is connected to the input terminal V4a of the first pulse width modulator 5a. The second offset adjustment signal adder 15f has one input terminal connected to the output terminal V3b of the second amplification output unit 3b and the other input terminal connected to the output terminal of the selection circuit 13b. The output terminal of the second offset adjustment signal adder 15f is connected to the input terminal V4b of the second pulse width modulator 5b. The offset adjustment circuit 200E is configured as described above.

Here, the principle of offset adjustment in the load driving device of the sixth embodiment will be described.
When the input signals of the feedback amplifier 10 are set to the same potential, only b × B that is the output offset voltage of the feedback amplifier 10 is output to the input resistor 23 and the first input terminal V1A of the input amplifier 3B. When there is no offset voltage component when the differential input voltage of the drive signal and the reference signal is 0, the output terminals V3a and V3a of the first and second amplification output units 3a and 3b are respectively created by the triangular wave generation unit 7 A voltage Vc corresponding to the midpoint voltage of the triangular wave signal is output. Further, the drive signal and the reference signal are set to the same potential. The output terminal V3A of the first amplification output unit 3a is added with the input offset a1 and b × B of the first amplification output unit 3a and multiplied by the amplification factor A ′ of the first amplification output unit 3a. A signal {(a1 + b × B) × A ′ + Vc} obtained by adding the voltage Vc is output. Since the second amplification output unit 3b outputs a signal obtained by inverting the output signal of the first amplification output unit 3a, the amplification factor of the second amplification output unit 3b is −A ′. Therefore, the output terminal V3b of the second amplification output unit 3b is multiplied by the input offset a2 and b × B of the second amplification output unit 3b and multiplied by the amplification factor −A ′ of the second amplification output unit 3b. Further, a signal {− (a2 + b × B) × A ′ + Vc} obtained by adding the voltage Vc is output.

  Since the offset voltage of the first and second amplification output units 3a and 3b is the difference from the voltage Vc, the offset voltage of the first amplification output unit 3a is (a1 + b × B) × A ′, The offset voltage of the amplification output unit 3b is − (a2 + b × B) × A ′. When the first offset adjustment signal adder 15e adds the first offset correction voltage as − (a1 + b × B) × A ′, the voltage Vc is applied to the input terminal V4a of the first pulse width modulator 5a. Is output. When the second offset correction signal adder 15f adds the second offset correction voltage as (a2 + b × B) × A ′, the voltage Vc is applied to the input terminal V4b of the second pulse width modulator 5b. Is output.

According to the above method, when the differential input voltage of the drive signal and the reference signal is 0, each input signal of the first and second pulse width modulators 5a and 5b corresponds to the midpoint voltage of the triangular wave signal. Voltage. That is, the difference voltage between the input signals of the first and second pulse width modulators 5a and 5b becomes substantially zero. Therefore, the offset voltage components of the feedback amplifier 10 and the input amplifier 3B are reduced.
In addition, since the input signals of the first and second pulse width modulators 5a and 5b become voltages corresponding to the midpoint voltage of the triangular wave signal, the output signal of the pulse width modulator 5B is 50% duty. The load 9 can be driven around the center. Therefore, it can be driven to the peak of the triangular wave signal, and the linear characteristic can be maintained up to the vicinity of the output dynamic range.

The offset adjustment operation in the load driving apparatus according to the sixth embodiment will be described with reference to FIGS. 11 and 12. FIG. 12 is a flowchart of offset adjustment in the load driving apparatus according to the sixth embodiment.
First, an offset adjustment start signal is input to the offset control unit 14D via the offset adjustment start signal input terminal 11 (step 61). The offset control unit 14D switches the switch 17a in order to make the drive signal input to the input amplifier 3B and the reference signal have the same potential, and short-circuits the reference signal input terminal 2 and the input resistor 23. That is, the output signal of the input amplifier input signal setting unit 17 is set to the same potential. At the same time, the offset control unit 14D switches the switches 18a and 18b of the feedback amplifier input signal setting unit 18 to connect to the fixed voltage source 18c in order to set the input signal of the feedback amplifier 10 to the same potential, and the fixed voltage source is equal to each other (Step 62). Next, the offset control unit 14D outputs a control signal that causes the offset adjustment signal adding unit 15D to create the first and second offset adjustment signals via the selection circuit unit 13D.

  Based on the control signal, the offset adjustment signal adding unit 15D creates initial signals of the first and second offset adjustment signals (step 63). After the initial signal is generated, the switches 20a, 20b, 21a, and 21b are turned on. As a result, an offset reference signal corresponding to the midpoint voltage of the triangular wave signal is input via the offset reference terminal 16 (step 64). The offset adjustment signal adding unit 15D generates first and second offset adjustment signals in which the offset control unit 14D increases the step from the minus minimum value or decreases the step from the plus maximum value by the control signal (step 65). ). The first offset determination unit 12a determines the polarity of the difference voltage between the output signal of the first offset adjustment signal adding unit 15e to which the first offset adjustment signal is added and the offset reference signal. The second offset determination unit 12b determines the polarity of the difference voltage between the output signal of the first offset adjustment signal adding unit 15 to which the second offset adjustment signal is added and the offset reference signal (step 66).

  During the period in which the polarity does not change, the selection circuit unit 13D outputs the control signal from the offset control unit 14D to the offset adjustment signal addition unit 15D as it is. When the polarity changes, the selection circuit unit 13D holds the control signal at that time, and thereafter stops accepting the change of the control signal (step 67). At this time, the first and second offset adjustment signals created by the offset adjustment signal adding unit 15D are set as the first and second offset correction voltages, respectively, based on the control signal held in the selection circuit unit 13D. After detection of the first and second offset correction voltages, the input amplifier input signal setting unit 17, the feedback amplifier input signal setting unit 18, and the switches 20a, 20b, 21a, and 21b are returned to the original state (step 68). Thus, the offset adjustment operation is completed.

In the load driving device according to the sixth embodiment of the present invention, the first and second offsets in which the difference voltage between the output signal of the input amplifier 3B and the midpoint voltage of the triangular wave signal becomes substantially zero by the offset adjustment operation. Detect the correction voltage. By adding this, the offset voltage components of the feedback amplifier 10 and the input amplifier 3B can be reduced, and the output offset voltage of the entire system can be reduced.
The load driving device according to the sixth embodiment of the present invention drives the outputs of the pulse width modulators 5a and 5b at 50% duty when the difference voltage between the input signals of the pulse width modulators 5a and 5b is zero. Thus, it is possible to improve the linearity when the differential voltage of the output signal of the drive output circuit 8A is near zero. Furthermore, good linear characteristics can be maintained near the output dynamic range.

Note that, similarly to the load driving device of the first embodiment, the load driving device of the sixth embodiment, when the initial signals of the first and second offset adjustment signals are added, When the output signals of the offset determination units 12a and 12b change, the selection circuits 13a and 13a hold the initial values of the output signals of the first and second offset determination units 12a and 12b, respectively. Further, if the output signals of the first and second offset determination units 12a and 12b do not change even when the maximum values of the first and second offset adjustment signals are added, the selection circuit units 13a and 13b are respectively The last output signals of the first and second offset determination units 12a and 12b are held.
In the load driving device of the sixth embodiment, the first and second offset adjustment signals created by the offset adjustment signal adding unit 15D are increased or decreased by steps, but the load driving device of the fourth embodiment is the same as the load driving device of the fourth embodiment. A binary search method may be used.

<< Embodiment 7 >>
A load driving device according to a seventh embodiment of the present invention will be described with reference to FIG. FIG. 13 is a block diagram of the load driving device according to the seventh embodiment of the present invention. The load driving device of the seventh embodiment is different from the load driving device of the first embodiment in that an offset adjustment circuit 200E is provided instead of the offset adjustment circuit 200. The other points have the same configuration as that of the load driving device of the first embodiment, and those given the same reference numerals have the same functions, and therefore redundant description is omitted.

  The offset adjustment circuit 200E includes an input amplifier offset determination unit 12, an offset control unit 14E, an offset adjustment signal addition unit 15, an input amplifier input signal setting unit 17, a feedback amplifier input signal setting unit 18, a switch unit 19, switches 20, 21 and A storage unit 24 is included. The offset control unit 14E has its input terminal connected to the offset adjustment start signal input terminal 11. The offset control unit 14E has its output terminal connected to the selection circuit 13, the input amplifier input signal setting unit 17, the feedback amplifier input signal setting unit 18, the switch unit 19, and the switches 20 and 21, respectively. The storage unit 24 is connected to the selection circuit unit 13 and the offset adjustment signal addition unit 15 via the switch unit 19. The storage unit 24 includes a storage element such as a memory in order to store the offset correction voltage. The offset adjustment circuit 200E is configured as described above.

Next, the offset adjustment operation of the load driving device according to the seventh embodiment will be described.
When an offset adjustment start signal is input via the offset adjustment start signal input terminal 11, the offset control unit 14 controls the switch unit 19 to short-circuit the selection circuit unit 13 and the offset adjustment signal addition unit 15. After detecting the offset correction voltage and holding a control signal for causing the selection circuit unit 13 to create the offset correction voltage, the offset control unit 14 switches the switch unit 19 to switch the storage unit 24, the selection circuit unit 13, and the storage unit 24. The offset adjustment signal adding unit 15 is short-circuited. The control signal held in the selection circuit unit 13 is stored in the storage unit 24. Thereafter, the control signal stored in the storage unit 24 is read and input to the offset adjustment signal adding unit 15. Since other operations are the same as those of the offset adjustment of the first embodiment, a duplicate description is omitted.

In the load driving device according to the seventh embodiment of the present invention, since the control signal for generating the offset correction voltage is stored in the storage unit 24, it is not necessary to perform the offset adjustment every time the power is turned on. Can save time.
While the present invention has been described in its preferred form with a certain degree of detail, the present disclosure of this preferred form should vary in the details of construction, and combinations and changes in order of elements are claimed. The present invention can be realized without departing from the scope and spirit of the invention.

  The present invention is useful for a load driving device and a load driving method having an offset adjustment function for reducing the output offset voltage.

1 is a block diagram of a load driving device according to a first embodiment of the present invention. Flowchart of offset adjustment of load drive device according to embodiment 1 of the present invention Waveform diagram of each signal of the offset adjustment circuit of the load driving device according to the first embodiment of the present invention. Configuration diagram of an offset adjustment signal adding unit of the load driving device according to the first embodiment of the present invention. Block diagram of a load driving apparatus according to a second embodiment of the present invention Block diagram of a load driving device according to a third embodiment of the present invention Block diagram of a load driving apparatus according to a fourth embodiment of the present invention Waveform diagram of offset adjustment signal of load driving device of embodiment 4 of the present invention Block diagram of a load driving apparatus according to a fifth embodiment of the present invention Waveform diagram of each signal of the load driving circuit of the load driving device according to the fifth embodiment of the present invention. Block diagram of a load driving apparatus according to a sixth embodiment of the present invention Flowchart of offset adjustment of load drive device according to embodiment 6 of the present invention Block diagram of a load driving device according to a seventh embodiment of the present invention Block diagram of a conventional load driving device Waveform diagram of each signal of the load driving circuit of the conventional load driving device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Drive signal input terminal 2 Reference signal input terminal 3 Input amplifier 4 Absolute value circuit 5 Pulse width modulation part 6 Polarity determination part 7 Triangle wave generation part 8 Drive output circuit 9 Load 10 Feedback amplifier 11 Offset adjustment start signal input terminal 12 Input amplifier offset Determination unit 13 Selection circuit unit 14 Offset control unit 15 Offset adjustment signal addition unit 16 Offset reference terminal,
17 Input amplifier input signal setting unit 18 Feedback amplifier input signal setting unit 22 Filter 23 Input resistance 24 Storage unit 25 Up counter 26 Clock generation unit 27 Start signal generation unit 100 Load drive circuit 200 Offset adjustment circuit

Claims (22)

An input amplifier that inputs a drive signal and a reference signal, differentially amplifies and outputs the input signal,
A triangular wave generator that outputs a triangular wave signal,
A pulse width modulation unit that outputs a pulse width modulation signal by inputting the output signal of the input amplifier as a modulated signal and the triangular wave signal as a modulation signal;
A drive output circuit for outputting a signal for driving a load based on the pulse width modulation signal; and a feedback amplifier for amplifying the output signal of the drive output circuit and feeding it back to the input amplifier;
A load driving device comprising:
An offset adjustment signal adding unit for adding an offset correction voltage to the input terminal of the input amplifier and outputting the same;
An input amplifier input signal setting unit for making the drive signal and the reference signal substantially the same potential by a predetermined signal;
A feedback amplifier input signal setting unit for setting two input signals of the feedback amplifier to substantially the same potential by a predetermined signal, and determining whether or not the output signal of the input amplifier is substantially zero by a predetermined signal Input amplifier offset determination unit
A load driving device further comprising:   2. The offset control unit according to claim 1, further comprising an offset control unit that outputs a control signal for causing the offset adjustment signal adding unit to create the offset correction voltage in accordance with an output signal of the input amplifier offset determination unit. The load driving device described.   An offset control unit that outputs the control signal that causes the offset adjustment signal addition unit to create the offset correction voltage, and outputs the control signal to the offset adjustment signal addition unit according to the output signal of the input amplifier offset determination unit The load driving device according to claim 1, further comprising a selection circuit unit for performing the operation.   The load driving device according to claim 2, further comprising a storage unit that stores the control signal.   The input amplifier includes a first input terminal to which the drive signal is input and a second input terminal to which the reference signal is input, and the offset correction voltage is added to the second input terminal. The load driving device according to claim 1, wherein   The input amplifier includes a first input terminal to which the drive signal is input and a second input terminal to which the reference signal is input, and the offset correction voltage is added to the first input terminal. The load driving device according to claim 1, wherein An absolute value circuit for converting an output signal of the input amplifier into an absolute value signal;
A polarity determination unit for determining the polarity of the difference voltage of the input signal of the input amplifier;
Further comprising
The pulse width modulation unit, instead of inputting the output signal of the input amplifier, inputs the absolute value signal of the absolute value circuit and outputs a pulse width modulation signal,
The drive output circuit outputs a signal for driving a load based on the output signal of the polarity determination unit and the pulse width modulation signal,
The load driving device according to claim 1, wherein the feedback amplifier differentially amplifies an output signal of the drive output circuit. The input amplifier is
A first amplification output unit that amplifies a value obtained by subtracting the reference signal from the drive signal and outputs the amplified value to a predetermined reference value;
A second amplification output unit that amplifies a value obtained by subtracting the drive signal from the reference signal and outputs the amplified value to a predetermined reference value;
The pulse width modulator is
A first pulse width modulator that inputs an output signal of the first amplification output unit and the triangular wave signal and outputs a first pulse width modulation signal;
A second pulse width modulator that inputs the output signal of the second amplification output section and the triangular wave signal and outputs a second pulse width modulation signal;
The drive output circuit is
A first drive signal for driving a load based on the first pulse width modulation signal;
Outputting a second drive signal for driving a load based on the second pulse width modulation signal;
The load driving device according to claim 1, wherein the feedback amplifier differentially amplifies the first drive signal and the second drive signal. The offset adjustment signal adding unit is
A first offset adjustment signal adder for adding a first offset correction voltage to the output signal of the first amplification output unit;
A second offset adjustment signal adder for adding a second offset correction voltage to the output signal of the second amplification output unit;
Instead of adding an offset correction voltage to the input terminal of the input amplifier,
Adding a first offset correction voltage to the first pulse width modulation signal;
9. The load driving device according to claim 8, wherein a second offset correction voltage is added to the second pulse width modulation signal. The input amplifier offset determination unit
Instead of determining whether or not the difference voltage of the output signal of the input amplifier is substantially zero,
An output signal of the first offset adjustment signal adder;
10. The load driving device according to claim 9, wherein it is determined whether or not a voltage difference from an output signal of the second offset adjustment signal adder is substantially zero. The input amplifier offset determination unit
Instead of determining whether the differential voltage of the output signal of the input amplifier is substantially zero,
A first offset determiner and a second offset determiner;
The first offset determiner determines whether or not a difference voltage between the output signal of the first offset adjustment signal adder and the output signal of the input amplifier is substantially zero.
A second offset determiner for determining whether or not a difference voltage between an output signal of the second offset adjustment signal adder and an output signal of the input amplifier is substantially zero;
The load driving device according to claim 9, wherein   The load according to any one of claims 8 to 11, wherein the predetermined reference value serving as a reference of outputs of the first and second amplification output units is a substantially average value of the triangular wave signal. Drive device.   The load driving device according to claim 1, wherein the offset adjustment signal adding unit includes at least one constant current source, at least one resistor, and at least one switch.   The offset adjustment signal adding unit includes at least one resistor arranged in series between a reference signal input terminal to which the reference signal is input and the input amplifier, and at least one for causing a current to flow through the resistor. It has a current source, The load drive device in any one of Claims 1-11 characterized by the above-mentioned.   The offset adjustment signal adding unit includes at least one resistor arranged in series between a drive signal input terminal to which the drive signal is input and the input amplifier, and at least one for causing a current to flow through the resistor. 7. The load driving device according to claim 1, further comprising a current source.   The load driving device according to claim 15 or 16, wherein a substantial resistance value of the resistor or a substantial current value flowing through the resistor is variable. An input amplifier that inputs a drive signal and a reference signal and differentially amplifies and outputs it, a triangular wave generator that outputs a triangular wave signal, an output signal of the input amplifier as a modulated signal, and the triangular wave signal as a modulated signal A pulse width modulation unit for outputting a width modulation signal, a drive output circuit for outputting a signal for driving a load based on the pulse width modulation signal, and a feedback amplifier for amplifying the output signal of the drive output circuit and feeding it back to the input amplifier An offset adjustment signal adding unit for adding an offset correction voltage to the input terminal of the input amplifier and outputting it; an input amplifier input signal setting unit for making the drive signal and the reference signal substantially the same potential by a predetermined signal A feedback amplifier input signal setting unit for making two input signals of the feedback amplifier substantially the same potential by a predetermined signal, and a predetermined signal In the load driving apparatus including a determining input amplifier offset determination unit output signal of the filling power amplifier whether substantially zero,
The load driving method of the load driving device has an offset adjustment step of adjusting an offset voltage of the input amplifier and the feedback amplifier,
The offset adjustment step includes
Based on a predetermined signal, the input amplifier input signal setting unit sets the drive signal and the reference signal to substantially the same potential, and the feedback amplifier input signal setting unit sets the input signal of the feedback amplifier to substantially the same potential. Setting steps to set,
A control step for sequentially and variably controlling the offset correction voltage added to the input terminal of the input amplifier by the offset adjustment signal adding unit;
A detection step of detecting that the output signal of the input amplifier is substantially zero by the input amplifier offset determination unit, and generating the offset correction voltage when the output signal of the input amplifier is detected to be substantially zero. Holding step for holding the control signal;
A load driving method for a load driving device. An input amplifier that inputs a drive signal and a reference signal, differentially amplifies and outputs a predetermined reference value, a triangular wave generator that outputs a triangular wave signal, and modulates the triangular wave signal using the output signal of the input amplifier as a modulated signal A pulse width modulation section for inputting a signal and outputting a pulse width modulation signal; a drive output circuit for outputting a signal for driving a load based on the pulse width modulation signal; and an input amplifier for amplifying an output signal of the drive output circuit A feedback amplifier that feeds back to the input amplifier, an offset adjustment signal adding unit that outputs the output signal of the input amplifier by adding an offset correction voltage, and an input for making the drive signal and the reference signal substantially the same potential by a predetermined signal An amplifier input signal setting unit, a feedback amplifier input signal setting unit for setting the input signal of the feedback amplifier to substantially the same potential by a predetermined signal, and a predetermined signal In the load driving apparatus including a determining input amplifier offset determining unit that determines whether an output signal of said offset adjusting signal adding section is substantially zero, the
The load driving method of the load driving device has an offset adjustment step of adjusting an offset voltage of the input amplifier and the feedback amplifier,
The offset adjustment step includes
Based on a predetermined signal, the input amplifier input signal setting unit sets the drive signal and the reference signal to substantially the same potential, and the feedback amplifier input signal setting unit sets the input signal of the feedback amplifier to substantially the same potential. Setting steps to set,
A control step of sequentially variably controlling the offset correction voltage to be added to the output signal of the input amplifier output to the predetermined reference value by the offset adjustment signal adding unit according to a predetermined signal;
A detection step of detecting that the output signal of the offset adjustment signal adding unit is substantially zero by the input amplifier offset determining unit; and an offset when detecting that the output signal of the offset adjustment signal adding unit is substantially zero A holding step for holding a control signal for generating a correction voltage;
A load driving method for a load driving device.   The load driving device further includes a storage unit that stores the control signal, and the offset adjustment step further includes a step of storing the offset correction signal in the storage unit after the holding step. The load driving method according to claim 17 and claim 18.   The load driving method according to claim 17, wherein the control step performs control so that the offset correction voltage monotonously increases or monotonously decreases.   20. The load driving method according to claim 17, wherein the control step controls the offset correction voltage by a binary search method for finding a target correction value while narrowing a search range by half.   The load driving method according to claim 18, wherein the predetermined reference value of the control step is a substantially average value of the triangular wave signal.

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